code: public static byte[] sha3(byte[] input, int offset, int length) {
          Keccak.DigestKeccak kecc = new Keccak.Digest256();
          kecc.update(input, offset, length);
          return kecc.digest();
      }
docs: Keccak-256 hash function.
  
  @param input binary encoded input data
  @param offset of start of data
  @param length of data
  @return hash value