code: public static boolean isPotentiallyEncryptedBytes(byte[] bytes) {
          checkNotNull(bytes, "bytes");
  
          // The number of bytes is a non-zero multiple of the block size.
          try {
              return bytes.length != 0 && bytes.length % Cipher.getInstance(CIPHER).getBlockSize() == 0;
          } catch (Throwable t) {
              // This shouldn't happen since AES is supported by all JVMs.
              throw Throwables.propagate(t);
          }
      }
docs: Returns true if the provided bytes _could_ be encrypted credentials, even if they can't be decrypted
  by a specific instance.