Penetration Testing
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Re: Determining the encryption used
From: iccsabr () dsv su se
Date: 12 May 2006 13:43:02 0000
To determine the encryption of a message should be really hard. That's the whole point of cryptography. Base64 is just
an encoding so that's why is easy. Some classic encryptions leave a "trademark" signature on the cyphertext. In theory,
modern encryptions should aim to produce cyphertext that is indistinguishable from random noise, however the truth is
that far (not too far) from that.
An effective cryptologist should have an arsenal of cryptanalysis techniques. I suggest you research cryptanalysis
tools and techniques and try to decipher classic ciphers before moving to the likes of DES, AES, etc.
The first and foremost effective way to analyze a cipher is to look for patterns and correlations (linguistic,
statistical and mathematical) and try to find a weakness on either the key or the cipher (if you manage to know which
one is it).
So, if you only aim to find out what cipher was used, you can try to create samples of text (or any other type of
message) encrypted with different ciphers and try to extract a statistical analysis on how a cipher encrypts and
produces patterns independent of the cleartext and/or key in the ciphertext. Then analyze your cipher text and try to
find a match.
Sounds tedious, but the other approach involves mathematical analysis and Im not so good at that so I cannot say
anything in the respect.

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