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I have a set of keys e.g (IENDKCAGI, RZRLBYBFH) and now I want to find the algorithm of it. I allready know the basics of cryptography but I don't know how to start reverse engeneering the algorithm.

I don't search a certain algorithm, I'm just interested how the process would look like.

cheers

EDIT: I don't want to crack any key!!! I buy the software I need! I'm just interested in the approach of reengeneering a checksum from the result, thats my conceptual formulation, without knowing the algorythm. This topic is more theorethical, but in my opinion it has a certain relevancy also for stackoverflow

AsTeR
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endo.anaconda
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    I think you've probably bit off more than you can chew. Encryption is a very complex and intensely mathematical subject, and you'd probably have to study it several years to be able to reverse-engineer the algorithm from the keys and encrypted text. Though perhaps if you study the popular algorithms you'll get lucky and find the one being used. – Hot Licks Nov 13 '11 at 23:44
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    If these are license keys, it's probably infeasible to figure out from first principles. See http://stackoverflow.com/questions/2869582/ for details. –  Nov 14 '11 at 00:58
  • I'am not interested in hack any license keys! But I'm interested in the approach of algorithms. EG how to findout what checksum formula was used. etc. Therefore I think it is unfair to downgrade this post, because someone thought i want to crack some keys. – endo.anaconda Nov 14 '11 at 10:36

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You can analyze it to some degree, at least enough to rule out several possibilities. You say you have a set of keys, and I'm not sure what you mean by that, so pretend for discussion that the left value is the plaintext and the right value is the encrypted equivalent.

You can determine that the left value has only one repeating character, "I", and that the right value has two, "R" and "B". From that you can rule out a simple substitution cipher, even one with characters rearranged.

Both values appear to have only characters in the range [A-Z] (a larger sample would help confirm), so you can rule out encryption techniques that yield binary results, like most block and stream ciphers. In fact, use of such a limited character set implies that it was designed for use by people rather than machines. That would imply a relatively simple cipher technique, but may also involve an additional key to which you do not have access.

phatfingers
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    Note that if those are two "keys", then it really says almost nothing about an algorithm. A key is essentially just a password. – phatfingers Nov 14 '11 at 00:49