Re: [TLS] Elliptic Curve J-PAKE

Hi Hannes,

J-PAKE is a symmetric PAKE. Both parties store the same password. It is not
suitable for most client-server scenarios where using J-PAKE would mean
that an attacker that breaks into the server simply steals all plaintext
passwords. OPAQUE is an asymmetric (or augmented) PAKE where user remembers
a password (and nothing else, including no public key of the server) while
the server stores a one-way image of the password. Security requires that
if the server is compromised, the attacker needs to run an offline
dictionary attack for each user in the database to find the password.

If what you need is a symmetric PAKE then there are better candidates than
J-PAKE such as SPAKE2 described in draft-irtf-cfrg-spake2-08. SPAKE2 is
*much* more efficient than J-PAKE and while both J-PAKE and SPAKE2 have
proofs of security, SPAKE2 is proven in a stronger security model relative
to J-PAKE.

I am not aware of any advantage of J-PAKE over SPAKE2 - but I may be
missing something. Maybe the PAKE presentation in cfrg will clarify these
issues further.

Hugo

On Tue, Mar 26, 2019 at 1:03 PM Hannes Tschofenig <Hannes.Tschofenig@arm.com>
wrote:

> Hi all,
>
> in context of the OPAQUE talk by Nick today at the TLS WG meeting I
> mentioned that the Thread Group has used the Elliptic Curve J-PAKE for IoT
> device onboarding.
> Here is the draft written for TLS 1.2:
> https://tools.ietf.org/html/draft-cragie-tls-ecjpake-01
>
> The mechanism is described in https://tools.ietf.org/html/rfc8236
>
> @Nick & Richard: Have a look at it and see whether it fits your needs.
>
> Ciao
> Hannes
>
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