Atbash Cipher: Encode and Decode Online Atbash cipher is a monoalphabetic substitution cipher that encrypts by reversing the letters of the alphabet. It was initially used with the Hebrew alphabet. For example, in the Atbash cipher, A would be replaced by Z, B would become Y, C would become X, and so on. Use the above Atbash cipher decoder and encoder to encrypt/decrypt simple messages. If this tool was helpful, tweet it or share it.