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

[Magnus Westerlund <[e-mail]>]

Den 2016-10-07 kl. 15:32, skrev Jonathan Lennox:
>
>> On Oct 7, 2016, at 4:41 AM, Magnus Westerlund
>> <[e-mail]
>> <mailto:[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.
>
> RFC 7904 (SDES header extensions) says:
>
>    In RTP sessions where any type of confidentiality protection is
>    enabled for RTCP, the SDES item header extensions MUST also be
>    protected.  This implies that to provide confidentiality, users of
>    the Secure Real-time Transport Protocol (SRTP) need to implement and
>    use encrypted header extensions per [RFC6904 <https://tools.ietf.org/html/rfc6904>].
>
>
> This was after a fair bit of back-and-forth with the security ADs.  MID
> is a 7904 header extension, so I don’t think BUNDLE can override this MUST.
>

Okay, forgot about that requirement. However, I don't think that really 
contradicts what was written. The proposed text recommends use of 
encryption of RTCP. RFC7904 mandates that if RTCP is encrypted then RTP 
header extension must also be encrypted. There should be a reference to 
this requirement in the text below, so I will update the text proposal.


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 RECOMMENDED that the MID SDES item is confidentiality protected as 
well as source authenticated. The SDES RTP header extensions [RFC7904] 
requires encryption of the header extension in cases when the RTCP 
encrypts the SDES item. 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.

>
>>> 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]
>>>> <mailto:[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]
>>>> <mailto:[e-mail]>
>>>> ----------------------------------------------------------------------
>>>>
>>>>
>>>>
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>>>
>>>
>>
>>
>> --
>>
>> 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]
>> <mailto:[e-mail]>
>> ----------------------------------------------------------------------
>>
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>


-- 

Magnus Westerlund

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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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