phc-discussions - Re: [PHC] Design Rationale and Security Analysis of PHC candidates

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Date: Thu, 2 Oct 2014 12:50:31 +0200
From: Dmitry Khovratovich <khovratovich@...il.com>
To: "discussions@...sword-hashing.net" <discussions@...sword-hashing.net>
Subject: Re: [PHC] Design Rationale and Security Analysis of PHC candidates

The value "Explored" stands for the case when the designers actually try to
mount a collision/preimage attack on their design and show why it fails. It
is not the best possible option: ideally, one would provide some sort of
security proof that reduces the security of the mode of operation (which
the hashing scheme is) to the security of the underlying primitive, and
thus get the grade "Verified" or "Proven".

The reason is that collision/preimage-resistance/PRF properties of the
primitive do not translate automatically to the mode of operation. Examples
are well-known: forgeries for CBC-MAC, length extension for Merkle-Damgard,
etc.Security proofs might be easy (Merkle-Damgard) or sophisticated (HMAC).

Even if the inputs are short (as in the password hashing) you can still
easily mess things up. For example, if in Gambit you did not encode both
password and salt lengths in the Absorb operation, you'd be in trouble even
though you use the sponge construction properly.

That was the motivation not to give the "perfect" grade to _any_ submission
in the list.

Hope this resolves the problem,
Dmitry

On Thu, Oct 2, 2014 at 9:46 AM, Krisztián Pintér <pinterkr@...il.com> wrote:

> On Tue, Sep 30, 2014 at 1:12 PM, Dmitry Khovratovich
> <khovratovich@...il.com> wrote:
> > https://www.cryptolux.org/images/4/4f/PHC-overview.pdf
>
> one more question/observation: i don't understand the reason for
> gambit's basic crypto being "claimed" as opposed to "explored", since
> it inherits these properties from the underlying sponge, in the
> proposed instance, keccak. what other exploration is needed?
>

-- 
Best regards,
Dmitry Khovratovich

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