bugtraq - MD5 To Be Considered Harmful Today

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Message-ID: <20041208013941.GA5210@elf.ucw.cz>
Date: Wed, 8 Dec 2004 02:39:41 +0100
From: Pavel Machek <pavel@....cz>
To: Dan Kaminsky <dan@...para.com>
Cc: bugtraq@...urityfocus.com
Subject: MD5 To Be Considered Harmful Today

Hi!

> I've been doing some analysis on MD5 collision announced by Wang et al.  
> Short version:  Yes, Virginia, there is no such thing as a safe hash 
> collision -- at least in a function that's specified to be 
> cryptographically secure.  The full details may be acquired at the 
> following link:

Yes, nice paper, and here you have nice story:

Okay, lets have two friends and one horse. Let's say Pavel and
Bara. Bara owns a horse, and needs money, so she wants to sell
it. Horse has some problems with its back, and Bara would be willing
to sell it for around $1300. Therefore she's quite surprised when
Pavel offers her $14000, and agrees immediately.

From: Pavel
To: Bara

Hi!

I'd like to buy Fita. If you accept my offer (msg1), just sign and
send it back.

:~/misc/md5$ cat msg1
I agree to sell you my horse ^Fita^, its saddle and harness for price   14000 dollars. Signed Bara

:~/misc/md5$ md5sum msg1
57ce330a6c6ca8e9ffab4f3b36b2a1a5  msg1
:~/misc/md5$

(Bara signs msg1 and sends it back to Pavel). Two days later, Pavel
comes with a car, and $1000. Bara denies she offered Fita for $1000,
but can not find copy of the e-mail exchange. Fortunately Pavel has a
copy with him, digitaly signed by Bara. They view it on her computer,
and verify the signatures. At that point Bara agrees she probably made
a mistake, and accepts $1000...

:~/misc/md5$ cat msg2
I agree to sell you my horse ^Fita^, its saddle and harness for price   1´000 dollars. Signed Bara

:~/misc/md5$ md5sum msg2
57ce330a6c6ca8e9ffab4f3b36b2a1a5  msg2
:~/misc/md5$

(With apologies to Bara; let's hope she'll never find out).

								Pavel
PS: I tried it on linux console, and it does some nasty terminal
tricks. Of course, if Bara investigated, she'd probably found out
how...

-- 
People were complaining that M$ turns users into beta-testers...
...jr ghea gurz vagb qrirybcref, naq gurl frrz gb yvxr vg gung jnl!

Download attachment "msg1" of type "application/octet-stream" (247 bytes)

Download attachment "msg2" of type "application/octet-stream" (247 bytes)