This tool can be used to encode and decode messages using a Atbash cipher, which reverses the alphabet. Want to encode or decode a message? Just copy the plaintext into the message box and hit translate.
The atbash cipher is a simple substitution cipher from Biblical times; it reverses the alphabet such that each letter is mapped to the letter in the same position in the reverse of the alphabet (A -> Z, B -> Y). The original implementation (ca. 500 BC) was for the Hebrew alphabet and there are Old Testament references to it. The Atbash cipher has also been associated with various forms of mysticism. In modern times, it is referred to as a reverse alphabet code (see these cubscout materials). The atbash cipher is trivial to crack, once you realize that you're dealing with a substitution cipher, and is highly vulnerable to letter frequency analysis. It's primary modern application is puzzles and games. This atbash translater (including both atbash encoder and atbash decoder) can help you decode these cipher messages.
This tool is an atbash decoder; it is also an atbash encoder, since the two are exactly identical. To use the atbash translator to translate a message (atbash encoder setting), paste your message into the text box and hit translate message. The result will appear below. To decipher the atbash cipher message, copy the text from the results box into the text box (which serves as the atbash encoder) and hit translate message. You should be looking at your original text.
For a low-tech cipher, the atbash cipher is surprisingly effective. While it relies completely upon suprise (hint: don't use it to encode truly secret messages), most decoders mentally try the caesar cipher (fixed letter shift), which fails, and assume a mixed alphabet cipher. This is a much more complicated cipher to attack, even with a computer. So don't laugh at the atbash encoder and atbash decoder - they may be rustic, but they are certainly enough to confuse most of the people some of the time. Granted the task of an atbash decoder was harder before computer automation.
The first cipher use in recorded history to protect information was in Mesopotamia. We've found some clay tablets that were clearly designed to protect information. Military and diplomatic use of ciphers picked up around 500 - 400 B.C., with documented cipher use in many areas of the world (Greeks, Hebrew, India).
The Atbash cipher is one of the easiest cipher systems out there; the atbash ciphertext is trivial to decrypt once you understand the pattern. The Rot13 cipher, A1Z26 cipher, morse code, and affine cipher, while an artifact of the machine age, are similarly trivial to solve. From there you move to a full monoalphabetic cipher, with a more complex monoalphabetic substitution system to jumble the secret message. Modern cryptogram puzzles are based around a monoalphabetic substitution cipher. Solving the puzzle involves mapping the ciphertext alphabet to the plaintext alphabet.
As experienced cryptogram solvers know, the decryption weakness of a substitution cipher that maintains the same basic message structure in the plaintext letter. For example, single letter clues such as the first letter, second letter, and last letter of a word restrict the range of possible words and facilitate guessing. Punctuation helps as well.
There are several options for making a cipher harder, beyond the ability of most human analysts to crank. The first is to layer a shift cipher into the system, so word patterns are obscured. The other is to use multiple alphabets and rotate between them (this is the basis of a polyalphabetic cipher system such as the vigenere cipher. The combined cipher is better protected, since it is far harder to crack both coding systems at once.