Leon Alberti

Leon Alberti invented the cipher disk and cryptographic key. Alberti's cipherdisk was polyalphabetic, meaning that a new alphabet could be created each time by turning the disk. This type of disk was the only method of using this type of cipher until the 16th century. Alberti thought his cipher was unbreakable. This assumption was based on his inquiries into frequency analysis, which is the most effective method of deciphering monoalphabetic cryptograms. Given enough cryptotext, one can use the frequency of the letters in reference to a normal distribution to find the shift and solve the cryptogram. This system fails to solve polyalphabetic cryptograms, however, since the letter distribution is garbled.