[42163] in Cypherpunks
Re: MD5 weakness ? [was Re: Netscape Logic Bomb detailed by IETF]
daemon@ATHENA.MIT.EDU (hallam@w3.org)
Tue Oct 24 13:51:57 1995
To: fc@all.net (Dr. Frederick B. Cohen), cypherpunks@toad.com
Cc: hallam@w3.org
In-Reply-To: Your message of "Tue, 24 Oct 95 10:42:10 EDT."
<9510241442.AA12411@all.net>
Date: Tue, 24 Oct 95 13:14:41 -0400
From: hallam@w3.org
>As to weaknesses, I seem to remember that someone managed to forge a
>modification to a program used to observe networks on a Sun so that it
>had the same MD5 checksum as the official trusted version. But whether
>this is real is not strictly the issue.
Ron has not mentioned such an event to me and if that were the case I would
seriously doubt that he would not have been told about it. The only comment he
generally makes is that he wrote MD5 because "MD4 was making me nervous".
>In the case of the trust being placed in MD5 by Netscape, the assumption
>being made (without adequate support as far as I can tell) is that an
>MD5 checksum cannot be forced, through a chosen plaintext attack, to
Netscape do not simply use the MD5 of the message, they are using (as I
understand it) the PKCS#1 standard for makoing the signature. If not they
probably have severe problems.
>There has been no limit given by anyone on this list to the level of
>trust they place in MD5. Several people have posted (without
>contention) that MD5 is sufficiently trustworthy to trust billions of
>dollars in commerce to it's being able to prevent a selected plaintext
>attack as eluded to above.
NIST and the NSA trusted MD4 sufficiently to base SHA upon it. SHA is preferable
in many ways to MD5, it has a different approach to extending the scheduling and
resist differential cryptanalysis. There is a problem with the compressor
function of MD5 which I dislike. This is fairly irrelevant though since SSL
allows other digests to be used.
Phill
