Re: [AVTCORE] [MMUSIC] zrtp: draft-ietf-mmusic-sdp-mux-attributes vs draft-ietf-avtcore-rfc5764-mux-fixes

[Alan Johnston <[e-mail]>]

On Wed, May 25, 2016 at 8:59 PM, Gonzalo Salgueiro (gsalguei) <
[e-mail]> wrote:

>
>
> > On May 25, 2016, at 8:50 PM, Ben Campbell <[e-mail]> wrote:
> >
> > Since I'm the one who originally complained about TRANSPORT I should
> probably respond :-)
> >
> > I agree TRANSPORT makes sense if people agree to the changes in
> mux-fixes.
>
> Well, as mentioned in my earlier email, changes to both mux-fixes and 6189
> are needed.
>

Agreed.  I will make the changes to RFC 6189.

- Alan -


>
> Gonzalo
>
>
> > Ben.
> >
> >> On 25 May 2016, at 22:09, Suhas Nandakumar wrote:
> >>
> >> Thanks Ben, Alan , Gonzalo & Marc for driving these discussions.
> >>
> >>
> >> Just getting back to the original question that Ben had on the
> mux-cateory
> >> for ZRTP - Do we all agree that with the changes to rfc5764-mux-fixes
> the
> >> category TRANSPORT makes sense ? Since that helps clarify demuxing ...
> >>
> >> Thanks
> >> Suhas
> >>
> >> On Wed, May 25, 2016 at 8:05 PM, Gonzalo Salgueiro (gsalguei) <
> >> [e-mail]> wrote:
> >>
> >>> OK, cool  Thanks, Alan.  Once we get consensus from the WG(s) that
> this is
> >>> the best way forward we will make this change to
> >>> draft-ietf-avtcore-rfc5764-mux-fixes.
> >>>
> >>> Cheers,
> >>>
> >>> Gonzalo
> >>>
> >>>>> On May 25, 2016, at 8:01 PM, Alan Johnston <
> [e-mail]>
> >>>> wrote:
> >>>>
> >>>> Hi Gonzalo,
> >>>>
> >>>> Thanks for the clarification - I had it backwards in my head.
>  Existing
> >>> ZRTP implementations will be compliant to the proposal, and we can
> >>> constrain those bits to 0 in the 6189bis draft to lock it down.
> >>>>
> >>>> So I am OK with this proposal.
> >>>>
> >>>> - Alan -
> >>>>
> >>>>> On Wed, May 25, 2016 at 1:56 PM, Gonzalo Salgueiro (gsalguei) <
> >>>> [e-mail]> wrote:
> >>>> Hi Alan -
> >>>>
> >>>> One of the reasons we made the suggestion was because (in our
> >>> estimation) it did not have a major impact to the ZRTP packet format.
> >>> Currently the packet format is:
> >>>>
> >>>>
> >>>>    0                   1                   2                   3
> >>>>    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
> >>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >>>>   |0 0 0 1|Not Used (set to zero) |         Sequence Number       |
> >>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >>>>   |                 Magic Cookie 'ZRTP' (0x5a525450)              |
> >>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >>>>   |                        Source Identifier                      |
> >>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >>>>   |                                                               |
> >>>>   |           ZRTP Message (length depends on Message Type)       |
> >>>>   |                            . . .                              |
> >>>>   |                                                               |
> >>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >>>>   |                          CRC (1 word)                         |
> >>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >>>>
> >>>>
> >>>> Our proposal was to set bits 4 and 5 to zero, which is currently what
> >>> the protocol calls for and should implicitly make all existing
> >>> implementations compliant.  All we are proposing is is to take bits 4
> and 5
> >>> out of the “Not Used” range and leave them fixed to the value that
> current
> >>> implementations use.  Does this make sense?
> >>>>
> >>>> In any case, I’d like to try and understand what impact this has to
> the
> >>> current rfc5764-mux-fix text.  Is it as simple as explicitly reserving
> >>> values 16 - 19 for ZRTP? Or did you have something else in mind?  If
> you
> >>> can make specific text suggestions that will simplify things.
> >>>>
> >>>> Thanks,
> >>>>
> >>>> Gonzalo
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>> On May 25, 2016, at 1:35 PM, Alan Johnston <
> [e-mail]>
> >>> wrote:
> >>>>>
> >>>>> Hi Marc,
> >>>>>
> >>>>> Changing the packet format for ZRTP is a pretty major change to the
> >>> protocol...
> >>>>>
> >>>>> I think the only case where this is an issue would be if both ZRTP
> and
> >>> DTLS-SRTP are offered opportunistically (OSRTP), and either ZRTP or
> >>> DTLS-SRTP arrives before the answer is received.    During this window
> of
> >>> time, a slightly more complicated algorithm could be used to
> distinguish
> >>> ZRTP from DTLS-SRTP, such as checking the 32-bit magic cookie that is
> >>> present in every ZRTP message. Otherwise, only one of these protocols
> will
> >>> be used at a time, so it is not the same as distinguishing either from
> STUN
> >>> and RTP, which happens throughout a session.
> >>>>>
> >>>>> We could put this guidance in a RFC6189bis draft, and the other
> >>> documents could just defer to that guidance if they support ZRTP in
> >>> addition to DTLS-SRTP opportunistically.
> >>>>>
> >>>>> - Alan -
> >>>>>
> >>>>> On Wed, May 25, 2016 at 10:56 AM, Ben Campbell <[e-mail]>
> >>> wrote:
> >>>>> Hi Marc,
> >>>>>
> >>>>> That's along the lines that I expected, if the working group chooses
> >>> this path. What do others think?
> >>>>>
> >>>>> Thanks!
> >>>>>
> >>>>> Ben.
> >>>>>
> >>>>> On 25 May 2016, at 12:37, Marc Petit-Huguenin wrote:
> >>>>>
> >>>>> As you mention, there are several ways to handle this issue. We leave
> >>> it to the community to decide whether to include zrtp in bundle or
> not. If
> >>> we were to update the 5764-mux-fix draft, we felt that the cleanest
> way to
> >>> handle it is in two steps.
> >>>>>
> >>>>> One thing to note is that there is no clash/overlap with STUN, so
> >>> using magic cookie to distinguish from STUN is a moot point. The
> overlap
> >>> with the DTLS range is what we need to avoid. The right thing to do
> seems
> >>> to be to work on a rfc6189bis draft that would set bit 4 and 5 of the
> first
> >>> byte of the zrtp message to 0. This way zrtp cannot clash with DTLS.
> >>>>>
> >>>>> On the rfc5764-mux-fixes draft, we just change the algorithm to:
> >>>>>
> >>>>>           +----------------+
> >>>>>           |        [0..3] -+--> forward to STUN
> >>>>>           |                |
> >>>>>           |      [16..19] -+--> forward to ZRTP
> >>>>>           |                |
> >>>>> packet --> |      [20..63] -+--> forward to DTLS
> >>>>>           |                |
> >>>>>           |      [64..79] -+--> forward to TURN Channel
> >>>>>           |                |
> >>>>>           |    [128..191] -+--> forward to RTP/RTCP
> >>>>>           +----------------+
> >>>>>
> >>>>>
> >>>>> Does this seem like a reasonable approach?
> >>>>>
> >>>>>
> >>>>> On 05/24/2016 04:21 PM, Ben Campbell wrote:
> >>>>> Hi,
> >>>>>
> >>>>> There appears to be a discrepancy between
> >>> draft-ietf-mmusic-sdp-mux-attributes and
> >>> draft-ietf-avtcore-rfc5764-mux-fixes concerning whether zrtp can be
> used
> >>> with bundle.
> >>>>>
> >>>>> mux-attributes puts the zrtp-hash attribute [RFC6189] in the
> >>> "transport" category, meaning, among other things, that it can be used
> in a
> >>> bundle group. However, as the demux rules are currently defined
> >>> 5764-mux-fixes, zrtp messages cannot actually be demuxed. (If I read
> things
> >>> correctly, the first byte of a zrtp message will be 16, which is not
> in any
> >>> of the "known ranges" described in 5765 or 5764-mux-fixes, and
> therefore
> >>> the message MUST be dropped.
> >>>>>
> >>>>> That seems to leave the choice of adding zrtp messages to the demux
> >>> rules in 5764-mux-fixes, or removing the implication that zrtp can be
> >>> bundled from mux-attributes.
> >>>>>
> >>>>> Adding rules for demuxing zrtp to 5765-mux-fixes would probably not
> be
> >>> hard, but would be non-trivial. RFC 6189 calls for using the magic
> cookie
> >>> to distinguish zrtp messages from stun messages.
> >>>>>
> >>>>> Do people have opinions how to move forward with this? Am I
> >>> interpreting the conflict correctly?Keep in mind that ZRTP is not a
> >>> standards-track spec. But at the same time, I'm not sure we want to
> exclude
> >>> it from the bundle mechanism.
> >>>>>
> >>>>> Thanks!
> >>>>>
> >>>>> Ben.
> >>>>>
> >>>>>
> >>>>> _______________________________________________
> >>>>> Audio/Video Transport Core Maintenance
> >>>>> [e-mail]
> >>>>> https://www.ietf.org/mailman/listinfo/avt
> >>>>>
> >>>>>
> >>>>> _______________________________________________
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> >>>
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