Re: Importance of salt

From: Dominick Baier [DevelopMentor] (dbaier_at_pleasepleasenospamdevelop.com)
Date: 09/16/05 

Date: Fri, 16 Sep 2005 01:36:22 -0700

Hello vla10d@gmail.com,

yes - again that slows him down - and give the number of computations necessary
for these kind of attacks, this is an important factor

in general, try to keep the amount of data encrypted with a long term secret
as small as possible.

so what would be a practical solution

0) enforce password complexity (this is the most important step)
1) generate a key from the password, use salting and hashing and iterations
if you like
2) generate a random key
3) encrypt using random key
4) encrypt key using key from password

you should get a copy of "Schneier, Ferguson: Practical Cryptography"
 
---------------------------------------
Dominick Baier - DevelopMentor
http://www.leastprivilege.com

> Precomputed tables... now this really sheds some light. :) I didn't
> think about the hashed dictionaries. Okay, I see now how any kind of
> salting helps against that kind of dictionaries. On the other hand, if
> the attacker uses plain dictionaries and computes the hash at runtime
> (with my salt), then I can use high number of iterations to slow him
> down a bit. Thanks for the explanation... :)
>
> As for your suggestions... this means that the attacker will first
> have to try to decrypt a key by lets say dictionary attack, and for
> each attempt (each retrieved key) he has to try to decrypt the entire
> message with that key. I'm not sure that this is dramatically better
> than the original situation where the attacker tries to generate a key
> and use that key to decrypt the message. The only advantage that I see
> is that in your case, he will spend a bit more time, since he has to
> decypt twice. At least thats my understanding, please correct me if
> i'm wrong... :)
>
> V.
>

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