This site contains a brief outline of the various types of cipher systems that have been used historically, and tries to relate them to each other while avoiding a lot of mathematics.
Its chapters are:
You can also go directly to a complete table of contents.
Thus, although this page is about cryptography, it does not fall into certain categories of worthwhile and helpful pages about cryptography that are more common; it is neither:
There are links to some of the pages in these categories in the Links section of this site.
Occasionally, some methods of cryptanalysis are briefly touched upon here, but the details are very limited, compared to the excellent material available elsewhere.
This site has a great deal in common with sites of the third category, but alas, it doesn't include any photographs. What it does have are schematic diagrams (in my own, somewhat nonstandard symbolism, designed to be easy to recognize at small sizes) and descriptions of the operation of many historical cipher machines. The story of the Enigma's decryption, derived from a multitude of secondary sources, is, I hope, explained with both completeness and clarity here.
It covers forms of cryptography ranging from the simple paper-and-pencil methods to the modern computer cipher systems, and attempts to point out the common features that link them.
One word of warning, however: I have indulged my own ego rather shamelessly here, and have described a series of block ciphers of my own design (under the name of "Quadibloc"; the first one was inspired by DES and Blowfish, although in a way it was the opposite of Blowfish, and the others are the result of appropriating various ideas found in the AES candidate ciphers), some paper-and-pencil fancies of mine, and a rather elaborate fractionation scheme for converting the binary output of modern encryption methods to letters for transmission by Morse, or base-78 armor (more efficient than base-64, if less efficient than base-85), or encryption by classical letter-based methods.
In only one section do I discuss, and very briefly, codes, in which words or phrases rather than letters, bits, or digits are the unit of encipherment. However, the word code is used legitimately in mathematics to refer to substitutions which are non-linguistic (and hence, in cryptology, would be called ciphers) from Morse code to Hamming code (used for error-correction) and Huffman code (used for data compression). I have, therefore, been unable to be rigorous about the use of the word "code" in these pages.
Copyright (c) 1998, 1999, 2000, John J. G. Savard