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Re: Determining the encryption used
From: iccs-abr () 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 I’m not so good at that so I cannot say 
anything in the respect.

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