Re: [kitten] SPAKE Preauth

Nico Williams <nico@cryptonector.com> Mon, 04 May 2015 01:04 UTC

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Date: Sun, 3 May 2015 20:04:28 -0500
From: Nico Williams <nico@cryptonector.com>
To: Simo Sorce <simo@redhat.com>
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Subject: Re: [kitten] SPAKE Preauth
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On Sun, May 03, 2015 at 06:32:44PM -0400, Simo Sorce wrote:
> On Sat, 2015-05-02 at 18:08 -0500, Nico Williams wrote:
> > I don't buy this.  I understand and agree about how a dependency on
> > _FAST_ made RFC6560 difficult to deploy, and also how RFC6560's
> > incomplete/missing handling of *multiple* factors made it less useful
> > than expected.  I don't think that means "generality -> bad".
> > 
> > Also, I don't think a generic OTP 2nd factor here would necessarily lead
> > to a low-quality user experience.  For all user-input OTPs, all the user
> > needs is a prompt, which can be sent in UTF-8 and already localized to
> > a language of the user's preference (since the AS ought to know what
> > that might be).  I don't see how the user-input OTP experience can get
> > much better than that.
> 
> I think we explicitly exclude sending unauthenticated prompts from the
> KDC, as it would be easy to confuse/subvert the user experience by an
> attacker.
> 
> Because the prompts would have to be sent unauthenticated in the SPAKE
> algorithm we'd have to define either generic, unhelpful prompts, or
> define specific OTP mechanisms so that clients have prompts backed in
> and just reference them by id internally.

Ah, I see.  OK, thanks.

Nico
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