[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]

Re: Open Xlock as root



At 10:10 08/12/99 -0500, Michael K. Johnson wrote:
>"Craig R.P. Heath" writes:
>>...  I understand that the MD5 algorithm itself
>>is now believed to be weaker than was first thought, so I would be
>>wary of suggesting it is a better solution for password encryption
>>without some thorough justification.
>
>Last I heard (someone please tell me if I'm not up-to-date) the only
>attacks against MD5 so far involve being able to control the plaintext
>message, meaning that someone could possible come up with two passwords
>that had the same hash, but given a hash, the attacks don't make it
>any easier to come up with a password that has that hash -- and even
>given an arbitrary password, it doesn't help come up with another
>password that has that hash.

No, you're right, that was the weakness I was thinking of.  I do think
that collisions are of significant concern in password algorithm
though.  If I'm doing an exhaustive search against an encrypted
password, and there are actually four possible strings which hash to
that value, then on average I will find a password that works four
times more quickly.  Having said that, I'm sure collisions are possible
with the libcrypt algorithm too, and I don't have any information as to
which is worse.  I only wished to point out that MD5 wasn't necessarily
better.

>One problem with the current "md5" hash is that it is based on 1000
>rounds of md5, something that I do not think has been seriously
>analyzed.  It's done on the spurious grounds that it slows down brute
>force cracking attempts, without any attempt to analyze the effects
>from a cryptographic standpoint.
>
>Nevertheless, it seems pretty clear that it is stronger than the
>8-character-limited DES-based crypt.

Quite right, I wasn't defending the 8 character limit.  Several
implementations (ours among them) use an extension of the libcrypt
algorithm which handles long passwords as a chain of 8-character
chunks; each chunk provides the salt for the next one.  I'm quite
happy with that.

			- Craig.



[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index] []