A simple example for a transposition cipher is columnar transposition cipher where each character in the plain text is written horizontally with specified alphabet width. The cipher is written vertically, which creates an entirely different cipher text. One of the oldest of cipher types was the simple substitution or monoalphabetic substitution ciphers in which each letter of the alphabet is replaced by another letter. Each plaintext letter is substituted by a unique ciphertext letter. The earliest known example is the Atbash cipher which is found in the Old Testament and dates from around 600-500BC.
Types of Mixed Cipher Alphabets As mentioned at the beginning of this section, a mixed alphabet is any alphabet that uses one or more mixed sequences. The simplest types are those which use a standard sequence in one component and a mixed sequence in the other. These are the easiest for a cryptanalyst to reconstruct. In order to cipher a text, take the first letter of the message and the first letter of the key, add their value (letters have a value depending on their rank in the alphabet, starting with 0). The result of the addition modulo 26 (26=the number of letter in the alphabet) gives the rank of the ciphered letter.