code: private static byte[] withCorrectBlockSize(final byte[] key) {
          if (key.length != CcAes.BLOCK) {
              throw new IllegalArgumentException(
                  String.format(
                      "the length of the AES key must be exactly %d bytes",
                      CcAes.BLOCK
                  )
              );
          }
          return key;
      }
docs: Check the block size of the key.
  
  @param key The encryption key
  @return The verified encryption key