[VOIPSEC] Secure Real-time Transport Protocol (SRTP)

[Brian Raymond]

I had a couple of comments for the thread.

Avaya has always supported H.235 for security on H.323 calls so I would
imagine they are still doing the same now. I'm not sure however which
profile they are working with these days. There are a number of security
profiles (Annexes) specifying different algorithms for encryption and key
management. Related to MIKEY is H.235 Annex G, which is MIKEY and SRTP for
transport. Signaling of H.225 is generally encrypted via TLS or IPSEC, at
least what I've seen. Key exchange for media is over H.245 however the
method is specific to the profile.

I agree with some of the other members that the main reason there isn't a
focus on application level security is that the market just hasn't demanded
it. That's starting to shift now but as someone who has previously worked
for a commercial vendor of a number of H.323/SIP products we never saw a
real demand from customers for that type of support. Any customers who
required security implemented it at layer 2/3 using some sort of VPN. This
was generally not an issue because that type of system was already in place
most of the time and provided much greater endpoint flexibility.

I have supported the government sector for a few years now and even in what
are considered high(er) security environments with arguably critical data to
protect transport encryption was never a real issue. Again this is all
changing now and I'm seeing a number of splintered implementations popping
up. Most people I have talked to are only familiar with their specific
application's protocol implementation and when designing a solution aren't
concerned about interoperability. This is actually quite interesting because
these same applications are using standards to foster interoperability.


- Brian



On 3/23/05 6:05 PM, "Ken Peterson" <kapnet at mindspring.com> wrote:

> Ian,
> 
> The only major vendor doing official SRTP, to my knowledge, is Cisco in
> release 4.1 of their CallManager, which was just released last fall. The
> signaling channel is protected via TLS - both phone and CM server have
> certificates to authenticate each other. Over this "always-up" control
> channel, they speak Cisco's proprietary Skinny protocol. During call setup,
> the CM sends a shared symmetric key to both IP endpoints. The endpoints then
> speak SRTP using AES-128 encryption and SHA-1 HMAC.
> 
> I know of one major government organization that is implementing this
> solution as we speak. They are the rare exception, however.
> 
> Avaya's solution is supposed perform a similar process, but using H.323.
> Their release date was pushed back last time I checked (was supposed to be
> out now.) Currently Avaya is using 102-bit AEA (Avaya Encryption Algorithm)
> between phones... I assume the voice is encapsulated in SRTP, but I could be
> wrong... anyone else know? The key exchange (again Im not confident in this,
> due to Avaya's lack of documentation) should be a Diffie-Helman exchange
> over the H.225 control channel. Is that D-H exchange authenticated to avoid
> MITM attacks? I would hope so, but I've seen no evidence to support that.
> 
> Cheers,
>  Ken
> 
> ************************************************************************
> *                             *
> *  Ken Peterson, CCIE 4297 *  Cisco Certified Security Professional
> *  PacketBrain, Inc.          *  Cisco IP Telephony Support Specialist
> *  Cary, NC 27511             *  Cisco Content Networking Specialist
> *                             *
> ************************************************************************
> 
> 
> 
> -----Original Message-----
> From: Voipsec-bounces at voipsa.org [mailto:Voipsec-bounces at voipsa.org]On
> Behalf Of Brian Rosen
> Sent: Wednesday, March 23, 2005 4:44 PM
> To: Ian.Cuthbertson at nokia.com; Voipsec at voipsa.org
> Subject: RE: [VOIPSEC] Secure Real-time Transport Protocol (SRTP)
> 
> 
> There is not much deployment yet.
> One of the reasons is confusion on key exchanges.
> Another is there is not (yet) much demand.
> 
> Brian
> 
>> -----Original Message-----
>> From: Voipsec-bounces at voipsa.org [mailto:Voipsec-bounces at voipsa.org] On
>> Behalf Of Ian.Cuthbertson at nokia.com
>> Sent: Wednesday, March 23, 2005 12:10 PM
>> To: Voipsec at voipsa.org
>> Subject: [VOIPSEC] Secure Real-time Transport Protocol (SRTP)
>> 
>> Hi,
>> 
>> Does anyone have a take on how widely deployed SRTP is in the real
>> world? Are all vendors offing solutions which include this (gateway,
>> handset etc)? Which key exchange methods do they support?
>> 
>> Thanks, Ian
>> 
>> 
>> 
>> _______________________________________________
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>> Voipsec at voipsa.org
>> http://voipsa.org/mailman/listinfo/voipsec_voipsa.org
>> 
> 
> 
> 
> 
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