Atbash is a simple substitution cipher that was invented by the ancient Hebrews. It consists of substituting the first letter of the alphabet for the last, the second letter for the one before last, and so on. In other words, it reverses the alphabet.

A couple of words in the Book of Jeremiah, Leb Kamai and Sheshakh, are atbash for Kasdim/Kasdin (Chaldeans) and Babel respectively, probably written thus (Jer. 25:26; 51:1, 41). It has been associated with the esoteric methodologies of Jewish mysticism's interpretations of Hebrew religious texts as in the Kabbalah.

The Atbash method of encryption played a major role in Dan Brown’s book The Da Vinci Code.

Below, is a little program I wrote which will convert text to or from the Atbash cipher.  Feel free to enter any words you'd like. This code only works for the English, German, and Spanish alphabets, so it won't properly convert the Hebrew words mentioned above, since those words are phonetic translations of the Hebrew characters.