SubtleCrypto: generateKey() method

The generateKey() method of the SubtleCrypto interface is used to generate a new key (for symmetric algorithms) or key pair (for public-key algorithms).

Syntax

generateKey(algorithm, extractable, keyUsages)

Parameters

algorithm

An object defining the type of key to generate and providing extra algorithm-specific parameters.

• For RSASSA-PKCS1-v1_5, RSA-PSS, or RSA-OAEP: pass an RsaHashedKeyGenParams object.
• For ECDSA or ECDH: pass an EcKeyGenParams object.
• For HMAC: pass an HmacKeyGenParams object.
• For AES-CTR, AES-CBC, AES-GCM, or AES-KW: pass an AesKeyGenParams object.
• For Ed25519: pass the string Ed25519 or an object of the form { name: "Ed25519" }.
• For X25519: pass the string X25519 or an object of the form { name: "X25519" }.

extractable

A boolean value indicating whether it will be possible to export the key using SubtleCrypto.exportKey() or SubtleCrypto.wrapKey().

keyUsages

An Array of strings indicating what can be done with the newly generated key. Possible values for array elements are:

encrypt

The key may be used to encrypt messages.

decrypt

The key may be used to decrypt messages.

sign

The key may be used to sign messages.

verify

The key may be used to verify signatures.

deriveKey

The key may be used in deriving a new key.

deriveBits

The key may be used in deriving bits.

wrapKey

The key may be used to wrap a key.

unwrapKey

The key may be used to unwrap a key.

Return value

A Promise that fulfills with a CryptoKey (for symmetric algorithms) or a CryptoKeyPair (for public-key algorithms).

Exceptions

The promise is rejected when the following exception is encountered:

SyntaxError DOMException

Raised when the result is a CryptoKey of type secret or private but keyUsages is empty, or invalid for the algorithm type.

SyntaxError DOMException

Raised when the result is a CryptoKeyPair and its privateKey.usages attribute is empty, or invalid for the algorithm type.

Examples

RSA key pair generation

This code generates an RSA-OAEP encryption key pair. See the complete code on GitHub.

let keyPair = await window.crypto.subtle.generateKey(
  {
    name: "RSA-OAEP",
    modulusLength: 4096,
    publicExponent: new Uint8Array([1, 0, 1]),
    hash: "SHA-256",
  },
  true,
  ["encrypt", "decrypt"],
);

Elliptic curve key pair generation

This code generates an ECDSA signing key pair. See the complete code on GitHub.

let keyPair = await window.crypto.subtle.generateKey(
  {
    name: "ECDSA",
    namedCurve: "P-384",
  },
  true,
  ["sign", "verify"],
);

HMAC key generation

This code generates an HMAC signing key. See the complete code on GitHub.

let key = await window.crypto.subtle.generateKey(
  {
    name: "HMAC",
    hash: { name: "SHA-512" },
  },
  true,
  ["sign", "verify"],
);

AES key generation

This code generates an AES-GCM encryption key. See the complete code on GitHub.

let key = await window.crypto.subtle.generateKey(
  {
    name: "AES-GCM",
    length: 256,
  },
  true,
  ["encrypt", "decrypt"],
);

Ed25519 key generation

This code generates an Ed25519 signing key pair. It is derived from this source code on GitHub, which you can run live here.

JavaScript

Code for generating a key pair using the Ed25519 algorithm and logging the information in each key is shown below. Note that the code is run in a try..catch block because not all browsers support this algorithm.

The JavaScript first gets the #sign-button and #message <input> elements, then adds a listener for the click event on the button. The event handler clears the log and runs the other operations passing the content of the <input> element.

const button = document.querySelector("#run-button");
const input = document.querySelector("#log");

button.addEventListener("click", () => {
  // Clear log
  logElement.innerText = "";
  logElement.scrollTop = logElement.scrollHeight;
  // Run test
  test();
});

async function test() {
  try {
    // Create a key pair and use destructuring assignment to assign to variables
    const { publicKey, privateKey } = await crypto.subtle.generateKey(
      {
        name: "Ed25519",
      },
      true,
      ["sign", "verify"],
    );

    // Log the properties of the keys
    log(`publicKey: ${publicKey}`);
    log(` type: ${publicKey.type}`);
    log(` extractable: ${publicKey.extractable}`);
    log(` algorithm: ${JSON.stringify(publicKey.algorithm)}`);
    log(` usages: ${publicKey.usages}`);
    log(`privateKey: ${privateKey}`);
    log(` type: ${privateKey.type}`);
    log(` extractable: ${privateKey.extractable}`);
    log(` algorithm: ${JSON.stringify(privateKey.algorithm)}`);
    log(` usages: ${privateKey.usages}`);
  } catch (error) {
    log(error);
  }
}

Result

The information about the created keys is logged below (or an error string if the browser does not allow the key to be created).

X25519 key generation

This code generates an X25519 public and private key pair that can be used in SubtleCrypto.deriveKey() to create a shared key, or in SubtleCrypto.deriveBits() to create a shared secret.

JavaScript

Code for generating a key pair using the X25519 algorithm and logging the information in each key is shown below. Note that the code is run in a try..catch block because not all browsers support this algorithm.

The JavaScript first gets the #run-button and #log <input> elements, then adds a listener for the click event on the button. The event handler clears the log, generates an X25519 key pair, and logs some of its properties.

const button = document.querySelector("#run-button");
const input = document.querySelector("#log");

button.addEventListener("click", () => {
  // Clear log
  logElement.innerText = "";
  logElement.scrollTop = logElement.scrollHeight;
  // Run test
  test();
});

async function test() {
  try {
    // Create a key pair and use destructuring assignment to assign to variables
    const { publicKey, privateKey } = await crypto.subtle.generateKey(
      {
        name: "X25519",
      },
      true,
      ["deriveKey", "deriveBits"],
    );

    // Log the properties of the keys
    log(`publicKey: ${publicKey}`);
    log(` type: ${publicKey.type}`);
    log(` extractable: ${publicKey.extractable}`);
    log(` algorithm: ${JSON.stringify(publicKey.algorithm)}`);
    log(` usages: ${publicKey.usages}`);
    log(`privateKey: ${privateKey}`);
    log(` type: ${privateKey.type}`);
    log(` extractable: ${privateKey.extractable}`);
    log(` algorithm: ${JSON.stringify(privateKey.algorithm)}`);
    log(` usages: ${privateKey.usages}`);
  } catch (error) {
    log(error);
  }
}

Result

The information about the created keys is logged below (or an error string if the browser does not allow the key to be created).

Specifications

Browser compatibility

See also

• Cryptographic key length recommendations.
• NIST Transitioning the Use of Cryptographic Algorithms and Key Lengths.