Re: [MMUSIC] Review of draft-ietf-mmusic-sdp-bundle-negotiation-32 - Magnus' comments - MID security

[Eric Rescorla <[e-mail]>]

ISTM that there are two risks:
1. That people might use structured RIDs, MIDs, etc. and that that will
leak a lot of information about
2. That just the structure of the media streams is a fingerprinting risk.

The first of these seems addressable by guidance about how to construct
these IDs. I note that we
have only very limited guidance on how to construct ICE ufrag/passwords....
The second seems
not that interesting as I bet you can get a lot by other metadata (packet
size, PT, etc).

-Ekr


On Fri, Oct 7, 2016 at 1:41 AM, Magnus Westerlund <
[e-mail]> wrote:

> Den 2016-10-06 kl. 23:59, skrev Cullen Jennings:
>
>>
>> I'm not getting the problem here and mandating 6904 is not an easy
>> thing to do.
>>
>
> So, lets be clear on what I have proposed. For bundle in general it is
> RECOMMENDED to encrypt MIDs in RTP header extensions. I have also proposed
> that for RTCWeb implementation and use should be mandated. I was not clear
> in what applies when an WebRTC endpoint talks to a legacy endpoint what is
> expected here. I guess this is the thorny issue.
>
>
>> I'm not getting what the issue is here. If mid are random, or are
>> just a count of n'th m-line in the sdp, what is the problem with
>> exposing them to people are getting the media?
>>
>
> The issue is that these identifiers are going from having only been
> visiable in the signalling messages to be visible also on the RTP media
> plane. And without RFC6904 even if one uses SRTP, these values are exposed.
> This have several different effects as I see it. So if the generation
> algorithm are not strictly defined, the implementation gets possible to
> fingerprint. In addition the device gets to be fingerprinted based on the
> number of streams offered and their identifiers. Thus, it is not only what
> is actually used that is exposed, but what was originally offered, i.e. the
> full offer leaks into unencrypted domain on the media plane. Note, this
> later can't be dealt with any mid id creation rules, it will still leak.
> Thus devices that have more exotic configurations when it comes to media
> streams, i.e. number of cameras etc this can still be fingerprinted by
> passive attacks from third parties.
>
> It is the passive attack from third parties that has me worried here. A
> peer in the signalling has massively more powerful fingerprinting, but that
> requires one to be in the signalling context, not passively observe traffic
> that goes past.
>
>
> Cheers
>
> Magnus
>
>
>
>
>>
>>
>> On Oct 6, 2016, at 7:39 AM, Magnus Westerlund
>>> <[e-mail]> wrote:
>>>
>>> Den 2016-10-06 kl. 14:49, skrev Christer Holmberg:
>>>
>>>>
>>>> Hi,
>>>>
>>>> Magnus suggested usage of RFC 6904 for encryption of the RTP SDES
>>>> header extension for MID. I guess it would be a SHUOLD?
>>>>
>>>> In addition, we would say that a corresponding level of security
>>>> must be applied to the RTP SDES header extension for MID and to
>>>> the RTCP SDES MID item.
>>>>
>>>> Any opinions?
>>>>
>>>
>>> I think this is fine solution to this issue. I would probably
>>> formulate the security considerations like this.
>>>
>>> The identfication-tag when included in the RTP MID SDES item,
>>> independent of transport, RTCP SDES packet or RTP header extension,
>>> can expose the value to parties beyond the signaling chain.
>>> Therefore, the identification-tag MUST NOT contain any user related
>>> information. However, the implementation's method for generating
>>> identfication-tags combined with hardware configuration can enable
>>> fingerprinting of the endpoint device and thus its user. As the
>>> identification-tag is also used to route the media stream to the
>>> right application functionality it is also important that the value
>>> received is the one intended by the sender, thus integrity and the
>>> authenticity of the source are important to prevent denial of
>>> service on the application. At least to prevent third parties from
>>> modifying the identification-tag value.
>>>
>>> Due to the security risks associated with the MID values in RTP and
>>> RTCP it is strongly RECOMMENDED that the MID SDES item is both
>>> confidentiality protected as well as source authenticated when
>>> transported in either RTCP or RTP header extensions. The security
>>> mechanisms used SHALL provide corresponding levels of security for
>>> both RTP header extensions and RTCP. Confidentiality mechanisms for
>>> RTP/RTCP are discussed in Options for Securing RTP Sessions
>>> [RFC7201], for example SRTP [RFC3711] with SRTCP encryption enabled
>>> combined with [RFC6904] can provide the necessary security
>>> functions.
>>>
>>>
>>> Cheers
>>>
>>> Magnus Westerlund
>>>
>>> ----------------------------------------------------------------------
>>>
>>>
>>> Services, Media and Network features, Ericsson Research EAB/TXM
>
>> ----------------------------------------------------------------------
>>>
>>>
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>
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>>
>>
>
> --
>
> Magnus Westerlund
>
> ----------------------------------------------------------------------
> Services, Media and Network features, Ericsson Research EAB/TXM
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