bugtraq - Re: MD5 To Be Considered Harmful Someday

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Date: Tue, 07 Dec 2004 22:36:27 -0600
From: Gandalf The White <gandalf@...ital.net>
To: <davids@...master.com>, Dan Kaminsky <dan@...para.com>,
	BugTraq <bugtraq@...urityfocus.com>
Subject: Re: MD5 To Be Considered Harmful Someday

Greetings and Salutations:

In my first e-mail I meant to congratulate Dan Kaminsky for the fine work
and write-up he did.  Excellent.

On 12/7/04 10:01 PM, "David Schwartz" <davids@...master.com> wrote:
>> From my reading it appears that you need the original source to create the
>> doppelganger blocks.  It also appears that given a MD5 hash you could not
>> create a input that would give that MD5 back.  Passwords encoded with MD5
>> would not fall prey to your discovery.  Is this correct?
> 
> Correct. You will never be able to find the input given an MD5 hash. It
> might be possible to, eventually, come up with an input that has the same
> hash given just the hash, but you could never know if that was the original
> input or not. (At least, not in general.)

That is the worry that I have for MD5 hashed passwords.  It doesn't matter
that you get the *correct* password, just that you have input that will hash
(collide) to the correct MD5 hash.

What I am worried about is the integrity of MD5 hashed passwords.  This
concern is for both Cisco and *NIX passwords.  Lets say that I have a
password:
"ThisIsMySecretPassphrase" MD5 = $1$Vjuf$t5QYnzXL0Sy4tThvqKDGa1

Lets say that I am very smart and I can use software that is able to
generate a collision in the passwords such that the MD5 hashes are the same,
say for example:
"AshEr37WesW28Er4E2" MD5 = $1$Vjuf$t5QYnzXL0Sy4tThvqKDGa1

It does not matter that I don't know the correct password, I have a password
that collides into the correct hash.  I can log into the system with my
generated password.

I just want to make sure that the MD5 hash passwords don't end up being as
easy to compute as the Cisco 7 passwords or the NTLM passwords.  It actually
is beginning to sound like there might be enough of a hole in MD5 that "we"
(collectively) had better start working on SHA-2 hashed passwords ...

Ken

---------------------------------------------------------------
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Ken Hollis - Gandalf The White - gandalf@...ital.net - O- TINLC
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