Subject: [OAUTH-WG] draft-ietf-oauth-mtls-03: jwk / x5c sanity checks when registering for pub_key_tls_client_auth

From: Vladimir Dzhuvinov <[email-masked]>
Date: Tue, 29 Aug 2017 10:28:53 +0300

Aspects of this were previously discussed, on and off list.

According to section 2.3, clients registering for public key bound mTLS
auth must register their public keys as JWKs, or client X.509
certificate (as x5c parameter in RSA and EC JWK).

In the latter case, are there any security implications if there is
mismatch between the registered x5c and the top-level public key JWK
parameters? Should the AS perform some sanity checks on the JWK parameters?

A client could for instance register a JWK where the top-level JWK
public key doesn't match the public key in the x5c (as key type, or
public key value).

Thanks,

Vladimir

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From: Brian Campbell <[email-masked]>
Date: Tue, 29 Aug 2017 09:14:05 -0600

Sec 4.7 of RFC 7517 <https://tools.ietf.org/html/rfc7517#section-4.7>,
which defines "x5c" for JWK, says that the "key in the first certificate
MUST match the public key represented by other members of the JWK." Thus,
how I read it anyway, the check you mention is already a requirement of the
JWK layer.

On Tue, Aug 29, 2017 at 1:28 AM, Vladimir Dzhuvinov <[email-masked]
> wrote:

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From: Vladimir Dzhuvinov <[email-masked]>
Date: Wed, 30 Aug 2017 08:10:33 +0300

> how I read it anyway, the check you mention is already a requirement of the
Thanks Brian, I missed that bit!

And just realised that the Nimbus lib doesn't check the x5c pub key when
creating / parsing JWKs! I suppose other JOSE libs may have the same
omission. A reason to add a note to the MTLS spec perhaps?

Vladimir

-- 
Vladimir Dzhuvinov :: [email-masked]

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From: Brian Campbell <[email-masked]>
Date: Wed, 30 Aug 2017 08:51:07 -0600

I suppose a note or reference like that couldn't hurt. I'll look to add
something along those lines. Obviously, a spec like this can't restate
everything from the specs it builds on. But sometimes a call-out or pointer
is useful.