At Mon, 5 May 2008 15:48:30 -0700,
Dan Wing wrote:
At Mon, 5 May 2008 15:48:30 -0700,
Dan Wing wrote:
>   * R-CERTS now reads:
> 
>       The media security key management protocol MUST NOT constrain   
>       the set of trust anchors that a peer can use to validate        
>       certificates used in the protocol.

I don't mean to be difficult, but I don't think that this actually
captures the relevant issue particularly well.

One of the primary reasons why the RTPSEC work got started was that it
became clear that one could not safely assume that end-users would
have certificates which were verifiable by others. If we could assume
that, then life would be a lot simpler. For instance, we could have
ubiquitous S/MIME and use S/MIME signatures instead of RFC 4474.  For
that matter, we could use DTLS-SRTP without any screwing around with
fingerprints, just based on the certificates.

So, I don't think the requirement is that the protocol not constrain
the set of trust anchors. [Honestly, I'm not really sure what that
means. Does HTTPS meet this requirement?] Without trying to wordsmith
it, I would say that the requirement is that the protocol be secure
even if the users do not have credentials attested to by *any* trust
anchor.[0] That is what the relevant distinction is between self-signed
and third-party certificates.

-Ekr

[0] Incidentally, one of Dan's messages stated that he believed that
IBE would be consistent with R-12. I suppose that might be technically
true, but I think it pretty clearly does not meet the spirit of the
requirement. In order to use an IBE system, the user has to get a
private key from the PKG. This is just as inconvenient as what
we are trying to avoid with this requirement, namely forcing the
user to deal with the CA/PKG.


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