md5 vs md5(Unix)

KAMIKAZE_ · Guru Joined: 09 Oct 2003 Posts: 309 Location: Riga, Latvia

Hello. Does anybody know why md5 hash length is longer than md5(unix)? Is there any specification on md5(unix)? RFC1321 (regular md5) does not know anything about salt...
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manaka · Apprentice Joined: 23 Jul 2007 Posts: 178 Location: Spain

MD5 is a cryptographic hash algorithm. UNIX md5 password hashing is based upon MD5, but it's not MD5. It uses some techniques to be stronger. One of them is the use of a salt to make rainbow table attacks unfeasible.

As for the length, UNIX md5 strings are encoded in the [a-zA-Z0-9./] character set. The output of md5sum is encoded in the [0-9af] character set. That's why the output of the latter contains more characters.

You can find the specs of the password encryption function strings on the man page for crypt (man 3 crypt).

As for the actual algorithm, I guess the best way to know it would be searching for a paper that describes it. Or browsing the source code of the relevant files of glibc.
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BitJam · Posted: Sat Nov 13, 2010 7:10 pm Post subject:

LMGTFY

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