Re: [kitten] SPAKE Preauth

[Nathaniel McCallum <[e-mail]>]

On Mon, 2015-05-04 at 10:40 -0400, Ken Hornstein wrote:
> > Essentially, the answer is different whether OTP is supposed to be 
> > the
> > first (and only) authentication factor, or a second factor to be 
> > used in
> > conjunction with a password.
> 
> See, I think you've got the question all wrong.  My question is NOT,
> "Is OTP supposed to be the only authentication factor?", it's, "Which
> protocol is it actually possible for me to deploy successfully?"

I believe the tension you are seeing here is the result of
commoditization of 2FA. Early on, 2FA systems were entirely parallel
authentication stacks which authenticators would need to integrate
with. As 2FA commoditized, we see open protocols which can be
integrated into existing authentication stacks.

Pre-commiditized 2FA is the context of RFC 6560. There is no attempt
here to use the existing 1FA infrastructure of Kerberos. RFC 6560 is
just a fancy method for passing credentials in cleartext through
Kerberos protected by FAST. The KDC then passes these credentials
directly to the parallel authentication stack. It is the HTTPS Basic
Auth of the Kerberos world.

However, after 2FA commoditized the question becomes how can I augment
my existing authentication stack (1FA Kerberos) with a 2FA method.
This is what SPAKE Preauth provides.

Now, I think your questions here raise an interesting point: can and
should we require some standardization to use the 2FA feature of SPAKE
preauth? I think the answer is no. And I've come to think that the
SPAKESecondFactor type field should really be OBJECT IDENTIFIER.

Nathaniel