Re: [rtcweb] Last Call: <draft-ietf-rtcweb-data-channel-12.txt> (WebRTC Data Channels) to Proposed Standard

[Michael Tuexen <[e-mail]>]

On 12 Oct 2014, at 19:46, Harald Alvestrand <[e-mail]> wrote:

> On 10/12/2014 06:50 PM, Michael Tuexen wrote:
>> On 12 Oct 2014, at 17:28, Harald Alvestrand <[e-mail]> wrote:
>> 
>>> On 10/12/2014 03:30 PM, Michael Tuexen wrote:
>>>> On 12 Oct 2014, at 12:18, Harald Alvestrand <[e-mail]> wrote:
>>>> 
>>>>> Given that the middle box has to:
>>>>> 
>>>>> - decrypt and encrypt all packets (because the keys are different)
>>>>> - assert its own identity towards both endpoints (because otherwise DTLS
>>>>> doesn't work)
>>>>> - be trusted by both endpoints (otherwise it's a MITM attack by definition)
>>>>> - manage SCTP congestion control independently on the two legs (because
>>>>> that's how SCTP works)
>>>>> 
>>>>> I don't see the reshuffling of packets between channel numbers to be an
>>>>> excessive *additional* burden.
>>>> I agree CPU wise. But I have a question: Don't expect both endpoints of a
>>>> data channel to see the same "id" attribute? And isn't this attribute
>>>> the stream ID? So can conceptually a middlebox map the streams IDs?
>>> The two ends don't see the same identity either, so the middle box is not transparent.
>> OK. So this means that the ID defined in 
>> http://w3c.github.io/webrtc-pc/#widl-RTCDataChannel-id
>> doesn't have to be the same on both ends, right?
> 
> It has to be the same on both ends of the SCTP connection.
This means you can't remap the streams. Or am I missing something?

Best regards
Michael
> 
> It's just that (I think) you can't splice SCTP connections together;
> either you terminate them, or you don't.
> 
> That's my understanding - YMMV.
> 
>> It would be useful
>> to make that clear in the document. I always assumed that they are the same
>> on both ends...
>> 
>> Best regards
>> Michael
>>> The application has to know the middle box is there. So it has to be written to deal with differing numbers at the two ends too.
>>> 
>>> 
>>> 
> 
> 
> -- 
> Surveillance is pervasive. Go Dark.
> 
>