SubtleCrypto.wrapKey()
Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.
The wrapKey()
method of the SubtleCrypto
interface "wraps" a key. This means that it exports the key in an external, portable
format, then encrypts the exported key. Wrapping a key helps protect it in untrusted
environments, such as inside an otherwise unprotected data store or in transmission over
an unprotected network.
As with SubtleCrypto.exportKey()
,
you specify an export format
for the key. To export a key, it must have CryptoKey.extractable
set to true
.
But because wrapKey()
also encrypts the key to be imported, you also need
to pass in the key that must be used to encrypt it. This is sometimes called the
"wrapping key".
The inverse of wrapKey()
is SubtleCrypto.unwrapKey()
: while
wrapKey
is composed of export + encrypt, unwrapKey
is composed
of import + decrypt.
Syntax
const result = crypto.subtle.wrapKey(
format,
key,
wrappingKey,
wrapAlgo
);
Parameters
-
format
is a string describing the data format in which the key will be exported before it is encrypted. It can be one of the following:raw
: Raw format.pkcs8
: PKCS #8 format.-
spki
: SubjectPublicKeyInfo format. -
jwk
: JSON Web Key format.
key
is theCryptoKey
to wrap.-
wrappingkey
is theCryptoKey
used to encrypt the exported key. The key must have thewrapKey
usage set. -
wrapAlgo
is an object specifying the algorithm to be used to encrypt the exported key, and any required extra parameters:-
To use RSA-OAEP,
pass an
RsaOaepParams
object. -
To use AES-CTR,
pass an
AesCtrParams
object. -
To use AES-CBC,
pass an
AesCbcParams
object. -
To use AES-GCM,
pass an
AesGcmParams
object. -
To use AES-KW,
pass the string
"AES-KW"
, or an object of the form{ "name": "AES-KW }
.
-
To use RSA-OAEP,
pass an
Return value
-
result
is aPromise
that fulfills with anArrayBuffer
containing the encrypted exported key.
Exceptions
The promise is rejected when one of the following exceptions is encountered:
InvalidAccessError
-
Raised when the wrapping key is not a key for the requested wrap algorithm.
NotSupported
-
Raised when trying to use an algorithm that is either unknown or isn't suitable for encryption or wrapping.
TypeError
-
Raised when trying to use an invalid format.
Supported algorithms
All algorithms that are usable for encryption are also usable for key wrapping, as long as the key has the "wrapKey" usage set. For key wrapping you have the additional option of AES-KW.
AES-KW
AES-KW is a way to use the AES cipher for key wrapping.
One advantage of using AES-KW over another AES mode such as AES-GCM is that AES-KW does not require an initialization vector. To use AES-KW, the input must be a multiple of 64 bits.
AES-KW is specified in RFC 3394.
Examples
Note: You can try the working examples out on GitHub.
Raw wrap
This example wraps an AES key. It uses "raw" as the export format and AES-KW, with a password-derived key, to encrypt it. See the complete code on GitHub.
let salt;
/*
Get some key material to use as input to the deriveKey method.
The key material is a password supplied by the user.
*/
function getKeyMaterial() {
const password = window.prompt("Enter your password");
const enc = new TextEncoder();
return window.crypto.subtle.importKey(
"raw",
enc.encode(password),
{name: "PBKDF2"},
false,
["deriveBits", "deriveKey"]
);
}
/*
Given some key material and some random salt
derive an AES-KW key using PBKDF2.
*/
function getKey(keyMaterial, salt) {
return window.crypto.subtle.deriveKey(
{
"name": "PBKDF2",
salt: salt,
"iterations": 100000,
"hash": "SHA-256"
},
keyMaterial,
{ "name": "AES-KW", "length": 256},
true,
[ "wrapKey", "unwrapKey" ]
);
}
/*
Wrap the given key.
*/
async function wrapCryptoKey(keyToWrap) {
// get the key encryption key
const keyMaterial = await getKeyMaterial();
salt = window.crypto.getRandomValues(new Uint8Array(16));
const wrappingKey = await getKey(keyMaterial, salt);
return window.crypto.subtle.wrapKey(
"raw",
keyToWrap,
wrappingKey,
"AES-KW"
);
}
/*
Generate an encrypt/decrypt secret key,
then wrap it.
*/
window.crypto.subtle.generateKey(
{
name: "AES-GCM",
length: 256,
},
true,
["encrypt", "decrypt"]
)
.then((secretKey) => {
return wrapCryptoKey(secretKey);
})
.then((wrappedKey) => {
console.log(wrappedKey);
});
PKCS #8 wrap
This example wraps an RSA private signing key. It uses "pkcs8" as the export format and AES-GCM, with a password-derived key, to encrypt it. See the complete code on GitHub.
let salt;
let iv;
/*
Get some key material to use as input to the deriveKey method.
The key material is a password supplied by the user.
*/
function getKeyMaterial() {
const password = window.prompt("Enter your password");
const enc = new TextEncoder();
return window.crypto.subtle.importKey(
"raw",
enc.encode(password),
{name: "PBKDF2"},
false,
["deriveBits", "deriveKey"]
);
}
/*
Given some key material and some random salt
derive an AES-GCM key using PBKDF2.
*/
function getKey(keyMaterial, salt) {
return window.crypto.subtle.deriveKey(
{
"name": "PBKDF2",
salt: salt,
"iterations": 100000,
"hash": "SHA-256"
},
keyMaterial,
{ "name": "AES-GCM", "length": 256},
true,
[ "wrapKey", "unwrapKey" ]
);
}
/*
Wrap the given key.
*/
async function wrapCryptoKey(keyToWrap) {
// get the key encryption key
const keyMaterial = await getKeyMaterial();
salt = window.crypto.getRandomValues(new Uint8Array(16));
const wrappingKey = await getKey(keyMaterial, salt);
iv = window.crypto.getRandomValues(new Uint8Array(12));
return window.crypto.subtle.wrapKey(
"pkcs8",
keyToWrap,
wrappingKey,
{
name: "AES-GCM",
iv: iv
}
);
}
/*
Generate a sign/verify key pair,
then wrap the private key.
*/
window.crypto.subtle.generateKey(
{
name: "RSA-PSS",
// Consider using a 4096-bit key for systems that require long-term security
modulusLength: 2048,
publicExponent: new Uint8Array([1, 0, 1]),
hash: "SHA-256",
},
true,
["sign", "verify"]
)
.then((keyPair) => {
return wrapCryptoKey(keyPair.privateKey);
})
.then((wrappedKey) => {
console.log(wrappedKey);
});
SubjectPublicKeyInfo wrap
This example wraps an RSA public encryption key. It uses "spki" as the export format and AES-CBC, with a password-derived key, to encrypt it. See the complete code on GitHub.
let salt;
let iv;
/*
Get some key material to use as input to the deriveKey method.
The key material is a password supplied by the user.
*/
function getKeyMaterial() {
const password = window.prompt("Enter your password");
const enc = new TextEncoder();
return window.crypto.subtle.importKey(
"raw",
enc.encode(password),
{name: "PBKDF2"},
false,
["deriveBits", "deriveKey"]
);
}
/*
Given some key material and some random salt
derive an AES-CBC key using PBKDF2.
*/
function getKey(keyMaterial, salt) {
return window.crypto.subtle.deriveKey(
{
"name": "PBKDF2",
salt: salt,
"iterations": 100000,
"hash": "SHA-256"
},
keyMaterial,
{ "name": "AES-CBC", "length": 256},
true,
[ "wrapKey", "unwrapKey" ]
);
}
/*
Wrap the given key.
*/
async function wrapCryptoKey(keyToWrap) {
// get the key encryption key
const keyMaterial = await getKeyMaterial();
salt = window.crypto.getRandomValues(new Uint8Array(16));
const wrappingKey = await getKey(keyMaterial, salt);
iv = window.crypto.getRandomValues(new Uint8Array(16));
return window.crypto.subtle.wrapKey(
"spki",
keyToWrap,
wrappingKey,
{
name: "AES-CBC",
iv: iv
}
);
}
/*
Generate an encrypt/decrypt key pair,
then wrap it.
*/
window.crypto.subtle.generateKey(
{
name: "RSA-OAEP",
// Consider using a 4096-bit key for systems that require long-term security
modulusLength: 2048,
publicExponent: new Uint8Array([1, 0, 1]),
hash: "SHA-256",
},
true,
["encrypt", "decrypt"]
)
.then((keyPair) => {
return wrapCryptoKey(keyPair.publicKey);
})
.then((wrappedKey) => {
console.log(wrappedKey);
});
JSON Web Key import
This code wraps an ECDSA private signing key. It uses "jwk" as the export format and AES-GCM, with a password-derived key, to encrypt it. See the complete code on GitHub.
let salt;
let iv;
/*
Get some key material to use as input to the deriveKey method.
The key material is a password supplied by the user.
*/
function getKeyMaterial() {
const password = window.prompt("Enter your password");
const enc = new TextEncoder();
return window.crypto.subtle.importKey(
"raw",
enc.encode(password),
{name: "PBKDF2"},
false,
["deriveBits", "deriveKey"]
);
}
/*
Given some key material and some random salt
derive an AES-GCM key using PBKDF2.
*/
function getKey(keyMaterial, salt) {
return window.crypto.subtle.deriveKey(
{
"name": "PBKDF2",
salt: salt,
"iterations": 100000,
"hash": "SHA-256"
},
keyMaterial,
{ "name": "AES-GCM", "length": 256},
true,
[ "wrapKey", "unwrapKey" ]
);
}
/*
Wrap the given key.
*/
async function wrapCryptoKey(keyToWrap) {
// get the key encryption key
const keyMaterial = await getKeyMaterial();
salt = window.crypto.getRandomValues(new Uint8Array(16));
const wrappingKey = await getKey(keyMaterial, salt);
iv = window.crypto.getRandomValues(new Uint8Array(12));
return window.crypto.subtle.wrapKey(
"jwk",
keyToWrap,
wrappingKey,
{
name: "AES-GCM",
iv: iv
}
);
}
/*
Generate a sign/verify key pair,
then wrap the private key
*/
window.crypto.subtle.generateKey(
{
name: "ECDSA",
namedCurve: "P-384"
},
true,
["sign", "verify"]
)
.then((keyPair) => {
return wrapCryptoKey(keyPair.privateKey);
})
.then((wrappedKey) => {
console.log(wrappedKey);
});
Specifications
Specification |
---|
Web Cryptography API # SubtleCrypto-method-wrapKey |
Browser compatibility
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