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

[Magnus Westerlund <[e-mail]>]

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
>> ----------------------------------------------------------------------
>>
>>
Ericsson AB                 | Phone  [phone]
>> Färögatan 6                 | Mobile [phone] SE-164 80
>> Stockholm, Sweden | mailto: [e-mail]
>> ----------------------------------------------------------------------
>>
>>
>>
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>
>


-- 

Magnus Westerlund

----------------------------------------------------------------------
Services, Media and Network features, Ericsson Research EAB/TXM
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Ericsson AB                 | Phone  [phone]
Färögatan 6                 | Mobile [phone]
SE-164 80 Stockholm, Sweden | mailto: [e-mail]
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