The Trithemius Cipher is a polyalphabetic substitution cipher. In this cipher, a message is encrypted using an encryption table (tabula recta). The tabula recta typically contains the 26 letters of the from A to Z along the top of each column, and repeated along the left side at the beginning of each row. Each row of the square has the 26 letters, shifted one position to the right in a cyclic way as the rows progress downwards. Once B moves to the front, A moves down to the end. This continues for the entire square.