FYI -- some discussion on PKIX list about the sip-eku issue I
pointed out in my email yesterday.  It may be the case that
the use of EKU as we have it in sip-eku-02 is okay after all.

Scott and I will let the SIP WG know of the final outcome.
We will summarize discussion from PKIX list to the SIP WG list
as needed.

Thanks,

- vijay
--
Vijay K. Gurbani, Bell Laboratories, Alcatel-Lucent
2701 Lucent Lane, Rm. 9F-546, Lisle, Illinois 60532 (USA)
Email: [EMAIL PROTECTED],bell-labs.com,acm.org}
WWW:   http://www.alcatel-lucent.com/bell-labs
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Paul,

...

A brief history here. The document is specifying "the semantics of the domain name that is the subject of this certificate is Foo, not Bar which is what you might have expected". They used an EKU because other people had used EKUs for things they thought were similar.

I pointed out that a KU describes a usage of the key, not a semantic for the subject. From a PKIX semantics standpoint, they way to talk about the semantics of the subject is with an extension.

I think it is more appropriate to focus on the EKU text from 5280, vs. the KU text, since the proposal is to assign an EKU OID for this use of certs. Section 4.2.1.12 describes the EKU extension and gives examples. The examples include TLS server vs. client authentication, code signing, time stamping, and OCSP response signing. These examples from 5280 illustrate using EKU to signal what type of entity holds the corresponding private key, and for what purpose that key is being used.

So, using an EKU to signal that the private key holder is a SIP proxy (e.g., vs. a SIP end entity) is clearly consistent with the examples cited in 5280. I think that using an EKU to signal that the DNS SAN in the cert is to be used to constrain the range of SIP IDs can be verified using the cert is not completely inappropriate either.

Steve

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