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From: mdw@sol4.ebi.ac.uk (Mark Wooding)
Subject: Re: how MD5 works
Sender: news@ebi.ac.uk (usenet news)
Message-ID: <slrn5lq4r0.322.mdw@sol4.ebi.ac.uk>
Date: Tue, 22 Apr 1997 19:37:13 GMT
Reply-To: mdw@ebi.ac.uk
References: <01bc4ecf$0b2c9840$2fa56bc7@jasmin> <1997Apr22.095500.5437@nntp.muohio.edu>
Organization: European Bioinformatics Institute
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Steven J. Madsen <madsensj@titan.sas.muohio.edu> wrote:
> My understanding is that it can be used as a replacement to
> standard UNIX crypt because it takes significantly longer (relatively)
> to generate an MD5 hash. This makes dictionary attacks harder since
> you can't test as many possible passwords in the same period of time.
1. Raw MD5 is almost certainly faster than the traditional DES-based
crypt(3) and probably ought to be slowed down (possibly by hashing
some known but large text) if it's to be used in this way. In
fact, MD5 is about the same speed as CRC32 on a large chunk of data
(it was actually slightly faster when I tested them).
2. You must add some salt when hashing passwords, otherwise an
attacker can precompute hashes for all the entries in his
dictionary and just index by hash to find passwords.
--
[mdw]
`How can you be so mean to someone so meaningless?'
-- Selina Kyle