http://qs321.pair.com?node_id=386282


in reply to Re^2: MD5 - what's the alternative
in thread MD5 - what's the alternative

I agree with you that it doesn't matter whether the attacker generates the "original plaintext" or some "collision plaintext". This is because for passwords, the original plaintext is not stored anywhere, just the hashed MD5 value of the password is stored. That means that the computer can only compare the MD5 value of the entered password with the MD5 value which has been stored. Any text which produces the same MD5 value will be accepted as the correct password. If the original plaintext was stored somewhere, then the attacker would only need to steal the file with the plaintext passwords in it; which is why the plaintext is not stored.

Replies are listed 'Best First'.
Re^4: MD5 - what's the alternative
by BrowserUk (Patriarch) on Aug 27, 2004 at 10:06 UTC

    If the attacker has managed to access the file of password md5's, hasn't he already cracked your system?

    Examine what is said, not who speaks.
    "Efficiency is intelligent laziness." -David Dunham
    "Think for yourself!" - Abigail
    "Memory, processor, disk in that order on the hardware side. Algorithm, algorithm, algorithm on the code side." - tachyon
[reply]
      That's something else I was wondering about. Where is the attacker supposedly snooping that they can capture an MD5'd password? Why doesn't the attacker just snoop to capture the plaintext password instead? This "vulnerability" is very light on details.
[reply]

        I agree. Very light. All the description I've read say is that they have found a way of finding or generation collisions. So what? We always knew there were collisions.

        The only "evidence", shows two pre-calculated datasets that produce the same md5. What I haven't seen (though maybe the conference gave more detail than I can find), is any technique for generating the plaintext from the md5?

        If the mechanism starts with the original plaintext, to generate another plaintext with the same md5--why are they bothering? They already have the original!

        Hmmm. Maybe there is some real information out there somewhere.

        Examine what is said, not who speaks.
        "Efficiency is intelligent laziness." -David Dunham
        "Think for yourself!" - Abigail
        "Memory, processor, disk in that order on the hardware side. Algorithm, algorithm, algorithm on the code side." - tachyon
[reply]

In Section Seekers of Perl Wisdom