public static CommittedKey generate()

in src/main/java/com/amazonaws/encryptionsdk/internal/CommittedKey.java [53:112]
54 lines of code
10 McCabe index (conditional complexity)

  public static CommittedKey generate(CryptoAlgorithm alg, SecretKey dataKey, byte[] nonce)
      throws InvalidKeyException {
    if (!alg.isCommitting()) {
      throw new IllegalArgumentException("Algorithm does not support key commitment.");
    }
    if (nonce.length != alg.getCommitmentNonceLength()) {
      throw new IllegalArgumentException("Invalid nonce size");
    }
    if (dataKey.getFormat() == null || !dataKey.getFormat().equalsIgnoreCase(RAW_DATA_FORMAT)) {
      throw new IllegalArgumentException(
          "Currently only RAW format keys are supported for HKDF algorithms. Actual format was "
              + dataKey.getFormat());
    }
    if (dataKey.getAlgorithm() == null
        || !dataKey.getAlgorithm().equalsIgnoreCase(alg.getDataKeyAlgo())) {
      throw new IllegalArgumentException(
          "DataKey of incorrect algorithm. Expected "
              + alg.getDataKeyAlgo()
              + " but was "
              + dataKey.getAlgorithm());
    }
    final byte[] rawDataKey = dataKey.getEncoded();
    if (rawDataKey.length != alg.getDataKeyLength()) {
      throw new IllegalArgumentException(
          "DataKey of incorrect length. Expected "
              + alg.getDataKeyLength()
              + " but was "
              + rawDataKey.length);
    }

    final String macAlgorithm;
    switch (alg.getKeyCommitmentAlgo_()) {
      case HKDF_SHA_512:
        macAlgorithm = HMAC_SHA_512;
        break;
      default:
        throw new UnsupportedOperationException(
            "Support for commitment with " + alg.getKeyCommitmentAlgo_() + " not yet built.");
    }

    HmacKeyDerivationFunction kdf = null;
    try {
      kdf = HmacKeyDerivationFunction.getInstance(macAlgorithm);
    } catch (NoSuchAlgorithmException e) {
      throw new IllegalStateException(e);
    }
    kdf.init(rawDataKey, nonce);

    final byte[] commitment = kdf.deriveKey(COMMITKEY_LABEL, alg.getCommitmentLength());

    // Clone to prevent modification of the master copy
    final byte[] deriveKeyLabel = DERIVE_KEY_LABEL_TEMPLATE.clone();
    final short algId = alg.getValue();
    deriveKeyLabel[0] = (byte) ((algId >> 8) & 0xFF);
    deriveKeyLabel[1] = (byte) (algId & 0xFF);
    SecretKey ek =
        new SecretKeySpec(kdf.deriveKey(deriveKeyLabel, alg.getKeyLength()), alg.getKeyAlgo());

    return new CommittedKey(ek, commitment);
  }