Password hashing

[Martin James Cochran]

On Oct 12, 2007, at 6:47 PM, Sandy Harris wrote:

> On 10/13/07, Martin James Cochran <Martin.Cochran at colorado.edu> wrote:
>
>> ...  What's wrong with starting
>> with input SALT || PASSWORD and iterating N times, ....
>
> Shouldn't it be USERID || SALT || PASSWORD to guarantee that if
> two users choose the same password they get different hashes?
> It looks to me like this wold make dictionary attacks harder too.

If the salt space is large enough ( > 128 bits, say) and the salts  
are generated with a good source of randomness, then it's  
overwhelmingly likely that an attacker will have to do a dictionary  
attack per user anyway, even across many different machines.  Also,  
with such a large salt space it's extremely unlikely that users who  
choose the same passwords will have the same salt.


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