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This specification describes a JavaScript API for discovering named, origin-specific pre-provisioned cryptographic keys for use with the Web Cryptograpy API. Pre-provisioned keys are keys which have been made available to the UA by means other than the generation, derivation, imporation functions of the Web Cryptography API. Origin-specific keys are keys that are available only to a specified origin. Named keys are identified by a name assumed to be known to the origin in question and provisioned with the key itself.
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This section is non-normative.
The Web Cryptography API [WEBCRYPTO] describes a JavaScript API for performing basic cryptographic
operations in web applications. Cryptographic keys in are represented in this API using
Key objects. The API provides methods to generate, derive or import cryptographic
keying material, so creating Key objects.
This document concerns the discovery of cryptographic keys which are made available to the UA by other means. Specifically, this document provides an API for the discovery of cryptographic keys which have been pre-provisioned into a UA or device for use by a specific origin. Such keys are identified by names which are assumed to be known to the origin in question and thus they are referred to as named origin-specific pre-provisioned keys.
This enables web applications to establish secure proof that the UA has access to a particular pre-provisioned key. Depending on the nature of the key and its associated storage - for example within a Hardware Security Module or available only within a Trusted Execution Environment - further properties of the device on which the UA is running may be inferred.
The use of pre-provisioned keys requires the informed consent of the user, because such keys may be used for tracking and may reveal information about the users device. The privacy and security implications of origin-specific pre-provisioned keys are discussed further in Security and Privacy Considerations.
As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.
The key words must, must not, required, should, should not, recommended, may, and optional in this specification are to be interpreted as described in [RFC2119].
The following conformance classes are defined by this specification:
A user agent is considered to be a conforming user agent if it satisfies all of the must-, required- and shall-level criteria in this specification that apply to implementation. This specification uses both the terms "conforming user agent" and "user agent" to refer to this product class.
User agents may implement algorithms in this specification in any way desired, so long as the end result is indistinguishable from the result that would be obtained from the specification's algorithms.
User agents that use ECMAScript to implement the APIs defined in this specification must implement them in a manner consistent with the ECMAScript Bindings defined in the Web IDL specification [WEBIDL] as this specification uses that specification and terminology.
This section is non-normative.
The considerations in the Scope section of [WEBCRYPTO] apply to this specification as well. In particular, although this specification directly addresses the discovery of named origin-specific pre-provisioned keys, it does not address the processes used to provision those keys or the type and properties of the hardware or software components in which they are stored.
This section is non-normative.
The Privacy considerations of [WEBCRYPTO] apply to this specification.
This section is non-normative.
A third-party host (or any object capable of getting content distributed to multiple sites) could use a named origin-specific pre-provisioned key to track a user across multiple sessions, building a profile of the user's activities. In conjunction with a site that is aware of the user's real identity (for example an 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.
There are a number of techniques that can be used to mitigate this risk of tracking without user consent:
User agents should require the user to explicitly authorize access to named origin-specific pre-provisioned keys before a site can use the keys.
User agents should enable users to revoke this authorization either temporarily or permanently.
User agents may restrict access to named origin-specific pre-provisioned keys to scripts originating at the domain of the top-level document of the browsing context, for instance returning empty key search results for pages from other domains running in iframes.
User agents should present the named origin-specific pre-provisioned keys feature to the user in a way that associates it strongly with HTTP session cookies. [COOKIES]
This might encourage users to view such keys with healthy suspicion.
User agents may record the origins of sites that contained content from third-party origins that used pre-provisioned keys.
If this information is then used to present a view of pre-provisioned keys to the user, it would allow the user to make informed decisions about authorizing sites to make use of keys. Combined with a blacklist ("delete this key" or "prevent this domain from ever accessing this key again"), the user can restrict the use of pre-provisioned keys to sites that he trusts.
User agents may allow users to share their pre-provisioned key domain blacklists.
This would allow communities to act together to protect their privacy.
While these suggestions prevent trivial use of this feature for user tracking, they do not block it altogether. Where a browser supports a mode of operation intended to preserve user anonymity, access to pre-provisioned keys should be disabled in this mode. Even so, within a single domain, a site can continue to track the user during a session, and can then pass all this information to the 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, a profile can still be created.
However, user tracking is to some extent possible even with no cooperation from the user agent whatsoever, for instance by using session identifiers in URLs, a technique already commonly used for innocuous purposes but easily repurposed for user tracking (even retroactively). This information can then be shared with other sites, using visitors' IP addresses and other user-specific data (e.g. user-agent headers and configuration settings) to combine separate sessions into coherent user profiles.
User agents should treat pre-provisioned keys and material generated using such keys as potentially sensitive; it is quite possible for the user privacy to be compromised by the release of this information.
To this end, user agents should ensure that when deleting data, it is promptly deleted from the underlying storage.
This specification relies on underlying specifications.
A conforming user agent must support the Web Cryptography API [WEBCRYPTO].
The terms origin and same origin are defined by the HTML specification [HTML5].
This section is non-normative.
This specification defines a new cryptokeys attribute on the Window object. This attribute is an object supporting a method, getkeysByName which may be used to get an array of all keys matching a DOMString name specifier. The array of keys is returned through a callback function, in the form of a KeyArray object.
interface KeyArray {
readonly attribute unsigned long length;
Key? get (unsigned long index);
};length of type unsigned long, readonlyget| Parameter | Type | Nullable | Optional | Description |
|---|---|---|---|---|
| index | unsigned long | ? | ? |
Key, nullable[Callback]
interface GetKeysByNameCallback {
void complete (KeyArray keys);
};dictionary GetKeysByNameParams {
DOMString name;
GetKeysByNameCallback oncompletion;;
};GetKeysByNameParams Membersname of type DOMStringoncompletion; of type GetKeysByNameCallback[NoInterfaceObject]
interface CryptoKeys {
void getKeysByName (GetKeysByNameParams params);
};getKeysByName| Parameter | Type | Nullable | Optional | Description |
|---|---|---|---|---|
| params | | ? | ? |
voidThe WindowCryptoKeys interface is exposed on the Window object.
Window implements WindowCryptoKeys;All instances of the Window type are defined to also implement the WindowCryptoKeys interface.
[NoInterfaceObject]
interface WindowCryptoKeys {
readonly attribute CryptoKeys cryptokeys;
};cryptokeys of type CryptoKeys, readonly