Subject: RE: [Ipsec] certificate payloads/requests in IKEv2

From: [email-masked]
Date: Mon, 26 Sep 2005 17:48:10 +0300

Michael Richardson wrote:

> Is it permissible to send a certificate payload or certificate 
> request when the authentication method is PSK?
> 
> It is forbidden?
> 
> I don't ask for any reason. I just changed some code in IKEv1 to 
> log the reason for not sending a certificate as being because, we 
> are using PSK.  

Sending CERTREQ is allowd because at that point (message 2 or 3),
you don't necessarily know yet which authentication method the
other guy is going to use (it's possible to use shared secret in
one direction and certificate/public-key in the other
direction). On the other hand, if you do know that it's going to
be shared secret in both directions (you're not going to accept a
certificate no matter what), then sending CERTREQ doesn't make
much sense.

About CERT, it seems that it's not allowed: Section 1.2 says that
"If any CERT payloads are included, the first certificate
provided MUST contain the public key used to verify the AUTH
field" (which it can't contain if the AUTH field is shared secret
based). And it wouldn't make any sense anyway (at least with
X.509/raw RSA key CERT types)...

Best regards,
Pasi

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---

From: Paul Hoffman <[email-masked]>
Date: Mon, 26 Sep 2005 08:59:41 -0700

>X.509/raw RSA key CERT types)...

That sentence from the spec can be read sensibly in two fashions:

- If any CERT payloads are included and public keys are being used 
for authentication, then the first certificate provided is the one 
that contains the public key used to verify the AUTH field.

- If any CERT payloads are included, that means that public keys are 
being used for authentication, and that the first certificate 
provided is the one that contains the public key used to verify the 
AUTH field.

I read the sentence the first way, definitely. I cannot find anything 
on the mailing list that says that we intended the existence of a 
CERT payload to be a MUST-level signal that we were using public key 
authentication.

--Paul Hoffman, Director
--VPN Consortium