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Re: Determining the encryption used
From: Peter Kosinar <goober () ksp sk>
Date: Fri, 12 May 2006 02:04:30 +0200 (CEST)

Hello,

While doing a pen-test I came across a database with
encrypted fields and I was curious to try and see what
I would do with it.

Could you provide an example of such an (possibly) encrypted field?

Is it possible to determine the encryption used by
"looking" at the encrypted results or lenght ?

Sometimes. Very much depends on the structure of the data -- for example, if all the "encrypted" values (in one column of the database) have the same length, it might be some kind of hash, used for authentication purposes. Some applications store their passwords hashed either using crypt() or some variation of MD5; structure of the latter is quite easy-to-recognize. It's also often quite helpful to find out what application creates / uses those encrypted fields, it might provide some clues as of what kind of encryption/hashing is used.

If nothing obvious appears at the first and second glance, it might be useful to look if the values seem to have some additional structure -- for example, are there some repeating patterns at the beginning/end? If so, the values might represent some textual data, these are quite often reduntant and repeating.

I know that with Base64 it's pretty easy because of
the "==" at the end.

This is not completely true, "=" characters are used as padding in Base64 encoding. If the length of the original text is a multiple of 3, there won't be any ='s at the end, otherwise you should find one or two of them.

In general, if the field looks too much letter/number-ish, it's most likely some kind of ASCII-armor used to store binary data while avoiding problems with different encodings/codepages or such. I've also seen MD5 sums stored in a database in textual form (in general, fields consisting purely of [0-9A-F] are usually just hexadecimal descriptions of some other data).

Also if there are any tools besides openssl that you
found usefull to try all the cipher, consecutively
with a passphrase/keyword against a file/string

Depending on the kind of cipher (if it is some kind of password-hash), you might find tools like John the Ripper much faster for dictionary-style attacks.

Peter

--
[Name] Peter Kosinar   [Quote] 2B | ~2B = exp(i*PI)   [ICQ] 134813278


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