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Re: encryption program
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 <[email protected]> --- 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.