The Atbash code is a “secret” but very simple code sometimes used to keep the true wording hidden from those unfamiliar with Atbash (sometimes spelled “Athbash”). The code was originally developed for Hebrew, but it can easily be applied to other languages as well.
In Atbash, the first letter of an alphabet is replaced with the last letter; the second letter is replaced with the next-to-last letter; etc. So, in English, A is written as “Z”; B becomes “Y”; C is “X”; etc. In Atbash, “roses are red, violets are blue” is “ilhvh ziv ivw, erlovgh ziv yofv.”
Atbash is most commonly found in Kabalistic writings and in Jewish mysticism and allegory. However, the Bible also contains three uses of the Atbash code in the book of Jeremiah. In Jeremiah 25:26, the prophet predicts a punishment for a nation called “Sheshak”: “And after all of them, the king of Sheshak will drink it too.” In the original Hebrew, the letters of the word Sheshak commute into “Babylon” using the Atbash code.
The word Sheshak is also used in Jeremiah 51:41: “How Sheshak will be captured, the boast of the whole earth seized! How desolate Babylon will be among the nations!” Interestingly, both the cipher, Sheshak, and its interpretation, Babylon, are side by side in this verse. The NET Bible dispenses with transliterating the Atbash code word and just puts “Babylon” instead.
The other instance of Atbash is in Jeremiah 51:1, “See, I will stir up the spirit of a destroyer against Babylon and the people of Leb Kamai.” Following the Atbash code, the term Leb Kamai transforms into “Chaldeans.” The NET Bible simply translates the code word as “the people who inhabit Babylonia.”
Sheshak and Leb Kamai are indeed words written in the Atbash code. However, there is some question about whether Jeremiah himself used the code or if the words were inserted by a later scribe. The fact that the words question in do not appear in the Septuagint supports the idea that they were not original with Jeremiah.
Whoever used the Atbash code in Jeremiah likely meant to protect the prophet (or the later scribe) from the wrath of Babylonian/Chaldean officials.