The Atbash cipher is one of the simplest and oldest known encryption techniques. Its name derives from the first and last letters of the Hebrew alphabet, "Aleph" and "Tav", which correspond to the letters "A" and "Z" in Western alphabets. This cipher operates following a substitution principle, where each letter of the alphabet is replaced by its corresponding letter at the end of the alphabet. For example, the letter "A" is replaced by "Z", "B" by "Y", and so on.

Some scholars suggest that the Atbash cipher may have been used in certain Hebrew biblical texts. For example, in Jeremiah 25:26 and 51:41, there are references to "Sheshach", which some interpret as a code name for Babylon using the Atbash cipher, where "Shin" (?) is replaced by "Tav" (?) , "Shin" (?) is replaced by "Tav" (?), "Kaf" (?) is replaced by "Mem" (?), and "Chet" (?) is replaced by "Yod" (?).