phc-discussions - Re: [PHC] Re: Native server relief support for password hashing in browsers

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Message-ID: <9181.1390171025@critter.freebsd.dk>
Date: Sun, 19 Jan 2014 22:37:05 +0000
From: "Poul-Henning Kamp" <phk@....freebsd.dk>
To: discussions@...sword-hashing.net, Alex Elsayed <eternaleye@...il.com>
Subject: Re: [PHC] Re: Native server relief support for password hashing in browsers

In message <lbhi56$1dj$1@....gmane.org>, Alex Elsayed writes:
>Poul-Henning Kamp wrote:
>

>> Without going into too much detail, I don't think the salt should
>> be revealed to the client and the eavesdroppers, so we cannot involve
>> the client in anything from the point in the algorithm where the
>> salt is mixed in.
>
>I think detail may well be warranted here - salt is a public parameter.

I disagree.  If it can be snooped beforehand, it will give an
attacker a head-start and we should not do that.

>> It should not be overlooked that the client and server do in fact
>> have a shared secret, even though the server does not keep it around
>> in readble form.
>
>I think this is a key insight, but which isn't sufficiently leveraged by 
>what you suggest. 

Ohh, absolutely not, that was just to give the general outline of
the issues involved.

I don't buy your rationale for offloading "during busy", as a means
for load-mitigation, it is no different from just rate-limiting the
password validations in the first place, and the additional complexity
does not seem attractive for so little benefit.

But as I said:  I can be convinced, but it'll take more than that.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@...eBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.