CryptoAnalysis Game3: Crack the code !(+hints)
in [Cryptography]
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From: Dave -Turner on 22 Jan 2010 18:57 Rjxctbj!hr!`!qd`otu!9(
From: Skybuck Flying on 22 Jan 2010 19:16 Sigh ;) :) Ok very good. +3 points for you ! ;) The solution was to add +1, +2, +3, +4, +5, +6, to each next character so char1 + 1, char2 + 2, char3 + 3, char4 + 4, char5 + 5, and so forth ;) How did you crack it ? ;) Maybe you can enlighten us a little bit ;) Bye, Skybuck =D "Phoenix" <ribeiroalvo(a)gmail.com> wrote in message news:b2b0bf0a-57a4-4bfe-b4ac-88bdbc83832f(a)l11g2000yqb.googlegroups.com... > > > Rumor: Angeline Jolie and her Dialect Teacher ****** like > rabbits ?! ;) :) Naughty Naughty ! ;) :) > > Alvo
From: Phoenix on 22 Jan 2010 19:54 > Maybe you can enlighten us a little bit ;) I guessed.
From: Ilmari Karonen on 22 Jan 2010 21:00
On 2010-01-23, Phoenix <ribeiroalvo(a)gmail.com> wrote: > >> Maybe you can enlighten us a little bit ;) > > I guessed. That's what I did for the previous one: assumed from the hint that it was a simple xor, guessed that 138 was space and figured it out from that. For this one, I actually ended up printing out all the characters in binary and noting that the frequency of the most significant bit being set showed a clear trend. That suggested the possibility that there might be a linear relation between the character position and whatever transformation was being applied to the characters. I then tried to decipher the message as p[i] = (a*i + b + c[i]) % 256 for all possible values a and b and looked for an output consisting entirely of printable ASCII. Alas, I got nothing. After trying a few other possible variations, I decided to try again and this time look for outputs that were _mostly_ printable ASCII. That got me two partial solutions (plus a bunch of others that were mostly ASCII but nonsense) with the same a but different b. Piecing those together and observing the two undecodable characters in between, I concluded that the original ciphertext must've contained a misprint, which was then easy enough to spot ("180" -> "18 0"). I might've guessed the solution faster if I hadn't been expecting something more like a Vigenere cipher this time. It was only the anomalous trend in the high bits that convinced me I was heading in the wrong direction. -- Ilmari Karonen To reply by e-mail, please replace ".invalid" with ".net" in address. |