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

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Date: Thu, 11 Dec 2014 17:32:03 -0800
From: epixoip <epixoip@...dshell.nl>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] How important is salting really?

(Top posting because you did.)

Sorry, but that's not correct.. No one is using salts now, and we still
don't use rainbow tables.

Rainbow tables are massive, slow, and don't scale worth crap. GPUs are
the reason rainbow tables are considered deprecated.

Bitweasil is correct -- the primary advantage to salting today is the
factor of N slowdown in cracking. If you have 1M unique salts, then your
effective speed is 1/1000000 of your total speed. 30 GH/s becomes 30
KH/s. It limits the types and variety of attacks we can run.

But salting alone is insufficient. For each hash we crack a salt is
eliminated and never checked again. Therefore our attacks speed up with
each hash we crack. Using the example above, if our effective speed is
30 KH/s then that means it would take ~20 seconds to run through the top
10k passwords.  If 40% of the people are using a top 10k password, then
we only have 600k salts left and our effective speed has increased to 50
KH/s after just one dictionary.

On 12/11/2014 5:10 PM, Ben Harris wrote:
> "Dictionaries and candidate generation algorithms" are the main
> attacks precisely because we use salts. If nobody used salts the
> prevalent attack would still be rainbow tables.
>
> On 12 December 2014 at 08:58, Bitweasil . <bitweasil@...ptohaze.com
> <mailto:bitweasil@...ptohaze.com>> wrote:
>
>     A factor of N slowdown in cracking, where N is the number of
>     unique salts in the uncracked list of hashes.
>
>     On Dec 11, 2014 4:57 PM, "Marsh Ray" <maray@...rosoft.com
>     <mailto:maray@...rosoft.com>> wrote:
>
>         Password security researchers learn more and more from data
>         breaches seemingly every week. Dictionaries and candidate
>         generation algorithms get better all the time. So here’s a
>         question. Maybe the answer has changed over the last few years
>         and we should revisit our assumptions.
>
>          
>
>         Two different people independently choose this same password.
>         It could be “ilovecats” or it could be something less obvious.
>
>          
>
>         What is the probability that this password will not be in
>         attackers’ dictionaries or it will be hard to crack?
>
>          
>
>         (If this chance is small, then what do we gain by salting?)
>
>          
>
>         -          Marsh
>
>          
>