From owner-freebsd-bugs@FreeBSD.ORG  Sun May 11 16:17:48 2003
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To: Stephen Samuel <samuel@bcgreen.com>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Sun, 11 May 2003 16:05:37 PDT."
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Date: Mon, 12 May 2003 01:17:08 +0200
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cc: freebsd-bugs@freebsd.org
cc: Robin Carey <robin@wizardsworks.org>
cc: bugs@openbsd.org
Subject: Re: /dev/random and /dev/urandom 
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There is one current concern with MD5: over-ratio of collisions.

What this means is that it may be a bit too easy to find a
MD5 input which generates a given MD5 output.

This has an impact where one uses MD5 in authentication schemes
like:

	server			client
	-----------------------------------------------------------

	WHO ARE YOU ?
	(magic=234287234)
				Calculate MD5(password + 234287234)
				and send the result:
				abd344...

	Calculate MD5(password + 234287234)
	receive clients bid
	compare
	"they are identical, so the client knows the password"
	OK WELCOME!

In such a setting an over-ratio of collisions will at the very least
reduce the probabilities and

In applications where MD5 is simply used as a bit-blender, this is
of no concern.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.