Paul Foley wrote:
On Wed, 8 Jan 1997 19:32:20 -0600 (CST), Igor Chudov wrote:
Cypherpunks, why don't we try to crack his encryption program? It seems like a fun exercise.
Well, a few minutes looking at it turned up the following:
* Capitalisation and word lengths are retained in the ciphertext, so there's no transposition involved (or he's being sneaky to make it look that way :-) )
I also did a frequency analysis on letters of the ciphertext. Here's the output of my frequency program: a:71 b:72 c:66 d:55 e:48 f:57 g:68 h:49 i:72 j:52 k:59 l:48 m:77 n:80 o:41 p:70 q:59 r:63 s:62 t:63 u:53 v:55 w:62 x:60 y:45 z:66 Min = 41, Max = 80, mean = 60.500000, std = 10.044899 16 letters' frequencies are within 50--70, 10 are out, which suggests that the distribution may not be "normal". For a normal the proportion should be something like 84:16. I also tried xoring the plaintext line with the ciphertext line, w/o much enlightenment.
* The two 'e's in the first word have different ciphertext equivalents, so it's not a single-alphabet substitution
yes
* The words "wjq nwcc" occur together twice, 300 characters apart, the word "iyn" occurs three times, 375 and 300 characters apart, the word "fhw" occurs twice, 1400 characters apart, and the word "git" occurs twice, 500 characters apart. This suggests a repeating key of length 5 or 25 characters.
I also likes "follows": "vkbcjtp" note how ll gets translated to "bc". That suggest that after some encryption of each letter from the plaintext there is a consecutively increasing number added.
* However, the letter 'r' in "Here" and "encryption" and the letters 'am' in "example" and "program" occur 25 characters apart and have different ciphertext equivalents. Possibly the key position is being incremented when "encrypting" digits and other non-alphabetic symbols, so my counts above (only letters) are wrong.
Also, I suspect that in the following ciphertext, EJMDLH.WKN and ZFIYVZ.XGA are "CONFIG.SYS", KALMF is "FILES" and "ZPKQUST" is "BUFFERS".
agree, there is a lot of other similar stuff
##> Pbg qpypmjf EJMDLJ.WKN prbthucy hxzb tbcmsfs iyn bsfijsyey hdokz: ##> ##> KALMF=20 ##> ZPKQUST=20 ##> ##> Z ixyh ZFIYVZ.XGA crxg ckqm wam wjq nwcc qjt QMUSAXH dsi ei:
-- Paul Foley <mycroft@actrix.gen.nz> --- PGPmail preferred
PGP key ID 0x1CA3386D available from keyservers fingerprint = 4A 76 83 D8 99 BC ED 33 C5 02 81 C9 BF 7A 91 E8 ---------------------------------------------------------------------- Life is a POPULARITY CONTEST! I'm REFRESHINGLY CANDID!!
- Igor.