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

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Message-ID: <op.xqsq0gemyldrnw@laptop-air>
Date: Fri, 12 Dec 2014 23:56:30 -0800
From: "Jeremy Spilman" <jeremy@...link.co>
To: discussions@...sword-hashing.net, epixoip <epixoip@...dshell.nl>
Subject: Re: [PHC] How important is salting really?

On Fri, 12 Dec 2014 23:03:13 -0800, epixoip <epixoip@...dshell.nl> wrote:

> 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.

I'm going to try (and likely fail) to channel @scoobz here;

If you are optimizing the attack by iterating through each salt and then  
going on to incrementally less popular passwords, (makes perfect sense)  
then I would imagine if the defender naively does H(pwd||salt) you could  
gain a significant optimization from that. Do you ever see this in  
practice?

Always ensuring the salt are the FIRST bits being presented to the hashing  
function would minimize the amount of initial setup/state you could ever  
reuse between rounds?

If the salt is fed first, and padded to a full block, that would make it  
potentially faster to iterate over a salt? Or is the speedup just not  
significant enough to warrant changing iteration strategies like testing  
Top-10,000 for each salt?

Is there ever a case where you would NOT want the salt to be the leading  
bits fed into the hash?