Ok, I was just going through Phrack 51again and found this...I don't know if you people care or are seeing it for the 51 time, but if you want the whole thing, e-mail me or just go do a search for Phrack and look at there archives...There is a lot more to the artical, but this little bit lets you know what it is about. D. ---[ Phrack Magazine Volume 7, Issue 51 September 01, 1997, article 13 of 17 -------------------------[ Monoalphabetic Cryptanalysis (Cyphers, Part One) --------[ Jeff Thompson aka 'Mythrandir' <jwthomp@cu-online.com> Written for Phrack and completed on Sunday, August 31st, 1997. --------- First a quick hello to all of those I met at DefCon this year. It was incredible fun to finally put faces to many of the people I have been talking with for some time. It was truly was a treat to meet so many others who are alive with the spirit of discovery. ---------- This is the first in a series of articles on Cryptology that I am writing. The goals of these articles will be to attempt to convey some of the excitement and fun of cyphers. A topic of much discussion in regards to cryptography currently, is about computer based cyphers such as DES, RSA, and the PGP implementation. I will not be discussing these. Rather, these articles will cover what I will term classical cryptology. Or cryptology as it existed before fast number crunching machines came into existance. These are the sorts of cyphers which interested cryptographers throughout time and continue to be found even to this very day. Even today, companies are producing software whose encryption methods are attackable. You will find these commonly among password protection schemes for software programs. Through the course of these articles I will explain in practical terms several common cypher types and various implementations of them as well as cryptanalytic techniques for breaking these cyphers. Creating cyphers is fun and all, but the real excitement and often times tedium is found in Cryptanalysis. Many of the ideas presented in these articles will based on three sources. The following two books: The Codebreakers by David Kahn (ISBN: 0-684-83130-9) and Decrypted Secrets by F.L. Bauer (ISBN: 3-540-60418-9). Both authors have put together wonderful books which both cover the history and methods of Cryptology. Do yourself and the authors a favor and purchase these books. You will be very pleased with the lot. Finally, a miniscule amount of these articles will be written based on my own personal experience. The fun is in the journey and I welcome you on what is certain to be an interesting trip. Please feel free to raise questions, engage me in discussions, correct me, or simply offer suggestions at jwthomp@cu-online.com. Please be patient with me as I am traveling extensively currently, and may be away from the computer at length occasionally. Out the door and into the wild... --Monoalphabetic Cyphers Monoalphabetic cyphers are often currently found in simple cryptograms in books and magazines. These are just simple substitution cyphers. This does not mean that they are always simple for the beginning amateur to solve. Three common monoalphabetic cyphers which are used are substitution, cyclical, and keyed cyphers. -Substitution Cyphers By taking an alphabet and replacing each letter with another letter in a unique fashion you create a simple monoalphabetic cypher. Plaintext Alphabet A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Cypher Alphabet Z I K M O Q S U W Y A C E B D F H J L N P R T V X G Plaintext Message The blue cow will rise during the second moon from the west field. Cyphertext Message nuo icpo kdt twcc jwlo mpjwbs nuo lokdbm eddb qjde nuo toln qwocm. -Cyclical Cyphers By taking an alphabet and aligning it with a rotated alphabet you get a cyclical cypher. For example: Plaintext Alphabet A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Cypher Alphabet N O P Q R S T U V W X Y Z A B C D E F G H I J K L M Indeed, you may recognize this cypher as a ROT13 which is commonly used on news groups to obscure messages. -Keyed Cypher Another way to create a monoalphabetic cypher is to choose a keyword or phrase as the beginning of the cypher alphabet. Usually, only the unique letters from the phrase are used in order to make sure the plaintext to cyphertext behaves in a one to one fashion. For example: Plaintext Alphabet: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Cypher Alphabet L E T O S H D G F W A R B C I J K M N P Q U V X Y Z The passphrase in this cypher is "Let loose the dogs of war" The advantage of such a system is that the encryption method is easy to remember. Also, a method of key change can be created without ever having to distribute the keys. For example, one could use the 4 words at a time of some piece of literature. Every message could use the next four words. Indeed, this change could occur more frequently, but that is a subject for another article. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]