full-disclosure - Re: MD5 algorithm considered toxic (and harmful)

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Date: Sat, 01 Dec 2007 15:21:02 -0600
From: Paul Schmehl <pauls@...allas.edu>
To: full-disclosure@...ts.grok.org.uk
Subject: Re: MD5 algorithm considered toxic (and harmful)

--On December 1, 2007 2:20:21 PM -0500 Tim 
<tim-security@...tinelchicken.org> wrote:

>> because they perform risk-analysis:
>> - what are the threats to my assets?
>> - which role does MD5 play there?
>> - any subsequent risk then from using it?
>> - high priority risk? mitigating controls or risk acceptance?
>
> Don't kid yourself.  Very few businesses in my experience think about
> this stuff when they go to use a hash.  Most just use whatever hash
> they're used to using.  I rarely see clients actually sitting down and
> thinking about what the application of a given hash is and what the
> threats are in their specific case.
>
>
>> would you be so kind to show me a real-world attack against a VPN
>> using MD5 hashing? ...
>
> Assuming there are no real-world attacks against your particular VPN
> that uses MD5, does that make it safe for the rest of us in any given
> application?  A rather leading question IMO.
>
While I don't think it's time to panic, it's definitely time to begin 
moving to SHA-256 and stop using MD-5.  FreeBSD has already done so in its 
ports system, although you can still use MD-5 as well.  But far too many 
downloads still use MD-5 or **no checksum at all**, and that is a problem.

While collisions in MD-5 are now proven, what I've not seen yet is the 
ability to alter a legitimate file or tarball yet generate the same 
checksum.  It *is* theoretically possible, however, and the fact that 
collisions have been proven should be enough to begin abandoning its use 
IMO.

Paul Schmehl (pauls@...allas.edu)
Senior Information Security Analyst
The University of Texas at Dallas
http://www.utdallas.edu/ir/security/

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