outer@utcsri.UUCP (Richard Outerbridge) (10/14/86)
> I am academically interested in obtaining a program for aiding in the > decryption of simple substitution ciphers. Are there any available > programs or algorithms in public domain? Software to assist in the solution of several of the basic types of ciphers is readily available from members of the American Cryptogram Association. A lot of it is in one or another dialect of BASIC, and most of it has been written for one or another variety of home computer. Some of it is very slick - it's amazing what you can do with an online dictionary, some pattern word lists, and digraph frequency counts. The co-ordinator of the A.C.A.'s computer supplement (I guess he's really its Editor) is an enthusiastic chap who will probably be more than willing to help you find what you need or at least point you at the right person. Besides the semi-annual computer supplement, the bi-monthly >Cryptogram< carries a computer column which discusses using PC's to assist solving. The programming is intentionally pitched at computer novices, but the cryptanalysis represents the distillation of the body of amateur expertise built up by the Krewe over the past thirty years or so. Anyway, the person to write to is: Mike Barlow 5052 Chestnut Ave Pierrefonds, Quebec, CANADA H8Z 2A8 Tell him you got his name from me; that will give him another thing to curse me for! Richard Outerbridge Secretary, American Cryptogram Association -- Richard Outerbridge <outer@utcsri.UUCP> (416) 961-4757 Payload Deliveries: N 43 39'36", W 79 23'42", Elev. 106.47m.
augustss@chalmers.UUCP (Lennart Augustsson) (10/15/86)
Monoalphabetic substitution can be handled by an algorithm described in
"Breaking Substitution Ciphers Using a Relaxation Algorithm" by Peleg and
Rosenfeld, published in CACM Vol 22 pp. 598-605 (Nov 1979).
--
Lennart Augustsson
UUCP: {seismo,philabs,decvax}!mcvax!enea!chalmers!augustss
ARPA,CSNET: augustss@chalmers.csnetouter@utcsri.UUCP (Richard Outerbridge) (10/18/86)
> Monoalphabetic substitution can be handled by an algorithm described in > "Breaking Substitution Ciphers Using a Relaxation Algorithm" by Peleg and > Rosenfeld, published in CACM Vol 22 pp. 598-605 (Nov 1979). > -- > > Lennart Augustsson > UUCP: {seismo,philabs,decvax}!mcvax!enea!chalmers!augustss > ARPA,CSNET: augustss@chalmers.csnet If anyone has been able to duplicate the results reported in that particular paper, some friends of mine would be interested to learn >how<. They've tried. -- Richard Outerbridge <outer@utcsri.UUCP> (416) 961-4757 Payload Deliveries: N 43 39'36", W 79 23'42", Elev. 106.47m.
fair@ucbarpa.Berkeley.EDU (Erik E. Fair) (10/20/86)
There is a program in the netnews distribution called `caesar.c' that will decrypt substitution ciphers by frequency analysis from an english language letter frequency table. This was used in the early days of the USENET to decrypt "rotated" articles with arbitrary letter rotation (this was before "rot13" became the accepted convention for scrambling potentially offensive jokes). I just checked, and it's still in the 2.11 netnews distribution. Erik E. Fair ucbvax!fair fair@ucbarpa.berkeley.edu
jim@randvax.UUCP (Jim Gillogly) (10/20/86)
augustss@chalmers.UUCP (Lennart Augustsson) writes: >Monoalphabetic substitution can be handled by an algorithm described in >"Breaking Substitution Ciphers Using a Relaxation Algorithm" by Peleg and >Rosenfeld, published in CACM Vol 22 pp. 598-605 (Nov 1979). Have you (or anyone other than the authors) been able to duplicate the results in this paper? Independently I and three other members of the American Cryptogram Association tried to program this up (one each PL/1 and Pascal, two C efforts) and we weren't able to reproduce the reported success. At least three of us corresponded with the authors, who were forthcoming with both their data ... but we couldn't make it happen. Each of our efforts died the same way: the substitution would degenerate to translating the same ciphertext letter into one plaintext letter (e.g. converting everything to a "T"). The examples they gave in the paper used very long texts by puzzle standards: the Gettysburg Address, for one; and we couldn't get it to work with that either. If anyone has *successfully* implemented this algorithm, I'd like very much to see your code and data. -- Jim Gillogly {hplabs, ihnp4}!sdcrdcf!randvax!jim jim@rand-unix.arpa
jbuck@epimass.UUCP (Joe Buck) (10/21/86)
In article <16191@ucbvax.BERKELEY.EDU> fair@ucbarpa.Berkeley.EDU (Erik E. Fair) writes: >There is a program in the netnews distribution called `caesar.c' that >will decrypt substitution ciphers by frequency analysis from an english >language letter frequency table. Sorry, Erik. As its name suggests, that program only solves "Caesar ciphers". A Caesar cipher corresponds to "rot n" for some n (1-25). The program will not solve general simple substitution ciphers. -- - Joe Buck {hplabs,ihnp4}!oliveb!epimass!jbuck Entropic Processing, Inc., Cupertino, California
sow@luthcad.UUCP (10/24/86)
In article <2121@mtuxo.UUCP> jasond@mtuxo.UUCP writes: >I am academically interested in obtaining a program for aiding in the >decryption of simple substitution ciphers. Are there any available >programs or algorithms in public domain? > In Forsythe, Malcolm and Molers book Computer Methods for Mathematical Computations there is problem on page 238. Where they solve the problem with singular value analysis. I tested the algoritm and it works well. But it didn't work on languages other than English. Sven-Ove Westberg Computer Aided Analysis and Design (CAAD)
bandholm@daimi.UUCP (Anders Bandholm) (10/28/86)
The decryption algorithm presented by Peleg & Rosenfeld in CACM Vol 22 c a n be implemented. I wrote such a program this spring. The program was written in pascal, and was run on a DecSystem10. Unfortunately the algorithm is very complex - both in terms of time and space. The Dec10-version used more than 27k words of RAM. I tested the program on a small example in which the cipher was approx. 60 characters and where the background text contained about 6000 characters. The background text is the text used as "standard-english" by the program (Peleg & Rosenfeld used a novel of about one million letters). The ciphertext was a sentence made of words taken from the background text. After 4 iterations the text was readable. Though this sounds as a succes, there was still one problem - the processing-time used for the 4 iterations was about 4 hours !!! We don't have the Dec10 any more, and I am presently translating the program into Modula2 for the IBM PC or perhaps for our Sun's. Anders Bandholm (bandholm@daimi.UUCP)