phc-discussions - Re: [PHC] PHC output specifics

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Date: Wed, 4 Mar 2015 20:47:13 -0800
From: Tony Arcieri <bascule@...il.com>
To: "discussions@...sword-hashing.net" <discussions@...sword-hashing.net>
Subject: Re: [PHC] PHC output specifics

I think a parallelism knob could be extremely helpful, particularly if
you're talking about something like doing password-based key derivation on
e.g. an increasingly parallel smartphone (that probably won't get clocked
that much higher much soon)

Attackers get parallelism for free. It'd be nice if the good guys could use
it too.

On Wed, Mar 4, 2015 at 11:12 AM, Marsh Ray <maray@...rosoft.com> wrote:

>  I posted this to the panel list, but we’d like to move the discussion
> here.
>
>
>
> At the same time I’d like to clarify: Where I listed three specific knobs,
> I was not so much trying to specify the behavior of the function and just
> give examples. Different functions will have different knobs as
> appropriate, but it’s important that we think in terms of physical units of
> the defender’s hardware.
>
>
>
> -          Marsh
>
>
>
> *From:* Marsh Ray [mailto:maray@...rosoft.com]
> *Sent:* Monday, March 2, 2015 11:48 AM
>
>
>
> Obviously the most important thing is the selection of the algorithm. But
> in practice there are lots of other ways users of password hashing
> algorithms can get pwned too.
>
>
>
> So I’d like to reiterate my desire for the PHC to produce:
>
>
>
> ·         One winning function.
>
> ·         A standard C language API definition. Could be separate
> ‘create’ and ‘verify’ functions.
>
> ·         A recommendation for string encoding (e.g., UTF-8 code points)
>
> ·         A standalone credential (hash value, salt, metadata, etc)
> format. Probably this would be binary with a standard Base64 encoding.
>
> ·         A minimal number of knobs to turn for the defender to a) fit
> the algorithm to their hardware, and to b) fit it to their work factor
> budget.
>
> ·         Conservative recommended default values for these parameters
> and advice on other reasonable choices.
>
>
>
> I see two or three knobs here, max.
>
> ·         Total memory consumption
>
> ·         Total CPU consumption
>
> ·         Total memory bus operations.
>
>
>
> The first two parameters are probably best expressed logarithmically. The
> third, I’m not so sure.
>
>
>
> If we don’t define these things, other people will. Lots of other people,
> incompatibly, and hilarity will ensue. J
>
>
>
> -          Marsh
>
>
>



-- 
Tony Arcieri

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