phc-discussions - Re: [PHC] A review per day

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Message-ID: <1366853113.13978050.1409707634927.JavaMail.root@larc.usp.br>
Date: Tue, 2 Sep 2014 22:27:14 -0300 (BRT)
From: Marcos Antonio Simplicio Junior <mjunior@...c.usp.br>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] A review per day - Schvrch

> "Krisztián Pintér" <pinterkr@...il.com> (at Tuesday, September 2,
> 2014, 17:32:04

> Thomas Pornin (at Tuesday, September 2, 2014, 10:16:30 PM):

> > the SHA-3 competition, Keccak's hardware performance was a big
> > selling
> > point, making up for somewhat poor software performance. For PHC,
> > we
> > really want it to work the other way round.

> i'm not sure about that. another example to consider would be
> dedicated login servers. i can imagine for server with a large number
> of logins, the password authentication becomes bottleneck. it can be
> aided by a dedicated hashing hardware. so in fact, high performance
> ASIC can be a friend too.

> my point is: we need controlled hardness. we need to put much "good"
> hardness, but avoid dropping in arbitrary random hardnesses just
> because we can. a good password hash is efficient and lightweight,
> while has a carefully chosen tunable cost.

> ah, one more point. i'm also not sure that the attacker uses ASICs.
> how about botnets? i'm pretty sure that besides some governments, the
> biggest computing power on earth is a botnet accessing CPUs and GPUs.

Well, if I understood your point, then I have to take back my statement in another thread that "flexibility" (in the sense of "choose the hash that better suits your scenario") can be seen as a disadvantage and say that it is probably a good property for a PHS. I can agree with that and actually that is quite usual in many cryptographic schemes (MACs, AEADs, etc.) 

On the other hand, that also means that *there is no silver bullet*, be it Keccak or an "arcane-Blake2-based-sponge" design :) 

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