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<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Secure Curves in the Web Cryptography API</title>
<script src="https://www.w3.org/Tools/respec/respec-w3c" class="remove"></script>
<script class='remove'>
"use strict";
// See https://github.com/w3c/respec/wiki/ for how to configure ReSpec
var respecConfig = {
"github": "WICG/webcrypto-secure-curves",
"editors": [
{
name: "Daniel Huigens",
url: "mailto:daniel.huigens@proton.ch",
company: "Proton AG",
companyURL: "https://proton.me/",
},
],
"shortName": "webcrypto-secure-curves",
"specStatus": "CG-DRAFT",
"group": "wicg",
"xref": ["WebIDL", "webcrypto"],
"localBiblio": {
"SafeCurves": {
"title": "Daniel J. Bernstein and Tanja Lange. SafeCurves: choosing safe curves for elliptic-curve cryptography",
"href": "https://safecurves.cr.yp.to/",
}
},
};
</script>
</head>
<body>
<section id="abstract">
<p>
This specification defines a number of algorithms for the [[webcrypto | Web Cryptography API]],
namely X25519 and X448 [[RFC7748]], and Ed25519 and Ed448 [[RFC8032]].
</p>
</section>
<section id="sotd">
<p>
This is an unofficial proposal.
</p>
</section>
<section id="introduction" class="informative">
<h2>Introduction</h2>
<p>
The [[webcrypto | Web Cryptography API]] currently does not specify any "safe curves" [[SafeCurves]].
Among the safe curves, Curve25519 and Curve448 have gained the most traction, and
have been specified for use in TLS 1.3, among others. This specification aims to
expose these algorithms to the web platform.
To this end, this specification defines a number of algorithms and operations for
the [[webcrypto | Web Cryptography API]], namely key agreement using X25519 and X448 [[RFC7748]], and
signing and verifying using Ed25519 and Ed448 [[RFC8032]].
</p>
</section>
<section id="specification-conventions">
<h2>Specification Conventions</h3>
<p>
This specification follows the <a data-cite="WebCryptoAPI#algorithm-conventions">conventions</a>
laid out in Section 18.3 of [[webcrypto]]. None of the algorithms defined here
are required to be implemented, but if a conforming User Agent implements an
algorithm, it MUST implement all of the supported operations specified in this
document, and must perform the steps to <a data-cite="WebCryptoAPI#concept-define-an-algorithm">define an algorithm</a>
specified in section 18.4.3 of [[webcrypto]] for each of the supported operations.
</p>
</section>
<section id="x25519">
<h3>X25519</h3>
<section id="x25519-description" class="informative">
<h4>Description</h4>
<p>
The "`X25519`" algorithm identifier is used to perform
key agreement using the X25519 algorithm specified in
[[RFC7748]].
</p>
</section>
<section id="x25519-registration">
<h4>Registration</h4>
<p>
The <a data-cite="WebCryptoAPI#recognized-algorithm-name">recognized algorithm name</a>
for this algorithm is "`X25519`".
</p>
<table>
<thead>
<tr>
<th><a data-cite="WebCryptoAPI#supported-operations">Operation</a></th>
<th><a data-cite="WebCryptoAPI#algorithm-specific-params">Parameters</a></th>
<th><a data-cite="WebCryptoAPI#algorithm-result">Result</a></th>
</tr>
</thead>
<tbody>
<tr>
<td>deriveBits</td>
<td>{{EcdhKeyDeriveParams}}</td>
<td><a data-cite="WebCryptoAPI#dfn-octet-string">octet string</a></td>
</tr>
<tr>
<td>generateKey</td>
<td>None</td>
<td>{{CryptoKeyPair}}</td>
</tr>
<tr>
<td>importKey</td>
<td>None</td>
<td>{{CryptoKey}}</td>
</tr>
<tr>
<td>exportKey</td>
<td>None</td>
<td>object</td>
</tr>
</tbody>
</table>
</section>
<section id="x25519-operations">
<h4>Operations</h4>
<dl>
<dt>Derive Bits</dt>
<dd>
<ol>
<li>
<p>
If the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-type">[[\type]]</a> internal slot of
|key| is not {{KeyType/"private"}}, then [= exception/throw =] an {{InvalidAccessError}}.
</p>
</li>
<li>
<p>
Let |publicKey| be the
{{EcdhKeyDeriveParams/public}} member of
|normalizedAlgorithm|.
</p>
</li>
<li>
<p>
If the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-type">[[\type]]</a> internal slot of
|publicKey| is not "`public`", then [= exception/throw =] an {{InvalidAccessError}}.
</p>
</li>
<li>
<p>
If the {{KeyAlgorithm/name}} attribute of
the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-algorithm">[[\algorithm]]</a> internal slot of
|publicKey| is not equal to the {{KeyAlgorithm/name}} property of the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-algorithm">[[\algorithm]]</a> internal slot of
|key|, then [= exception/throw =] an {{InvalidAccessError}}.
</p>
</li>
<li>
<p>
Let |secret| be the result of performing the X25519 function specified in
[[RFC7748]] Section 5 with |key| as the X25519 private key |k|
and the X25519 public key represented by the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-handle">[[\handle]]</a>
internal slot of |publicKey| as the X25519 public key |u|.
</p>
</li>
<li>
<p>
If |secret| is the all-zero value,
then [= exception/throw =] a {{OperationError}}.
This check must be performed in constant-time, as per [[RFC7748]] Section 6.1.
</p>
</li>
<li>
<dl class="switch">
<dt>If |length| is null:</dt>
<dd>Return |secret|</dd>
<dt>Otherwise:</dt>
<dd>
<dl class="switch">
<dt>
If the length of |secret| in bits is less than
|length|:
</dt>
<dd>
[= exception/throw =] an
{{OperationError}}.
</dd>
<dt>Otherwise:</dt>
<dd>
Return an <a data-cite="WebCryptoAPI#octet-string-containing">octet string containing</a> the first |length| bits of |secret|.
</dd>
</dl>
</dd>
</dl>
</li>
</ol>
</dd>
<dt>Generate Key</dt>
<dd>
<ol>
<li>
<p>
If |usages| contains an entry which is not
"`deriveKey`" or "`deriveBits`"
then [= exception/throw =] a
{{SyntaxError}}.
</p>
</li>
<li>
<p>
Generate an X25519 key pair, with the private key being 32 random bytes,
and the public key being `X25519(a, 9)`,
as defined in [[RFC7748]], section 6.1.
</p>
</li>
<li>
<p>
Let |algorithm| be a new {{KeyAlgorithm}} object.
</p>
</li>
<li>
<p>
Set the {{KeyAlgorithm/name}} attribute of
|algorithm| to "`X25519`".
</p>
</li>
<li>
<p>
Let |publicKey| be a new {{CryptoKey}} associated with the
[= relevant global object =]
of `this` [[HTML]], and
representing the public key of the generated key pair.
</p>
</li>
<li>
<p>
Set the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-type">[[\type]]</a> internal slot of
|publicKey| to "`public`"
</p>
</li>
<li>
<p>
Set the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-algorithm">[[\algorithm]]</a> internal
slot of |publicKey| to |algorithm|.
</p>
</li>
<li>
<p>
Set the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-extractable">[[\extractable]]</a> internal
slot of |publicKey| to true.
</p>
</li>
<li>
<p>
Set the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-usages">[[\usages]]</a> internal slot of
|publicKey| to be the empty list.
</p>
</li>
<li>
<p>
Let |privateKey| be a new {{CryptoKey}} associated with the
[= relevant global object =]
of `this` [[HTML]], and
representing the private key of the generated key pair.
</p>
</li>
<li>
<p>
Set the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-type">[[\type]]</a> internal slot of
|privateKey| to {{KeyType/"private"}}
</p>
</li>
<li>
<p>
Set the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-algorithm">[[\algorithm]]</a> internal
slot of |privateKey| to |algorithm|.
</p>
</li>
<li>
<p>
Set the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-extractable">[[\extractable]]</a> internal
slot of |privateKey| to |extractable|.
</p>
</li>
<li>
<p>
Set the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-usages">[[\usages]]</a> internal slot of
|privateKey| to be the
<a data-cite="WebCryptoAPI#concept-usage-intersection">usage intersection</a> of
|usages| and `[ "deriveKey", "deriveBits" ]`.
</p>
</li>
<li>
<p>
Let |result| be a new {{CryptoKeyPair}}
dictionary.
</p>
</li>
<li>
<p>
Set the {{CryptoKeyPair/publicKey}} attribute
of |result| to be |publicKey|.
</p>
</li>
<li>
<p>
Set the {{CryptoKeyPair/privateKey}} attribute
of |result| to be |privateKey|.
</p>
</li>
<li>
<p>
Return the result of converting |result| to an ECMAScript Object, as
defined by [[WebIDL]].
</p>
</li>
</ol>
</dd>
<dt>Import Key</dt>
<dd>
<ol>
<li>
<p>Let |keyData| be the key data to be imported.</p>
</li>
<li>
<dl class="switch">
<dt>If |format| is {{KeyFormat/"spki"}}:</dt>
<dd>
<ol>
<li>
<p>
If |usages| is not empty
then [= exception/throw =] a
{{SyntaxError}}.
</p>
</li>
<li>
<p>
Let |spki| be the result of running the
<a data-cite="WebCryptoAPI#concept-parse-a-spki">parse a subjectPublicKeyInfo</a>
algorithm over |keyData|.
</p>
</li>
<li>
<p>
If an error occurred while parsing,
then [= exception/throw =] a
{{DataError}}.
</p>
</li>
<li>
<p>
If the `algorithm` object identifier field of the
`algorithm` AlgorithmIdentifier field of |spki| is
not equal to the `id-X25519`
object identifier defined in [[RFC8410]],
then [= exception/throw =] a
{{DataError}}.
</p>
</li>
<li>
<p>
If the `parameters` field of the `algorithm`
AlgorithmIdentifier field of |spki| is present,
then [= exception/throw =] a
{{DataError}}.
</p>
</li>
<li>
<p>
Let |publicKey| be the X25519 public key identified by
the `subjectPublicKey` field of |spki|.
</p>
</li>
<li>
<p>
Let |key| be a new {{CryptoKey}} associated with the
[= relevant global object =]
of `this` [[HTML]], and
that represents |publicKey|.
</p>
</li>
<li>
<p>
Set the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-type">[[\type]]</a> internal slot
of |key| to "`public`"
</p>
</li>
<li>
<p>
Let |algorithm| be a new {{KeyAlgorithm}}.
</p>
</li>
<li>
<p>
Set the {{KeyAlgorithm/name}} attribute of
|algorithm| to "`X25519`".
</p>
</li>
<li>
<p>
Set the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-algorithm">[[\algorithm]]</a>
internal slot of |key| to |algorithm|.
</p>
</li>
</ol>
</dd>
<dt>If |format| is {{KeyFormat/"pkcs8"}}:</dt>
<dd>
<ol>
<li>
<p>
If |usages| contains an entry which is not
"`deriveKey`" or "`deriveBits`"
then [= exception/throw =] a
{{SyntaxError}}.
</p>
</li>
<li>
<p>
Let |privateKeyInfo| be the result of running the
<a data-cite="WebCryptoAPI#concept-parse-a-privateKeyInfo">parse a privateKeyInfo</a>
algorithm over |keyData|.
</p>
</li>
<li>
<p>
If an error occurs while parsing,
then [= exception/throw =] a
{{DataError}}.
</p>
</li>
<li>
<p>
If the `algorithm` object identifier field of the
`privateKeyAlgorithm` PrivateKeyAlgorithm field of
|privateKeyInfo| is not equal to the
`id-X25519` object identifier defined in [[RFC8410]],
then [= exception/throw =] a
{{DataError}}.
</p>
</li>
<li>
<p>
If the `parameters` field of the
`privateKeyAlgorithm` PrivateKeyAlgorithmIdentifier field
of |privateKeyInfo| is present,
then [= exception/throw =] a
{{DataError}}.
</p>
</li>
<li>
<p>
Let |curvePrivateKey| be the result of performing the <a data-cite="WebCryptoAPI#concept-parse-an-asn1-structure">parse an ASN.1 structure</a>
algorithm, with |data| as the `privateKey` field
of |privateKeyInfo|, |structure| as the ASN.1
`CurvePrivateKey` structure specified in Section 7 of [[RFC8410]], and |exactData| set to true.
</p>
</li>
<li>
<p>
If an error occurred while parsing,
then [= exception/throw =] a
{{DataError}}.
</p>
</li>
<li>
<p>
Let |key| be a new {{CryptoKey}} associated with the
[= relevant global object =]
of `this` [[HTML]], and
that represents the X25519 private key identified by |curvePrivateKey|.
</p>
</li>
<li>
<p>
Set the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-type">[[\type]]</a> internal slot
of |key| to {{KeyType/"private"}}
</p>
</li>
<li>
<p>
Let |algorithm| be a new {{KeyAlgorithm}}.
</p>
</li>
<li>
<p>
Set the {{KeyAlgorithm/name}} attribute of
|algorithm| to "`X25519`".
</p>
</li>
<li>
<p>
Set the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-algorithm">[[\algorithm]]</a>
internal slot of |key| to |algorithm|.
</p>
</li>
</ol>
</dd>
<dt>If |format| is {{KeyFormat/"jwk"}}:</dt>
<dd>
<ol>
<li>
<dl class="switch">
<dt>If |keyData| is a {{JsonWebKey}} dictionary:</dt>
<dd><p>Let |jwk| equal |keyData|.</p></dd>
<dt>Otherwise:</dt>
<dd><p>[= exception/Throw =] a {{DataError}}.</p></dd>
</dl>
</li>
<li>
<p>
If the {{JsonWebKey/d}} field is present and if |usages|
contains an entry which is not
"`deriveKey`" or "`deriveBits`"
then [= exception/throw =] a
{{SyntaxError}}.
</p>
</li>
<li>
<p>
If the {{JsonWebKey/d}} field is not present and if |usages| is not
empty
then [= exception/throw =] a
{{SyntaxError}}.
</p>
</li>
<li>
<p>
If the {{JsonWebKey/kty}} field of |jwk| is not
"`OKP`",
then [= exception/throw =] a
{{DataError}}.
</p>
</li>
<li>
<p>
If the {{JsonWebKey/crv}} field of |jwk| is not
"`X25519`",
then [= exception/throw =] a
{{DataError}}.
</p>
</li>
<li>
<p>
If |usages| is non-empty and the {{JsonWebKey/use}} field of |jwk| is present
and is not equal to "`enc`" then [= exception/throw =] a
{{DataError}}.
</p>
</li>
<li>
<p>
If the {{JsonWebKey/key_ops}} field of |jwk| is present, and
is invalid according to the requirements of JSON Web
Key [[JWK]], or it does not contain all of the specified |usages|
values,
then [= exception/throw =] a
{{DataError}}.
</p>
</li>
<li>
<p>
If the {{JsonWebKey/ext}} field of |jwk| is present and
has the value false and |extractable| is true,
then [= exception/throw =] a
{{DataError}}.
</p>
</li>
<li>
<dl class="switch">
<dt>If the {{JsonWebKey/d}} field is present:</dt>
<dd>
<ol>
<li>
<p>
If |jwk| does not meet the requirements of
the JWK private key format described in Section 2
of [[RFC8037]], then [= exception/throw =] a {{DataError}}.
</p>
</li>
<li>
<p>
Let |key| be a new {{CryptoKey}} object that represents the
X25519 private key identified by interpreting
|jwk| according to Section 2 of [[RFC8037]].
</p>
</li>
<li>
<p>
Set the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-type">[[\type]]</a>
internal slot of |Key| to {{KeyType/"private"}}.
</p>
</li>
</ol>
</dd>
<dt>Otherwise:</dt>
<dd>
<ol>
<li>
<p>
If |jwk| does not meet the requirements of
the JWK public key format described in Section 2
of [[RFC8037]], then [= exception/throw =] a {{DataError}}.
</p>
</li>
<li>
<p>
Let |key| be a new {{CryptoKey}} object that represents the
X25519 public key identified by interpreting
|jwk| according to Section 2 of [[RFC8037]].
</p>
</li>
<li>
<p>
Set the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-type">[[\type]]</a>
internal slot of |Key| to {{KeyType/"public"}}.
</p>
</li>
</ol>
</dd>
</dl>
</li>
<li>
<p>
Let |algorithm| be a new instance of a {{KeyAlgorithm}} object.
</p>
</li>
<li>
<p>
Set the {{KeyAlgorithm/name}} attribute of
|algorithm| to "`X25519`".
</p>
</li>
<li>
<p>
Set the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-algorithm">[[\algorithm]]</a>
internal slot of |key| to |algorithm|.
</p>
</li>
</ol>
</dd>
<dt>If |format| is {{KeyFormat/"raw"}}:</dt>
<dd>
<ol>
<li>
<p>
If |usages| is not empty
then [= exception/throw =] a
{{SyntaxError}}.
</p>
</li>
<li>
<p>
Let |data| be |keyData|.
</p>
</li>
<li>
<p>
If the <a data-cite="webcrypto#dfn-length-in-bits">length in bits</a> of |data| is not 256 then [= exception/throw =] a {{DataError}}.
</p>
</li>
<li>
<p>
Let |algorithm| be a new {{KeyAlgorithm}} object.
</p>
</li>
<li>
<p>
Set the {{KeyAlgorithm/name}} attribute of
|algorithm| to "`X25519`".
</p>
</li>
<li>
<p>
Let |key| be a new {{CryptoKey}} associated with the
[= relevant global object =]
of `this` [[HTML]], and that represents |data|.
</p>
</li>
<li>
<p>
Set the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-type">[[\type]]</a> internal slot
of |key| to "`public`"
</p>
</li>
<li>
<p>
Set the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-algorithm">[[\algorithm]]</a>
internal slot of |key| to |algorithm|.
</p>
</li>
</ol>
</dd>
<dt>Otherwise:</dt>
<dd>
<p>
[= exception/throw =] a
{{NotSupportedError}}.
</p>
</dd>
</dl>
</li>
<li>
<p>
Return |key|
</p>
</li>
</ol>
</dd>
<dt>Export Key</dt>
<dd>
<ol>
<li>
<p>
Let |key| be the {{CryptoKey}} to be
exported.
</p>
</li>
<li>
<p>
If the underlying cryptographic key material represented by the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-handle">[[\handle]]</a> internal slot of |key|
cannot be accessed, then [= exception/throw =] an {{OperationError}}.
</p>
</li>
<li>
<dl class="switch">
<dt>If |format| is {{KeyFormat/"spki"}}:</dt>
<dd>
<ol>
<li>
<p>
If the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-type">[[\type]]</a> internal slot
of |key| is not "`public`", then [= exception/throw =] an {{InvalidAccessError}}.
</p>
</li>
<li>
<p>
Let |data| be an instance of the `subjectPublicKeyInfo`
ASN.1 structure defined in [[RFC5280]]
with the following properties:
</p>
<ul>
<li>
<p>
Set the |algorithm| field to an
`AlgorithmIdentifier` ASN.1 type with the following
properties:
</p>
<ul>
<li>
<p>
Set the |algorithm| object identifier to the
`id-X25519` OID defined in [[RFC8410]].
</p>
</li>
</ul>
</li>
<li>
<p>
Set the |subjectPublicKey| field to |keyData|.
</p>
</li>
</ul>
</li>
<li>
<p>
Let |result| be a new {{ArrayBuffer}} associated with the
[= relevant global object =]
of `this` [[HTML]], and containing
|data|.
</p>
</li>
</ol>
</dd>
<dt>If |format| is {{KeyFormat/"pkcs8"}}:</dt>
<dd>
<ol>
<li>
<p>
If the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-type">[[\type]]</a> internal slot
of |key| is not {{KeyType/"private"}}, then [= exception/throw =] an {{InvalidAccessError}}.
</p>
</li>
<li>
<p>
Let |data| be an instance of the `privateKeyInfo`
ASN.1 structure defined in [[RFC5208]]
with the following properties:
</p>
<ul>
<li>
<p>
Set the |version| field to `0`.
</p>
</li>
<li>
<p>
Set the |privateKeyAlgorithm| field to a
`PrivateKeyAlgorithmIdentifier` ASN.1 type with the
following properties:
</p>
<ul>
<li>
<p>
Set the |algorithm| object identifier to the
`id-X25519` OID defined in [[RFC8410]].
</p>
</li>
</ul>
</li>
<li>
<p>
Set the |privateKey| field to the result of DER-encoding
a `CurvePrivateKey` ASN.1 type, as defined in Section 7 of [[RFC8410]], that represents the
X25519 private key represented by the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-handle">[[\handle]]</a> internal slot of
|key|
</p>
</li>
</ul>
</li>
<li>
<p>
Let |result| be a new {{ArrayBuffer}} associated with the
[= relevant global object =]
of `this` [[HTML]], and containing
|data|.
</p>
</li>
</ol>
</dd>
<dt>If |format| is {{KeyFormat/"jwk"}}:</dt>
<dd>
<ol>
<li>
<p>
Let |jwk| be a new {{JsonWebKey}}
dictionary.
</p>
</li>
<li>
<p>
Set the `kty` attribute of |jwk| to
"`OKP`".
</p>
</li>
<li>
<p>
Set the `crv` attribute of |jwk| to
"`X25519`".
</p>
</li>
<li>
<p>
Set the {{JsonWebKey/x}} attribute of |jwk| according to the
definition in Section 2 of [[RFC8037]].
</p>
</li>
<li>
<dl class="switch">
<dt>
If the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-type">[[\type]]</a> internal slot
of |key| is {{KeyType/"private"}}
</dt>
<dd>
Set the {{JsonWebKey/d}} attribute of |jwk| according to the
definition in Section 2 of [[RFC8037]].
</dd>
</dl>
</li>
<li>
<p>
Set the `key_ops` attribute of |jwk| to the {{CryptoKey/usages}} attribute of |key|.
</p>
</li>
<li>
<p>
Set the `ext` attribute of |jwk| to the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-extractable">[[\extractable]]</a> internal slot
of |key|.
</p>
</li>
<li>
<p>
Let |result| be the result of converting |jwk|
to an ECMAScript Object, as defined by [[WebIDL]].
</p>
</li>
</ol>
</dd>
<dt>
If |format| is {{KeyFormat/"raw"}}:
</dt>
<dd>
<ol>
<li>
<p>
If the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-type">[[\type]]</a> internal slot
of |key| is not "`public`", then [= exception/throw =] an {{InvalidAccessError}}.
</p>
</li>
<li>
<p>
Let |data| be an <a data-cite="WebCryptoAPI#dfn-octet-string">octet string</a> representing the X25519
public key represented by the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-handle">[[\handle]]</a> internal slot of
|key|.
</p>
</li>
<li>
<p>
Let |result| be a new {{ArrayBuffer}} associated with the
[= relevant global object =]
of `this` [[HTML]], and containing
|data|.
</p>
</li>
</ol>
</dd>
<dt>Otherwise:</dt>
<dd>
<p>
[= exception/throw =] a
{{NotSupportedError}}.
</p>
</dd>
</dl>
</li>
<li>
<p>
Return |result|.
</p>
</li>
</ol>
</dd>
</dl>
</section>
</section>
<section id="x448">
<h3>X448</h3>
<section id="x448-description" class="informative">
<h4>Description</h4>
<p>
The "`X448`" algorithm identifier is used to perform
key agreement using the X448 algorithm specified in
[[RFC7748]].
</p>
</section>
<section id="x448-registration">
<h4>Registration</h4>
<p>
The <a data-cite="WebCryptoAPI#recognized-algorithm-name">recognized algorithm name</a>
for this algorithm is "`X448`".
</p>
<table>
<thead>
<tr>
<th><a data-cite="WebCryptoAPI#supported-operations">Operation</a></th>
<th><a data-cite="WebCryptoAPI#algorithm-specific-params">Parameters</a></th>
<th><a data-cite="WebCryptoAPI#algorithm-result">Result</a></th>
</tr>
</thead>
<tbody>
<tr>
<td>deriveBits</td>
<td>{{EcdhKeyDeriveParams}}</td>
<td><a data-cite="WebCryptoAPI#dfn-octet-string">octet string</a></td>
</tr>
<tr>
<td>generateKey</td>
<td>None</td>
<td>{{CryptoKeyPair}}</td>
</tr>
<tr>
<td>importKey</td>
<td>None</td>
<td>{{CryptoKey}}</td>
</tr>
<tr>
<td>exportKey</td>
<td>None</td>
<td>object</td>
</tr>
</tbody>
</table>
</section>
<section id="x448-operations">
<h4>Operations</h4>
<dl>
<dt>Derive Bits</dt>
<dd>
<ol>
<li>
<p>
If the <a data-cite="WebCryptoAPI#dfn-CryptoKey-slot-type">[[\type]]</a> internal slot of
|key| is not {{KeyType/"private"}}, then [= exception/throw =] an {{InvalidAccessError}}.
</p>
</li>
<li>
<p>
Let |publicKey| be the
{{EcdhKeyDeriveParams/public}} member of
|normalizedAlgorithm|.
</p>