Polyalphabetic substitutions utilize several different cipher alphabets which differentiates it from the one cipher alphabet monoalphabetic substitutions. And, unlike the monoalphabetic substitutions with variants that have the encoder choose when to replace only a few select letters with different ciphertext equivalents, polyalphabetic substitutions use full ciphertext alphabets and a regular pattern to choose which alphabet to use for every letter. Polyalphabet ciphers are fairly strong, and require a good deal more time and effort by the cryptanalyst than the previous forms of cryptography explored. And despite popular myth, forms of polyalphabetic such as Viginere are not 'impossible of translation' (as stated in a 1917 Scientific American, despite it had been solved over 50 years before.)

The first printed book on cryptology was written by Johannes Trittenheim, a German monk whose reputation mingled with black magic and occult powers, in large part due to his interest in the dark art of cryptology. Trittenhein wrote several books, ranging in subject from the classification of witches, and of the science of alchemy to the dating of the Earth's creation at 5206 b.c. His contributions to poly alphabetic substitutions come from his six book series entitled 'Polygraphia,' which were first published in 1518.

Book V of the series includes the first table (often referred to as tableau in cryptology) of cipheralphabets for use in polyalphabetic substitution. The table repeats the normal alphabet in order, row after row, each time sliding it one letter to the right, as shown to the left.

To encipher a message using the table, one finds the plaintext letter to be enciphered from the bolded first row and then uses a letter from a different row but the same column for the ciphertext. The row to use for the ciphertext equivalent changes with each letter. In Trittenheim's system, the encoder would use the first row for the first letter, the second row for the second letter, and so on, as the following message shows.

plaintext:  in politics stupidity is not a handicap - Napoleon Bonaparte
ciphertext: jp ssqoaqlc dfhdxtzlr cn jkq y gbpgmhgk

This particular polyalphabetic substitution, although it looks like an extravagant Caesar substitution, is far more powerful. Frequency distributions provide almost no information since each letter will represent a different plaintext each time, effectively masking the identities. Additionally, all ciphertext alphabets of the Trittenheim cipher would be used before repeating again. With more ciphertext alphabets, this concept of repeating only after exhausting would produce very secure ciphers. One downside to this cipher, as with most polyalphabetic, is that the absence of just one letter will yield completely unintelligible text.

Trittenheim's blazing of cryptography frontiers opened the trails for other cryptological greats to come, the first being Giovannia Porta.