KeyObject

Node.js uses a KeyObject class to represent a symmetric or asymmetric key, and each kind of key exposes different functions. The crypto.createSecretKey(), crypto.createPublicKey() and crypto.createPrivateKey() methods are used to create KeyObject instances. KeyObject objects are not to be created directly using the new keyword.

Most applications should consider using the new KeyObject API instead of passing keys as strings or Buffers due to improved security features.

KeyObject instances can be passed to other threads via postMessage(). The receiver obtains a cloned KeyObject, and the KeyObject does not need to be listed in the transferList argument.

KeyObject.from(key): KeyObject

Returns the underlying KeyObject of a CryptoKey. The returned KeyObject does not retain any of the restrictions imposed by the Web Crypto API on the original CryptoKey, such as the allowed key usages, the algorithm or hash algorithm bindings, and the extractability flag. In particular, the underlying key material of the returned KeyObject can always be exported.

const { KeyObject } = await import('node:crypto');
const { subtle } = globalThis.crypto;

const key = await subtle.generateKey({
  name: 'HMAC',
  hash: 'SHA-256',
  length: 256,
}, true, ['sign', 'verify']);

const keyObject = KeyObject.from(key);
console.log(keyObject.symmetricKeySize);
// Prints: 32 (symmetric key size in bytes)

const { KeyObject } = require('node:crypto');
const { subtle } = globalThis.crypto;

(async function() {
  const key = await subtle.generateKey({
    name: 'HMAC',
    hash: 'SHA-256',
    length: 256,
  }, true, ['sign', 'verify']);

  const keyObject = KeyObject.from(key);
  console.log(keyObject.symmetricKeySize);
  // Prints: 32 (symmetric key size in bytes)
})();

This property exists only on asymmetric keys. Depending on the type of the key, this object contains information about the key. None of the information obtained through this property can be used to uniquely identify a key or to compromise the security of the key.

For RSA-PSS keys, if the key material contains a RSASSA-PSS-params sequence, the hashAlgorithm, mgf1HashAlgorithm, and saltLength properties will be set.

Other key details might be exposed via this API using additional attributes.

For asymmetric keys, this property represents the type of the key. See the supported asymmetric key types.

This property is undefined for unrecognized KeyObject types and symmetric keys.

keyObject.equals(otherKeyObject): boolean

Returns true or false depending on whether the keys have exactly the same type, value, and parameters. This method is not constant time.

keyObject.export(options?): string | Buffer | Object

For symmetric keys, the following encoding options can be used:

For public keys, the following encoding options can be used:

For private keys, the following encoding options can be used:

The result type depends on the selected encoding format, when PEM the result is a string, when DER it will be a buffer containing the data encoded as DER, when JWK it will be an object. Raw formats return a Buffer containing the raw key material.

Private keys can be encrypted by specifying a cipher and passphrase. The PKCS#8 type supports encryption with both PEM and DER format for any key algorithm. PKCS#1 and SEC1 can only be encrypted when the PEM format is used. For maximum compatibility, use PKCS#8 for encrypted private keys. Since PKCS#8 defines its own encryption mechanism, PEM-level encryption is not supported when encrypting a PKCS#8 key. See RFC 5208 for PKCS#8 encryption and RFC 1421 for PKCS#1 and SEC1 encryption.

For secret keys, this property represents the size of the key in bytes. This property is undefined for asymmetric keys.

keyObject.toCryptoKey(algorithm, extractable, keyUsages): void

Converts a KeyObject instance to a CryptoKey.

Depending on the type of this KeyObject, this property is either 'secret' for secret (symmetric) keys, 'public' for public (asymmetric) keys or 'private' for private (asymmetric) keys.