phc-discussions - Re: [PHC] Why protect against side channel attacks

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Message-ID: <20150625072616.GA2738@openwall.com>
Date: Thu, 25 Jun 2015 10:26:16 +0300
From: Solar Designer <solar@...nwall.com>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Why protect against side channel attacks

On Thu, Jun 25, 2015 at 03:06:08PM +0800, Ben Harris wrote:
> On 25 June 2015 at 14:25, Solar Designer <solar@...nwall.com> wrote:
> 
> > In fact, to fully defeat the attack, it is sufficient to have s or h;
> > it is not necessary to have both.  (In practice, it may be helpful to
> > have both for other reasons.)
> 
> 'h' being preferred over 's', as a system without 'h' would still leak
> password information as identical passwords would have the same
> side-channel data.

You're right.  Thank you for correcting me.

Side-channels aside, there are other good reasons why per-hash salts are
important to have even in presence of a system-wide secret.

Alexander