Cryptanalysis

Wednesday 9 September 2020, 03:39  #1
Cryptanalysis - GEDEFU
CR4xR3V
  • 5 posts

Hello,

Tough challenge, been trying to solve it for 3 days but no luck so far..

I did manage to get an idea about the probable key lengths, maybe with that also, I can figure out the position of 1 key character? don’t know exactly..

but anyhow, I’ve been trying to automate the search through two of possible key lengths and sort according the transposed ic (maybe optimize for longer key lengths?), tried also one known gui tool for such cryptography tasks, but still with no luck..

I may have also an idea about the plain-text, but not sure as I’ve tried to use it in a more optimized key search (same consecutive character, or spaces nbr between same characters, ..) but with no good result..

Anyway, I just need to know if I’m on a good path, and maybe a hint?

NB: please remove/hide if I did spoil anything, I’ll contact then via #irc

Thanks  🙂

Wednesday 9 September 2020, 17:20  #2
Cryptanalysis - GEDEFU
nonstandardmodel
  • 37 posts

Hello,
it seems that you are on good path.
You seem to have noticed the possible key lengths. This will help you narrow the search.

I will just share my experience.
Some tool on GitHub, that looked like it should help a lot, had a bug. So I had to write my own simple tool.
I did not use any text assumed known at the beginning. The tool I wrote returned best candidates for key. I had to look closely to the decryption made with one of them, to notice what seemed like words. Than I just did the final tweaking by hand to get the correct key.

Hope it helps,
NonStandardModel