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I am writing a basic Unix password cracker in Python that would work for MD5, SHA-1 and SHA512.

I know that the salt in MD5 correspond to the 2 first chars of the encrypted password, and thus I assumed that it would be the same for SHA.

But after looking at some answers on SO (here for example), it seems that a Salt can be any string you want.
So, my question is how can I determine the salt part from a hashed password in SHA in the /etc/shadow file ?

I think it is between two $ but I am not completely sure.

I wondered in which SO site it would be the most usefull (Unix or Security) so pardon me in advance if I mischoose.

Thanks

  • 2
    Simply said, you cannot. However, the salt is in most cases no secret so your cracker should have an option to specify the salt. See f.e. hashcat hashcat.net/wiki/doku.php?id=hashcat – bayo Aug 24 '15 at 8:56
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On most modern distributions, the salts and the hashed passwords are stored in the shadow file /etc/shadow (which is only readable by root), not the /etc/passwd file. For each user record in /etc/shadow, the salt is between the 2nd $ and the third $. See answer by mti2935 in https://stackoverflow.com/questions/18035093/given-a-linux-username-and-a-password-how-can-i-test-if-it-is-a-valid-account for more info.

  • Thank you, that what I thought, but I prefered to be sure (and passwd instead of shadow was a mistake). – P1kachu Aug 24 '15 at 11:37
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Since you are talking about Unix, and since you are rather talking about /etc/passwd file instead of /etc/shadaw, I presume you are talking either about a Unix system (as you said) or an old based distribution, so I prefer to quote you this directly as it answers your question:

Earlier versions of Unix used a password file (/etc/passwd) to store the hashes of salted passwords (passwords prefixed with two-character random salts). In these older versions of Unix, the salt was also stored in the passwd file (as cleartext) together with the hash of the salted password.

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