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Re: [kitten] SPAKE Preauth

Nico Williams <nico@cryptonector.com> Fri, 01 May 2015 21:30 UTC

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Date: Fri, 01 May 2015 16:30:56 -0500
From: Nico Williams <nico@cryptonector.com>
To: Nathaniel McCallum <npmccallum@redhat.com>
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Subject: Re: [kitten] SPAKE Preauth
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On Fri, May 01, 2015 at 05:27:03PM -0400, Nathaniel McCallum wrote:
> On Fri, 2015-05-01 at 16:23 -0500, Nico Williams wrote:
> > It doesn't seem like overkill to me.  Unless the property that an
> > attacker can't distinguish which factor was wrong is not that
> > important.
> > 
> > Note that AS implementations could just always send continuations as
> > EncryptedData, leaking that way.  What I want is for it to be
> > possible to implement an AS that doesn't leak.
> 
> I don't think that is possible. The cost for sending data in the clear
> to avoid leaking EncryptedData is the loss of integrity protection.

Any OTPs that require continuation then result in this leak.  This has
to be documented, since avoiding this leak is a core feature of this
protocol.

Nico
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