Function ecdhDeriveBits

lib/internal/crypto/diffiehellman.js:374–430

(algorithm, baseKey, length)

// The ecdhDeriveBits function is part of the Web Crypto API and serves both
// deriveKeys and deriveBits functions.
function ecdhDeriveBits(algorithm, baseKey, length) {
  const { 'public': key } = algorithm;

  if (getCryptoKeyType(baseKey) !== 'private') {
    throw lazyDOMException(
      'baseKey must be a private key', 'InvalidAccessError');
  }

  const keyAlgorithm = getCryptoKeyAlgorithm(key);
  const baseKeyAlgorithm = getCryptoKeyAlgorithm(baseKey);
  if (keyAlgorithm.name !== baseKeyAlgorithm.name) {
    throw lazyDOMException(
      'The public and private keys must be of the same type',
      'InvalidAccessError');
  }

  if (
    keyAlgorithm.name === 'ECDH' &&
    keyAlgorithm.namedCurve !== baseKeyAlgorithm.namedCurve
  ) {
    throw lazyDOMException('Named curve mismatch', 'InvalidAccessError');
  }

  const bits = jobPromise(() => new DHBitsJob(
    kCryptoJobWebCrypto,
    getCryptoKeyHandle(key),
    undefined,
    undefined,
    undefined,
    undefined,
    getCryptoKeyHandle(baseKey),
    undefined,
    undefined,
    undefined,
    undefined));

  // If a length is not specified, return the full derived secret
  if (length === null)
    return bits;

  return jobPromiseThen(bits, (bits) => {
    const sliceLength = numBitsToBytes(length);

    const { byteLength } = bits;
    // If the length is larger than the derived secret, throw.
    if (byteLength < sliceLength)
      throw lazyDOMException('derived bit length is too small', 'OperationError');

    if (length % 8 === 0) {
      if (byteLength === sliceLength)
        return bits;
      return ArrayBufferPrototypeSlice(bits, 0, sliceLength);
    }

    return TypedArrayPrototypeGetBuffer(truncateToBitLength(length, bits));
  });
}