Re: [dispatch] draft-davis-valverde-srtp-assurance [was: Re: IETF 117 - do you have something for DISPATCH?]

[Brian Rosen <[e-mail]>]

A piece of info that might affect the discussion of prolonging SDES vs DTLS-SRTP.

In the US, the regulator announced an intention to require all carriers, including VoIP carriers to support “Next Generation 9-1-1” signaling.  That requires SIP with DTLS-SRTP.  The emergency call service side does not support SDES.  Of course, security is hop by hop, and nearly every carrier anchors media, so the DTLS-SRTP connection is likely from the carrier’s SBC to the emergency services SBC, and the phone could still support SDES, but it’s another nail in the SDES coffin.

I would be opposed to enhancing SDES.  Implementing this draft would require code changes in the device that needed it.  I would prefer those changes implement DTLS-SRTP.  While I do recognize that the magnitude of a change to implement DTLS-SRTP, with EKT-SRTP would be much greater than implementing this draft on a device that implemented SDES, a change is a change, and I think the security of DTLS-SRTP is so much better than SDES, that I believe we should not encourage continuing deployment of SDES.

Brian



> On Jul 17, 2023, at 5:09 PM, Kyzer Davis (kydavis) <kydavis=[e-mail]> wrote:
> 
> Hello Dan,
>  
> I reached out to the MMUSIC chairs (along with AVTCORE Chairs and Dispatch chairs CC’d) 
> MMUSIC felt like it belonged but still wanted the dispatch time since there is no MMUSIC meeting at 117.
>  
> To address a few other statements:
>  
> > I would like to understand where EKT-SRTP (RFC8870) fails to meet needs.  
> I think EKT-SRTP does a great job. That is, if we are using DTLS-SRTP. I am only aiming to do the same for SDP Security (SDES).
>  
> > I would rather see RFC8870 extended to work with SDP Security Descriptions because it moves us on a path towards DTLS-SRTP:  DTLS-SRTP-signaled endpoints could interop with SDP Security Descriptions-signaled endpoints because they're both using EKT to handle SSRC/ROC and key changes when group membership changes.  
> I believe you are referencing the act of an SBC/B2BUA interoperating SDP Security and DTLS-SRTP w/EKT?
> I found some older EKT-SRTP drafts that I think are the topic:
> https://www.ietf.org/archive/id/draft-mcgrew-srtp-ekt-06.html#anchor6
> https://www.ietf.org/archive/id/draft-mcgrew-srtp-ekt-06.html#anchor21
>  
> One point discussed in there was “SDP Security Descriptions however does not negotiate SSRCs and their associated Rollover Counter (ROC). Instead, SDES relies on a so-called "late binding", where a newly observed SSRC will have its crypto context initialized to a ROC value of zero. Clearly, this does not work for participants joining an SRTP session that has been established for a while and hence has a non-zero ROC.”
>  
> If that is the point then I agree; having the SSRC, ROC, SEQ in SDES/SDP security could allow for an intermediary to easily interwork SDES<>DTLS-EKT-SRTP.
> Note: I would need to audit EKT-SRTP to see if there is anything else SDES is missing that could help that Key Management Interworking.
>  
> > We really should be deprecating SDP Security Descriptions because it has far worse security properties compared with DTLS-SRTP.
> I also know SDP as a means for conveying keying material for SRTP isn't exactly the best method in the grand scheme when compared to the other available options.
> That being said, there are many millions of devices across different vendors still using SDP Security as the SRTP key management protocol.
> Further, I continue to see more modern internet telephony service providers providing TLS SIP w/SRTP via SDES and the acceleration of cloud registered SIP endpoints utilizing SDP Security. 
> Ignoring the problem that could positively affect so many does not seem like the right thing to do.
>  
> Other:
> I started an audit of various enterprise, cloud and service provider offerings to compare MIKEY, DTLS-SRTP, EKT-SRTP, and SDP Security but I will not be able to finish this by the time for dispatch so I have dropped the slide. I can create a wiki page on the drafts GitHub if the group wants to help crowdsource a “Current State of SRTP Key Management Protocol offerings in 2023”. Similarly, if a similar study already exists I would love to give it a read.
>  
> Lastly, I have a WIP draft-01 which provides an alternative solution to draft-00’s a=srtpctx SDP attribute.
> The alternative solution reuses the sdp security session parameter postfix options to convey SSRC, ROC, SEQ. 
> https://www.iana.org/assignments/sdp-security-descriptions/sdp-security-descriptions.xhtml#sdp-security-descriptions-4
> I plan to have a slide on both solutions for the dispatch discussion.
>  
> Thanks,
>  
> From: Dan Wing <[e-mail] <mailto:[e-mail]>> 
> Sent: Monday, July 17, 2023 3:41 PM
> To: [e-mail] <mailto:[e-mail]>
> Cc: Kyzer Davis (kydavis) <[e-mail] <mailto:[e-mail]>>; Robert Sparks <[e-mail] <mailto:[e-mail]>>; [e-mail] <mailto:[e-mail]>
> Subject: draft-davis-valverde-srtp-assurance [was: Re: [dispatch] IETF 117 - do you have something for DISPATCH?]
>  
> Yeah, it feels like draft-davis-valverde-srtp-assurance could go straight to MMUSIC.
>  
> The I-D needs to discuss what happens when SSRC collision occurs, which I think is "send new SDP indicating the new SSRC and ROC=0".
>  
> I would like to understand where EKT-SRTP (RFC8870) fails to meet needs.  The design of EKT-SRTP avoids signaling SSRC or ROC in the signaling channel and, instead, allow them both to be indicated in the SRTP channel itself.  This design allows SSRC collisions to be handled very much like how they are handled with RTP (that is, without the "S").  I would rather see RFC8870 extended to work with SDP Security Descriptions because it moves us on a path towards DTLS-SRTP:  DTLS-SRTP-signaled endpoints could interop with SDP Security Descriptions-signaled endpoints because they're both using EKT to handle SSRC/ROC and key changes when group membership changes.  We really should be deprecating SDP Security Descriptions because it has far worse security properties compared with DTLS-SRTP.
>  
> -d
>  
> 
> 
> Hi Kyzer (et. al.) -
>  
> Why aren't you taking this straight to mmusic? Am I missing something 
> that says that's not the obvious place for the work?
>  
> RjS
>  
>  
> On 6/27/23 7:31 AM, Kyzer Davis (kydavis) wrote:
> > 
> > Hello,
> > 
> > I would like to request a bit of dispatch time for the draft just posted:
> > 
> > https://datatracker.ietf.org/doc/draft-davis-valverde-srtp-assurance/
> > 
> > I also plan to attend IETF 117 in person to represent.
> > 
> > Thanks,
> > 
>  
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