Re: Determining the encryption used

[Peter Kosinar <goober () ksp sk>]

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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