Subject: RE: 4.2.5 Register Re: General Comments on the SIP Protocol

From: Yaron Goland <[email-masked]>
Date: Tue, 28 Apr 1998 22:10:22 -0700

Yeah, I'm working off the 05 draft available from
http://www.cs.columbia.edu/~hgs/sip/.

I have rewritten that section of my comments to read:

4.4 4.2.6 Register

The sentence "A site MAY wish to advertise a common public key for all local
proxies to allow users to encrypt their registration for privacy." caused me
some confusion. I only realized it meant that there may have been an out of
band transmission of a public key after that interpretation was pointed out
to me by Lewis McCarthy ([email-masked]). I would suggest rephrasing
it so as to mention that the Encryption header could be used in this
context, if a public key has been previously obtained and verified, in order
to ensure privacy. I would also remove the requirement level "MAY" as the
purpose of the sentence is to guide an implementer, not provide or remove a
restriction.

			Yaron

-----Original Message-----
From: Lewis McCarthy [mailto:[email-masked]]
Sent: Tuesday, April 28, 1998 9:32 PM
To: Yaron Goland
Cc: MMUSIC List
Subject: Re: 4.2.5 Register Re: General Comments on the SIP Protocol

[It took me a little while to realize that the SIP draft you're reviewing
(-05, I guess) is not the version available at www.ietf.org -- the latest
there is -04.]

Yaron Goland writes:
> 4.4 4.2.6 Register
> 
> What is the point of the broadcasted public key? Since you have nary a
clue
> whose public key has been broadcasted this doesn't seem to be a good idea
> from a security point of view.

Sec 4.2.5 says that

   A site MAY wish to advertise a common public key for all local proxies to

   allow users to encrypt their registration for privacy.

I take this to mean that a sysadmin may configure all the proxies in the
administrative domain with a single public key, and then notify all users
in that domain of that key out-of-band (w.r.t. SIP). Thus REGISTERs can be 
kept confidential from other users on the local subnet. I don't see this
local key distribution as part of the SIP protocol per se.

-- 
Lewis    http://www.cs.umass.edu/~lmccarth/

---

From: Henning Schulzrinne <[email-masked]>
Date: Sat, 02 May 1998 13:16:17 -0400

Three possibilities:

(1) Announce key in Response-Key in some kind of registrar advertisement
message (to be defined).

(2) Two-step registration: REGISTER first with no information, get key
and then register again including sensitive information (such as CPL).
One possibility:

C->S: REGISTER

S->C: 401 Unauthorized
      WWW-Authenticate: ... publickey="..."

C->S: REGISTER
      Authorization: ...

[Encrypted using the public key.]

(3) Out-of-band.

(1) and (2) are preferable, but (1) overlaps with server location
functionality.