An Atbash cipher is a type of simple cipher that encrypts the message by taking the position of a letter in the alphabet and changing it to the letter that many places from the end of the alphabet. For example, the first letter of the alphabet is A, which would become the last letter of the alphabet, Z. If we wanted to encrypt the phrase "FOR ALL IS SACRED" using Atbash, using the below table we would get "ULI ZOO RH HZXIVW".
Unlike other ciphers, decrypting an Atbash cipher uses the same process as encrypting it and does not need to be reversed. For example, to decrypt a message that was created using a Caesar cipher you will need to shift each letter backwards instead of forwards through the alphabet. With the Atbash cipher, performing the encryption as-is on the ciphertext will be enough to decrypt it.