phc-discussions - Re: [PHC] How important is salting really?

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Date: Fri, 12 Dec 2014 23:03:13 -0800
From: epixoip <epixoip@...dshell.nl>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] How important is salting really?

On 12/12/2014 2:25 PM, Dennis E. Hamilton wrote:
>  --Responding to--
> From: epixoip [mailto:epixoip@...dshell.nl] 
> Sent: Friday, December 12, 2014 13:10
> To: discussions@...sword-hashing.net
> Subject: Re: [PHC] How important is salting really?
>
> [ ... ]
>
> It's not just about indexing by salt, though. You still have to maintain
> a list of salts to hash each plaintext candidate with, and remove salts
> from said list when a salt is eliminated. Regardless of how you do it,
> it is the number of salts, not the number of hashes, that slows down a
> cracking job. Unless you are working with very large lists on AMD GPUs,
> but that's a whole nother can of worms.
>
> <orcnote>
>    I believe there is no need for the defender to maintain an index of 
>    used salts

We're talking about password cracking software, not defenders.

>    In this way, the adversary has to deal with each salt||hash combo as
>    unique, with no opportunity to exploit duplications.

We don't get an opportunity to exploit duplications, but we still get a
speedup by maintaing a separate salt table, even if all salts are
unique. You eliminate more salts faster by looping over the salts for
each word in a wordlist, as opposed to looping over the wordlist for
each hash.