The simple substitution cipher is a cipher that has been in use for many hundreds of years (an excellent history is given in Simon Singhs 'the Code Book'). It basically consists of substituting every plaintext character for a different ciphertext character. It differs from the Caesar cipher in that the cipher alphabet is not simply the alphabet shifted, it is completely jumbled. The simple substitution cipher offers very little communication security, and it will be shown that it can be easily broken even by hand, especially as the messages become longer (more than several hundred ciphertext characters). Read More