SubtleCrypto: exportKey() method
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.
Note: This feature is available in Web Workers.
The exportKey()
method of the SubtleCrypto
interface exports a key: that is, it takes as input a CryptoKey
object
and gives you the key in an external, portable format.
To export a key, the key must have CryptoKey.extractable
set to
true
.
Keys can be exported in several formats: see Supported formats in the
SubtleCrypto.importKey()
page for details.
Keys are not exported in an encrypted format: to encrypt keys when exporting them use
the
SubtleCrypto.wrapKey()
API instead.
Syntax
exportKey(format, key)
Parameters
format
-
A string value describing the data format in which the key should be exported. It can be one of the following:
raw
: Raw format.pkcs8
: PKCS #8 format.spki
: SubjectPublicKeyInfo format.jwk
: JSON Web Key format.
key
-
The
CryptoKey
to export.
Return value
A Promise
.
-
If
format
wasjwk
, then the promise fulfills with a JSON object containing the key. -
Otherwise the promise fulfills with an
ArrayBuffer
containing the key.
Exceptions
The promise is rejected when one of the following exceptions is encountered:
InvalidAccessError
DOMException
-
Raised when trying to export a non-extractable key.
NotSupported
DOMException
-
Raised when trying to export in an unknown format.
TypeError
-
Raised when trying to use an invalid format.
Examples
Note: You can try the working examples out on GitHub.
Raw export
This example exports an AES key as an ArrayBuffer
containing the bytes for
the key. See the complete code on GitHub.
/*
Export the given key and write it into the "exported-key" space.
*/
async function exportCryptoKey(key) {
const exported = await window.crypto.subtle.exportKey("raw", key);
const exportedKeyBuffer = new Uint8Array(exported);
const exportKeyOutput = document.querySelector(".exported-key");
exportKeyOutput.textContent = `[${exportedKeyBuffer}]`;
}
/*
Generate an encrypt/decrypt secret key,
then set up an event listener on the "Export" button.
*/
window.crypto.subtle
.generateKey(
{
name: "AES-GCM",
length: 256,
},
true,
["encrypt", "decrypt"],
)
.then((key) => {
const exportButton = document.querySelector(".raw");
exportButton.addEventListener("click", () => {
exportCryptoKey(key);
});
});
PKCS #8 export
This example exports an RSA private signing key as a PKCS #8 object. The exported key is then PEM-encoded. See the complete code on GitHub.
/*
Convert an ArrayBuffer into a string
from https://developer.chrome.com/blog/how-to-convert-arraybuffer-to-and-from-string/
*/
function ab2str(buf) {
return String.fromCharCode.apply(null, new Uint8Array(buf));
}
/*
Export the given key and write it into the "exported-key" space.
*/
async function exportCryptoKey(key) {
const exported = await window.crypto.subtle.exportKey("pkcs8", key);
const exportedAsString = ab2str(exported);
const exportedAsBase64 = window.btoa(exportedAsString);
const pemExported = `-----BEGIN PRIVATE KEY-----\n${exportedAsBase64}\n-----END PRIVATE KEY-----`;
const exportKeyOutput = document.querySelector(".exported-key");
exportKeyOutput.textContent = pemExported;
}
/*
Generate a sign/verify key pair,
then set up an event listener on the "Export" button.
*/
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) => {
const exportButton = document.querySelector(".pkcs8");
exportButton.addEventListener("click", () => {
exportCryptoKey(keyPair.privateKey);
});
});
SubjectPublicKeyInfo export
This example exports an RSA public encryption key as a PEM-encoded SubjectPublicKeyInfo object. See the complete code on GitHub.
/*
Convert an ArrayBuffer into a string
from https://developer.chrome.com/blog/how-to-convert-arraybuffer-to-and-from-string/
*/
function ab2str(buf) {
return String.fromCharCode.apply(null, new Uint8Array(buf));
}
/*
Export the given key and write it into the "exported-key" space.
*/
async function exportCryptoKey(key) {
const exported = await window.crypto.subtle.exportKey("spki", key);
const exportedAsString = ab2str(exported);
const exportedAsBase64 = window.btoa(exportedAsString);
const pemExported = `-----BEGIN PUBLIC KEY-----\n${exportedAsBase64}\n-----END PUBLIC KEY-----`;
const exportKeyOutput = document.querySelector(".exported-key");
exportKeyOutput.textContent = pemExported;
}
/*
Generate an encrypt/decrypt key pair,
then set up an event listener on the "Export" button.
*/
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) => {
const exportButton = document.querySelector(".spki");
exportButton.addEventListener("click", () => {
exportCryptoKey(keyPair.publicKey);
});
});
JSON Web Key export
This example exports an ECDSA private signing key as a JSON Web Key object. See the complete code on GitHub.
/*
Export the given key and write it into the "exported-key" space.
*/
async function exportCryptoKey(key) {
const exported = await window.crypto.subtle.exportKey("jwk", key);
const exportKeyOutput = document.querySelector(".exported-key");
exportKeyOutput.textContent = JSON.stringify(exported, null, " ");
}
/*
Generate a sign/verify key pair,
then set up an event listener on the "Export" button.
*/
window.crypto.subtle
.generateKey(
{
name: "ECDSA",
namedCurve: "P-384",
},
true,
["sign", "verify"],
)
.then((keyPair) => {
const exportButton = document.querySelector(".jwk");
exportButton.addEventListener("click", () => {
exportCryptoKey(keyPair.privateKey);
});
});
Specifications
Specification |
---|
Web Cryptography API # SubtleCrypto-method-exportKey |
Browser compatibility
BCD tables only load in the browser