James Trimm’s Nazarene Commentary on Jeremiah Chapter 25

25:26

And all the kings of the north, far and near, one with another, and all the kingdoms of the world, which are upon the face of the earth. And the king of Sheshach shall drink after them.
(Jer. 25:26 HRV)

Rashi says of this verse: Sheshach: That is ‘Babylon’ in אתבש.

Atbash is a form of Temura (permutation). One method of Temura involves letter substitution whereby the Hebrew alphabet is divided into two group of 11 letters, with each letter from one group, corresponding to a letter in the other group. Imagine theses two sets of Hebrew letters each written in order in concentric circles which can move relative to one another as a “dial”. Eleven different “codes” emerge.

Each of these ciphers or methods of temura are named by the first two pairs being switched. The simplest code is called Atbash (אתבש) meaning א becomes ת and ב becomes ש.

In Jeremiah 25:26 ששך (Sheshach) is actually a temura Atbash cipher for בבל “Babylon”.