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Introduction[Next][Up/Previous/Index]A Cryptographic Compendium This site contains a brief outline of the various types of ciphersystems that have been used historically, and tries to relate themto each other while avoiding a lot of mathematics.Its chapters are:Paper and Pencil SystemsElectrical and Mechanical Cipher MachinesTelecipher MachinesThe Computer EraPublic-Key CryptographyMiscellaneous TopicsYou can also go directly to a complete tableof contents.It deals with methods of sending secret messages ranging frompencil and paper systems performed by hand to today's advanced blockciphers, such as Rijndael, the cipher chosenas the Advanced Encryption Standard, as depicted at right.IntroductionThis page is about codes and ciphers, which people useto communicate with each other in ways that other partiescannot (it is hoped) understand. Although secrecy in communicationcan precede literacy, for example by the use of obscureallusions, a spoken language that is different from theone commonly spoken, a jargon or cant of terms with specialor secondary meanings, or a conventionalized way of speakingsuch as Pig Latin, the efflorescence of many andsophisticated methods of secret communications waited forthe development of alphabetic writing, which allows any thoughtto be represented by a small number of easily manipulatedcharacters.Even then, it took a conceptual breakthrough to realize thatletters can be represented by other symbols;particularly in introductory books on the subject forchildren, this is often illustrated by various examples that areused today, such as Morse code, signal flags, Baudot, ASCII, Braille, and semaphore: And, for another even more prosaic illustration, here is the colorcode used on resistors (as well as on the old mica capacitors) and thecolor code, if one can call it that, of pool balls: Of course, today, cryptography has extended into the realm of advancedmathematics, including number theory, which is concerned with prime numbers.One early and entertaining historical survey of the use of codesand ciphers was the book Secret and Urgent, by FletcherPratt, also the author of several novels. This book came out in thesame year as Elementary Cryptanalysis, by HelenFouché Gaines, which will be mentioned below. The title ofthis book is a particularly apt description of why methods ofscrambling messages to keep them secret are used.Obviously, if a message contains nothing that is confidential,there is no need to bother putting it into code or cipher.But equally, if a message is not urgent, then even if it issecret, it can be communicated at some time when there is an opportunityto meet privately.Only when both conditions exist: when the contents of a messagemust be kept secret, and yet the message is so urgent that the riskmust be taken of sending it by a means that may allow others to read it,would people take the time and effort to put a message into cipher,and take the risk involved in relying on cipher to maintain itssecrecy.Of course, today computers carry out the steps involved in enormouslycomplicated cipher schemes at the push of a button, so neither theeffort nor the risk looms as large as it did during most of the historyof the subject.This site contains a brief outline of the various types of ciphersystems that have been used historically, and tries to relate themto each other while avoiding a lot of mathematics.Suggestions for Further ReadingThe following books can be recommended for someone beginning to learn aboutthe subject of secret writing:The Codebreakers, David Kahn,Macmillan (1st ed.) Simon and Schuster (2nd ed.).This book is a fascinating history of cryptography,dealing with the role it has played in many historical events.There are also some nuggets of technicalinformation not seen in other books aimedat the general public, and there ishistorical information about subjects related tosecret codes, such as cable codes (which do not involve secrecy,and were for saving money on sending telegrams).Elementary Cryptanalysis, HelenFouché Gaines, Dover. Published underthe title Cryptanalysis to avoidconfusion with a book by Abraham Sinkov (also agood book), this book deals with pencil and paperciphers, and is particularly aimedat people who solve such ciphers as a hobby.It describes a wide variety of ciphersand a multitude of solving methods.And I will also mention two other books here:Machine Cryptography and Modern Cryptanalysis, Cipher A.Deavours and Louis Kruh; Artech House. This book is a gold mine of informationand was the source for much of what you will see in this web site aboutcipher machines of the rotor era. I had believed this book to be out of print,but in fact it is still available through Artech House, which has selected itas one of those works sufficiently valuable that it will be reprinted shouldtheir stocks run out, as part of its "In Print Forever" program. Unfortunately,it was marred by a number of typographical errors. I had thought thatregrettable, but felt that this was a common occurrence in books witha limited anticipated sale. An otherwise positivereview in Cryptologia magazine (also a significantsource, particularly for my account of the Siemens T-52) did includethe comment that one might expect better than that, and as a resultmy faulty memory led me to categorize the review as "scathing", forwhich I apologize to its author (himself a significant source ofinformation for my section on the Enigma's Uhr box), Frode Weierud.A number of the illustrations from this bookwere reprinted (with full permission, of course) in the more recentbook Decrypted Secrets from Springer-Verlag.Applied Cryptography, Bruce Schneier; John Wiley and Sons.This book is aimed at the computer professional who needs toimplement secure systems involving cryptography. As it describesa wide selection of algorithms and protocols, it will be of interestto anyone concerned with cryptography in the computer era. Thisbook is one of the most widely available books covering the subjectmatter, and it is frequently cited as a source and as an authorityon the USENET newsgroup sci.crypt. The 2nd edition is considerablyexpanded, with fascinating detail on a much larger number ofcipher systems.Notes on the Purpose of this PageThis page is about cryptography, it does not fall intocertain categories of worthwhile and helpful pages about cryptography thatare more common; it is neither:a page introducing beginners to methods of solving different kinds ofpaper and pencil ciphers,a page explaining how you can obtain a copy of PGP, ScramDisk, orPrivate Idaho to start protecting your own communications, ora page devoted to the history of cipher machines, with photographs ofvarious ones.There are links to some of the pages in these categories in theLinkssection of this site.Occasionally, some methods of cryptanalysis are briefly touched uponhere, but the details are very limited, compared to the excellent materialavailable 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 areschematic diagrams (in my own, somewhat nonstandard symbolism, designed tobe easy to recognize at small sizes) and descriptions of the operation ofmany historical cipher machines. One such schematic diagram is the onebelow of the workings of the Enigma: The story of the Enigma's decryption, derived from a multitude of secondary sources, is, I hope, explainedwith both completeness and clarity here.It covers forms of cryptography ranging from the simplepaper-and-pencil methods to the modern computer cipher systems, andattempts to point out the common features that link them.It also deals with other related topics, such as protocols for securecommunications, such as Kerberos: and it deals with related topics, such aserror-correcting codes: One word of warning, however: I have indulged my own ego rathershamelessly here, and have described a series of block ciphers of my owndesign (under the name of "Quadibloc";the first one was inspired by DESand Blowfish, although in a way it was the opposite of Blowfish, and theothers are the result of appropriating various ideas found in the AEScandidate ciphers), some paper-and-pencil fancies of mine, and a ratherelaborate fractionation scheme for converting the binary output of modernencryption methods to letters for transmission by Morse, or base-78 armor(more efficient than base-64, if less efficient than base-85), orencryption by classical letter-based methods.In only one section do I discuss, and very briefly, codes, in whichwords or phrases rather than letters, bits, or digits are the unit ofencipherment. However, the word code is used legitimately inmathematics 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.[Next][Up/Previous/Index]Return to Home PageMain ScreenCopyright (c) 1998, 1999, 2000, 2003 John J. G. Savard |
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