On 06/01/2006, at 12:06 PM, exon wrote:
> Charles Miller wrote:
>> From my back-of-the-envelope calculation, your intuition is
>> misplaced. :)
>> Even if you assume only 6 bits of variance per password character
>> (which is just a-zA-Z0-9 plus two punctuation chars), that's
>> 2^144 possible 24-character passwords. MD5 is a 128 bit hash, so
>> that's 2^16 passwords for every hash value, or only a 1 in 65,000
>> chance that the
>> first matching hash you come across in the password space is, in
>> fact, the correct password.
>
> Without knowing the correct password there is no way of knowing
> that the collision isn't it, and from a practical point of view it
> doesn't matter in the slightest.
It's unfeasable to brute-force 2^144 passwords anyway. It was just an
intellectual exercise.
There is, however, a significant theoretical difference between "some
data that hashes the same as a password" and the original password
itself. Most people re-use passwords between different applications.
The former will only be portable between apps that use the same
hashing algorithm and salt, while the latter will work everywhere.
> Considering the fact that MD5 has been broken though, I'm fairly
> surprised it even came up to discussion. It's not exactly hard to
> find info or even collision-generators.
The attack on MD5 is a collision attack, not a preimage attack. You
can create differing messages with identical hashes, but you don't
get to choose what that hash is. You can't match an existing hash any
easier than you could before.
http://www.cryptography.com/cnews/hash.html
This vulnerability makes MD5 unsuitable for certain cryptographic
applications, but it makes no difference to MD5 as a password-hashing
algorithm. The collision has to be generated by the person coming up
with the original data to be hashed, and I can't think of any way
someone could benefit from doing this on their own password.
Charles
-------------------------------------------------------------------------------
Watchfire's AppScan is the industry's first and leading web application
security testing suite, and the only solution to provide comprehensive
remediation tasks at every level of the application. See for yourself.
Download AppScan 6.0 today.
https://www.watchfire.com/securearea/appscansix.aspx?id=701300000003Ssh
-------------------------------------------------------------------------------
Received on Jan 06 2006
Intro
