AW: AW: [MMUSIC] Working group last call:draft-ietf-mmusic-securityprecondition-00.txt
"Stach Thomas" <thomas.stach@siemens.com> Thu, 06 October 2005 10:56 UTC
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Subject: AW: AW: [MMUSIC] Working group last call:draft-ietf-mmusic-securityprecondition-00.txt
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Date: Thu, 06 Oct 2005 12:54:47 +0200
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From: Stach Thomas <thomas.stach@siemens.com>
To: Flemming Andreasen <fandreas@cisco.com>
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Cc: Colin Perkins <csp@csperkins.org>, dwing@cisco.com, IETF MMUSIC working group <mmusic@ietf.org>
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Hi Flemming, thanks for the response. I think we are pretty much on the same track. More inline. > -----Ursprüngliche Nachricht----- > Von: Flemming Andreasen [mailto:fandreas@cisco.com] > Gesendet: Mittwoch, 05. Oktober 2005 21:22 > An: Stach Thomas > Cc: dwing@cisco.com; Colin Perkins; IETF MMUSIC working group > Betreff: Re: AW: [MMUSIC] Working group last > call:draft-ietf-mmusic-securityprecondition-00.txt > > > > Stach Thomas wrote: > > >Hi Fleming and Dan, > > > >first of all sorry for sending my comments rather late. > Nevertheless, I'd like to ask for some clarification since > details on the usage of SDP Security Description and > Key-Management extensions are rather scarce. You are > referencing SDP Security Description [SDESC] and > Key-Management extensions [KMGMT] as means to exchange the > necessary keys. > >Since both IDs say that preconditions are out of scope, I > expect the pre-conditions document to specify some necessary details. > >I can't find normative text on how to exactly do key > exchange in conjunction with the security pre-conditions. > > > >My problem is how exactly shall one construct the crypto > line/key-mgmt line for the second offer/answer exchange? > > > >The shown examples seem to indicate that in the second offer > the same keys shall be sent as in the first offer, which of > course makes sense. But since this is marked as an example I > can't rely. > >I could imagine that in the second offer/answer someone > might send some other key material or omit the > crypto/key-mgmt line since the keys are already exchanged. > > > By definition, SIP preconditions follow SIP offer/answer rules, and > offer/answer rules imply that each offer and each answer convey the > complete set of current media stream parameters, it is not partial, > differential, or anything like that, so we cannot omit the > crypto/key-mgt lines. > > >I would rather like to see some normative language that > requires a certain behavior. > > > > > In terms of offers and answers containing complete information, that > normative text is found in RFC 3264. I'll be happy to add a > reference on that point. > In terms of the actual value to use in the > subsequent offer, > we'll add some text (basically saying that in order to satisfy the > security precondition, you need to use the same key material > etc. in the > subsequent offer). That would be great. Of course 3264 must be satisfied. Therefore, this document could concentrate on the security preconditon handling. > > >Furthermore, assuming that the second offer contains the > same key material as the first, I would also expect to find > the same data in the second answer as in the first one, > especially when I use Diffie-Hellmann key exchange. > > > > > Offer/answer does not require the same answer to be given, to > the same > offer, however, in order for the security precondition to be > meaningful, > we actually want the subsequent answer to contain the same keying > material, etc. We'll add some text around that. My intention was to clarify the handling of the key material. I agree on the rest of the offer/answer exchange. Just for completeness, the second offer could already be different (within the constraints of the offer/answer model). Here, I think at the one of N codec selection as mentioned in RFC 3264. > > >Sending again the same MIKEY message in the second offer can > interfere with the replay attack handling of MIKEY. Of course > we don't want to regard the second message as a replay. > >How should that be handled? > >Maybe it is fine to e.g. hide the second MIKEY message from > the MIKEY handler and just check if it is identical to the first one? > >Or I could also imagine that some one updates the time stamp > for the second MIKEY message? But will/should that be > interpreted as re-keying by the MIKEY handler? Remembering > postings on implementor's lists I could imagine other weird > interpretations too. > > > > > > > There are two issues here really: > 1. kmgmt is a container that can be used to carry pretty much > anything, > so I'm not sure we can come up with a set of procedures that are > guaranteed to work for everything here. Some general statements will > probably have to be provided with a note that specific requirements > above and beyond those may have to be provided by the actual key > management protocol being used. In the current document, we > have simply > noted that the details depend on the actual key management protocol > being used, but we can probably say a bit more than that > (specifically > on subsequent offers and answers). Fully agreed. > 2. MIKEY is an example of a specific key management protocol > used with > the kmgmt extensions, and, as you point out, we should probably say > something about how to deal with MIKEY in here. If you have any > specific suggestions for how to deal with MIKEY here, they > would be very > welcome. > I guess you want some proposal before the cut-off for IETF-64. I'll try to send it during next week, if that's alright. Kind Regards Thomas > > >More comments: > >I'm missing RFC2119 as a normative reference although it is > mentioned in sec 1. Please add. > > > >The MIKEY examples show the same key-mgmt lines in the offer > and answer which is not the case. > > > > > > > Will fix both of these. > > Thanks for the comments. > > -- Flemming > > >Kind Regards > > > >Thomas > > > > > > > > > > > >>-----Ursprüngliche Nachricht----- > >>Von: mmusic-bounces@ietf.org [mailto:mmusic-bounces@ietf.org] > >>Im Auftrag von Colin Perkins > >>Gesendet: Montag, 01. August 2005 18:05 > >>An: IETF MMUSIC working group > >>Betreff: [MMUSIC] Working group last > >>call:draft-ietf-mmusic-securityprecondition-00.txt > >> > >>This is to announce a working group last call on the Security > >>Preconditions for SDP <draft-ietf-mmusic- > >>securityprecondition-00.txt>. Please send any final comments > >>on this > >>draft to the <mmusic@ietf.org> mailing list by 29th August 2005. > >> > >>If no substantive issues are raised by that time, we will > >>request the > >>IETF publish this draft as a Proposed Standard RFC. > >> > >>Colin > >> > >> > >>_______________________________________________ > >>mmusic mailing list > >>mmusic@ietf.org > >>https://www1.ietf.org/mailman/listinfo/mmusic > >> > >> > >> > > > > > > > _______________________________________________ mmusic mailing list mmusic@ietf.org https://www1.ietf.org/mailman/listinfo/mmusic
- AW: AW: [MMUSIC] Working group last call:draft-ie… Stach Thomas
- Re: AW: AW: [MMUSIC] Working group last call:draf… Flemming Andreasen