Copyright © 2014 W3C® (MIT, ERCIM, Keio, Beihang), All Rights Reserved. W3C liability, trademark and document use rules apply.
This proposal extends HTMLMediaElement
[HTML5] providing APIs to control playback of protected 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.
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 groups maintains a list of all bug reports that the editors have not yet tried to address. 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.
Note: It is an open issue whether and how the specification should do more to encourage/ensure CDM-level interoperability. See Bug 20944.
Note: 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 August 2014 W3C Process Document.
This section is non-normative.
This proposal allows JavaScript 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 also enables content providers to develop a single application solution for all devices. A generic stack implemented using the proposed APIs is shown below. This diagram shows an example flow: other combinations of API calls and events are possible.
The Content Decryption Module (CDM) is a generic term for the client component that provides the functionality, including decryption, for one or more Key Systems.
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.
A user agent MAY support one or more CDMs.
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. The Common Key Systems are supported by all user agents. 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.
For example, "com.example.somesystem".
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.
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 by the CDM for decryption when the session is closed, including when the MediaKeySession
object is destroyed.
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.
Session IDs for "persistent"
sessions MUST be unique within the origin over time, including across browsing sessions.
The underlying content protection protocol does not necessarily need to support Session IDs.
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.)
A key is considered usable if the CDM is certain the key is currently usable for decryption.
For example, a key is not usable if its license has expired.
A key is associated with a key ID, which uniquely identifies a 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.
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.
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.
Initialization data found with the media data is provided to the application in the initData
attribute of the encrypted
event.
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 what format the initialization data is provided in. 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-REGISTRY] provides the mapping from initialization data type string to the specification for each format.
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.
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].
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.
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 resolving or rejecting a promise.
Bug 25923 - Feature detection, including isTypeSupported(), and MediaKeys creation may change significantly.
enum IsTypeSupportedResult {
"/* empty string */",
"maybe",
"probably"
};
Enumeration description | |
---|---|
/* empty string */ | The combination is not supported. |
maybe | The combination may be supported. |
probably | The combination is likely supported. |
enum SessionType {
"temporary",
"persistent"
};
Enumeration description | |
---|---|
temporary | A session for which a record of or data related to the session MUST NOT be persisted. The application need not worry about managing such storage. |
persistent | A session for which a record of or data related to the session MAY be persisted. The application is responsible for managing any such storage that may be generated by the CDM. See Session Storage and Persistence. |
interface MediaKeys {
readonly attribute DOMString keySystem;
MediaKeySession
createSession (optional SessionType
sessionType = "temporary");
Promise<void> setServerCertificate ((ArrayBuffer or ArrayBufferView) serverCertificate);
static Promise<MediaKeys
> create (DOMString keySystem);
static IsTypeSupportedResult
isTypeSupported (DOMstring keySystem, optional DOMString initDataType, optional DOMString contentType, optional DOMString capability);
};
keySystem
of type DOMString, readonly create
, staticCreates a new MediaKeys
object for keySystem.
Parameter | Type | Nullable | Optional | Description |
---|---|---|---|---|
keySystem | DOMString | ✘ | ✘ |
Promise<MediaKeys
>
When this method is invoked, the user agent must run the following steps:
If keySystem is an empty string, return a promise rejected with a new DOMException
whose name is InvalidAccessError
.
If keySystem is not one of the Key Systems supported by the user agent, return a promise rejected with a new DOMException
whose name is NotSupportedError
. String comparison is case-sensitive.
If keySystem is not supported or not allowed in the origin of the calling context's Document, return a promise rejected with a new DOMException
whose name is NotSupportedError
.
Let promise be a new promise.
Run the following steps asynchronously:
Let cdm be the CDM corresponding to keySystem.
Load and initialize the cdm if necessary.
If cdm fails to load or initialize, reject promise with a new DOMException
whose name is the appropriate error name.
Let media keys be a new MediaKeys
object, and initialize it as follows:
Set the keySystem
attribute to keySystem.
Resolve promise with media keys.
Return promise.
createSession
Returns a new MediaKeySession
object.
Parameter | Type | Nullable | Optional | Description |
---|---|---|---|---|
sessionType |
| ✘ | ✔ |
MediaKeySession
When this method is invoked, the user agent must run the following steps:
If sessionType is not supported by the CDM corresponding to the keySystem
attribute, throw a new DOMException
whose name is NotSupportedError
.
Let session be a new MediaKeySession
object, and initialize it as follows:
Let the sessionId
attribute be the empty string.
Let the expiration
attribute be NaN
.
Let the closed
attribute be a new promise.
Let the session type be sessionType.
Let uninitialized be true.
Let callable be false.
Return session.
isTypeSupported
, staticReturns whether keySystem is supported with the initDataType, container and codec(s) specified by contentType, and capability.
The following list shows some examples.
Parameter | Type | Nullable | Optional | Description |
---|---|---|---|---|
keySystem | DOMstring | ✘ | ✘ | |
initDataType | DOMString | ✘ | ✔ | |
contentType | DOMString | ✘ | ✔ | |
capability | DOMString | ✘ | ✔ |
IsTypeSupportedResult
When this method is invoked, the user agent must run the following steps:
If keySystem is an empty string or contains an unrecognized or unsupported Key System, return ""
and abort these steps. String comparison is case-sensitive.
If the keySystem implementation is not available and usable, return ""
and abort these steps.
Follow the steps for the first matching condition from the following list:
create()
"probably"
."maybe"
.This may, for example, be the case for strings that are only used for discovery.
If initDataType was not provided, follow the steps for the first matching condition from the following list and abort these steps:
"maybe"
.If initDataType is an empty string or contains an unrecognized or unsupported Initialization Data, return ""
and abort these steps. String comparison is case-sensitive.
If initDataType is not an Initialization Data supported by the keySystem implementation, return ""
and abort these steps.
If the keySystem implementation supporting initDataType is not available and usable, return ""
and abort these steps.
If contentType was not provided, follow the steps for the first matching condition from the following list and abort these steps:
"maybe"
.If contentType is an empty string or contains an invalid or unrecognized MIME type, return ""
and abort these steps.
Let container be the container type specified by contentType.
Let parameters be the RFC 6381 [RFC6381] parameters, if any, specified by contentType.
Let media types be the set of media types specified by parameters. It MAY be empty. The case-sensitivity of string comparisons is determined by the appropriate RFC or other specification.
For example, all of the codecs. Case-sensitive string comparison is RECOMMENDED because RFC 6381 [RFC6381] says, "Values are case sensitive" for some formats.
If the user agent does not support container, return ""
and abort these steps. The case-sensitivity of string comparisons is determined by the appropriate RFC.
Per RFC 6838 [RFC6838], "Both top-level type and subtype names are case-insensitive."
If the user agent and keySystem implementation do not support playback of encrypted media data for all media types, return ""
and abort these steps.
If capability was not provided, follow the steps for the first matching condition from the following list and abort these steps:
"maybe"
."maybe"
.If capability is an empty string, return ""
and abort these steps.
If the keySystem implementation does not support capability, return ""
and abort these steps. String comparison is case-sensitive.
Follow the steps for the first matching condition from the following list:
"maybe"
."maybe"
.setServerCertificate
Provides a server certificate to be used to encrypt messages to the license server.
The contents of serverCertificate are Key System-specific.
Key systems that use such certificates should also support requesting the certificate from the server via an additional round trip. This simplifies interoperability for applications that are not designed to provide certificates to specific key systems.
Parameter | Type | Nullable | Optional | Description |
---|---|---|---|---|
serverCertificate | (ArrayBuffer or ArrayBufferView) | ✘ | ✘ |
Promise<void>
When this method is invoked, the user agent must run the following steps:
If serverCertificate is an empty array, return a promise rejected with a new a new DOMException
whose name is InvalidAccessError
.
If the CDM corresponding to the keySystem
attribute does not support server certificates, return a promise rejected with a new DOMException
whose name is NotSupportedError
.
Let certificate be a copy of the contents of the serverCertificate parameter.
Let promise be a new promise.
Run the following steps asynchronously:
Let cdm be the cdm during the initialization of this object.
Use the cdm to process certificate.
If any of the preceding steps failed, reject promise with a new DOMException
whose name is the appropriate error name.
Resolve promise.
Return promise.
The MediaKeySession object represents a key session.
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 resolving or rejecting a promise.
interface MediaKeySession : EventTarget {
readonly attribute DOMString sessionId;
readonly attribute unrestricted double expiration;
readonly attribute Promise<void> closed;
Promise<void> generateRequest (DOMString initDataType, (ArrayBuffer or ArrayBufferView) initData);
Promise<boolean> load (DOMString sessionId);
Promise<void> update ((ArrayBuffer or ArrayBufferView) response);
Promise<void> close ();
Promise<void> remove ();
Promise<sequence<ArrayBuffer>> getUsableKeyIds ();
};
closed
of type Promise<void>, readonly Signals when object becomes closed as a result of the session close algorithm being run. This promise can only be fulfilled and is never rejected.
expiration
of type unrestricted double, readonly The time, in milliseconds since 01 January, 1970 UTC, after which the key(s) in the session will no longer be usable to decrypt media data, or NaN
if no such time exists, as determined by the CDM.
sessionId
of type DOMString, readonly The Session Id for this object and the associated key(s) or license(s).
close
Indicates that the application no longer needs the session and the CDM should release any resources associated with this object and close it.
The returned promise is resolved when the request has been processed, and the closed
attribute promise is resolved when the session is closed.
Promise<void>
When this method is invoked, the user agent must run the following steps:
If this object's callable value is false, return a promise rejected with a new DOMException
whose name is InvalidStateError
.
If the session close algorithm has been run on this object, return a resolved promise.
Let promise be a new promise.
Run the following steps asynchronously:
Let cdm be the CDM loaded during the initialization of the MediaKeys
object that created this object.
Use the cdm to execute the following steps:
Process the close request.
Do not remove stored session data.
If the previous step caused the session to be closed, run the session close algorithm on this object.
Resolve promise.
Return promise.
generateRequest
Generates a request based on the initData.
initData is Initialization Data, and initDataType is an Initialization Data that indicates how to interpret initData.
Parameter | Type | Nullable | Optional | Description |
---|---|---|---|---|
initDataType | DOMString | ✘ | ✘ | |
initData | (ArrayBuffer or ArrayBufferView) | ✘ | ✘ |
Promise<void>
When this method is invoked, the user agent must run the following steps:
If this object's uninitialized value is false, return a promise rejected with a new DOMException
whose name is InvalidStateError
.
Let this object's uninitialized be false.
If initDataType is an empty string, return a promise rejected with a new DOMException
whose name is InvalidAccessError
.
If initData is an empty array, return a promise rejected with a new DOMException
whose name is InvalidAccessError
.
Let media keys be the MediaKeys
object that created this object.
If the CDM corresponding to media keys's keySystem
attribute does not support initDataType as an Initialization Data, return a promise rejected with a new DOMException
whose name is NotSupportedError
. String comparison is case-sensitive.
Let init data be a copy of the contents of the initData parameter.
Let session type be this object's session type.
Let promise be a new promise.
Run the following steps asynchronously:
If the init data is not valid for initDataType, reject promise with a new DOMException
whose name is InvalidAccessError
.
Let sanitized init data be a validated and/or sanitized version of init data.
The user agent should thoroughly validate the Initialization Data 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. For Initialization Data formats that support multiple entries, the user agent should remove entries that are not needed by the CDM.
If the previous step failed, reject promise with a new DOMException
whose name is InvalidAccessError
.
Let session id be the empty string.
Let message be null.
Let cdm be the CDM loaded during the initialization of media keys.
Use the cdm to execute the following steps:
If the init data is not supported by the cdm, reject promise with a new DOMException
whose name is NotSupportedError
.
Follow the steps for the first matching condition from the following list:
"temporary"
The returned license must not be persistable.
"persistent"
The returned license may be persistable.)
The license server determines the type of license that is returned, either persistent or non-persistent. A persistent license cannot be added to a non-persistable session.
Let session id be a unique Session Id string.
If session type is "persistent"
, the ID MUST be unique within the the origin of this object's Document over time, including across Documents and browsing sessions.
Let message be a request for the requested session type generated based on the init data, which is interpreted per initDataType.
For example, a license request.
The cdm MUST NOT use any stream-specific data, including media data, not provided via the init data.
The cdm SHOULD NOT store session data, including the session ID, at this point. See Session Storage and Persistence.
If any of the preceding steps failed, reject promise with a new DOMException
whose name is the appropriate error name.
Set the sessionId
attribute to session id.
Let this object's callable be true.
Run the queue a "message" event algorithm on the session, providing "licenserequest"
and message.
Resolve promise.
Return promise.
getUsableKeyIds
Bug 26372 - getUsableKeyIds() may be replaced.
Gets the key IDs for keys in the session that the CDM knows are currently usable to decrypt media data.
Promise<sequence<ArrayBuffer>>
When this method is invoked, the user agent must run the following steps:
If this object's callable value is false, return a promise rejected with a new DOMException
whose name is InvalidStateError
.
Let promise be a new promise.
Run the following steps asynchronously:
Let cdm be the CDM loaded during the initialization of the MediaKeys
object that created this object.
Use the cdm to execute the following steps:
Let usable key ids be a list of the key IDs for keys in the session that the CDM knows are currently usable to decrypt media data. usable key ids MUST NOT contain IDs for keys that may not currently be usable. Each element MUST be unique.
If the preceding step failed, reject promise with a new DOMException
whose name is the appropriate error name.
Resolve promise with a new Sequence object, each element of which contains one element of usable key ids.
load
Loads the data stored for the sessionId into the session represented by the object.
Parameter | Type | Nullable | Optional | Description |
---|---|---|---|---|
sessionId | DOMString | ✘ | ✘ |
Promise<boolean>
When this method is invoked, the user agent must run the following steps:
If this object's uninitialized value is false, return a promise rejected with a new DOMException
whose name is InvalidStateError
.
Let this object's uninitialized be false.
If sessionId is an empty string, return a promise rejected with a new DOMException
whose name is InvalidAccessError
.
If this object's session type is not "persistent"
, return a promise rejected with a new DOMException
whose name is InvalidAccessError
.
Let media keys be the MediaKeys
object that created this object.
If the CDM corresponding to media keys's keySystem
attribute does not support loading previous sessions, return a promise rejected with a new DOMException
whose name is NotSupportedError
.
Let promise be a new promise.
Run the following steps asynchronously:
Let sanitized session ID be a validated and/or sanitized version of sessionId.
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.
If the previous step failed, reject promise with a new DOMException
whose name is InvalidAccessError
.
Let expiration time be NaN
.
Let message be null.
Let message type be null.
Let cdm be the CDM loaded during the initialization of media keys.
Use the cdm to execute the following steps:
If there is no data stored for the sanitized session ID in the origin, resolve promise with false
.
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.
If there is an unclosed "persistent"
session in any Document representing the session data, reject promise with a new DOMException
whose name is QuotaExceededError
.
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.
Load the session data.
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.
If the CDM needs to send a message:
Let message be a message generated by the CDM based on the session data.
Let message type be the appropriate MediaKeyMessageType
for the message.
If any of the preceding steps failed, reject promise with a new DOMException
whose name is the appropriate error name.
Set the sessionId
attribute to sanitized session ID.
Let this object's callable be true.
If the loaded session contains usable keys, run the usable keys changed algorithm on the session.
The algorithm MAY also be run later should additional processing be necessary to determine with certainty whether one or more keys is usable.
Run the update expiration algorithm on the session, providing expiration time.
If message is not null, run the queue a "message" event algorithm on the session, providing message type and message.
Resolve promise with true
.
Return promise.
remove
Removes stored session data associated with this object.
Promise<void>
When this method is invoked, the user agent must run the following steps:
If this object's callable value is false, return a promise rejected with a new DOMException
whose name is InvalidStateError
.
If this object's session type is not "persistent"
, return a promise rejected with a new DOMException
whose name is InvalidAccessError
.
If the session close algorithm has been run on this object, return a promise rejected with a new DOMException
whose name is InvalidStateError
.
Let promise be a new promise.
Run the following steps asynchronously:
Let cdm be the CDM loaded during the initialization of the MediaKeys
object that created this object.
Use the cdm to execute the following steps:
Process the remove request.
This MAY involve exchanging message(s) with the application.
Unless this step fails, the CDM MUST have cleared all stored session data associated with this object, including the sessionId
, before proceeding to the next step.
Run the following steps asynchronously once the above step has completed:
If any of the preceding steps failed, reject promise with a new DOMException
whose name is the appropriate error name.
Run the session close algorithm on this object.
Resolve promise.
Return promise.
update
Provides messages, including licenses, to the CDM.
The contents of response are Key System-specific.
Parameter | Type | Nullable | Optional | Description |
---|---|---|---|---|
response | (ArrayBuffer or ArrayBufferView) | ✘ | ✘ |
Promise<void>
When this method is invoked, the user agent must run the following steps:
If this object's callable value is false, return a promise rejected with a new DOMException
whose name is InvalidStateError
.
If response is an empty array, return a promise rejected with a new DOMException
whose name is InvalidAccessError
.
Let response copy be a copy of the contents of the response parameter.
Let promise be a new promise.
Run the following steps asynchronously:
Let sanitized response be a validated and/or sanitized version of response copy.
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.
If the previous step failed, reject promise with a new DOMException
whose name is InvalidAccessError
.
Let cdm be the CDM loaded during the initialization of the MediaKeys
object that created this object.
Let message be null.
Let message type be null.
Use the cdm to execute the following steps:
If the format of sanitized response is invalid in any way, reject promise with a new DOMException
whose name is InvalidAccessError
.
Process sanitized response, following the stipulation for the first matching condition from the following list:
"temporary"
and sanitized response does not specify that session data, including any license, key(s), or similar session data it contains, should be stored"persistent"
DOMException
whose name is InvalidAccessError
.See also Session Storage and Persistence.
When sanitized response contains key(s) and/or related data, cdm will likely cache the key and related data indexed by key ID.
The replacement algorithm within a session is Key System-dependent.
Keys from different sessions SHOULD be cached independently such that closing one session does not affect keys in other sessions, even if they have overlapping key IDs.
It is RECOMMENDED that CDMs 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 the set of usable keys changed, run the usable keys changed algorithm on the session.
The algorithm MAY also be run later should additional processing be necessary to determine with certainty whether one or more keys is usable.
If the expiration time for the session changed, run the update expiration algorithm on the session, providing the new expiration time.
If a message needs to be sent to the server, execute the following steps:
Let message be that message.
Let message type be the appropriate MediaKeyMessageType
for the message.
If any of the preceding steps failed, reject promise with a new DOMException
whose name is the appropriate error name.
If message is not null, run the queue a "message" event algorithm on the session, providing message type and message.
Resolve promise.
Return promise.
The MediaKeyMessageEvent object is used for the message
event.
Events are constructed as defined in Constructing events [DOM].
enum MediaKeyMessageType {
"licenserequest",
"licenserenewal",
"licenserelease"
};
Enumeration description | |
---|---|
licenserequest | The message contains a request for a new license. |
licenserenewal | The message contains a request to renew an existing license. |
licenserelease | The message contains a proof of key release. |
[ Constructor (DOMString type, optional MediaKeyMessageEventInit
eventInitDict)]
interface MediaKeyMessageEvent : Event {
readonly attribute MediaKeyMessageType
type;
readonly attribute ArrayBuffer message;
};
MediaKeyMessageEvent
Parameter | Type | Nullable | Optional | Description |
---|---|---|---|---|
type | DOMString | ✘ | ✘ | |
eventInitDict |
| ✘ | ✔ |
message
of type ArrayBuffer, readonly type
of type MediaKeyMessageType
, readonly dictionary MediaKeyMessageEventInit : EventInit {
MediaKeyMessageType
type = "licenserequest";
ArrayBuffer message = ArrayBuffer();
};
MediaKeyMessageEventInit
Membersmessage
of type ArrayBuffer, defaulting to ArrayBuffer()
type
of type MediaKeyMessageType
, defaulting to "licenserequest"
This section is non-normative.
In some implementations, MediaKeySession
objects may not fire any events until the MediaKeys
object is associated with a media element using setMediaKeys()
.
Event name | Interface | Dispatched when... |
---|---|---|
keyschange |
Event |
There has been a change in usable keys in the session. |
message |
MediaKeyMessageEvent |
The CDM has generated a message for the session. |
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.
The following steps are run:
Let the session be the specified MediaKeySession
object.
Queue a task to fire a simple event named message
at the session.
The event is of type MediaKeyMessageEvent
and has:
The Usable Keys Changed algorithm is run when the CDM changes the set of keys in the session that may be used for decryption.
This can happen as the result of an update()
call or some other event.
Requests to run this algorithm include a target MediaKeySession
object.
The following steps are run:
Let the session be the associated MediaKeySession
object.
Queue a task to fire a simple event named keyschange
at the session.
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.
The user agent MAY choose to skip this step if it knows resuming will fail.
For example, the user agent may skip this step if no additional keys became available.
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:
Let the session be the associated MediaKeySession
object.
Let expiration time be NaN
.
If the new expiration time is not NaN
, let expiration time be the new expiration time in milliseconds since 01 January 1970 UTC.
Set the session's expiration
attribute to expiration time.
The Session Close algorithm is run when the CDM closes the session associated with a MediaKeySession
object.
The CDM may close a session at any point, such as in response to a close()
call, when the session is no longer needed, or when system resources are lost.
Keys in other sessions SHOULD be unaffected, even if they have overlapping key IDs.
The following steps are run:
Let the session be the associated MediaKeySession
object.
Let media keys be the MediaKeys
object that created this object.
Let promise be the closed
attribute of the session.
Resolve promise.
The methods report errors by rejecting the returned promise with a DOMException
.
The following 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) |
---|---|
NotSupportedError |
The existing MediaKeys object cannot be removed. The key system is not supported. The key system is not supported on insecure origins. 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. |
InvalidAccessError |
The parameter is empty. Invalid initialization data. The operation is not supported on sessions of this type. Invalid response format. A persistent license was provided for a "temporary" session. |
QuotaExceededError |
The MediaKeys object cannot be used with additional HTMLMediaElements. A non-closed session already exists for this sessionId. |
This section provides an overview of session stroage and persistence that complements the algorithms.
If this object's session type is not "persistent"
, 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), and the Session Id.
The remainder of this section applies to "persistent"
sessions, which are OPTIONAL for implementatations to support.
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.
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 close algorithm has not been run on the object representing it.
An application that creates a "persistent"
session 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 Considerations and Privacy Considerations sections for additional considerations when supporting persistent storage.
This section specifies additions to and modifications of the HTMLMediaElement
[HTML5] when the Encrypted Media Extensions are supported.
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 resolving or rejecting a promise.
enum MediaWaitingFor {
"none",
"data",
"key"
};
Enumeration description | |
---|---|
none | The media element is not waiting for anything. |
data | The media element is not waiting for data. |
key | The media element is not waiting for a key. |
partial interface HTMLMediaElement : EventTarget {
readonly attribute MediaKeys
? mediaKeys;
readonly attribute MediaWaitingFor
waitingFor;
attribute EventHandler onencrypted;
Promise<void> setMediaKeys (MediaKeys
? mediaKeys);
};
mediaKeys
of type MediaKeys
, readonly , nullableThe 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.
waitingFor
of type MediaWaitingFor
, readonly Indicates what the media element is waiting for, if anything (indicated by the waiting
and canplay
events). This is described in the encrypted block encountered algorithm.
setMediaKeys
Provides the MediaKeys
to use when decrypting media data during playback.
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.
As a best practice, applications should create a MediaKeys object and call setMediaKeys()
before providing media data (for example, setting the src
attribute). This avoids potential delays in some implementations.
Parameter | Type | Nullable | Optional | Description |
---|---|---|---|---|
mediaKeys |
| ✔ | ✘ |
Promise<void>
When this method is invoked, the user agent must run the following steps:
If mediaKeys and the mediaKeys
attribute are the same object, return a resolved promise.
If this object's attaching media keys value is true, return a promise rejected with a new DOMException
whose name is InvalidStateError
.
Let this object's attaching media keys value be true.
Let promise be a new promise.
Run the following steps asynchronously:
If mediaKeys is not null, it 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 new DOMException
whose name is QuotaExceededError
.
If the mediaKeys
attribute is not null, run the following steps:
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 new DOMException
whose name is NotSupportedError
.
If the association cannot currently be removed, let this object's attaching media keys value be false and reject promise with a new DOMException
whose name is InvalidStateError
.
For example, some implementations may not allow removal during playback.
Stop using the CDM instance represented by the mediaKeys
attribute to decrypt media data and remove the association with the media element.
If the preceding step failed, let this object's attaching media keys value be false and reject promise with a new DOMException
whose name is the appropriate error name.
If mediaKeys is not null, run the following steps:
Associate the CDM instance represented by mediaKeys with the media element for decrypting media data.
If the preceding step failed, run the following steps:
Set the mediaKeys
attribute to null.
Let this object's attaching media keys value be false.
Reject promise with a new DOMException
whose name is the appropriate error name.
Queue a task to run the attempt to resume playback if necessary algorithm on the media element.
The user agent MAY choose to skip this step if it knows resuming will fail.
For example, the user agent may skip this step if mediaKeys has no sessions.
Set the mediaKeys
attribute to mediaKeys.
Let this object's attaching media keys value be false.
Resolve promise.
Return promise.
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;
};
MediaEncryptedEvent
Parameter | Type | Nullable | Optional | Description |
---|---|---|---|---|
type | DOMString | ✘ | ✘ | |
eventInitDict |
| ✘ | ✔ |
initData
of type ArrayBuffer, readonly , nullableinitDataType
of type DOMString, readonly initData
attribute.
dictionary MediaEncryptedEventInit : EventInit {
DOMString initDataType = "";
ArrayBuffer? initData = null;
};
MediaEncryptedEventInit
MembersinitData
of type ArrayBuffer, nullable, defaulting to null
initDataType
of type DOMString, defaulting to ""
This section is non-normative.
Event name | Interface | Dispatched when... | Preconditions |
---|---|---|---|
encrypted |
MediaEncryptedEvent |
The user agent encounters Initialization Data in the media data. | readyState is equal to HAVE_METADATA or greater.
Note It is possible that the element is playing or has played. |
The following steps are run when the media element encounters Initialization Data in the media data during the resource fetch algorithm:
Let initDataType be the empty string.
Let initData be null.
If the media data is CORS-same-origin and not mixed content, run the following steps:
Let initDataType be the string representing the Initialization Data of the Initialization Data.
Let initData be the Initialization Data.
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.
Queue a task to fire a simple event named encrypted
at the media element.
The event is of type MediaEncryptedEvent
and has:
initDataType
= initDataTypeinitData
= initData
readyState
is not changed and no algorithms are aborted. This event merely provides information.
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.
Continue Normal Flow: Continue with the existing media element's resource fetch algorithm.
The following steps are run when the media element encounters a block of encrypted media data during the resource fetch algorithm:
If the media element's mediaKeys
attribute is not null, run the following steps:
Let media keys be the MediaKeys
object referenced by that atribute.
Let cdm be the CDM loaded during the initialization of the media keys.
If there is at least one MediaKeySession
created by the media keys on which the session close algorithm has not been run, run the following steps:
This check ensures the cdm has finished loading and is a prequisite for a matching key being available.
Let the block key ID be the key ID of the current block.
The key ID is generally specified by the container.
Use the cdm to execute the following steps:
Let available keys be the union of keys in sessions that were created by the media keys.
Follow the steps for the first matching condition from the following list:
Let block key be the matching key.
If multiple sessions contain a usable key for the block key ID, which key to use is Key System-dependent.
Use the cdm to decrypt the block using block key.
Follow the steps for the first matching condition from the following list:
If the waitingFor
attribute on the media element is "key"
, set the waitingFor
attribute on the media element to "none"
.
Abort these steps and process the decrypted block as normal.
In other words, decode the block.
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.
Bug 26372 - It is TBD whether anything should happen in this case.
Otherwise, there is no key for the block key ID in any session so continue.
Run the following steps:
These steps are reached when there is no usable key for the block.
Run the queue a "waiting" event algorithm on the media element.
Wait for a signal to resume playback.
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:
Let encrypted be false.
Detect whether the frame is encrypted.
Decode the frame.
Provide the frame for rendering.
The Queue a "waiting" Event algorithm is run when the CDM needs to queue a waiting event to a HTMLMediaElement
object.
Requests to run this algorithm include a target HTMLMediaElement
object.
The following steps are run:
Let the media element be the specified HTMLMediaElement
object.
If the waitingFor
attribute on the media element is not "key"
, run the following steps:
Set the waitingFor
attribute on the media element to "key"
.
Queue a task to fire a simple event named waiting
at the media element.
Suspend playback.
The Attempt to Resume Playback If Necessary algorithm is run when one or more keys becomes 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:
Let the media element be the specified HTMLMediaElement
object.
If the waitingFor
attribute on the media element is not "key"
, abort these steps.
Attempt to resume the resource fetch algorithm by running the encrypted block encountered algorithm.
If the user agent can advance the current playback position in the direction of playback, run the following steps:
Queue a task to fire a simple event named canplay
at the media element.
If the paused
attribute on the media element is false, queue a task to fire a simple event named playing
at the media element.
Otherwise, the waitingFor
attribute on the media element MUST NOT be "none"
.
The following steps are added to readyState
change algorithms in Playing the media resource:
readyState
change queues a task to fire a waiting
event, the user agent MUST also set the waitingFor
attribute on the Media Element to "data"
.readyState
change queues a task to fire a canplay
event, the user agent MUST also set the waitingFor
attribute on the Media Element to "none"
.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 protected 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.
All user agents MUST support the common key systems described in this section.
This ensures that there is a common baseline level of protection that is guaranteed to be supported in all user agents, including those that are entirely open source. Thus, content providers that need only basic protection can build simple applications that will work on all platforms without needing to work with any content protection providers.
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.
The following describe how Clear Key supports key system-specific capabilities:
The setMediaKeys()
method: Implementations MAY support associating the MediaKeys
object with more than one HTMLMediaElement
.
The setServerCertificate()
method: Not supported.
The isTypeSupported()
method: There are no supported capability values.
The "persistent"
SessionType
: Implementations MAY support this type.
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 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 a JWK Set as described in License Format.
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 media type.
The getUsableKeyIds()
method always returns all key IDs that have been provided via update()
.
Initialization Data: Implementations MAY support any combination of registered Initialization Data types [EME-REGISTRY].
Implementations SHOULD support the "keyids"
type and other types appropriate for content types supported by the user agent.
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:
SessionType
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].
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.)
{
"kids":
[
"67ef0gd8pvfd0",
"77ef0gd8pvfd0"
],
"type":"temporary"
}
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 [JWK].
For each JWK in the set, the parameter values are as follows:
The JSON object MAY have an optional "type" member value, which MUST be one of the SessionType
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].
This section is non-normative.
The following example is a JWK Set containing a single symmetric key. (Line breaks are for readability only.)
{
"keys":
[{
"kty":"oct",
"alg":"A128KW",
"k":"GawgguFyGrWKav7AX4VKUg"
"kid":"67ef0gd8pvfd0",
}],
"type":"temporary"
}
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 [JWS]. Specifically, there is no '=' padding, and the characters '-' and '_' MUST be used instead of '+' and '/', respectively.
This section is non-normative.
User Agent and Key System implementations must consider media data, Initialization Data, responses (i.e. 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 may want to validate data before passing it to the CDM, especially if the CDM does not run in the same (sandboxed) context as the DOM (i.e. rendering).
Implementations should not return active content or passive content that affects program control flow to the application.
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 should determine the URLs to use. The type
attribute of the message
event can be used by the application to select among a set of URLs if applicable.
User Agents are responsible for providing users with a secure way to browse the web. 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 properly asses the security implications of integrating with the Key System.
Unsandboxed CDMs (or CDMs that use platform features) and UAs that use them must be especially careful in all areas of security, including parsing of key and media data, etc. due to the potential for compromises to provide access to OS/platform features, interact with or run as root, access drivers, kernel, firmware, hardware, etc., all of which may not be written to be robust against hostile software or web-based attacks. Additionally, CDMs may not be updated with security fixes as frequently, especially when part of the OS, platform or hardware.
User agents may choose to only support the EME 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. Such user agents should also properly handle Mixed Content [MIXED-CONTENT] to avoid potential exposure to insecure content. See also Use Secure Origin and Transport.
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. See also User Alerts / Prompts.
This section is non-normative.
The presence or use of Key Systems 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 messages from Key Systems and (b) user-specific information that may be persistently stored on the users device.
User Agents should 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.
Concerns regarding information disclosed by EME and Key Systems fall into two categories, concerns about non-specific information that may nevertheless contribute to the possibility of fingerprinting a user agent or device and user-specific information that may be used directly for user tracking.
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 should not share key or other data between origins.
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 Incognito/Private Browsing sessions, across profiles, and even across different browsers, applications, and operating system user accounts.
To avoid such issues, user agent and CDM implementations should ensure that:
mediaKeys
attribute is not the MediaKeys object.User-specific information may be obtained over the EME API in two ways: through detection of stored keys and through Key System messages.
Key Systems may access or create persistent or semi-persistent identifiers 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. If not mitigated, such tracking may take three forms depending on the design of the Key System:
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 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.
There are a number of techniques that can be used to mitigate these risks of tracking without user consent:
While these suggestions prevent trivial use of this feature for user tracking, they do not block it altogether. Within a single domain, 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 per-origin, then a profile can still be created.
It is important to note that identifiers that are non-clearable, non-origin-specific or hardware-bound exceed the tracking impact of existing techniques such as cookies or session identifiers embedded in URLs.
Thus, in addition to the various mitigations described above, if a browser supports a mode of operation intended to preserve user anonymity, then User Agent implementers should carefully consider whether access to Key Systems should be disabled in this mode.
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.
There are a number of techniques that can be used to mitigate these privacy risk to users:
User agent and CDM implementations that allow the CDM to persist data should:
In order to protect identifiers and other information discussed in previous sections, user agents may choose to only support the EME 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 exposes identifiers or other such information without effectively anonymizing it in transit (i.e. without encrypting identifiers).
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 should 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.
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.
In this simple example, the source file and clear-text license are hard-coded in the page. Only one session will ever be created.
<script> function load() { var video = document.getElementById("video"); if (!video.mediaKeys
) { var promise =MediaKeys
.create
("org.w3.clearkey"); 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 initData = new Uint8Array([ ... ]); var keySession = createdMediaKeys.createSession
(); keySession.addEventListener("message
", handleMessage, false); return keySession.generateRequest
("webm", initData); } ).catch( console.error.bind(console, "Unable to create or initialize key session") ); } } function handleMessage(event) { var keySession = event.target; var license = new Uint8Array([ ... ]); keySession.update
(license).catch( console.error.bind(console, "update() failed") ); } </script> <body onload="load()"> <video src="foo.webm" autoplay id="video"></video> </body>
encrypted
EventThis example selects a supported Key System using the isTypeSupported()
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.
<script> var keySystem; var licenseUrl; var serverCertificate; function selectKeySystem() { if (MediaKeys
.isTypeSupported
("com.example.somesystem", "webm", "video/webm; codecs='vp8, vorbis'")) { licenseUrl = "https://license.example.com/getkey"; // OR "https://example.<My Video Site domain>" keySystem = "com.example.somesystem"; serverCertificate = new Uint8Array([ ... ]); } else if (MediaKeys
.isTypeSupported
("com.foobar", "webm", "video/webm; codecs='vp8, vorbis'")) { licenseUrl = "https://license.foobar.com/request"; keySystem = "com.foobar"; } else { throw "Key System not supported"; } } function handleInitData(event) { var video = event.target; if (video.mediaKeysObject === undefined) { selectKeySystem(); video.mediaKeysObject = null; // Prevent entering this path again. video.pendingSessionData = []; // Will store all initData until the MediaKeys is ready.MediaKeys
.create
(keySystem).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, "Unable to create or use new MediaKeys") ); } 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 src="foo.webm" autoplayonencrypted
="handleInitData(event)"></video>
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.
<script> var keySystem; var licenseUrl; var serverCertificate; var mediaKeys; // See the previous example for implementations of these functions. function selectKeySystem() { ... } function makeNewRequest(mediaKeys, initDataType, initData) { ... } function licenseRequestReady(event) { ... } function handleInitData(event) { makeNewRequest(mediaKeys, event.initDataType
, event.initData
); } selectKeySystem();MediaKeys
.create
(keySystem).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, "Unable to create or initialize key session") ); </script> <video id="v" autoplayonencrypted
="handleInitData(event)"></video>
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.
<script> var keySystem; var licenseUrl; var serverCertificate; var mediaKeys; // See previous examples for implementations of these functions. // selectKeySystem() additionally sets renewalUrl. function selectKeySystem() { ... } 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("keyschange
", handleKeysChange, 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 =="licenserenewal"
) 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.type
, event.message
, event.target); } function handleKeysChange(event) { event.target.getUsableKeyIds
().then( function(keyIdSequence) { // Process keyIdSequence and respond appropriately. } ).catch( console.error.bind(console, "Failed handling usable keys change") ); } function handleError(event) { // Report and do some bookkeeping with event.target.sessionId
if necessary. } selectKeySystem();MediaKeys
.create
(keySystem).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, "Unable to create or use new MediaKeys") ); </script> <video id="v" autoplayonencrypted
="handleInitData(event)"></video>
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.
<script> var keySystem; var licenseUrl; var serverCertificate; var mediaKeys; // See the previous examples for implementations of these functions. function selectKeySystem() { ... } function sendMessage(message, keySession) { ... } function handleMessage(event) { ... } function handleError(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"
); 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 create or initialize a persistable key session") ); } // Called if the application has a stored sessionId for the media resource. function loadStoredSession(mediaKeys, sessionId) { var keySession = mediaKeys.createSession
("persistent"
); 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") ); } selectKeySystem();MediaKeys
.create
(keySystem).then( function(createdMediaKeys) { mediaKeys = createdMediaKeys; var video = document.getElementById("v"); if (serverCertificate) mediaKeys.setServerCertificate
(serverCertificate); return video.setMediaKeys
(mediaKeys); } ).catch( console.error.bind(console, "Unable to create or use new MediaKeys") ); </script> <video id="v" src="foo.webm" autoplay></video>
Version | Comment |
---|---|
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 |