[curves] password authenticated key exchange (PAKE)

David Leon Gil coruus at gmail.com
Thu Oct 2 17:48:36 PDT 2014

Are you considering PAKE in something Dolev-Yao-ish (i.e., with a
strong KCI assumption) or a bideniable model?

(I assume Dolev-Yao-ish in the following.)

On Thu, Oct 2, 2014 at 6:54 PM, Michael Hamburg <mike at shiftleft.org> wrote:
> Explicit key confirmation: Require or no?

Should be optional but possible; am I right in thinking it always
requires an additional round?

> Augmentation: Should the server’s credential be insufficient to log in without a dictionary attack?  Maybe augmentation on both sides is even desirable, for some reason?

Certainly yes to the first for client-server; it's a lovely property.

Isn't it necessary in the peer-to-peer situation? (Otherwise, by
symmetry, a form of KCI is possible.)

(I'm assuming you mean a per-client credential. A PAKE protocol that
provides this also needs to be secure against KCI, in an appropriately
strong formulation.)

> Security model: Does anyone care about GapDH, DDH, SquareDH etc assumptions?  This is definitely in the random oracle model, by the way.

I'd very strongly prefer DDH. GapDH is okay. Anything more exotic is
asking for trouble, but eh, hardly anyone cares. (But the "generic
group" assumption would be unacceptable.)

Are there tightness issues? I'd be reasonably happy with a tight GapDH
reduction, even with a (very) non-tight DDH reduction.

> On a somewhat related note, is there any desire to encrypt the user name?  A man in the middle can recover it at the cost of disrupting the session, but it should be possible to hide it from passive eavesdroppers (at the cost of more rounds and more complexity).

Does it *require* more rounds? (I.e., what's the problem with the
obvious approach of encrypting under the server's static key, for the
client-server case?) PFS would require an additional round, I think...

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