phc-discussions - Re: [PHC] Re: [Cryptography] The proper way to hash password files

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Date: Mon, 26 May 2014 21:19:44 -0400
From: Peregrine <peregrinebf@...il.com>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Re: [Cryptography] The proper way to hash password files

I only used the "HMAC construction" phrase because the discussion was about
using MACs instead of password hashing functions. A keyed password hash has
equivalent security and some extra benefits (eg Catena's scheme still
allows for client-independent updates of the stored hash.) Sorry if that
wasn't clear.

--
Carl 'SAI' Mitchell


On Mon, May 26, 2014 at 8:59 PM, Andy Lutomirski <luto@...capital.net>wrote:

> On Mon, May 26, 2014 at 5:51 PM, Peregrine <peregrinebf@...il.com> wrote:
> > Of course, one can simply use an HMAC construction with any normal
> password
> > hashing function. If you have that in a dedicated hardware chip then you
> may
> > gain security, otherwise one should assume that any attack capable of
> > getting the hashed-password database is capable of getting any other
> secret
> > data, like private keys. Some of the submissions explicitly support keyed
> > password hashing, and with others any secure HMAC scheme should work.
> Using
> > a strong password hashing scheme with a key protects weak passwords, and
> > protects strong passwords even if the key is somehow leaked.
>
> I think it's sad that, even on a crypto list, people still talk about
> new uses of HMAC (that's a Hash-based Message Authentication Code) for
> things that require properties beyond what a MAC provides and do not
> require message authentication.
>
> In this particular case, using HMAC-fancy-password-hash is extra
> silly, because HMAC invokes the hash *twice*.
>
> I agree that there's some value in using a keyed password hashing
> function, and similar benefits can probably be obtained with a simple
> composition of a password hash with a keyed PRF or even just a simple
> encrypted password hash database.
>
> --Andy
>

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