The importKey()
method of the SubtleCrypto
interface imports a key: that is, it takes as input a key in an external, portable format and gives you a CryptoKey
object that you can use in the Web Crypto API.
The function accepts several import formats: see Supported formats for details.
importKey(format, keyData, algorithm, extractable, keyUsages)
A Promise
that fulfills with the imported key as a CryptoKey
object.
The promise is rejected when one of the following exceptions is encountered:
-
SyntaxError
DOMException
-
Raised when keyUsages
is empty but the unwrapped key is of type secret
or private
.
-
TypeError
-
Raised when trying to use an invalid format or if the keyData
is not suited for that format.
This API supports four different key import/export formats: Raw, PKCS #8, SubjectPublicKeyInfo, and JSON Web Key.
You can use this format to import or export AES or HMAC secret keys, or Elliptic Curve public keys.
In this format the key is supplied as an ArrayBuffer
containing the raw bytes for the key.
You can use this format to import or export RSA or Elliptic Curve private keys.
The PKCS #8 format is defined in RFC 5208, using the ASN.1 notation:
PrivateKeyInfo ::= SEQUENCE {
version Version,
privateKeyAlgorithm PrivateKeyAlgorithmIdentifier,
privateKey PrivateKey,
attributes [0] IMPLICIT Attributes OPTIONAL }
The importKey()
method expects to receive this object as an ArrayBuffer
containing the DER-encoded form of the PrivateKeyInfo
. DER is a set of rules for encoding ASN.1 structures into a binary form.
You are most likely to encounter this object in PEM format. PEM format is a way to encode binary data in ASCII. It consists of a header and a footer, and in between, the base64-encoded binary data. A PEM-encoded PrivateKeyInfo
looks like this:
-----BEGIN PRIVATE KEY-----
MIG2AgEAMBAGByqGSM49AgEGBSuBBAAiBIGeMIGbAgEBBDAU9BD0jxDfF5OV380z
9VIEUN2W5kJDZ3hbuaDenCxLiAMsoquKTfFaou71eLdN0TShZANiAARMUhCee/cp
xmjGc1roj0D0k6VlUqtA+JVCWigXcIAukOeTHCngZDKCrD4PkXDBvbciJdZKvO+l
ml2FIkoovZh/8yeTKmjUMb804g6OmjUc9vVojCRV0YdaSmYkkJMJbLg=
-----END PRIVATE KEY-----
To get this into a format you can give to importKey()
you need to do two things:
- base64-decode the part between header and footer, using
window.atob()
.
- convert the resulting string into an
ArrayBuffer
.
See the Examples section for more concrete guidance.
You can use this format to import or export RSA or Elliptic Curve public keys.
SubjectPublicKey
is defined in RFC 5280, Section 4.1 using the ASN.1 notation:
SubjectPublicKeyInfo ::= SEQUENCE {
algorithm AlgorithmIdentifier,
subjectPublicKey BIT STRING }
Just like PKCS #8, the importKey()
method expects to receive this object as an ArrayBuffer
containing the DER-encoded form of the SubjectPublicKeyInfo
.
Again, you are most likely to encounter this object in PEM format. A PEM-encoded SubjectPublicKeyInfo
looks like this:
-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA3j+HgSHUnc7F6XzvEbD0
r3M5JNy+/kabiJVu8IU1ERAl3Osi38VgiMzjDBDOrFxVzNNzl+SXAHwXIV5BHiXL
CQ6qhwYsDgH6OqgKIwiALra/wNH4UHxj1Or/iyAkjHRR/kGhUtjyVCjzvaQaDpJW
2G+syd1ui0B6kJov2CRUWiPwpff8hBfVWv8q9Yc2yD5hCnykVL0iAiyn+SDAk/rv
8dC5eIlzCI4efUCbyG4c9O88Qz7bS14DxSfaPTy8P/TWoihVVjLaDF743LgM/JLq
CDPUBUA3HLsZUhKm3BbSkd7Q9Ngkjv3+yByo4/fL+fkYRa8j9Ypa2N0Iw53LFb3B
gQIDAQAB
-----END PUBLIC KEY-----
Just as with PKCS #8, to get this into a format you can give to importKey()
you need to do two things:
- base64-decode the part between header and footer, using
window.atob()
.
- convert the resulting string into an
ArrayBuffer
.
See the Examples section for more concrete guidance.
You can use JSON Web Key format to import or export RSA or Elliptic Curve public or private keys, as well as AES and HMAC secret keys.
JSON Web Key format is defined in RFC 7517. It describes a way to represent public, private, and secret keys as JSON objects.
A JSON Web Key looks something like this (this is an EC private key):
{
"crv": "P-384",
"d": "wouCtU7Nw4E8_7n5C1-xBjB4xqSb_liZhYMsy8MGgxUny6Q8NCoH9xSiviwLFfK_",
"ext": true,
"key_ops": ["sign"],
"kty": "EC",
"x": "SzrRXmyI8VWFJg1dPUNbFcc9jZvjZEfH7ulKI1UkXAltd7RGWrcfFxqyGPcwu6AQ",
"y": "hHUag3OvDzEr0uUQND4PXHQTXP5IDGdYhJhL-WLKjnGjQAw0rNGy5V29-aV-yseW"
};
This example imports an AES key from an ArrayBuffer
containing the bytes to use. See the complete code on GitHub.
const rawKey = window.crypto.getRandomValues(new Uint8Array(16));
function importSecretKey(rawKey) {
return window.crypto.subtle.importKey(
"raw",
rawKey,
"AES-GCM",
true,
["encrypt", "decrypt"]
);
}
This example imports an RSA private signing key from a PEM-encoded PKCS #8 object. See the complete code on GitHub.
function str2ab(str) {
const buf = new ArrayBuffer(str.length);
const bufView = new Uint8Array(buf);
for (let i = 0, strLen = str.length; i < strLen; i++) {
bufView[i] = str.charCodeAt(i);
}
return buf;
}
const pemEncodedKey = `-----BEGIN PRIVATE KEY-----
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
-----END PRIVATE KEY-----`;
function importPrivateKey(pem) {
const pemHeader = "-----BEGIN PRIVATE KEY-----";
const pemFooter = "-----END PRIVATE KEY-----";
const pemContents = pem.substring(pemHeader.length, pem.length - pemFooter.length);
const binaryDerString = window.atob(pemContents);
const binaryDer = str2ab(binaryDerString);
return window.crypto.subtle.importKey(
"pkcs8",
binaryDer,
{
name: "RSA-PSS",
hash: "SHA-256",
},
true,
["sign"]
);
}
This example imports an RSA public encryption key from a PEM-encoded SubjectPublicKeyInfo object. See the complete code on GitHub.
function str2ab(str) {
const buf = new ArrayBuffer(str.length);
const bufView = new Uint8Array(buf);
for (let i = 0, strLen = str.length; i < strLen; i++) {
bufView[i] = str.charCodeAt(i);
}
return buf;
}
const pemEncodedKey = `-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAy3Xo3U13dc+xojwQYWoJLCbOQ5fOVY8LlnqcJm1W1BFtxIhOAJWohiHuIRMctv7dzx47TLlmARSKvTRjd0dF92jx/xY20Lz+DXp8YL5yUWAFgA3XkO3LSJgEOex10NB8jfkmgSb7QIudTVvbbUDfd5fwIBmCtaCwWx7NyeWWDb7A9cFxj7EjRdrDaK3ux/ToMLHFXVLqSL341TkCf4ZQoz96RFPUGPPLOfvN0x66CM1PQCkdhzjE6U5XGE964ZkkYUPPsy6Dcie4obhW4vDjgUmLzv0z7UD010RLIneUgDE2FqBfY/C+uWigNPBPkkQ+Bv/UigS6dHqTCVeD5wgyBQIDAQAB
-----END PUBLIC KEY-----`;
function importRsaKey(pem) {
const pemHeader = "-----BEGIN PUBLIC KEY-----";
const pemFooter = "-----END PUBLIC KEY-----";
const pemContents = pem.substring(pemHeader.length, pem.length - pemFooter.length);
const binaryDerString = window.atob(pemContents);
const binaryDer = str2ab(binaryDerString);
return window.crypto.subtle.importKey(
"spki",
binaryDer,
{
name: "RSA-OAEP",
hash: "SHA-256"
},
true,
["encrypt"]
);
}
This code imports an ECDSA private signing key, given a JSON Web Key object that represents it. See the complete code on GitHub.
const jwkEcKey = {
"crv": "P-384",
"d": "wouCtU7Nw4E8_7n5C1-xBjB4xqSb_liZhYMsy8MGgxUny6Q8NCoH9xSiviwLFfK_",
"ext": true,
"key_ops": ["sign"],
"kty": "EC",
"x": "SzrRXmyI8VWFJg1dPUNbFcc9jZvjZEfH7ulKI1UkXAltd7RGWrcfFxqyGPcwu6AQ",
"y": "hHUag3OvDzEr0uUQND4PXHQTXP5IDGdYhJhL-WLKjnGjQAw0rNGy5V29-aV-yseW"
};
function importPrivateKey(jwk) {
return window.crypto.subtle.importKey(
"jwk",
jwk,
{
name: "ECDSA",
namedCurve: "P-384"
},
true,
["sign"]
);
}