Alberti cipher

The outer ring also includes the numbers 1 to 4 for the superencipherment of a codebook containing 336 phrases with assigned numerical values.

The alphabets in use are (see figure): Dispatch: “La guerra si farà ...” The key letters A and Q are included in the cryptogram.

The encipherment will resume thus: The same procedure will be continued through the end of the message, using the four numbers to designate the alphabet shifts.

Caesar’s cipher is a simple substitution based on the sliding of a single ordinary alphabet with fixed key.

With the Alberti cipher there are two mixed alphabets and the key varies continuously during encryption, therefore the discovery of a single letter does not permit further progress.

The Vigenère cipher is based on a single ordinary alphabet like that of Caesar and is easily solved after discovering its fixed period by means of the Kasiski exam.