The Atbash Cipher was the first monoalphabetic substitution cipher. It's similar to the caesar cipher, the vingere cipher and others. Initially it worked with the Hebrew alphabet. It was initially created by Essenes, rebels who worked with Qatar and the Knights of Templar. This cipher sort of disappeared near 1200 AD but was detailed by the prophet Jeremiah.
Ciphertext:
Message:
The formula for the Atbash Cipher (and affine) can be expressed as $$ \ E(x) = -(x \mod m) + 1\, $$
This cipher and the other ciphers I'm working on rn are gonna be a part of an npm package for ciphers I'll link later :)