[Dshield] Crypto Question

[Jon Kibler]

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Valdis.Kletnieks at vt.edu wrote:
<SNIP!>
> 
> Or more concretely - if you're computing a SHA-256 hash because you don't trust
> the MD5 hash, maybe it's time to just *retire* the MD5 entirely.
> 

Okay, can I please drag this discussion back to the question of MAC vs.
Password Hash?

I think everyone can agree that using MD5 for MAC may be a bad idea. At
least for now, regardless of opinion, please let's drop that aspect.

Can someone please explain how MD5 is more than a trivial risk for
password hashes? I would have to think that the risk from lame user
password choices, choices that increased susceptibility to dictionary or
pattern attacks, would be a far greater risk.

Also, from the collisions I have seen, they have all involved high-order
bit-flips. Thus, if your passwords were created from the ASCII
characters on the keyboard, the collision would clearly give you a
non-ASCII value that would be an obvious translation into the actual
ASCII character password.

So even of there were 8 or 16 possible collisions for a given hash
value, the complexity of a properly salted MD5 password hash makes it so
many orders of magnitude more compute intensive to attack than the old
Unix DES-crypt, I would have to think that it will ALWAYS be a more
secure password.

I fail to see the practical issue for not using MD5 for password hashes.

Will someone please enlighten me?

Jon
- --
Jon R. Kibler
Chief Technical Officer
Advanced Systems Engineering Technology, Inc.
Charleston, SC  USA
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http://www.linkedin.com/in/jonrkibler

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