public void deriveKey()

in DynamoDbEncryption/runtimes/java/src/main/sdkv1/com/amazonaws/services/dynamodbv2/datamodeling/internal/Hkdf.java [231:273]

• 39 lines of code
• 7 McCabe index (conditional complexity)

  public void deriveKey(
    final byte[] info,
    final int length,
    final byte[] output,
    final int offset
  ) throws ShortBufferException, IllegalStateException {
    assertInitialized();
    if (length < 0) {
      throw new IllegalArgumentException(
        "Length must be a non-negative value."
      );
    }
    if (output.length < offset + length) {
      throw new ShortBufferException();
    }
    Mac mac = createMac();

    if (length > 255 * mac.getMacLength()) {
      throw new IllegalArgumentException(
        "Requested keys may not be longer than 255 times the underlying HMAC length."
      );
    }

    byte[] t = EMPTY_ARRAY;
    try {
      int loc = 0;
      byte i = 1;
      while (loc < length) {
        mac.update(t);
        mac.update(info);
        mac.update(i);
        t = mac.doFinal();

        for (int x = 0; x < t.length && loc < length; x++, loc++) {
          output[loc] = t[x];
        }

        i++;
      }
    } finally {
      Arrays.fill(t, (byte) 0); // Zeroize temporary array
    }
  }