Classical Cryptography

This page is a list of many of the cryptographic algorithms used in the past (pre WWII). Some of them have only ever been used by amateurs (e.g. bifid), while some of them have been used by armies to secure their top level communications (e.g. ADFGVX). None of these algorithms are very secure as far as protecting information goes (with todays computers to break them), so if real data security is needed you should probably look at the more modern algorithms on the modern cryptography page.

Much of the fun with these algorithms lies in cracking them. Some of the simpler algorithms such as the caeser cipher and the substitution cipher can be solved by hand, while others like the ADFGVX and the trifid cipher are more easily solved with the help of a computer.

Each cipher on this page has a javascript implementation that allows enciphering and deciphering of text using the cipher. Some of the history of each cipher is also included, and tips on cryptanalysis are also provided.

To find general information on cryptanalysing pre WW2 ciphers, try the Classical Cryptanalysis page.

Transposition Ciphers
Rail-fence Cipher	A simple transposition cipher.
Columnar Transposition	Another simple transposition cipher.
Route Cipher	Another simple transposition cipher.
Monoalphabetic Substitution Ciphers
Caesar cipher*	The oldest and simplest of ciphers. A description is included. Code is provided for encryption, decryption and cryptanalysis.
Polybius Square	A type of substitution cipher that replaces each plaintext character with 2 ciphertext characters.
Simple Substitution cipher*	A simple cipher used by governments for hundreds of years. Code is provided for encryption, decryption and cryptanalysis.
Codes and Nomenclators	Nomenclators were a mix between substitution ciphers and Codes, used extensively during the middle ages. Codes in various forms were used up until fairly recently.
Affine Cipher	A type of simple substitution cipher, much easier to crack compared to the general case though.
Polyalphabetic Substitution Ciphers
Vigenere, Gronsfeld and Autokey ciphers	A more complex polyalphabetic substitution cipher. Code is provided for encryption, decryption and cryptanalysis.
Beaufort Cipher	Very similar to the Vigenere cipher, but slightly different algorithm.
Polygraphic Substitution Ciphers
playfair cipher*	The technique encrypts pairs of letters (digraphs), instead of single letters as in the simple substitution cipher. The Playfair cipher is thus significantly harder to break since the frequency analysis used for simple substitution ciphers does not work with it.
Hill cipher	An algorithm based on matrix theory. Very good at diffusion.
Four-Square Cipher	An algorithm invented by Felix Delastelle in 1902
Combinations of the Above
Straddle checkerboard	A substitution cipher with variable length substitutions.
Bifid Cipher	A fractionating transposition cipher. Only ever used by amateur cryptographers. Can be broken fairly easily.
Trifid Cipher	A fractionating transposition cipher. A variant of Bifid.
ADFGVX cipher	A fractionating transposition cipher. Used by the Germans during the first world war, but cracked by the French. Can be broken with a little effort.
More Complex Ciphers
Lorenz	Used by the Germans during the second world war, solved at Blechley Park.
M-209	One of the more widely used American WW2 cipher systems.
Purple	Used by the Japanese during WWII for high level secrets, but cracked by the Americans. Quite secure unless you have determined attackers.
Enigma	Used by the Germans during WWII, but cracked by the Polish and British. Quite secure unless you have determined attackers.

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