Abstract

This proposal extends HTMLMediaElement [HTML5] providing APIs to control playback of encrypted content.

The API supports use cases ranging from simple clear key decryption to high value video (given an appropriate user agent implementation). License/key exchange is controlled by the application, facilitating the development of robust playback applications supporting a range of content decryption and protection technologies.

This specification does not define a content protection or Digital Rights Management system. Rather, it defines a common API that may be used to discover, select and interact with such systems as well as with simpler content encryption systems. Implementation of Digital Rights Management is not required for compliance with this specification: only the Clear Key system is required to be implemented as a common baseline.

The common API supports a simple set of content encryption capabilities, leaving application functions such as authentication and authorization to page authors. This is achieved by requiring content protection system-specific messaging to be mediated by the page rather than assuming out-of-band communication between the encryption system and a license or other server.

Status of This Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

The working group maintains a list of all bug reports that the editors have not yet tried to address; there are also open bugs in the previous bug tracker. This draft highlights some of the pending issues that are still to be discussed in the working group. No decision has been taken on the outcome of these issues including whether they are valid.

Implementors should be aware that this specification is not stable. Implementors who are not taking part in the discussions are likely to find the specification changing out from under them in incompatible ways. Vendors interested in implementing this specification before it eventually reaches the Candidate Recommendation stage should join the mailing list mentioned below and take part in the discussions.

Issue 1

Bug 20944 - The specification should do more to encourage/ensure CDM-level interoperability.

Issue 2

This specification contains sections for describing security and privacy considerations. These sections are not final and review is welcome.

This document was published by the HTML Working Group as an Editor's Draft. If you wish to make comments regarding this document, please send them to public-html-media@w3.org (subscribe, archives). All comments are welcome.

Publication as an Editor's Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

This document is governed by the 1 September 2015 W3C Process Document.

1. Introduction

This section is non-normative.

This specification enables script to select content protection mechanisms, control license/key exchange, and implement custom license management algorithms. It supports a wide range of use cases without requiring client-side modifications in each user agent for each use case. This enables content providers to develop a single application solution for all devices.

Supported content is encrypted per container-specific "common encryption" specifications, enabling use across key systems. Supported content has an unencrypted container, enabling metadata to be provided to the application and maintaining compatibility with other HTMLMediaElement features.

A generic stack implemented using the API is shown below. This diagram shows an example flow; other combinations of API calls and events are possible.

A generic stack implemented using the proposed APIs

2. Definitions

Content Decryption Module (CDM)

Content Decryption Module (CDM) is the client component that provides the functionality, including decryption, for one or more Key Systems.

Note

Implementations may or may not separate the implementations of CDMs or treat them as separate from the user agent. This is transparent to the API and application.

All messages and communication to and from the CDM, such as between the CDM and a license server, MUST be passed through the user agent. The CDM MUST NOT make direct out-of band network requests. All messages and communication other than those described in Origin-Independent Individualization MUST be passed through the application via the APIs defined in this specification. Specifically, all communication that contains application-, origin-, or content-specific information or is sent to a URL specified by the application or based on its origin, MUST pass through the APIs. This includes all license exchange messages.

Key System

A Key System is a generic term for a decryption mechanism and/or content protection provider. Key System strings provide unique identification of a Key System. They are used by the user agent to select a CDM and identify the source of a key-related event. User agents MUST support the Common Key Systems. User agents MAY also provide additional CDMs with corresponding Key System strings.

A Key System string is always a reverse domain name. Key System strings are compared using case-sensitive matching. It is RECOMMENDED that CDMs use simple lower-case ASCII key system strings.

Note

For example, "com.example.somesystem".

Note

Within a given system ("somesystem" in the example), subsystems may be defined as determined by the key system provider. For example, "com.example.somesystem.1" and "com.example.somesystem.1_5". Key System providers should keep in mind that these will be used for comparison and discovery, so they should be easy to compare and the structure should remain reasonably simple.

Key Session

A Key Session, or simply Session, provides a context for message exchange with the CDM as a result of which key(s) are made available to the CDM. Sessions are embodied as MediaKeySession objects. Each Key session is associated with a single instance of Initialization Data provided in the generateRequest() call.

Each Key Session is associated with a single MediaKeys object, and only media element(s) associated with that object may access key(s) associated with the session. Other MediaKeys objects, CDM instances, and media elements MUST NOT access the key session or use its key(s). Key sessions and the keys they contain are no longer usable for decryption once the session has been closed, including when the MediaKeySession object is destroyed.

All license(s) and key(s) associated with a Key Session which have not been explicitly stored MUST be destroyed when the Key Session is closed.

Key IDs MUST be unique within a session.

Session ID

A Session ID is a unique string identifier generated by the CDM that can be used by the application to identify MediaKeySession objects.

A new Session ID is generated each time the user agent and CDM successfully create a new session.

Each Session ID SHALL be unique within the browsing context in which it was created. For session types for which the Is persistent session type? algorithm returns true, Session IDs MUST be unique within the origin over time, including across browsing sessions.

Note

The underlying content protection protocol does not necessarily need to support Session IDs.

Key

Unless otherwise stated, key refers to a decryption key that can be used to decrypt blocks within media data. Each such key is uniquely identified by a key ID. A key is associated with the session used to provide it to the CDM. (The same key may be present in multiple sessions.) Such keys MUST only be provided to the CDM via an update() call. (They may later be loaded by load() as part of the stored session data.)

Note

Authors SHOULD encrypt each set of stream(s) that requires enforcement of a meaningfully different policy with a distinct key (and key ID). For example, if policies may differ between two video resolutions, stream(s) containing one resolution should not be encrypted with the key used to encrypt stream(s) containing the other resolution. When encrypted, audio streams SHOULD NOT use the same key as any video stream. This is the only way to ensure enforcement and compatibility across clients.

Usable For Decryption

A key is considered usable for decryption if the CDM is certain the key is currently usable to decrypt one or more blocks of media data.

Note

For example, a key is not usable for decryption if its license has expired. Even if its license has not expired, a key is not usable for decryption if other conditions (e.g. output protection) for its use are not currently satisfied.

Key ID

A key is associated with a key ID that is a sequence of octets and which uniquely identifies the key. The container specifies the ID of the key that can decrypt a block or set of blocks within the media data. Initialization Data MAY contain key ID(s) to identify the keys that are needed to decrypt the media data. However, there is no requirement that Initialization Data contain any or all key IDs used in the media data or media resource. Licenses provided to the CDM associate each key with a key ID so the CDM can select the appropriate key when decrypting an encrypted block of media data.

Known Key

A key is considered to be known to a session if the CDM's implementation of the session contains any information - specifically the key ID - about it, regardless of whether the actual key is usable or its value is known. Known keys are exposed via the keyStatuses attribute.

Keys are considered known even after they become unusable, such as due to expiration or if they are removed but a record of license destruction or record of key usage is available. Keys only become unknown when they are explicitly removed from a session and any license release message is acknowledged.

Note

For example, a key could become unknown if an update() call provides a new license that does not include the key and includes instructions to replace the license(s) that previously contained the key.

License

A license is key system-specific state information that includes one or more key(s) - each associated with a key ID - and potentially other information about key usage.

Initialization Data
Note

Key Systems usually require a block of initialization data containing information about the stream to be decrypted before they can construct a license request message. This block could be a simple key or content ID or a more complex structure containing such information. It SHOULD always allow unique identification of the key(s) needed to decrypt the content. This initialization information MAY be obtained in some application-specific way or provided with the media data.

Initialization Data is a generic term for container-specific data that is used by a CDM to generate a license request.

The format of the initialization data depends upon the type of container, and containers MAY support more than one format of initialization data. The Initialization Data Type is a string that indicates the format of the accompanying Initialization Data. Initialization Data Type strings are always matched case-sensitively. It is RECOMMENDED that Initialization Data Type strings are lower-case ASCII strings.

The Encrypted Media Extensions Stream Format and Initialization Data Format Registry [EME-INITDATA-REGISTRY] provides the mapping from Initialization Data Type string to the specification for each format.

When the user agent encounters Initialization Data in the media data, it provides that Initialization Data to the application in the initData attribute of the encrypted event. The user agent MUST NOT store the Initialization Data or use its content at the time it is encountered. The application provides Initialization Data to the CDM via generateRequest(). The user agent MUST NOT provide Initialization Data to the CDM by other means.

Initialization Data MUST be a fixed value for a given set of stream(s) or media data. It MUST only contain information related to the keys required to play a given set of stream(s) or media data. It MUST NOT contain application data, client-specific data, user-specific data, or executable code.

Initialization Data SHOULD NOT contain Key System-specific data or values. Implementations MUST support the common formats defined in [EME-INITDATA-REGISTRY] for each Initialization Data Type they support.

Note

Use of proprietary formats/contents is discouraged, and supporting or using only proprietary formats is strongly discouraged. Proprietary formats should only be used with pre-existing content or on pre-existing devices that do not support the common formats.

Distinctive Identifier
Issue 3

Issue 117 - The definition of Distinctive Identifier needs to be refined and will likely change.

A distinctive identifier is a piece of data, implication of the possession of a piece of data, or an observable behavior or timing for which all of the following criteria hold:

  • It is not shared across a large population of users or devices.

  • It is exposed outside the client device or exposed to the application such that the application has the opportunity to send it (even if in encrypted form if decryptable outside the device) or information about it outside the client device.

  • It is used in more than one session or is potentially used in one persistent session across the point of persistence.

Note

A distinctive identifier is typically unique to a user or device, but an identifier does not need to be strictly unique to be distinctive. For example, an identifier shared among a small number of users could still be distinctive.

Note

Examples of distinctive identifiers include but are not limited to:

  • A string of bytes that is included in key requests and that is different from the string included by other devices.

  • A public key included in key requests that is different from the public keys included in the requests by other devices.

  • Demonstration of possession of a private key (e.g. by signing some data) that other devices do not have.

  • An identifier for such a key.

Examples of things that are not distinctive identifiers:

  • A public key shared among all copies of a given CDM version if the installed base is large.

  • A nonce or ephemeral key that is unique but used in only one session.

  • Device-unique keys used in attestations between, for example, the video pipeline and the CDM when the CDM does not let these attestations further flow to the application and instead makes a new attestation on its own using a key that does not constitute a distinctive identifier.

Note

The source of the identifier does not affect whether it is distinctive. For example, an identifier that is permanently part of the client device, contained in the CDM, generated on the client, or generated as part of some individualization or other provisioning process is considered distinctive if it meets the criteria above.

Cross Origin Limitations

During playback, embedded media data is exposed to script in the embedding origin. In order for the API to provide Initialization Data in the encrypted event, media data MUST be CORS-same-origin with the embedding page. If media data is cross-origin with the embedding document, authors SHOULD use the crossorigin attribute on the HTMLMediaElement and CORS headers on the media data response to make it CORS-same-origin.

Mixed Content Limitations

During playback, embedded media data is exposed to script in the embedding origin. In order for the API to provide Initialization Data in the encrypted event, media data MUST NOT be Mixed Content [MIXED-CONTENT].

Time

Time represents an instant in time with millisecond accuracy. The instants in time it can represent are the same that can be represented with ECMAScript Date objects (ECMA-262, section 20.3 [ECMA-262]) – namely, every millisecond in the 200,000,000 days centered around midnight of 1 January, 1970 UTC, except for any millisecond that is part of an inserted leap second. Time does not include these added leap milliseconds.

Time will equal NaN if no such time exists or if the time is indeterminate. It should never have the value Infinity.

Time is intended to be consistent with Unix time.

3. Obtaining Access to Key Systems

This section defines the mechanism for obtaining access to a key system. The inclusion of capabilities in the request also enables feature detection.

The steps of an algorithm are always aborted when rejecting a promise.

3.2 MediaKeySystemConfiguration dictionary

enum MediaKeysRequirement {
    "required",
    "optional",
    "not-allowed"
};
Enumeration description
required
When used in a call to requestMediaKeySystemAccess()
The returned object MUST support this feature.
When returned by a MediaKeySystemAccess object
CDM instances created by the object MAY use this feature.
optional
When used in a call to requestMediaKeySystemAccess()
The returned object MAY support and use this feature.
When returned by a MediaKeySystemAccess object
This value cannot and MUST NOT be present in such an object.
not-allowed
When used in a call to requestMediaKeySystemAccess()
The returned object MUST function without using this feature and MUST NOT use it at any time.
When returned by a MediaKeySystemAccess object
CDM instances created by the object MUST NOT use this feature.
dictionary MediaKeySystemConfiguration {
             DOMString                               label = "";
             sequence<DOMString>                     initDataTypes;
             sequence<MediaKeySystemMediaCapability> audioCapabilities;
             sequence<MediaKeySystemMediaCapability> videoCapabilities;
             MediaKeysRequirement                    distinctiveIdentifier = "optional";
             MediaKeysRequirement                    persistentState = "optional";
             sequence<DOMString>                     sessionTypes;
};

3.2.1 Dictionary MediaKeySystemConfiguration Members

audioCapabilities of type sequence<MediaKeySystemMediaCapability>
A list of supported audio type and capability pairs. The audio capability of this object is considered supported if the list is empty or contains one or more values that are supported with all other members (as determined by the algorithm). When there is a conflict between values, the earlier value will be selected.
distinctiveIdentifier of type MediaKeysRequirement, defaulting to "optional"
Whether a persistent Distinctive Identifier is required.

Messages from the CDM, such as message events, MUST NOT contain a Distinctive Identifier, even in an encrypted form, when this member is "not-allowed".

initDataTypes of type sequence<DOMString>
A list of supported Initialization Data Type names. The Initialization Data Type capability of this object is considered supported if the list is empty or contains one or more values that are supported with all other members (as determined by the algorithm). Values in the sequence MUST not be the empty string.
label of type DOMString, defaulting to ""
An optional label that will be preserved in the MediaKeySystemConfiguration returned from the getConfiguration() method of MediaKeySystemAccess.
persistentState of type MediaKeysRequirement, defaulting to "optional"
Whether the ability to persist state is required. This includes session data and any other type of state.

The CDM MUST NOT persist any state related to the application or origin of this object's Document when this member is "not-allowed".

Note

For the purposes of this member, persistent state does not include persistent unique identifiers (Distinctive Identifiers) controlled by the Key System implementation. distinctiveIdentifier independently reflects this requirement.

Only "temporary" sessions may be created when persistent state is not supported.

Note

For "temporary" sessions, the need and ability to store state is Key System implementation-specific and may vary by feature used.

Note

Applications intending to create non-"temporary" sessions, should set this member to "required" when calling requestMediaKeySystemAccess().

sessionTypes of type sequence<DOMString>
A list of MediaKeySessionTypes that must be supported. All values must be supported.

If this member is not present [WebIDL] when the dictionary is passed to requestMediaKeySystemAccess(), the dictionary will be treated as if this member is set to [ "temporary" ].

videoCapabilities of type sequence<MediaKeySystemMediaCapability>
A list of supported video type and capability pairs. The video capability of this object is considered supported if the list is empty or contains one or more values that are supported with all other members (as determined by the algorithm). When there is a conflict between values, the earlier value will be selected.

Implementations SHOULD NOT add members to the this dictionary. Should member(s) be added, they MUST be of type MediaKeysRequirement, and it is RECOMMENDED that they have default values of "optional" to support the widest range of application and client combinations.

Note

Dictionary members not recognized by a user agent implementation are ignored per [WebIDL] and will not be considered in the requestMediaKeySystemAccess() algorithm. Should an application use non-standard dictionary member(s), it MUST NOT rely on user agent implementations rejecting a configuration that includes such dictionary members.

This dictionary MUST NOT be used to pass state or data to the CDM.

3.3 MediaKeySystemMediaCapability dictionary

dictionary MediaKeySystemMediaCapability {
             DOMString contentType = "";
             DOMString robustness = "";
};

3.3.1 Dictionary MediaKeySystemMediaCapability Members

contentType of type DOMString, defaulting to ""
The type of the media resource. Its value must be a valid MIME type [HTML5]. The codecs parameter, which certain MIME types define, might be necessary to specify exactly how the resource is encoded. [RFC6381] The empty string is invalid.
robustness of type DOMString, defaulting to ""
The robustness level associated with the content type. The empty string indicates that any ability to decrypt and decode the content type is acceptable.

In order for the capability represented by this object to be considered supported, contentType MUST NOT be the empty string and its entire value, including all codecs, MUST be supported with robustness.

Note

If any of a set of codecs is acceptable, use a separate instances of this dictionary for each codec.

4. MediaKeySystemAccess Interface

The MediaKeySystemAccess object provides access to a Key System.

interface MediaKeySystemAccess {
    readonly        attribute DOMString keySystem;
    MediaKeySystemConfiguration getConfiguration ();
    Promise<MediaKeys>          createMediaKeys ();
};

4.1 Attributes

keySystem of type DOMString, readonly
Identifies the Key System being used.

4.2 Methods

createMediaKeys

Creates a new MediaKeys object for keySystem.

No parameters.
Return type: Promise<MediaKeys>

When this method is invoked, the user agent must run the following steps:

  1. Let promise be a new promise.

  2. Run the following steps in parallel:

    1. Let configuration be the value of this object's configuration value.

    2. Let distinctive identifier requirement be the value of configuration's distinctiveIdentifier member.

    3. Follow the steps for the value of distinctive identifier requirement from the following list:

      "required"
      Let use distinctive identifier be true.
      "not-allowed"
      Let use distinctive identifier be false.
      Note

      The value of distinctive identifier requirement cannot be "optional".

    4. Let persistent state requirement be the value of configuration's persistentState member.

    5. Follow the steps for the value of persistent state requirement from the following list:

      "required"
      Let persistent state allowed be true.
      "not-allowed"
      Let persistent state allowed be false.
      Note

      The value of persistent state requirement cannot be "optional".

    6. Load and initialize the Key System implementation represented by this object's cdm implementation value if necessary.

    7. Let instance be a new instance of the Key System implementation represented by this object's cdm implementation value.

    8. If use distinctive identifier is false, prevent instance from using Distinctive Identifier(s).

    9. If persistent state allowed is false, prevent instance from persisting any state related to the application or origin of this object's Document.

    10. If any of the preceding steps failed, reject promise with a new DOMException whose name is the appropriate error name.

    11. Let media keys be a new MediaKeys object, and initialize it as follows:

      1. Let the use distinctive identifier value be use distinctive identifier.

      2. Let the persistent state allowed value be persistent state allowed.

      3. Let the supported session types value be be the value of configuration's sessionTypes member.

      4. Let the cdm implementation value be this object's cdm implementation value.

      5. Let the cdm instance value be instance.

    12. Resolve promise with media keys.

  3. Return promise.

getConfiguration

Returns the supported combination of configuration options selected by the requestMediaKeySystemAccess() algorithm.

The returned object is a non-strict subset (plus any implied defaults) of the first satisfiable MediaKeySystemConfiguration configuration passed to the requestMediaKeySystemAccess() call that returned the promise that was resolved with this object. It does not contain values capabilities not specified in that single configuration (other than implied defaults) and thus may not reflect all capabilities of the Key System implementation. All values in the configuration may be used in any combination. Members of type MediaKeysRequirement reflect whether the capability is required for any combination. They will not have the value "optional".

No parameters.
Return type: MediaKeySystemConfiguration

When this method is invoked, the user agent must run the following steps:

  1. Return this object's configuration value.

    Note

    This results in a new JavaScript object being created and initialized from configuration each time this method is called.

5. MediaKeys Interface

The MediaKeys object represents a set of keys that an associated HTMLMediaElement can use for decryption of media data during playback. It also represents a CDM instance.

If the CDM instance represented by a MediaKeys object media keys becomes unavailable for any reason, then the user agent shall run the CDM Unavailable algorithm on media keys.

A MediaKeys object may be destroyed by the user agent when it is no longer accessible (i.e. there are no JavaScript references and no attached media element).

For methods that return a promise, all errors are reported asynchronously by rejecting the returned Promise. This includes [WebIDL] type mapping errors.

The steps of an algorithm are always aborted when rejecting a promise.

enum MediaKeySessionType {
    "temporary",
    "persistent-usage-record",
    "persistent-license"
};
Enumeration description
temporary

A session for which the license and record of or data related to the session MUST NOT be persisted.

The application need not worry about managing such storage. Support for this session type is REQUIRED.

persistent-usage-record
Issue 5

Issue 85 - There are concerns about the architectural implications of "persistent-usage-record" sessions that are pending a TAG discussion. The outcome of this discussion could result in modification (including removal) of the feature.

A session for which the license and any key(s) it contains SHALL NOT be persisted and for which a record of key usage SHALL be persisted when the keys available within the session are destroyed. The record of key usage consists of:

  • A record of the key IDs of all the key(s) that were at any time known to the session,

  • first decryption time - The first decryption time, defined as the time at which the session was first used to decrypt content, accurate to key usage accuracy and

  • latest decryption time - The latest decryption time, defined as the latest time at which the session was used to decrypt content, accurate to key usage accuracy.

A message of type "license-release" containing the record of key usage will be generated when remove() is called until the record is acknowledged by a response passed to update().

The key usage accuracy is implementation-dependant but SHALL NOT be greater than 60 seconds.

Note

Because the license and keys are not persisted, this record implicitly proves that the keys are no longer available in the session.

Note

User agents MAY implement this mechanism by means other than persisting data on key destruction - for example by persisting data during playback which is later used to infer the fact of key destruction - provided the observable behavior is compliant to this specification.

The session MUST be loadable via its Session ID once update() is called successfully. The application is responsible for managing any such storage that may be generated by the CDM. See Session Storage and Persistence. Can only be created if the configuration associated with the MediaKeySystemAccess object that created this object has a persistentState value of "required". Support for this session type is OPTIONAL.

persistent-license

A session for which the license (and potentially other data related to the session) will be persisted. A record of license destruction SHALL be persisted when the license and key(s) it contains are destroyed. The record of license destruction is a Key System-specific attestation that the license and key(s) it contains are no longer usable by the client.

A message of type "license-release" containing the record of license destruction will be generated when remove() is called until the record is acknowledged by a response passed to update().

The session MUST be loadable via its Session ID once update() is called successfully. The application is responsible for managing any such storage that may be generated by the CDM. See Session Storage and Persistence. Can only be created if the configuration associated with the MediaKeySystemAccess object that created this object has a persistentState value of "required". Support for this session type is OPTIONAL.

interface MediaKeys {
    MediaKeySession  createSession (optional MediaKeySessionType sessionType = "temporary");
    Promise<boolean> setServerCertificate (BufferSource serverCertificate);
};

5.1 Methods

createSession

Returns a new MediaKeySession object.

Parameter Type Nullable Optional Description
sessionType MediaKeySessionType = "temporary" The type of session to create. The session type affects the behavior of the returned object.
Return type: MediaKeySession

When this method is invoked, the user agent must run the following steps:

  1. If this object's supported session types value does not contain sessionType, throw a NotSupportedError.

    Note

    sessionType values for which the Is persistent session type? algorithm returns true will fail if this object's persistent state allowed value is false.

  2. If the implementation does not support MediaKeySession operations in the current state, throw an InvalidStateError.

    Note

    Some implementations are unable to execute MediaKeySession algorithms until this MediaKeys object is associated with a media element using setMediaKeys(). This step enables applications to detect this uncommon behavior before attempting to perform such operations.

  3. Let session be a new MediaKeySession object, and initialize it as follows:

    1. Let the sessionId attribute be the empty string.

    2. Let the expiration attribute be NaN.

    3. Let the closed attribute be a new promise.

    4. Let key status be a new empty MediaKeyStatusMap object, and initialize it as follows:

      1. Let the size attribute be 0.

    5. Let the session type value be sessionType.

    6. Let the uninitialized value be true.

    7. Let the callable value be false.

    8. Let the use distinctive identifier value be this object's use distinctive identifier value.

    9. Let the cdm implementation value be this object's cdm implementation.

    10. Let the cdm instance value be this object's cdm instance.

  4. Return session.

setServerCertificate

Provides a server certificate to be used to encrypt messages to the license server.

Key Systems that use such certificates MUST also support requesting the certificate from the server via the Queue a "message" Event algorithm.

Note

This method allows an application to proactively provide a server certificate to implementations that support it to avoid the additional round trip should the CDM request it. It is intended as an optimization, and applications are not required to use it.

Parameter Type Nullable Optional Description
serverCertificate BufferSource The server certificate. The contents are Key System-specific. It MUST NOT contain executable code.
Return type: Promise<boolean>

When this method is invoked, the user agent must run the following steps:

  1. If the Key System implementation represented by this object's cdm implementation value does not support server certificates, return a promise resolved with false.

  2. If serverCertificate is an empty array, return a promise rejected with a new a newly created TypeError.

  3. Let certificate be a copy of the contents of the serverCertificate parameter.

  4. Let promise be a new promise.

  5. Run the following steps in parallel:

    1. Use this object's cdm instance to process certificate.

    2. If the preceding step failed, resolve promise with a new DOMException whose name is the appropriate error name.

    3. Resolve promise with true.

  6. Return promise.

5.2 Algorithms

5.2.1 Is persistent session type?

The Is persistent session type? algorithm is run to determine whether the specified session type supports persistence of any kind. Requests to run this algorithm include a MediaKeySessionType value.

The following steps are run:

  1. Let the session type be the specified MediaKeySessionType value.

  2. Follow the steps for the value of session type from the following list:

    "temporary"
    Return false.
    "persistent-usage-record"
    Return true.
    "persistent-license"
    Return true.

5.2.2 CDM Unavailable

The CDM unavailable algorithm is run to close all MediaKeySession objects associated with a MediaKeys object, media keys when the CDM instance becomes unavailable.

The following step is run:

  1. For each MediaKeySession created by the media keys on which the Session Closed algorithm has not been run, run the Session Closed algorithm.

6. MediaKeySession Interface

The MediaKeySession object represents a key session.

A MediaKeySession object SHALL NOT be destroyed and SHALL continue to receive events if it has not been closed and the MediaKeys object that created it remains accessible. Otherwise, a MediaKeySession object that is no longer accessible to JavaScript SHALL NOT receive further events and MAY be destroyed.

Note

The above rule implies that the CDM instance must not be destroyed until all MediaKeys objects and all MediaKeySession objects associated with the CDM instance are destroyed.

For methods that return a promise, all errors are reported asynchronously by rejecting the returned Promise. This includes [WebIDL] type mapping errors.

The following steps of an algorithm are always aborted when rejecting a promise.

interface MediaKeySession : EventTarget {
    readonly        attribute DOMString           sessionId;
    readonly        attribute unrestricted double expiration;
    readonly        attribute Promise<void>       closed;
    readonly        attribute MediaKeyStatusMap   keyStatuses;
    Promise<void>    generateRequest (DOMString initDataType, BufferSource initData);
    Promise<boolean> load (DOMString sessionId);
    Promise<void>    update (BufferSource response);
    Promise<void>    close ();
    Promise<void>    remove ();
};

6.1 Attributes

closed of type Promise<void>, readonly

Signals when object becomes closed as a result of the Session Closed algorithm being run. This promise can only be fulfilled and is never rejected.

expiration of type unrestricted double, readonly

The time after which the key(s) in the session will no longer be usable for decryption, or NaN if no such time exists or if the license explicitly never expires, as determined by the CDM.

Note

This value MAY change during the session lifetime, such as when an action triggers the start of a window.

keyStatuses of type MediaKeyStatusMap, readonly

A reference to a read-only map of key IDs known to the session to the current status of the associated key. Each entry MUST have a unique key ID.

Note

The map entries and their values may be updated whenever the event loop spins. The map MUST NOT ever be inconsistent or partially updated, but it may change between accesses if the event loop spins in between the accesses. Key IDs may be added as the result of a load() or update() call. Key IDs may be removed as the result of a update() call that removes knowledge of existing keys (or replaces the existing set of keys with a new set). Key IDs MUST NOT be removed because they became unusable, such as due to expiration. Instead, such keys MUST be given an appropriate status, such as "expired".

Note

Some older platforms may contain Key System implementations that do not expose key IDs, making it impossible to provide a compliant user agent implementation. To maximize interoperability, user agent implementations exposing such CDMs SHOULD implement this member as follows: Whenever a non-empty list is appropriate, such as when the key session represented by this object may contain key(s), populate the map with a single pair containing the one-byte key ID 0 and the MediaKeyStatus most appropriate for the aggregated status of this object.

sessionId of type DOMString, readonly

The Session ID for this object and the associated key(s) or license(s).

6.2 Methods

close

Indicates that the application no longer needs the session and the CDM should release any resources associated with the session and close it. Persisted data should not be released or cleared.

Note

The returned promise is resolved when the request has been processed, and the closed attribute promise is resolved when the session is closed.

No parameters.
Return type: Promise<void>

When this method is invoked, the user agent must run the following steps:

  1. Let session be the associated MediaKeySession object.

  2. If the Session Closed algorithm has been run on session, return a resolved promise.

  3. If session's callable value is false, return a promise rejected with an InvalidStateError.

  4. Let promise be a new promise.

  5. Run the following steps in parallel:

    1. Let cdm be the CDM instance represented by session's cdm instance value.

    2. Use cdm to close the session associated with session.

      Note

      Closing the key session results in the destruction of any license(s) and key(s) that have not been explicitly stored.

    3. Queue a task to run the following steps:

      1. Run the Session Closed algorithm on the session.

      2. Resolve promise.

        Note

        Since promise handlers are queued as microtasks, these will be executed ahead of any events queued by the preceding steps.

  6. Return promise.

generateRequest

Generates a license request based on the initData. A message of type "license-request" will always be queued if the algorithm succeeds and the promise is resolved.

Parameter Type Nullable Optional Description
initDataType DOMString The Initialization Data Type of the initData.
initData BufferSource Initialization Data
Return type: Promise<void>

When this method is invoked, the user agent must run the following steps:

  1. If the Session Closed algorithm has been run on this object, return a promise rejected with an InvalidStateError.

  2. If this object's uninitialized value is false, return a promise rejected with an InvalidStateError.

  3. Let this object's uninitialized value be false.

  4. If initDataType is the empty string, return a promise rejected with a newly created TypeError.

  5. If initData is an empty array, return a promise rejected with a newly created TypeError.

  6. If the Key System implementation represented by this object's cdm implementation value does not support initDataType as an Initialization Data Type, return a promise rejected with a NotSupportedError. String comparison is case-sensitive.

  7. Let init data be a copy of the contents of the initData parameter.

  8. Let session type be this object's session type.

  9. Let promise be a new promise.

  10. Run the following steps in parallel:

    1. If the init data is not valid for initDataType, reject promise with a newly created TypeError.

    2. Let sanitized init data be a validated and sanitized version of init data.

      The user agent MUST thoroughly validate the Initialization Data before passing it to the CDM. This includes verifying that the length and values of fields are reasonable, verifying that values are within reasonable limits, and stripping irrelevant, unsupported, or unknown data or fields. It is RECOMMENDED that user agents pre-parse, sanitize, and/or generate a fully sanitized version of the Initialization Data. If the Initialization Data format specified by initDataType supports multiple entries, the user agent SHOULD remove entries that are not needed by the CDM. The user agent MUST NOT re-order entries within the Initialization Data.

    3. If the preceding step failed, reject promise with a newly created TypeError.

    4. If sanitized init data is empty, reject promise with a NotSupportedError.

    5. Let session id be the empty string.

    6. Let message be null.

    7. Let cdm be the CDM instance represented by this object's cdm instance value.

    8. Use the cdm to execute the following steps:

      1. If the sanitized init data is not supported by the cdm, reject promise with a NotSupportedError.

      2. Follow the steps for the value of session type from the following list:

        "temporary"

        Let requested license type be a temporary non-persistable license.

        Note

        The returned license must not be persistable or require persisting information related to it.

        "persistent-usage-record"
        1. Initialize this object's record of key usage as follows.

          • Set the list of key IDs known to the session to an empty list.

          • Set the first decrypt time to null.

          • Set the latest decrypt time to null.

        2. Let requested license type be a non-persistable license that will persist a record of key usage.

        "persistent-license"

        Let requested license type be a persistable license.

      3. Let session id be a unique Session ID string.

        If the result of running the Is persistent session type? algorithm on session type is true, the ID MUST be unique within the origin of this object's Document over time, including across Documents and browsing sessions.

      4. Let message be a license request for the requested license type generated based on the sanitized init data, which is interpreted per initDataType.

        The cdm MUST NOT use any stream-specific data, including media data, not provided via the sanitized init data.

        The cdm SHOULD NOT store session data, including the session ID, at this point. See Session Storage and Persistence.

    9. Queue a task to run the following steps:

      1. If any of the preceding steps failed, reject promise with a new DOMException whose name is the appropriate error name.

      2. Set the sessionId attribute to session id.

      3. Let this object's callable value be true.

      4. Run the Queue a "message" Event algorithm on the session, providing "license-request" and message.

      5. Resolve promise.

        Note

        Since promise handlers are queued as microtasks, these will be executed ahead of any events queued by the preceding steps.

  11. Return promise.

load

Loads the data stored for the specified session into this object.

Parameter Type Nullable Optional Description
sessionId DOMString The Session ID of the session to load.
Return type: Promise<boolean>

When this method is invoked, the user agent must run the following steps:

  1. If the Session Closed algorithm has been run on this object, return a promise rejected with an InvalidStateError.

  2. If this object's uninitialized value is false, return a promise rejected with an InvalidStateError.

  3. Let this object's uninitialized value be false.

  4. If sessionId is the empty string, return a promise rejected with a newly created TypeError.

  5. If the result of running the Is persistent session type? algorithm on this object's session type is false, return a promise rejected with a newly created TypeError.

  6. Let origin be the origin of this object's Document.

  7. Let promise be a new promise.

  8. Run the following steps in parallel:

    1. Let sanitized session ID be a validated and/or sanitized version of sessionId.

      Note

      The user agent should thoroughly validate the sessionId value before passing it to the CDM. At a minimum, this should include checking that the length and value (e.g. alphanumeric) are reasonable.

    2. If the preceding step failed, or if sanitized session ID is empty, reject promise with a newly created TypeError.

    3. If there is an unclosed session in this object's Document whose sessionId attribute is sanitized session ID, reject promise with a QuotaExceededError.

      Note

      In other words, do not create a session if a non-closed session, regardless of type, already exists for this sanitized session ID in this browsing context.

    4. Let expiration time be NaN.

    5. Let message be null.

    6. Let message type be null.

    7. Let cdm be the CDM instance represented by this object's cdm instance value.

    8. Use the cdm to execute the following steps:

      1. If there is no data stored for the sanitized session ID in the origin, resolve promise with false and abort these steps.

      2. If the stored session's session type is not the same as the current MediaKeySession session type, reject promise with a newly created TypeError.

      3. Let session data be the data stored for the sanitized session ID in the origin. This MUST NOT include data from other origin(s) or that is not associated with an origin.

      4. If there is an unclosed session in any Document representing the session data, reject promise with a QuotaExceededError.

        Note

        In other words, do not create a session if a non-closed persistent session already exists for this sanitized session ID in any browsing context.

      5. Load the session data.

      6. If the session data indicates an expiration time for the session, let expiration time be the expiration time in milliseconds since 01 January 1970 UTC.

      7. If the CDM needs to send a message:

        1. Let message be a message generated by the CDM based on the session data.

        2. Let message type be the appropriate MediaKeyMessageType for the message.

    9. Queue a task to run the following steps:

      1. If any of the preceding steps failed, reject promise with a the appropriate error name.

      2. Set the sessionId attribute to sanitized session ID.

      3. Let this object's callable value be true.

      4. If the loaded session contains information about any keys (there are known keys), run the Update Key Statuses algorithm on the session, providing each key's key ID along with the appropriate MediaKeyStatus.

        Should additional processing be necessary to determine with certainty the status of a key, use "status-pending". Once the additional processing for one or more keys has completed, run the Update Key Statuses algorithm again with the actual status(es).

      5. Run the Update Expiration algorithm on the session, providing expiration time.

      6. If message is not null, run the Queue a "message" Event algorithm on the session, providing message type and message.

      7. Resolve promise with true.

        Note

        Since promise handlers are queued as microtasks, these will be executed ahead of any events queued by the preceding steps.

  9. Return promise.

remove

Removes stored session data associated with this object.

No parameters.
Return type: Promise<void>

When this method is invoked, the user agent must run the following steps:

  1. If the Session Closed algorithm has been run on this object, return a promise rejected with an InvalidStateError.

  2. If this object's callable value is false, return a promise rejected with an InvalidStateError.

  3. If the result of running the Is persistent session type? algorithm on this object's session type is false, return a promise rejected with a newly created TypeError.

  4. Let promise be a new promise.

  5. If this object's session type is "persistent-usage-record" or "persistent-license", run the following steps in parallel:

    1. Let cdm be the CDM instance represented by this object's cdm instance value.

    2. Let message be null.

    3. Use the cdm to execute the following steps:

      1. If any license(s) and/or key(s) are associated with the session:

        1. Destroy the license(s) and/or key(s) associated with the session.

        2. Follow the steps for the value of this object's session type from the following list:

          "persistent-usage-record"
          1. Store this object's record of key usage.
          2. Let message be a message containing or reflecting this object's record of key usage.

          "persistent-license"
          1. Let record of license destruction be a record of license destruction for the license represented by this object.

          2. Store the record of license destruction.

          3. Let message be a message containing or reflecting the record of license destruction.

    4. Queue a task to run the following steps:

      1. Run the Update Key Statuses algorithm on the session, providing all key ID(s) in the session along with the "released" MediaKeyStatus value for each.

      2. Run the Update Expiration algorithm on the session, providing NaN.

      3. If any of the preceding steps failed, reject promise with a new DOMException whose name is the appropriate error name.

      4. Let message type be "license-release".

      5. If message is not null, run the Queue a "message" Event algorithm on the session, providing message type and message.

      6. Resolve promise.

        Note

        Since promise handlers are queued as microtasks, these will be executed ahead of any events queued by the preceding steps.

  6. Return promise.

update

Provides messages, including licenses, to the CDM.

Parameter Type Nullable Optional Description
response BufferSource A message to be provided to the CDM. The contents are Key System-specific. It MUST NOT contain executable code.
Return type: Promise<void>

When this method is invoked, the user agent must run the following steps:

  1. If the Session Closed algorithm has been run on this object, return a promise rejected with an InvalidStateError.

  2. If this object's callable value is false, return a promise rejected with an InvalidStateError.

  3. If response is an empty array, return a promise rejected with a newly created TypeError.

  4. Let response copy be a copy of the contents of the response parameter.

  5. Let promise be a new promise.

  6. Run the following steps in parallel:

    1. Let sanitized response be a validated and/or sanitized version of response copy.

      Note

      The user agent should thoroughly validate the response before passing it to the CDM. This may include verifying values are within reasonable limits, stripping irrelevant data or fields, pre-parsing it, sanitizing it, and/or generating a fully sanitized version. The user agent should check that the length and values of fields are reasonable. Unknown fields should be rejected or removed.

    2. If the preceding step failed, or if sanitized response is empty, reject promise with a newly created TypeError.

    3. Let message be null.

    4. Let message type be null.

    5. Let session closed be false.

    6. Let cdm be the CDM instance represented by this object's cdm instance value.

    7. Use the cdm to execute the following steps:

      1. If the format of sanitized response is invalid in any way, reject promise with a newly created TypeError.

      2. Process sanitized response, following the stipulation for the first matching condition from the following list:

        If sanitized response contains a license or key(s)
        Note

        This includes an initial license, an updated license, and a license renewal message.

        Process sanitized response, following the stipulation for the first matching condition from the following list:

        If sessionType is "temporary" and sanitized response does not specify that session data, including any license, key(s), or similar session data it contains, should be stored
        Process sanitized response, not storing any session data.
        If sessionType is "persistent-usage-record" and sanitized response contains a non-persistable license

        Run the following steps:

        1. Process sanitized response, not storing any session data.

        2. If processing sanitized response results in the addition of keys to the set of known keys, add the key IDs of these keys to this object's record of key usage.

        If sessionType is "persistent-license" and sanitized response contains a persistable license
        Process sanitized response, storing the license/key(s) and related session data contained in sanitized response. Such data MUST be stored such that only the origin of this object's Document can access it.
        Otherwise

        Reject promise with a newly created TypeError.

        See also Session Storage and Persistence.

        State information, including keys, for each session MUST be stored in such a way that closing one session does not affect the observable state in other session(s), even if they contain overlapping key IDs.

        Note

        When sanitized response contains key(s) and/or related data, cdm will likely store (in memory) the key and related data indexed by key ID.

        Note

        The replacement algorithm within a session is Key System-dependent.

        Note

        It is RECOMMENDED that CDM implementations support a standard and reasonably high minimum number of keys per MediaKeySession object, including a standard replacement algorithm, and a standard and reasonably high minimum number of MediaKeySession objects. This enables a reasonable number of key rotation algorithms to be implemented across user agents and may reduce the likelihood of playback interruptions in use cases that involve various streams in the same element (i.e. adaptive streams, various audio and video tracks) using different keys.

        If sanitized response contains a license destruction acknowledgement and sessionType is "persistent-license"

        Run the following steps:

        1. Close the session and clear all stored session data associated with this object, including the sessionId and license destruction record.

          Note

          A subsequent call to load() with the value of this object's sessionId would fail because there is no data stored for that session ID.

        2. Set session closed to true.

        If sanitized response contains a key usage record acknowledgement and sessionType is "persistent-usage-record"

        Run the following steps:

        1. Close the session and clear all stored session data associated with this object, including the sessionId and the record of key usage.

          Note

          A subsequent call to load() with the value of this object's sessionId would fail because there is no data stored for that session ID.

        2. Set session closed to true.

        Otherwise
        Process sanitized response, not storing any session data.
        Note

        For example, sanitized response may contain information that will be used to generate another message event. In this case, there is no need to verify the contents against the sessionType.

      3. If a message needs to be sent to the server, execute the following steps:

        1. Let message be that message.

        2. Let message type be the appropriate MediaKeyMessageType for the message.

    8. Queue a task to run the following steps:

      1. If session closed is true:

        Run the Session Closed algorithm on this object.

        Otherwise:

        Run the following steps:

        1. If the set of keys known to the CDM for this object changed or the status of any key(s) changed, run the Update Key Statuses algorithm on the session, providing each known key's key ID along with the appropriate MediaKeyStatus.

          Should additional processing be necessary to determine with certainty the status of a key, use "status-pending". Once the additional processing for one or more keys has completed, run the Update Key Statuses algorithm again with the actual status(es).

        2. If the expiration time for the session changed, run the Update Expiration algorithm on the session, providing the new expiration time.

        3. If any of the preceding steps failed, reject promise with a new DOMException whose name is the appropriate error name.

        4. If message is not null, run the Queue a "message" Event algorithm on the session, providing message type and message.

      2. Resolve promise.

        Note

        Since promise handlers are queued as microtasks, these will be executed ahead of any events queued by the preceding steps.

  7. Return promise.

6.3 MediaKeyStatusMap Interface

The MediaKeyStatusMap object is a read-only map of key IDs to the current status of the associated key.

A key's status is independent of whether the key is currently being used and of media data.

Note

For example, if a key has output requirements that cannot currently be met, the key's status should be "output-downscaled" or "output-restricted", as appropriate, regardless of whether that key has been or is currently needed to decrypt media data.

Issue 6

Issue 75 - The exact behavior of the iterable declaration is still being determined and may change in incompatible ways. This includes the definition of the value pairs and the ForEachCallback parameters.

interface MediaKeyStatusMap {
    iterable<BufferSource,MediaKeyStatus>;
    readonly        attribute unsigned long size;
    boolean        has (BufferSource keyId);
    MediaKeyStatus get (BufferSource keyId);
    void           forEach (ForEachCallback callback);
};

This interface has "entries", "keys", "values" and @@iterator methods brought by iterable.

The value pairs to iterate over are a snapshot of the set of pairs formed from the key ID and associated MediaKeyStatus value for all known keys, sorted by key ID, where for Key IDs A and B, of lengths n and m respectively, with n <= m, then we define A < B if and only if the n octets of A are less in lexicographical order than the first n octets of B or those octets are equal and n < m.

6.3.1 Attributes

size of type unsigned long, readonly

The number of known keys.

6.3.2 Methods

forEach

Calls callback once for each key-value pair present in the MediaKeyStatus map.

Parameter Type Nullable Optional Description
callback ForEachCallback A callback function
Return type: void
get

Returns the MediaKeyStatus of the key identified by keyId or undefined if the status of the key identified by keyId is not known.

Parameter Type Nullable Optional Description
keyId BufferSource The key ID of the key.
Return type: MediaKeyStatus
has

Returns true if the status of the key identified by keyId is known.

Parameter Type Nullable Optional Description
keyId BufferSource The key ID of the key.
Return type: boolean
callback ForEachCallback = void (BufferSource keyId, MediaKeyStatus status);

6.3.3 Callback ForEachCallback Parameters

keyId of type BufferSource
The key ID.
status of type MediaKeyStatus
The key status.
enum MediaKeyStatus {
    "usable",
    "expired",
    "released",
    "output-restricted",
    "output-downscaled",
    "status-pending",
    "internal-error"
};
Enumeration description
usable The CDM is certain the key is currently usable for decryption.
Keys that may not currently be usable for decryption MUST NOT have this status.
expired The key is no longer usable for decryption because its expiration time has passed.
The time represented by the expiration attribute MUST be earlier than the current time. All other keys in the session MUST have this status.
released The key itself is no longer available to the CDM, but information about the key, such as a record of license destruction or record of key usage, is available.
output-restricted There are output restrictions associated with the key that cannot currently be met. Media data decrypted with this key may be blocked from presentation, if necessary according to the output restrictions. The application should avoid using streams that will trigger the output restrictions associated with the key.
output-downscaled There are output restrictions associated with the key that cannot currently be met. Media data decrypted with this key may be presented at a lower quality (e.g. resolution), if necessary according to the output restrictions. The application should avoid using streams that will trigger the output restrictions associated with the key.
Support for downscaling is OPTIONAL. Applications SHOULD NOT rely on downscaling to ensure uninterrupted playback when output requirements cannot be met.
status-pending The status of the key is not yet known and is being determined. The status will be updated with the actual status when it has been determined.
internal-error The key is not currently usable for decryption because of an error in the CDM unrelated to the other values. This value is not actionable by the application.

6.4 MediaKeyMessageEvent

The MediaKeyMessageEvent object is used for the message event.

Events are constructed as defined in Constructing events [DOM].

enum MediaKeyMessageType {
    "license-request",
    "license-renewal",
    "license-release",
    "individualization-request"
};
Enumeration description
license-request The message contains a request for a new license.
license-renewal The message contains a request to renew an existing license.
license-release The message contains a record of license destruction or record of key usage.
individualization-request The message contains a request for per-origin individualization (or re-individualization). See Per-Origin Individualization.
As with all other messages, any identifiers in the message MUST be distinctive per-origin and MUST NOT contain any non-origin-specific Distinctive Identifiers.
[ Constructor (DOMString type, optional MediaKeyMessageEventInit eventInitDict)]
interface MediaKeyMessageEvent : Event {
    readonly        attribute MediaKeyMessageType messageType;
    readonly        attribute ArrayBuffer         message;
};

6.4.1 Constructors

MediaKeyMessageEvent
Parameter Type Nullable Optional Description
type DOMString
eventInitDict MediaKeyMessageEventInit

6.4.2 Attributes

message of type ArrayBuffer, readonly
The message from the CDM. Messages are Key System-specific.
messageType of type MediaKeyMessageType, readonly
The type of the message.

Implementations MUST NOT require applications to handle message types. Implementations MUST support applications that do not differentiate messages and MUST NOT require that applications handle message types. Specifically, Key Systems MUST support passing all types of messages to a single URL.

Note

This attribute allows an application to differentiate messages without parsing the message. It is intended to enable optional application and/or server optimizations, but applications are not required to use it.

6.4.3 MediaKeyMessageEventInit

dictionary MediaKeyMessageEventInit : EventInit {
             MediaKeyMessageType messageType = "license-request";
             ArrayBuffer         message;
};
6.4.3.1 Dictionary MediaKeyMessageEventInit Members
message of type ArrayBuffer
The message.
messageType of type MediaKeyMessageType, defaulting to "license-request"
The type of the message.

6.5 Event Summary

This section is non-normative.

Event name Interface Dispatched when...
keystatuseschange Event There has been a change in the keys in the session or their status.
message MediaKeyMessageEvent The CDM has generated a message for the session.

6.6 Algorithms

6.6.1 Queue a "message" Event

The Queue a "message" Event algorithm is run when the CDM needs to queue a message event to a MediaKeySession object. Requests to run this algorithm include a target MediaKeySession object, a message type, and a message.

message MUST NOT contain a Distinctive Identifier, even in an encrypted form, if the MediaKeySession object's use distinctive identifier value is false.

The following steps are run:

  1. Let the session be the specified MediaKeySession object.

  2. Queue a task to create an event named message that does not bubble and is not cancellable using the MediaKeyMessageEvent interface with its type attribute set to message and its isTrusted attribute initialized to true, and dispatch it at the session.

    The event interface MediaKeyMessageEvent has:

6.6.2 Update Key Statuses

The Update Key Statuses algorithm is run when the CDM changes the set of keys known to the session or the status of one or more of the keys. This can happen as the result of a load() or update() call or some other event, such as expiration. Requests to run this algorithm include a target MediaKeySession object and a sequence of key ID and associated MediaKeyStatus pairs.

The following steps are run:

  1. Let the session be the associated MediaKeySession object.

  2. Let the input statuses be the sequence of pairs key ID and associated MediaKeyStatus pairs.

  3. Let the statuses be session's keyStatuses attribute.

  4. Run the following steps to replace the contents of statuses:

    1. Empty statuses.

    2. For each pair in input statuses.

      1. Let pair be the pair.

      2. Insert an entry for pair's key ID into statuses with the value of pair's MediaKeyStatus value.

    Note

    The effect of this steps is that the contents of session's keyStatuses attribute are replaced without invalidating existing references to the attribute. This replacement is atomic from a script perspective. That is, script MUST NOT ever see a partially populated sequence.

  5. Queue a task to fire a simple event named keystatuseschange at the session.

  6. Queue a task to run the Attempt to Resume Playback If Necessary algorithm on each of the media element(s) whose mediaKeys attribute is the MediaKeys object that created the session.

6.6.3 Update Expiration

The Update Expiration algorithm is run when the CDM changes the expiration time of a session. This can happen as the result of an update() call or some other event. Requests to run this algorithm include a target MediaKeySession object and the new expiration time, which may be NaN.

The following steps are run:

  1. Let the session be the associated MediaKeySession object.

  2. Let expiration time be NaN.

  3. If the new expiration time is not NaN, let expiration time be the new expiration time in milliseconds since 01 January 1970 UTC.

  4. Set the session's expiration attribute to expiration time.

6.6.4 Session Closed

The Session Closed algorithm updates the MediaKeySession state after a session has been closed.

Closing a session means that the license(s) and key(s) associated with it are no longer available to decrypt media data. All MediaKeySession methods will fail and no further events will be queued for this object after this algorithm is run.

Note

The CDM may close a session at any point, such as when the session is no longer needed or when system resources are lost. In that case, this algorithm MUST be run.

Keys in other sessions MUST be unaffected, even if they have overlapping key IDs.

After this algorithm has run, event handlers for the events queued by this algorithm will be executed, but no furter events can be queued. As a result, no messages can be sent by the CDM as a result of closing the session.

The following steps are run:

  1. Let session be the associated MediaKeySession object.

  2. If session's session type is "persistent-usage-record", store the record of key usage, if it exists.

    Note

    The record of key usage may not exist if no keys have been used in the session or if it has been deleted as a result of the update() method processing an acknowledgement of the record of key usage.

  3. Run the Update Key Statuses algorithm on the session, providing an empty sequence.

  4. Run the Update Expiration algorithm on the session, providing NaN.

  5. Let promise be the closed attribute of the session.

  6. Resolve promise.

6.7 Exceptions

The methods report errors by rejecting the returned promise with a simple exception [WebIDL] or a DOMException. The following simple exceptions and DOMException names from [WebIDL] are used in the algorithms. Causes specified specified in the algorithms are listed alongside each name, though these names MAY be used for other reasons as well.

Name Possible Causes (non-exhaustive)
TypeError The parameter is empty.
Invalid initialization data.
Invalid response format.
A persistent license was provided for a "temporary" session.
NotSupportedError The existing MediaKeys object cannot be removed.
The key system is not supported.
The key system is not supported in an insecure context.
The initialization data type is not supported by the key system.
The session type is not supported by the key system.
The initialization data is not supported by the key system.
The operation is not supported by the key system.
InvalidStateError The existing MediaKeys object cannot be removed at this time.
The session has already been used.
The session is not yet initialized.
The session is closed.
QuotaExceededError The MediaKeys object cannot be used with additional HTMLMediaElements.
A non-closed session already exists for this sessionId.

6.8 Session Storage and Persistence

This section provides an overview of session storage and persistence that complements the algorithms.

If the result of running the Is persistent session type? algorithm on this object's session type is false, the user agent and CDM MUST NOT persist a record of or data related to the session at any point. This includes license(s), key(s), records of key usage or proof of license destruction, and the Session ID.

The remainder of this section applies to session types for which the Is persistent session type? algorithm returns true.

Persisted data MUST always be stored such that only the origin of this object's Document can access it. In addition, the data MUST only be accessible by the current profile of this user agent; other user agent profiles, user agents, and applications MUST NOT be able to access the stored data. See Information Stored on User Devices.

The CDM SHOULD NOT store session data, including the Session ID, until update() is called the first time. Specifically, the CDM SHOULD NOT store session data during the generateRequest() algorithm. This ensures that the application is aware of the session and knows it needs to eventually remove it.

The CDM MUST ensure that data for a given session is only present in one active unclosed session in any Document. In other words, load() MUST fail when there is already a MediaKeySession representing the session specified by the sessionId parameter, either because the object that created it via generateRequest() is still active or it has been loaded into another object via load(). A session MAY only be loaded again after the Session Closed algorithm has not been run on the object representing it.

An application that creates a session using a type for which the Is persistent session type? algorithm returns true SHOULD later remove the stored data using remove(). The CDM MAY also remove sessions as appropriate, but applications SHOULD NOT rely on this.

See the Security and Privacy sections for additional considerations when supporting persistent storage.

7. HTMLMediaElement Extensions

This section specifies additions to and modifications of the HTMLMediaElement [HTML5] when the Encrypted Media Extensions are supported.

The following internal values are added to the HTMLMediaElement:

The following modifications are made to the behaviour of the HTMLMediaElement:

For methods that return a promise, all errors are reported asynchronously by rejecting the returned Promise. This includes [WebIDL] type mapping errors.

The steps of an algorithm are always aborted when rejecting a promise.

partial interface HTMLMediaElement : EventTarget {
    readonly        attribute MediaKeys?   mediaKeys;
                    attribute EventHandler onencrypted;
    Promise<void> setMediaKeys (MediaKeys? mediaKeys);
};

7.1 Attributes

mediaKeys of type MediaKeys, readonly , nullable

The MediaKeys being used when decrypting encrypted media data for this media element.

onencrypted of type EventHandler

Event handler for the encrypted event MUST be supported by all HTMLMediaElements as both a content attribute and an IDL attribute.

7.2 Methods

setMediaKeys

Provides the MediaKeys to use when decrypting media data during playback.

Note

Support for clearing or replacing the associated MediaKeys object during playback is a quality of implementation issue. In many cases it will result in a bad user experience or rejected promise.

Note

Some implementations may only support decrypting media data provided via Media Source Extensions [MEDIA-SOURCE]. This is not reflected in the results of calling requestMediaKeySystemAccess().

Parameter Type Nullable Optional Description
mediaKeys MediaKeys A MediaKeys object.
Return type: Promise<void>

When this method is invoked, the user agent must run the following steps:

  1. If mediaKeys and the mediaKeys attribute are the same object, return a resolved promise.

  2. If this object's attaching media keys value is true, return a promise rejected with an InvalidStateError.

  3. Let this object's attaching media keys value be true.

  4. Let promise be a new promise.

  5. Run the following steps in parallel:

    1. If mediaKeys is not null, the CDM instance represented by mediaKeys is already in use by another media element, and the user agent is unable to use it with this element, let this object's attaching media keys value be false and reject promise with a QuotaExceededError.

    2. If the mediaKeys attribute is not null, run the following steps:

      1. If the user agent or CDM do not support removing the association, let this object's attaching media keys value be false and reject promise with a NotSupportedError.

      2. If the association cannot currently be removed, let this object's attaching media keys value be false and reject promise with an InvalidStateError.

        Note

        For example, some implementations may not allow removal during playback.

      3. Stop using the CDM instance represented by the mediaKeys attribute to decrypt media data and remove the association with the media element.

      4. If the preceding step failed, let this object's attaching media keys value be false and reject promise with the appropriate error name.

    3. If mediaKeys is not null, run the following steps:

      1. Associate the CDM instance represented by mediaKeys with the media element for decrypting media data.

      2. If the preceding step failed, run the following steps:

        1. Set the mediaKeys attribute to null.

        2. Let this object's attaching media keys value be false.

        3. Reject promise with a new DOMException whose name is the appropriate error name.

      3. Queue a task to run the Attempt to Resume Playback If Necessary algorithm on the media element.

    4. Set the mediaKeys attribute to mediaKeys.

    5. Let this object's attaching media keys value be false.

    6. Resolve promise.

  6. Return promise.

7.3 MediaEncryptedEvent

The MediaEncryptedEvent object is used for the encrypted event.

Events are constructed as defined in Constructing events [DOM].

[ Constructor (DOMString type, optional MediaEncryptedEventInit eventInitDict)]
interface MediaEncryptedEvent : Event {
    readonly        attribute DOMString    initDataType;
    readonly        attribute ArrayBuffer? initData;
};

7.3.1 Constructors

MediaEncryptedEvent
Parameter Type Nullable Optional Description
type DOMString
eventInitDict MediaEncryptedEventInit

7.3.2 Attributes

initData of type ArrayBuffer, readonly , nullable
The Initialization Data for the event.
initDataType of type DOMString, readonly
Indicates the Initialization Data Type of the Initialization Data contained in the initData attribute.

7.3.3 MediaEncryptedEventInit

dictionary MediaEncryptedEventInit : EventInit {
             DOMString    initDataType = "";
             ArrayBuffer? initData = null;
};
7.3.3.1 Dictionary MediaEncryptedEventInit Members
initData of type ArrayBuffer, nullable, defaulting to null
The Initialization Data.
initDataType of type DOMString, defaulting to ""
The Initialization Data Type.

7.4 Event Summary

This section is non-normative.

Event name Interface Dispatched when... Preconditions
encrypted MediaEncryptedEvent The user agent encounters Initialization Data in the media data. The element's readyState is equal to HAVE_METADATA or greater.
Note

It is possible that the element is playing or has played.

waitingforkey Event Playback is blocked waiting for a key. The element is potentially playing and its readyState is equal to HAVE_FUTURE_DATA or greater.

7.5 Algorithms

7.5.1 Initialization Data Encountered

The following steps are run when the media element encounters Initialization Data in the media data during the resource fetch algorithm:

  1. Let initDataType be the empty string.

  2. Let initData be null.

  3. If the media data is CORS-same-origin and not mixed content, run the following steps:

    1. Let initDataType be the string representing the Initialization Data Type of the Initialization Data.

    2. Let initData be the Initialization Data.

    Note

    While the media element may allow loading of "Optionally-blockable Content" [MIXED-CONTENT], the user agent MUST NOT expose Initialization Data from such media data to the application.

  4. Queue a task to create an event named encrypted that does not bubble and is not cancellable using the MediaEncryptedEvent interface with its type attribute set to message and its isTrusted attribute initialized to true, and dispatch it at the session.

    The event interface MediaEncryptedEvent has:

    Note

    readyState is not changed and no algorithms are aborted. This event merely provides information.

    Note

    The initData attribute will be null if the media data is not CORS-same-origin or is mixed content. Applications may retrieve the Initialization Data from an alternate source.

  5. If the media element's mediaKeys attribute is null and the implementation requires specification of a MediaKeys object before decoding potentially-encrypted media data, run the following steps:

    Note

    These steps may be reached when the application provides media data before calling setMediaKeys() to provide a MediaKeys object. Selecting a CDM may affect the pipeline and/or decoders used, so some implementations may delay playback of media data that may contain encrypted blocks until a CDM is specified by passing a MediaKeys object to setMediaKeys().

    1. Run the Queue a "waitingforkey" Event algorithm on the media element.

    2. Wait for a signal to resume playback.

  6. Continue Normal Flow: Continue with the existing media element's resource fetch algorithm.

7.5.2 Encrypted Block Encountered

This algorithm queues a block of encrypted media data for decryption and attempts to decrypt if possible. The following steps are run:

  1. Let block be the block of encrypted media data.

  2. Add block to the end of the media element's encrypted block queue.

  3. If the media element's waiting for key value is false, run the Attempt to Decrypt algorithm.

7.5.3 Attempt to Decrypt

This algorithm attempts to decrypt media data that is queued for decryption. The following steps are run:

  1. If the media element's encrypted block queue is empty, abort these steps.

  2. If the media element's mediaKeys attribute is not null, run the following steps:

    1. Let media keys be the MediaKeys object referenced by that attribute.

    2. Let cdm be the CDM instance represented by media keys's cdm instance value.

    3. If cdm is no longer usable for any reason, run the following steps:

      Note

      These steps are intended to be run on unrecoverable failures of the CDM.

      1. Run the media data is corrupted steps of the resource fetch algorithm.

      2. Run the CDM Unavailable algorithm on media keys.

      3. Abort these steps.

    4. If there is at least one MediaKeySession created by the media keys on which the Session Closed algorithm has not been run, run the following steps:

      Note

      This check ensures the cdm has finished loading and is a prerequisite for a matching key being available.

      1. Let block be the first entry in the media element's encrypted block queue.

      2. Let the block key ID be the key ID of block.

        Note

        The key ID is generally specified by the container.

      3. Use the cdm to execute the following steps:

        1. Let available keys be the union of keys in sessions that were created by the media keys.

        2. Let block key be null.

        3. If any of the available keys corresponds to the block key ID and is usable for decryption, let session be a MediaKeySession object containing that key and let block key be that key.

          Note

          If multiple sessions contain a key that is usable for decryption for the block key ID, which session and key to use is Key System-dependent.

        4. If the status of any of the available keys changed as the result of running the preceding step, run the Update Key Statuses algorithm on each affected session, providing all key ID(s) in the session along with the appropriate MediaKeyStatus value(s) for each.

        5. If block key is not null, run the following steps:

          1. If session's session type is "persistent-usage-record", run the following steps:

            1. Let usage be session's record of key usage.

            2. If the first decrypt time of usage is null, set the first decrypt time of usage to the current time, accurate to within key usage accuracy.

            3. Set the latest decrypt time of usage to the current time, accurate to within key usage accuracy.

            Note

            Implementations MAY optimize the times at which this step is executed provided the recorded key usage times remain accurate to within key usage accuracy.

          2. Use the cdm to decrypt block using block key.

          3. Follow the steps for the first matching condition from the following list:

            If decryption fails
            1. Run the media data is corrupted steps of the resource fetch algorithm.

            2. If cdm is no longer usable for any reason then run the CDM Unavailable algorithm on media keys.

            3. Abort these steps.

            Otherwise
            1. Remove block from the front of the media element's encrypted block queue.

            2. Process the decrypted block as normal.

              Note

              In other words, decode the block.

            3. Return to the beginning of this algorithm.

            Note

            Not all decryption problems (i.e. using the wrong key) will result in a decryption failure. In such cases, no error is fired here but one may be fired during decode.

          Note

          Otherwise, there is no key for the block key ID in any session so continue.

  3. Run the following steps:

    Note

    These steps are reached when there is no key that is usable for decryption for block.

    1. Run the Queue a "waitingforkey" Event algorithm on the media element.

Note

For frame-based encryption, this may be implemented as follows when the media element attempts to decode a frame as part of the resource fetch algorithm:

  1. Let encrypted be false.

  2. Detect whether the frame is encrypted.

    If the frame is encrypted
    Run the steps above.
    Otherwise
    Continue.
  3. Decode the frame.

  4. Provide the frame for rendering.

7.5.4 Queue a "waitingforkey" Event

The Queue a "waitingforkey" Event algorithm is run when the CDM cannot decrypt the current block. It should only be called when the HTMLMediaElement object is potentially playing and its readyState is equal to HAVE_FUTURE_DATA or greater. Requests to run this algorithm include a target HTMLMediaElement object.

The following steps are run:

  1. Let the media element be the specified HTMLMediaElement object.

  2. If the media element's waiting for key value is true, abort these steps.

  3. Set the media element's waiting for key value to true.

    Note

    As a result of the above step, the media element will become a blocked media element if it wasn't already. In that case, the media element will stop playback.

  4. Queue a task to fire a simple event named waitingforkey at the media element.

  5. Suspend playback.

7.5.5 Attempt to Resume Playback If Necessary

The Attempt to Resume Playback If Necessary algorithm is run when one or more keys may be or may have become available. If playback is blocked waiting for a key, it resumes playback if a necessary key has been provided. Requests to run this algorithm include a target HTMLMediaElement object.

The following steps are run:

  1. Let the media element be the specified HTMLMediaElement object.

  2. If the media element's waiting for key is false, abort these steps.

  3. Run the Attempt to Decrypt algorithm on the media element.

  4. If the user agent can advance the current playback position in the direction of playback:

    1. Set the media element's waiting for key value to false.

      Note

      As a result of the above step, the media element may no longer be a blocked media element and thus playback may resume.

7.6 Media Element Restrictions

This section is non-normative.

Media data processed by a CDM MAY be unavailable through JavaScript APIs in the usual way (for example using the CanvasRenderingContext2D drawImage() method and the AudioContext MediaElementAudioSourceNode). This specification does not define conditions for such non-availability of media data, however, if media data is not available to JavaScript APIs then these APIs MAY behave as if no media data was present at all.

Where media rendering is not performed by the UA, for example in the case of a hardware-based media pipeline, then the full set of HTML rendering capabilities, for example CSS Transforms, MAY be unavailable. One likely restriction is that video media MAY be constrained to appear only in rectangular regions with sides parallel to the edges of the window and with normal orientation.

8. Implementation Requirements

This section defines implementation requirements - for both user agents and Key Systems, including the CDM and server - that may not be explicitly addressed in the algorithms.

8.1 Identifiers

The use of Distinctive Identifiers by implementations presents a privacy concern. This defines requirements for avoiding or at least mitigating such concerns.

8.1.1 Limit or Avoid use of Distinctive Identifiers

8.1.2 Encrypt Identifiers

When exposed to the application - either from a message event or a message from the server, such as one that is passed to update() - Distinctive Identifiers MUST be encrypted at the message exchange level. The encryption MUST ensure that the ciphertext cannot be used as a proxy for the actual identifier, even given the same plaintext. The CDM MUST verify that the encryption key belongs to a valid license server for its Key System.

Issue 7

Add more specific text about ensuring the desired privacy properties when encrypting identifiers.

This MAY be implemented using a server certificate.

The license server MUST NOT expose a Distinctive Identifier to any entity other than the CDM that sent it.

Note

Specifically, it should not be provided to the application or included unencrypted in messages to the CDM. This can be accomplished by encrypting the identifier or message with the identifier or such that it is only decryptable by that specific CDM.

Note

Among other things, this means that:

  • Every signature made with device-specific or user-specific keys MUST be different, even given the same plaintext.

  • Identifiers, keys, or certificates relating to device-specific or user-specific keys MUST be encrypted for the license server.

  • Messages from the license server to the CDM MUST NOT expose recipient-unique identifiers, such as the ID of the intended decryption key, on the outside of the encryption envelope.

8.1.3 Use Per-Origin Identifiers

All Distinctive Identifiers MUST be distinctive per origin. That is, the Distinctive Identifier(s) used for one origin using these APIs MUST be different from those used for any other origin using the APIs.

Issue 8

Issue 101 - It has been suggested that the Distinctive Identifiers be distinctive for the combination of top-level origin and the origin using these APIs.

It MUST NOT be possible (with a reasonable amount of time and effort) to correlate identifiers from multiple origins, such as to determine that they came from the same client or user. Specifically, implementations that derive per-origin identifiers from an origin-independent identifier, MUST do so in a non-reversible way.

Issue 9

Add more specific text about ensuring the desired non-reversible properties.

8.1.4 Allow Identifiers to be Cleared

Implementations that use Distinctive Identifier(s) MUST allow the user to clear those identifiers such that they are no longer retrievable both outside, such as via the APIs defined in this specification, and on the client device. Once cleared, new different values MUST be generated when Distinctive Identifier(s) are subsequently needed.

Implementations SHOULD allow users to clear Distinctive Identifier(s) along with cookies [COOKIES] and other site data. It is RECOMMENDED that users be offered the option to clear Distinctive Identifier(s) as part of user agent features to clear browsing history.

It is RECOMMENDED that users be able to request that Distinctive Identifiers be forgotten on a per-origin basis, particularly as part of a "Forget about this site" feature that forgets cookies [COOKIES], databases, etc. associated with a particular site in an operation that is sufficiently atomic to prevent "cookie resurrection" type of recorrelation of a new identifier with the old by relying on another type of locally stored data that did not get cleared at the same time.

8.2 Support Multiple Keys

Implementations MUST support multiple keys in each MediaKeySession object.

Note

The mechanics of how multiple keys are supported is an implementation detail, but it MUST be transparent to the application and these APIs.

Implementations MUST support seamless switching between keys during playback. This includes both keys in the same MediaKeySession and keys in separate MediaKeySession objects.

8.3 Initialization Data Type Support

8.3.1 Licenses Generated are Independent of Content Type

Implementations SHOULD allow licenses generated with any Initialization Data Type they support to be used with any content type.

Note

Otherwise, the requestMediaKeySystemAccess() algorithm might, for example, reject a MediaKeySystemConfiguration because one of the initDataTypes is not supported with one of the videoCapabilities.

8.3.2 Support Extraction From Media Data

For any supported Initialization Data Type that may appear in a supported container, the user agents MUST support extracting that type of Initialization Data from each such supported container.

Note

In other words, indicating support for an Initialization Data Type implies both CDM support for generating license requests and, for container-specific types, user agent support for extracting it from the container. This does not mean that implementations must be able to parse any supported Initialization Data from any supported content type.

8.4 Supported Media

This section defines properties of content (media resources) supported by implementations of this specification.

8.4.1 Unencrypted Container

The media container MUST NOT be encrypted. This specification relies on the user agent's ability to parse the media container without having to decrypt any of the media data. This includes the Encrypted Block Encountered and Initialization Data Encountered algorithms as well as supporting standard HTMLMediaElement [HTML5] functionality, such as seeking.

8.4.2 Interoperably Encrypted

Media resources, including all tracks, MUST be encrypted and packaged per a container-specific "common encryption" specification that allows the content to be decrypted in a fully specified and compatible way when a key or keys are provided.

Note

The Encrypted Media Extensions Stream Format and Initialization Data Format Registry [EME-STREAM-REGISTRY] provides references to such stream formats.

8.4.3 Unencrypted In-band Support Content

In-band support content, such as captions, described audio, and transcripts, SHOULD NOT be encrypted.

Note

Decryption of such tracks - especially such that they can be provided back the user agent - is not generally supported by implementations. Thus, encrypting such tracks would prevent them from being widely available for use with accessibility features in user agent implementations.

Implementations that choose to support encrypted support content MUST provide the decrypted data to the user agent to be processed in the same way as equivalent unencrypted timed text tracks.

9. Common Key Systems

All user agents MUST support the common key systems described in this section.

Note

This ensures that there is a common baseline level of functionality that is guaranteed to be supported in all user agents, including those that are entirely open source. Thus, content providers that need only basic decryption can build simple applications that will work on all platforms without needing to work with any content protection providers.

9.1 Clear Key

The "org.w3.clearkey" Key System uses plain-text clear (unencrypted) key(s) to decrypt the source. No additional client-side content protection is required. This Key System is described below.

9.1.1 Capabilities

The following describe how Clear Key supports key system-specific capabilities:

9.1.2 Behavior

The following describe how Clear Key implements key system-specific behaviors:

  • In the generateRequest() algorithm:

    • The generated message is a JSON object encoded in UTF-8 as described in License Request Format.

    • The request is generated by extracting the key IDs from the sanitized init data.

    • The "type" member value is the value of the sessionType parameter.

  • The sessionId attribute is a numerical value representable by a 32-bit integer.

  • The expiration attribute is always NaN.

  • In the update() algorithm:

    • The response parameter is either a JWK Set as described in License Format, or a JSON object encoded in UTF-8 as described in License Release Acknowledgement Format.

    • In the first case, sanitized response is considered invalid if it is not a valid JWK Set with at least one valid JWK key of a valid length for the audio/video type. In the second case sanitized response is considered invalid if it is not a valid JSON object.

  • For sessions of type "persistent-usage-record", in the remove() and load() algorithms, the message reflecting the object's record of key usage is a JSON object encoded in UTF-8 as described in License Release Format.

  • The keyStatuses attribute method initially contains all key IDs that have been provided via update(), with status "usable". When the remove() algorithm is executed, the keyStatuses attribute will be set to an empty list.

  • Initialization Data: Implementations MAY support any combination of registered Initialization Data Types [EME-INITDATA-REGISTRY]. Implementations SHOULD support the "keyids" type and other types appropriate for content types supported by the user agent.

9.1.3 License Request Format

This section describes the format of the license request provided to the application via the message attribute of the message event.

The format is a JSON object containing the following members:

"kids"
An array of key IDs. Each element of the array is the base64url encoding of the octet sequence containing the key ID value.
"type"
The requested MediaKeySessionType

When contained in the ArrayBuffer message attribute of a MediaKeyMessageEvent object, the JSON string is encoded in UTF-8 as specified in the Encoding specification [ENCODING]. Applications MAY decode the contents of the ArrayBuffer to a JSON string using the TextDecoder interface [ENCODING].

9.1.3.1 Example

This section is non-normative.

The following example is a license request for a temporary license for two key IDs. (Line breaks are for readability only.)

Example 1
{
  "kids":
    [
     "LwVHf8JLtPrv2GUXFW2v_A",
     "0DdtU9od-Bh5L3xbv0Xf_A"
    ],
  "type":"temporary"
}

9.1.4 License Format

This section describes the format of the license to be provided via the response parameter of the update() method.

The format is a JSON Web Key (JWK) Set containing representation of the symmetric key to be used for decryption, as defined in the JSON Web Key (JWK) specification [RFC7517].

For each JWK in the set, the parameter values are as follows:

"kty" (key type)
"oct" (octet sequence)
"k" (key value)
The base64url encoding of the octet sequence containing the symmetric key value
"kid" (key ID)
The base64url encoding of the octet sequence containing the key ID value

The JSON object MAY have an optional "type" member value, which MUST be one of the MediaKeySessionType values. If not specified, the default value of "temporary" is used. The update() algorithm compares this value to the sessionType.

When passed to the update() method as the ArrayBuffer response parameter, the JSON string MUST be encoded in UTF-8 as specified in the Encoding specification [ENCODING]. Applications MAY encode the JSON string using the TextEncoder interface [ENCODING].

9.1.4.1 Example

This section is non-normative.

The following example is a JWK Set containing a single symmetric key. (Line breaks are for readability only.)

Example 2
{
  "keys":
    [{
      "kty":"oct",
      "k":"tQ0bJVWb6b0KPL6KtZIy_A",
      "kid":"LwVHf8JLtPrv2GUXFW2v_A"
    }],
  'type':"temporary"
}

9.1.5 License Release Format

This section describes the format of the license release message to be provided via the message attribute of the message event.

The format is a JSON object containing the following members:

"kids"
An array of key IDs. Each element of the array is the base64url encoding of the octet sequence containing the key ID value.
"firstTime"
The first decryption time expressed as a number giving the time, in milliseconds since 01 January, 1970 UTC.
"latestTime"
The latest decryption time expressed as a number giving the time, in milliseconds since 01 January, 1970 UTC.

When contained in the ArrayBuffer message attribute of a MediaKeyMessageEvent object, the JSON string is encoded in UTF-8 as specified in the Encoding specification [ENCODING]. Applications MAY decode the contents of the ArrayBuffer to a JSON string using the TextDecoder interface [ENCODING].

9.1.5.1 Example

This section is non-normative.

The following example is a license release for a session which contained two keys. (Line breaks are for readability only.)

Example 3
{
  "kids": [ "LwVHf8JLtPrv2GUXFW2v_A", "0DdtU9od-Bh5L3xbv0Xf_A" ],
  "tfirst" : 1430425323757,
  "tlatest" : 1430425383757
}

9.1.6 License Release Acknowledgement Format

This section describes the format of the license release acknowledgement provided via the response parameter of the update() method.

The format is a JSON object containing the following members:

"kids"
An array of key IDs. Each element of the array is the base64url encoding of the octet sequence containing the key ID value.

When passed to the update() method as the ArrayBuffer response parameter, the JSON string MUST be encoded in UTF-8 as specified in the Encoding specification [ENCODING]. Applications MAY encode the JSON string using the TextEncoder interface [ENCODING].

9.1.6.1 Example

This section is non-normative.

The following example is a license request for a temporary license for two key IDs. (Line breaks are for readability only.)

Example 4
{
  "kids":
    [
     "LwVHf8JLtPrv2GUXFW2v_A",
     "0DdtU9od-Bh5L3xbv0Xf_A"
    ]
}

9.1.7 Using base64url

This section is non-normative.

For more information on base64url and working with it, see the "Base64url Encoding" terminology definition and "Notes on implementing base64url encoding without padding" in [RFC7515]. Specifically, there is no '=' padding, and the characters '-' and '_' MUST be used instead of '+' and '/', respectively.

10. Security

10.1 Input Data Attacks and Vulnerabilities

User Agent and Key System implementations MUST consider media data, Initialization Data, data passed to update(), licenses, key data, and all other data provided by the application as untrusted content and potential attack vectors. They MUST use appropriate safeguards to mitigate any associated threats and take care to safely parse, decrypt, etc. such data. User Agents SHOULD validate data before passing it to the CDM.

Note

Such validation is especially important if the CDM does not run in the same (sandboxed) context as, for example, the DOM.

Implementations MUST NOT return active content or passive content that affects program control flow to the application.

Note

For example, it is not safe to expose URLs or other information that may have come from media data, such as is the case for the Initialization Data passed to generateRequest(). Applications must determine the URLs to use. The messageType attribute of the message event can be used by the application to select among a set of URLs if applicable.

10.2 CDM Attacks and Vulnerabilities

User Agents are responsible for providing users with a secure way to browse the web, including any functionality, such as CDMs, from third parties. User agent implementers MUST obtain sufficient information from Key System implementers to enable them to properly assess the security implications of integrating with the Key System. User agent implementers MUST ensure CDM implementations provide and/or support sufficient controls for the user agent to provide security for the user. User agent implementers MUST ensure CDM implementations can and will be quickly and proactively updated in the event of security vulnerabilities.

Exploiting a CDM implementation that is not fully sandboxed and/or uses platform features may allow an attacker to access OS or platform features, elevate privilege (e.g. to run as system or root), and/or access drivers, kernel, firmware, hardware, etc. Such features, software, and hardware may not be written to be robust against hostile software or web-based attacks and may not be updated with security fixes, especially compared to the user agent. Lack of, infrequent, or slow updates for fixes to security vulnerabilities in CDM implementations increases the risk. Such CDM implementations and UAs that expose them MUST be especially careful in all areas of security, including parsing of all data.

Note

User agents should be especially diligent when using a CDM or underlying mechanism that is part of or provided by the client OS, platform and/or hardware.

If a user agent chooses to support a Key System implementation that cannot be sufficiently sandboxed or otherwise secured, the user agent SHOULD ensure that users are fully informed and/or give explicit consent before loading or invoking it. Such implementations SHOULD only be supported on secure contexts to mitigate the potential for Network Attacks.

Note

Granting permissions to unauthenticated origins is equivalent to granting the permissions to any origin in the presence of a network attacker. See also User Alerts / Prompts and Use Secure Origin and Transport.

10.3 Network Attacks

10.3.1 Potential Attacks

This section is non-normative.

Potential network attacks and their implications include:

  • DNS spoofing attacks: One cannot guarantee that a host claiming to be in a certain domain (origin) really is from that domain.

  • Passive network attacks: One cannot guarantee that data, including Distinctive Identifiers, transmitted between the client and server is not viewed by other entities. See User Tracking.

  • Active network attacks: One cannot guarantee that Additional scripts or iframes are not injected into pages (both those that use these APIs for legitimate purposes and pages that do not use these APIs). The consequences are that:

    • Calls to these APIs can be injected into any page.

    • Calls to these APIs from pages using them for legitimate reasons can be manipulated, including modifying the requested functionality, modifying or adding calls, and modifying or injecting data. See also Input Data Attacks and Vulnerabilities

    • Data, including Distinctive Identifiers, transmitted between the client and server can be viewed and/or modified by other entities. See User Tracking.

10.3.2 Mitigations

The following techniques may mitigate the risks:

Use TLS

Applications using TLS can be sure that only the user, software working on behalf of the user, and other pages using TLS that have certificates identifying them as being from the same domain, can interact with that application. Furthermore, origin-specific permissions in combination with a secure origin, ensure that permissions granted to an application cannot be abused by a network attacker.

User agents MAY choose to only support these APIs and/or specific Key Systems (i.e. based on privacy and security risks) on secure origins. This is especially important if a user agent chooses to support a Key System implementation that cannot be sufficiently sandboxed or otherwise secured. See also Secure Origin and Transport.

Block Mixed Content

User agents MUST properly handle Mixed Content [MIXED-CONTENT], including blocking "Blockable Content" [MIXED-CONTENT] to avoid potential exposure to insecure content. Such exposure could compromise other mitigations, such as use of TLS.

User agents MAY choose to block all Mixed Content, including "Optionally-blockable Content" [MIXED-CONTENT] to further increase security by preventing untrusted media data from being passed to the CDM (see CDM Attacks and Vulnerabilities).

Per-origin user alerts / prompts and permissions

User Agents SHOULD ensure that users are fully informed and/or give explicit consent before a Key System that presents security concerns that are greater than other user agent features (e.g. DOM content) may be accessed by an origin. Such alerts and consent SHOULD be per origin to avoid valid uses enabling subsequent malicious access. (A full origin MUST be used rather than just the domain because the protocol is important for security as described above.) User agents SHOULD only persist consent for secure origins (see Secure Origin and Transport), to mitigate the potential for future abuse via Network Attacks.

Note

Granting permissions to unauthenticated origins is equivalent to granting the permissions to any origin in the presence of a network attacker. Alerting or prompting the user for consent on insecure origins without persisting the choice provides at least a minimum level of security because the user would be alerted to unexpected use (e.g. on a site that does not use encrypted media).

10.4 iframe Attacks

10.4.1 Potential Attacks

This section is non-normative.

Malicious pages could host legitimate applications in an iframe in an attempt hide an attack or deceive the user as to the source, such as making the use appear to be from a legitimate content provider. This is especially relevent for user agents that support have user alerts, prompts, and/or permissions. In addition to Network Attacks, attackers could try to exploit legitimate uses of these APIs by hosting them in an iframe. By having the legitimate application performing the actions, the attacker can reuse existing granted permissions (or whitelisting) and/or appear to be a legitimate request or use.

10.4.2 Mitigations

User agents are RECOMMENDED to base the UI and persistence of user alerts, prompts, and/or permissions on the combination of origin of the top-level Document and the origin using these APIs. This ensures that users are informed of the main document making the request and that persisting a permission for one (legitimate) combination does not inadvertently allow malicious use to go undetected.

Authors are RECOMMENDED to prevent other entities from hosting their applications in iframes. Applications that must support being hosted for legitimate application-design reasons SHOULD NOT allow hosting documents to provide any data to be passed to the CDM - either via these APIs or as media data - and SHOULD NOT allow hosting frames to invoke these APIs.

10.5 Cross-Directory Attacks

This section is non-normative.

Different authors sharing one host name, for example users hosting content on geocities.com, all share one origin. User agents do not provide features to restrict access to APIs by pathname.

Using these APIs on shared hosts compromises origin-based security and privacy mitigations implemented by user agents. For example, per-origin Distinctive Identifiers are shared by all authors on one host name, and peristed data may be accessed and manipulated by any author on the host. The latter is especially important if, for example, modification or deletion of such data could erase a user's right to specific content.

Note

Even if a path-restriction feature was made available by user agents, the usual DOM scripting security model would make it trivial to bypass this protection and access the data from any path.

Authors on shared hosts are therefore RECOMMENDED to avoid using these APIs because doing so compromises origin-based security and privacy mitigations in user agents.

11. Privacy

The presence or use of Key System(s) on a user's device raises a number of privacy issues, falling into two categories: (a) user-specific information that may be disclosed by the EME interface itself or within Key System messages and (b) user-specific information that may be persistently stored on the user's device.

User Agents MUST take responsibility for providing users with adequate control over their own privacy. Since User Agents may integrate with third party CDM implementations, CDM implementers MUST provide sufficient information and controls to user agent implementers to enable them to implement appropriate techniques to ensure users have control over their privacy, including but not limited to the techniques described below.

11.1 Information Disclosed by EME and Key Systems

Concerns regarding information disclosed by EME and Key Systems fall into two categories: (a) concerns about non-specific information that may nevertheless contribute to the possibility of fingerprinting a user agent or device and (b) user-specific information that may be used directly for user tracking.

11.2 Fingerprinting

Malicious applications may be able to fingerprint users or user agents by detecting or enumerating the list of Key Systems that are supported and related information. If proper origin protections are not provided this could include detection of sites that have been visited and information stored for those sites. In particular, Key Systems MUST not share key or other data between origins.

11.3 Information Leakage

11.3.1 Concerns

This section is non-normative.

CDMs, especially those implemented outside the user agent, may not have the same fundamental isolations as the web platform. It is important that steps be taken to avoid information leakage, especially across origins. This includes both in-memory and stored data. Failure to do so could lead to information leakage to/from private browsing sessions, across profiles, and even across different browsers, applications, and operating system user accounts.

11.3.2 Mitigations

To avoid such issues, user agent and CDM implementations MUST ensure that:

  • CDMs have a concept of a CDM instance that is associated one-to-one with a MediaKeys object.

  • Keys, licenses, other session data, and the presence of sessions are restricted to the CDM instance associated with the MediaKeys object that created the session.

  • Session data is not shared between MediaKeys objects or CDM instances.

  • Session data is not shared with media elements not associated with the MediaKeys object that created the session. Among other things, this means a session's keys MUST not be used to decrypt content loaded by a media element whose mediaKeys attribute is not that MediaKeys object.

  • MediaKeys objects and the underlying implementation do not expose information outside the origin.

  • Persisted session data, if applicable, is stored on a per-origin basis.

  • Only data stored by the requesting origin may be loaded.

11.4 User Tracking

11.4.1 Concerns

This section is non-normative.

A third-party host (or any entity, such as an advertiser, capable of getting content distributed to multiple sites) could use a Distinctive Identifier or data, including keys, stored in the CDM's client-side database to track a user across multiple sessions (including across profiles and user accounts on the client device), building a profile of the user's activities or interests. Such tracking would undermine the privacy protections provided by the rest of the web platform and could, for example, enable highly-targeted advertising not otherwise possible. In conjunction with a site that is aware of the user's real identity (for example, a content provider or e-commerce site that requires authenticated credentials), this could allow oppressive groups to target individuals with greater accuracy than in a world with purely anonymous Web usage.

User- or client-specific information that could be obtained via the APIs in this specification includes:

  • Distinctive Identifier(s)

  • Origins visisted (via stored or in-memory data, permissions, etc.)

  • Content viewed (via stored or in-memory keys, key IDs, data, etc.)

This specification presents a specific concern because such information is commonly stored outside the user agent (and its profile storage), often in the CDM.

Key Systems may access or create persistent or semi-persistent identifier(s), Distinctive Identifier(s), for a device or user of a device. In some cases these identifiers may be bound to a specific device in a secure manner. If these identifiers are present in Key System messages, then devices and/or users may be tracked. If the mitigations below are not applied this could include both tracking of users / devices over time and associating multiple users of a given device.

It is important to note that such identifiers, especially those that are non-clearable, non-origin-specific or hardware-bound, exceed the tracking impact of existing techniques such as cookies [COOKIES] or session identifiers embedded in URLs.

If not mitigated, such tracking may take three forms depending on the design of the Key System:

  • In all cases, such identifiers are expected to be available to sites and/or servers that fully support the Key System (and thus can interpret Key System messages) enabling tracking by such sites.

  • If identifiers exposed by Key Systems are not origin-specific, then two sites and/or servers that fully support the Key System may collude to track the user.

  • If Key System messages contain information derived from a user identifier in a consistent manner, for example such that a portion of the initial Key System message for a specific content item does not change over time and is dependent on the user identifier, then this information could be used by any application to track the device or user over time.

In addition, if a Key System permits keys to be stored and to be re-used between origins, then it may be possible for two origins to collude and track a unique user by recording their ability to access a common key.

Finally, if any user interface for user control of Key Systems presents data separately from data in HTTP session cookies [COOKIES] or persistent storage, then users are likely to modify site authorization or delete data in one and not the others. This would allow sites to use the various features as redundant backup for each other, defeating a user's attempts to protect his privacy.

The following section describes techniques that may mitigate the risks of tracking without user consent.

11.4.2 Mitigations

Do not use Distinctive Identifiers

Key System implementations SHOULD avoid using Distinctive Identifiers whenever possible and only use them when they meaningfully contribute to the robustness of the implementation. See Limit or Avoid use of Distinctive Identifiers.

User deletion of Distinctive Identifiers

User agents MUST provide users with the ability to clear any Distinctive Identifiers maintained by Key Systems. See Allow Identifiers to be Cleared.

Use of (non-reversible) per-origin identifiers

Implementations that use Distinctive Identifiers MUST use a different value for each origin, either by allocation of different identifiers for different origins or by use of a non-reversible origin-specific mapping from an origin-independent identifier. See Use Per-Origin Identifiers and non-reversible identifiers.

Encryption of Distinctive Identifiers

Distinctive Identifiers in Key System messages MUST be encrypted, together with a timestamp or nonce, such that the Key System messages are always different. This prevents the use of Key System messages for tracking except by servers fully supporting the Key System. See Encrypt Identifiers.

Blocking third-party access

User agents MAY restrict access to Key Systems and/or features to scripts originating at the origin of the top-level Document of the browsing context. For example, requestMediaKeySystemAccess() may deny requests for certain configurations for pages from other origins running in iframes.

Expiring stored data

User agents MAY, possibly in a manner configured by the user, automatically delete Distinctive Identifiers and/or other Key System data after a period of time.

Note

For example, a user agent could be configured to such data as session-only storage, deleting the data once the user had closed all the browsing contexts that could access it.

This can restrict the ability of a site to track a user, as the site would then only be able to track the user across multiple sessions when he authenticates with the site itself (e.g. by making a purchase or logging in to a service).

However, this can also put the user's access to content, especially purchased or rented content, at risk if the user does not fully understand the implications of such expiration.

Treating Distinctive Identifiers and Key System stored data like cookies / web storage

User agents SHOULD present the presence of Distinctive Identifiers and data stored by Key Systems to the user in a way that associates them strongly with HTTP session cookies [COOKIES]. This might encourage users to view such identifiers with healthy suspicion. User agents SHOULD help the user avoid Incomplete Clearing of Data.

Site-specific white-listing of access to each Key System

User agents MAY require the user to explicitly authorize access to each Key System - and/or certain features - before a site can use it. User agents SHOULD enable users to revoke this authorization either temporarily or permanently.

Shared blacklists

User agents MAY allow users to share their Key System origin blacklists. This would allow communities to act together to protect their privacy.

Per-origin user alerts / prompts and permissions

User agents MUST ensure that users are fully informed and/or give explicit consent before Distinctive Identifier(s) are exposed, such as in messages from the Key System implementation.

User agents MUST prompt or otherwise inform the user before allowing use of a Distinctive Identifier that is not unique per-origin and/or not clearable is used. User agents SHOULD prompt or otherwise inform the user before allowing use of all other Distinctive Identifier.

Note

The "not unique per-origin" and "not clearable" conditions cannot be true in a compliant implementation because implementations MUST use per-origin identifiers and allow the user to clear identifiers.

Such alerts and consent SHOULD be per origin to avoid valid uses enabling subsequent malicious access. User agent implementers that consider such alerts or consent appropriate for a Key System implementation SHOULD only support such Key Systems on secure origins (see Secure Origin and Transport), especially if they allow such consent to be persisted.

Note

Granting permissions to unauthenticated origins is equivalent to granting the permissions to any origin in the presence of a network attacker.

User controls to disable Key Systems or Key System use of identifiers

User Agents SHOULD provide users with a global control of whether a Key System is enabled and/or whether Key System use of Distinctive Identifier(s) is enabled (if supported by the Key System). User agents SHOULD help the user avoid Incomplete Clearing of Data.

Note

While these suggestions prevent trivial use of this API for user tracking, they do not block it altogether. Within a single origin, a site can continue to track the user during a session, and can then pass all this information to a third party along with any identifying information (names, credit card numbers, addresses) obtained by the site. If a third party cooperates with multiple sites to obtain such information, and if identifiers are not unique per-origin, then a profile can still be created.

11.4.3 Individualization

Distinctive Identifier(s) are sometimes obtained via a process called individualization or provisioning.

Individualization MAY be origin-independent or per-origin. The resulting identifier MUST be origin-independent or per-origin, respectively. In the former case the resulting identifier MUST NOT be provided to the application. The mechanisms and flow for the two types of individualization are different, as described in the following sections.

In all cases, implementations SHOULD avoid sending origin(s) or origin-specific information to centralized servers since this could create a central record of all origins visited by a user or device.

Individualization MAY be performed multiple times, such as after identifier(s) are cleared.

11.4.3.1 Origin-Independent Individualization

Origin-independent individualization is performed between the CDM and an origin- and application-independent server. The process MUST be performed by the user agent and MUST NOT use these APIs.

Note

For example, such a process may initialize a client device by communicating with a pre-determined server hosted by the user agent or CDM vendor, possibly using identifiers from the client device. Such communication would not involve providing application- or origin-specific information.

The resulting identifier MUST be origin- and application-independent. Such identifiers MUST NOT be provided to applications (see Use Per-Origin Identifiers), even encrypted. Implementations MAY derive non-reversible per-origin identifiers from such identifiers and provide those to the application (encrypted)

For such individualization, all message exchanges:

  • MUST be handled by the user agent and performed by the user agent via the user agent's network stack.

  • MUST NOT be performed directly by the CDM.

  • MUST NOT be passed to or through the application via these APIs.

  • MUST be sent to a URL selected independently of any origin and application.

11.4.3.2 Per-Origin Individualization

Per-origin individualization is performed between the CDM and an application-selected server and results in a per-origin identifier. The process MUST be performed via these APIs and MUST NOT involve other types of communication. Any Distinctive Identifiers used MUST be origin-specific.

For such individualization, all message exchanges:

  • MUST be passed to or through the application via these APIs (message type "individualization-request").

  • MUST NOT be performed by the user agent.

  • MUST NOT be performed directly by the CDM.

  • MUST NOT contain non-origin-specific per-client information, such as a Distinctive Identifier.

  • As with all other uses of the APIs, responses passed to the CDM MUST NOT contain executable code.

With appropriate precautions, such individualization can provide better privacy than origin-independent individualization, though not as good as models that do not use Distinctive Identifiers. To preserve the benefits of such a design and to avoid introducing other privacy concerns:

  • Such implementations MUST NOT use Distinctive Identifier(s) for a device or user of a device in the individualization process.

  • Such implementations and the applications that support them SHOULD also avoid deferring or forwarding individualization messages to a central server or other server not controlled by the application author.

11.5 Information Stored on User Devices

11.5.1 Concerns

This section is non-normative.

Key Systems may store information on a user's device, or user agents may store information on behalf of Key Systems. Potentially, this could reveal information about a user to another user of the same device, including potentially the origins that have used a particular Key System (i.e. sites visited) or even the content that has been decrypted using a Key System.

If information stored by one origin affects the operation of the Key System for another origin, then potentially the sites visited or content viewed by a user on one site may be revealed to another, potentially malicious, site.

If information stored for one browsing profile, browser, or user account on the client device affects the operation of the Key System for other profiles, browsers, or accounts, then potentially the sites visited or content viewed by in one may be revealed by or correlatable with another profile, browser, or account.

11.5.2 Mitigations

In summary, user agent and CDM implementations that allow the CDM to persist data:

  • MUST ensure it is restricted to the origin for which it was created.

  • MUST ensure it is restricted to the current profile and does not leak to or from private browsing sessions.

  • MUST allow the user to clear it, preferably by origin.

  • SHOULD treat it like other site data, including presenting it along with cookies [COOKIES], including it in "remove all data", and presenting it in the same UI locations.

Origin-specific Key System storage

Any data persistently stored by the CDM that might impact messages or behavior in an application- or license server-visible way MUST be stored in an origin-specific way. Session data, licenses, and keys that are persistently stored MUST be stored per-origin. See Session Storage and Persistence.

User deletion of Key System storage

User agents SHOULD present the user with a way to delete Key System storage for a specific origin or all origins. User agents SHOULD help the user avoid Incomplete Clearing of Data.

Treating Distinctive Identifiers and Key System stored data like cookies / web storage

See the identical section above.

Encryption or obfuscation of Key System stored data

User agents SHOULD treat data stored by Key Systems as potentially sensitive; it is quite possible for user privacy to be compromised by the release of this information. To this end, user agents SHOULD ensure that such data is securely stored and when deleting data, it is promptly deleted from the underlying storage.

11.6 Incomplete Clearing of Data

11.6.1 Concerns

This section is non-normative.

A user's attempts to protect his or her privacy by clearing Distinctive Identifiers and stored data and/or disabling a Key System may be defeated if all such data and functionality as well as cookies [COOKIES] and other site data are not cleared and/or disabled at the same time. For example:

  • If a user clears cookies or other persistent storage without also clearing Distinctive Identifiers and data stored by Key Systems, sites can defeat those attempts by using the various features as redundant backup for each other.

  • If a user clears Distinctive Identifiers without also clearing data stored by Key Systems, including persistent sessions, as well as cookies and other persistent storage, sites can defeat those attempts by using the remaining data to associate the old and new identifiers.

  • If a user disables a key system, especially for a specific origin, without also clearing cookies or other persistent storage, sites can defeat those attempts by using the remaining features.

  • If a user disables a key system, then later decide to enable the key system, without also clearing clearing cookies or other persistent storage, Distinctive Identifiers, and data stored by Key Systems, sites may be able to associate data prior to the disabling with data and behavior after the key system is re-enabled.

11.6.2 Mitigations

User agents SHOULD present the interfaces for clearing Distinctive Identifiers and Key System stored data in a way that helps users to understand this possibility and enables them to delete data in all persistent identification and storage features, including HTTP session cookies [COOKIES] and web storage, simultaneously. Likewise, User agents SHOULD present the interfaces for disabling and re-enabling a Key System in a way that helps users to understand this possibility and enables them to delete all such data in all persistent storage features simultaneously.

11.7 Private Browsing Modes

User agents may support a mode (e.g. private browsing) of operation intended to preserve user anonymity and/or ensure records of browsing activity are not persisted on the client. The privacy concerns discussed in previous sections may be expecially concerning for users employing such modes.

User agent implementers that support such mode(s) SHOULD carefully consider whether access to Key Systems should be disabled in these mode(s). For example, such modes MAY prohibit creation of MediaKeySystemAccess objects that support or use persistentState or a distinctiveIdentifier (either as part of the CDM implementation or because the application indicated they were "required"). If implementations do not prohibit such creation, they SHOULD inform the user of the implications and potential consequences for the expected privacy properties of such modes before allowing their use.

11.8 Secure Origin and Transport

In order to protect identifiers and other information discussed in previous sections, user agents MAY choose to only support these APIs and/or specific Key Systems (i.e. based on privacy and security risks) on secure origins. This is especially important if a user agent chooses to support a Key System implementation that expose Distinctive Identifiers or other such information without effectively anonymizing it in transit.

Regardless of user agent limitations, applications SHOULD use secure transport (e.g. HTTPS) for all traffic containing messages from the CDM (i.e. all data passed from message events and to update()).

All user agents MUST properly handle Mixed Content [MIXED-CONTENT] to avoid exposure to insecure content or transport when the user agent or application wish to enforce secure origin and transport.

12. Examples

This section is non-normative.

This section contains example solutions for various use cases using the proposed extensions. These are not the only solutions to these use cases. Video elements are used in the examples, but the same would apply to all media elements. In some cases, such as using synchronous XHR, the examples are simplified to keep the focus on the extensions.

12.1 Source and Key Known at Page Load (Clear Key)

In this simple example, the source file and clear-text license are hard-coded in the page. Only one session will ever be created.

Example 5
<script>
  function onLoad() {
    var video = document.getElementById('video');

    if (!video.mediaKeys) {
      navigator.requestMediaKeySystemAccess('org.w3.clearkey', [
        { initDataTypes: ['webm'],
          videoCapabilities: [{ contentType: 'video/webm; codecs="vp8"' }] }
      ]).then(
        function(keySystemAccess) {
          var promise =  keySystemAccess.createMediaKeys();
          promise.catch(
            console.error.bind(console, 'Unable to create MediaKeys')
          );
          promise.then(
            function(createdMediaKeys) {
              return video.setMediaKeys(createdMediaKeys);
            }
          ).catch(
            console.error.bind(console, 'Unable to set MediaKeys')
          );
          promise.then(
            function(createdMediaKeys) {
              var te = new TextEncoder();
              var initData = te.encode( '{"kids":["LwVHf8JLtPrv2GUXFW2v_A"]}');
              var keySession = createdMediaKeys.createSession();
              keySession.addEventListener("message", handleMessage, false);
              return keySession.generateRequest('keyids', initData);
            }
          ).catch(
            console.error.bind(console, 'Unable to create or initialize key session')
          );
        }
      );
    }
  }

  function handleMessage(event) {
    var keySession = event.target;
    var te = new TextEncoder();
    var license = te.encode('{"keys":[{"kty":"oct","k":"tQ0bJVWb6b0KPL6KtZIy_A","kid":"LwVHf8JLtPrv2GUXFW2v_A"}],"type":"temporary"}');
    keySession.update(license).catch(
      console.error.bind(console, 'update() failed')
    );
  }
</script>

<body onload='onLoad()'>
  <video src='foo.webm' autoplay id='video'></video>
</body>

12.2 Selecting a Supported Key System and Using Initialization Data from the "encrypted" Event

This example selects a supported Key System using the requestMediaKeySystemAccess() method then uses the Initialization Data from the media data to generate the license request and send it to the appropriate license server. One of the supported key systems uses a serverCertificate, which is provided proactively.

Example 6
<script>
  var licenseUrl;
  var serverCertificate;

  // Returns a Promise<MediaKeys>.
  function createSupportedKeySystem() {
    someSystemOptions = [
     { initDataTypes: ['keyids', 'webm'],
       audioCapabilities: [
         { contentType: 'audio/webm; codecs="opus"' },
         { contentType: 'audio/webm; codecs="vorbis"' }
       ],
       videoCapabilities: [
         { contentType: 'video/webm; codecs="vp9"' },
         { contentType: 'video/webm; codecs="vp8"' }
       ]
     }
    ];
    clearKeyOptions = [
     { initDataTypes: ['keyids', 'webm'],
       audioCapabilities: [
         { contentType: 'audio/webm; codecs="opus"' },
         { contentType: 'audio/webm; codecs="vorbis"' }
       ],
       videoCapabilities: [
         { contentType: 'video/webm; codecs="vp9"',
           robustness: 'foo' },
         { contentType: 'video/webm; codecs="vp9"',
           robustness: 'bar' },
         { contentType: 'video/webm; codecs="vp8"',
           robustness: 'bar' },
       ]
     }
    ];

    return navigator.requestMediaKeySystemAccess('com.example.somesystem', someSystemOptions).then(
      function(keySystemAccess) {
        // Not shown:
        // 1. Use both attributes of keySystemAccess.getConfiguration().audioCapabilities[0]
        //    and both attributes of keySystemAccess.getConfiguration().videoCapabilities[0]
        //    to retrieve appropriate stream(s).
        // 2. Set video.src.

        licenseUrl = 'https://license.example.com/getkey';
        serverCertificate = new Uint8Array([ ... ]);
        return keySystemAccess.createMediaKeys();
      }
    ).catch(
      function(error) {
        // Try the next key system.
        navigator.requestMediaKeySystemAccess('org.w3.clearkey', clearKeyOptions).then(
          function(keySystemAccess) {
            // Not shown:
            // 1. Use keySystemAccess.getConfiguration().audioCapabilities[0].contentType
            //    and keySystemAccess.getConfiguration().videoCapabilities[0].contentType
            //    to retrieve appropriate stream(s).
            // 2. Set video.src.

            licenseUrl = 'https://license.example.com/clearkey/request';
            return keySystemAccess.createMediaKeys();
          }
        );
      }
    ).catch(
      console.error.bind(console, 'Unable to instantiate a key system supporting the required combinations')
    );
  }

  function handleInitData(event) {
    var video = event.target;
    if (video.mediaKeysObject === undefined) {
      video.mediaKeysObject = null; // Prevent entering this path again.
      video.pendingSessionData = []; // Will store all initData until the MediaKeys is ready.
      createSupportedKeySystem().then(
        function(createdMediaKeys) {
          video.mediaKeysObject = createdMediaKeys;

          if (serverCertificate)
            createdMediaKeys.setServerCertificate(serverCertificate);

          for (var i = 0; i < video.pendingSessionData.length; i++) {
            var data = video.pendingSessionData[i];
            makeNewRequest(video.mediaKeysObject, data.initDataType, data.initData);
          }
          video.pendingSessionData = [];

          return video.setMediaKeys(createdMediaKeys);
        }
      ).catch(
        console.error.bind(console, 'Failed to create and initialize a MediaKeys object')
      );
    }
    addSession(video, event.initDataType, event.initData);
  }

  function addSession(video, initDataType, initData) {
    if (video.mediaKeysObject) {
      makeNewRequest(video.mediaKeysObject, initDataType, initData);
    } else {
      video.pendingSessionData.push({initDataType: initDataType, initData: initData});
    }
  }

  function makeNewRequest(mediaKeys, initDataType, initData) {
    var keySession = mediaKeys.createSession();
    keySession.addEventListener("message", licenseRequestReady, false);
    keySession.generateRequest(initDataType, initData).catch(
      console.error.bind(console, 'Unable to create or initialize key session')
    );
  }

  function licenseRequestReady(event) {
    var request = event.message;

    var xmlhttp = new XMLHttpRequest();
    xmlhttp.keySession = event.target;
    xmlhttp.open("POST", licenseUrl);
    xmlhttp.onreadystatechange = function() {
      if (xmlhttp.readyState == 4) {
        var license = new Uint8Array(xmlhttp.response);
        xmlhttp.keySession.update(license).catch(
          console.error.bind(console, 'update() failed')
        );
      }
    }
    xmlhttp.send(request);
  }
</script>

<video autoplay onencrypted='handleInitData(event)'></video>

12.3 Create MediaKeys Before Loading Media

Initialization is much simpler if encrypted events do not need to be handled during MediaKeys initialization. This can be accomplished either by providing the Initialization Data in other ways or setting the source after the MediaKeys object has been created. This example does the latter.

Example 7
<script>
  var licenseUrl;
  var serverCertificate;
  var mediaKeys;

  // See the previous example for implementations of these functions.
  function createSupportedKeySystem() { ... }
  function makeNewRequest(mediaKeys, initDataType, initData) { ... }
  function licenseRequestReady(event) { ... }

  function handleInitData(event) {
    makeNewRequest(mediaKeys, event.initDataType, event.initData);
  }

  createSupportedKeySystem().then(
    function(createdMediaKeys) {
      mediaKeys = createdMediaKeys;
      var video = document.getElementById("v");
      video.src = 'foo.webm';
      if (serverCertificate)
        mediaKeys.setServerCertificate(serverCertificate);
      return video.setMediaKeys(mediaKeys);
    }
  ).catch(
    console.error.bind(console, 'Failed to create and initialize a MediaKeys object')
  );
</script>

<video id="v" autoplay onencrypted='handleInitData(event)'></video>

12.4 Using All Events

This is a more complete example showing all events being used.

Note that handleMessage() could be called multiple times, including in response to the update() call if multiple round trips are required and for any other reason the Key System might need to send a message.

Example 8
<script>
  var licenseUrl;
  var serverCertificate;
  var mediaKeys;

  // See previous examples for implementations of these functions.
  // createSupportedKeySystem() additionally sets renewalUrl.
  function createSupportedKeySystem() { ... }
  function handleInitData(event) { ... }

  // This replaces the implementation in the previous example.
  function makeNewRequest(mediaKeys, initDataType, initData) {
    var keySession = mediaKeys.createSession();
    keySession.addEventListener('message', handleMessage, false);
    keySession.addEventListener('keystatuseschange', handlekeyStatusesChange, false);
    keySession.closed.then(
      console.log.bind(console, 'Session closed')
    );
    keySession.generateRequest(initDataType, initData).catch(
      console.error.bind(console, 'Unable to create or initialize key session')
    );
  }

  function handleMessageResponse(keySession, response) {
    var license = new Uint8Array(response);
    keySession.update(license).catch(
      function(err) {
        console.error('update() failed: ' + err);
      }
    );
  }

  function sendMessage(type, message, keySession) {
    var url = licenseUrl;
    if (type == "license-renewal")
      url = renewalUrl;
    xmlhttp = new XMLHttpRequest();
    xmlhttp.keySession = keySession;
    xmlhttp.open('POST', url);
    xmlhttp.onreadystatechange = function() {
      if (xmlhttp.readyState == 4)
        handleMessageResponse(xmlhttp.keySession, xmlhttp.response);
    }
    xmlhttp.send(message);
  }

  function handleMessage(event) {
    sendMessage(event.messageType, event.message, event.target);
  }

  function handlekeyStatusesChange(event) {
    // Evaluate the current state using one of the map-like methods exposed by
    // event.target.keyStatuses.
    // For example:
    event.target.keyStatuses.forEach(function(keyId, status, map) {
      switch (status) {
        case "usable":
          break;
        case "expired":
          // Report an expired key.
          break;
        case "status-pending":
          // The status is not yet known. Consider the key unusable until the status is updated.
          break;
        default:
          // Do something with |keyId| and |status|.
      }
    })
  }

  createSupportedKeySystem().then(
    function(createdMediaKeys) {
      mediaKeys = createdMediaKeys;
      var video = document.getElementById("v");
      video.src = 'foo.webm';
      if (serverCertificate)
        mediaKeys.setServerCertificate(serverCertificate);
      return video.setMediaKeys(mediaKeys);
    }
  ).catch(
    console.error.bind(console, 'Failed to create and initialize a MediaKeys object')
  );
</script>

<video id="v" autoplay onencrypted='handleInitData(event)'></video>

12.5 Stored License

This example requests a persistent license for future use and stores it. It also provides functions for later retrieving the license and for destroying it.

Example 9
<script>
  var licenseUrl;
  var serverCertificate;
  var mediaKeys;

  // See the previous examples for implementations of these functions.
  // createSupportedKeySystem() additionally sets persistentState: "required" in each options dictionary.
  function createSupportedKeySystem() { ... }
  function sendMessage(message, keySession) { ... }
  function handleMessage(event) { ... }

  // Called if the application does not have a stored sessionId for the media resource.
  function makeNewRequest(mediaKeys, initDataType, initData) {
    var keySession = mediaKeys.createSession("persistent-license");
    keySession.addEventListener('message', handleMessage, false);
    keySession.closed.then(
      function() {
        console.log('Session ' + this.sessionId + ' closed');
      }.bind(keySession)
    );
    keySession.generateRequest(initDataType, initData).then(
      function() {
        // Store this.sessionId in the application.
      }.bind(keySession)
    ).catch(
      console.error.bind(console, 'Unable to request a persistent license')
    );
  }

  // Called if the application has a stored sessionId for the media resource.
  function loadStoredSession(mediaKeys, sessionId) {
    var keySession = mediaKeys.createSession("persistent-license");
    keySession.addEventListener('message', handleMessage, false);
    keySession.closed.then(
      console.log.bind(console, 'Session closed')
    );
    keySession.load(sessionId).then(
      function(loaded) {
        if (!loaded) {
          console.error('No stored session with the ID ' + sessionId + ' was found.');
          // The application should remove its record of |sessionId|.
          return;
        }
      }
    ).catch(
      console.error.bind(console, 'Unable to load or initialize the stored session with the ID ' + sessionId)
    );
  }

  // Called when the application wants to stop using the session without removing the stored license.
  function closeSession(keySession) {
    keySession.close();
  }

  // Called when the application wants to remove the stored license.
  // The stored session data has not been completely removed until the promise returned by remove() is fulfilled.
  // The remove() call may initiate a series of messages to/from the server that must be completed before this occurs.
  function removeStoredSession(keySession) {
    keySession.remove().then(
      function() {
        console.log('Session ' + this.sessionId + ' removed');
        // The application should remove its record of this.sessionId.
      }.bind(keySession)
    ).catch(
      console.error.bind(console, 'Failed to remove the session')
    );
  }

  // This replaces the implementation in the previous example.
  function handleMessageResponse(keySession, response) {
    var license = new Uint8Array(response);
    keySession.update(license).then(
      function() {
        // If this was the last required message from the server, the license is
        // now stored. Update the application state as appropriate.
      }
    ).catch(
      console.error.bind(console, 'update() failed')
    );
  }

  createSupportedKeySystem().then(
    function(createdMediaKeys) {
      mediaKeys = createdMediaKeys;
      var video = document.getElementById("v");
      if (serverCertificate)
        mediaKeys.setServerCertificate(serverCertificate);
      return video.setMediaKeys(mediaKeys);
    }
  ).catch(
    console.error.bind(console, 'Failed to create and initialize a MediaKeys object')
  );
</script>

<video id='v' src='foo.webm' autoplay></video>

13. Revision History

Version Comment
13 November 2014 Repository moved to GitHub.
10 October 2014 Converted to ReSpec.
3 September 2014 Reorganized by object.
27 August 2014 Moved license request generation and session loading to MediaKeySession.
18 August 2014 Produced candidate WD.
14 April 2014 Use promises.
1 April 2014 Moved Container Guidelines to the Encrypted Media Extensions Stream Format and Initialization Data Format Registry.
3 February 2014 Produced candidate WD.
17 September 2013 Produced candidate WD.
6 May 2013 Produced updated candidate FPWD.
14 January 2013 Produced candidate FPWD.
16 August 2012 Converted to the object-oriented API.
0.1b Last non-object-oriented revision.
0.1a Corrects minor mistakes in 0.1.
0.1 Initial Proposal

A. References

A.1 Normative references

[COOKIES]
A. Barth. IETF. HTTP State Management Mechanism. April 2011. Proposed Standard. URL: https://tools.ietf.org/html/rfc6265
[DOM]
Anne van Kesteren; Aryeh Gregor; Ms2ger; Alex Russell; Robin Berjon. W3C. W3C DOM4. 19 November 2015. W3C Recommendation. URL: http://www.w3.org/TR/dom/
[ECMA-262]
Ecma International. ECMAScript Language Specification. URL: https://tc39.github.io/ecma262/
[ENCODING]
Anne van Kesteren; Joshua Bell; Addison Phillips. W3C. Encoding. 20 October 2015. W3C Candidate Recommendation. URL: http://www.w3.org/TR/encoding/
[HTML5]
Ian Hickson; Robin Berjon; Steve Faulkner; Travis Leithead; Erika Doyle Navara; Edward O'Connor; Silvia Pfeiffer. W3C. HTML5. 28 October 2014. W3C Recommendation. URL: http://www.w3.org/TR/html5/
[MIXED-CONTENT]
Mike West. W3C. Mixed Content. 8 October 2015. W3C Candidate Recommendation. URL: http://www.w3.org/TR/mixed-content/
[POWERFUL-FEATURES]
Mike West. W3C. Secure Contexts. 26 April 2016. W3C Working Draft. URL: http://www.w3.org/TR/secure-contexts/
[RFC6381]
R. Gellens; D. Singer; P. Frojdh. IETF. The 'Codecs' and 'Profiles' Parameters for "Bucket" Media Types. August 2011. Proposed Standard. URL: https://tools.ietf.org/html/rfc6381
[RFC7517]
M. Jones. IETF. JSON Web Key (JWK). May 2015. Proposed Standard. URL: https://tools.ietf.org/html/rfc7517
[WebIDL]
Cameron McCormack; Boris Zbarsky. W3C. WebIDL Level 1. 8 March 2016. W3C Candidate Recommendation. URL: http://www.w3.org/TR/WebIDL-1/

A.2 Informative references

[EME-INITDATA-REGISTRY]
David Dorwin; Adrian Bateman; Mark Watson. W3C. Encrypted Media Extensions Initialization Data Format Registry. URL: format-registry/initdata/
[EME-STREAM-REGISTRY]
David Dorwin; Adrian Bateman; Mark Watson. W3C. Encrypted Media Extensions Stream Format Registry. URL: format-registry/stream/
[MEDIA-SOURCE]
Matthew Wolenetz; Jerry Smith; Mark Watson; Aaron Colwell; Adrian Bateman. W3C. Media Source Extensions. 3 May 2016. W3C Candidate Recommendation. URL: http://www.w3.org/TR/media-source/
[RFC6838]
N. Freed; J. Klensin; T. Hansen. IETF. Media Type Specifications and Registration Procedures. January 2013. Best Current Practice. URL: https://tools.ietf.org/html/rfc6838
[RFC7515]
M. Jones; J. Bradley; N. Sakimura. IETF. JSON Web Signature (JWS). May 2015. Proposed Standard. URL: https://tools.ietf.org/html/rfc7515