[Sip] RE: SRTP and MIKEY usage in SIP

Hi Steffen
the public-key based methods are most suitable for
client-to-client communications. The pre-shared could
be for ex a good choice for client(s)-to-server 
communications.
So, for SIP the public-key based may be more suitable,
generally speaking.

Cheers,
/E

> -----Original Message-----
> From: Steffen Fries [mailto:steffen.fries@siemens.com]
> Sent: den 17 januari 2003 16:20
> To: sip@ietf.org
> Cc: Elisabetta.Carrara@era.ericsson.se
> Subject: SRTP and MIKEY usage in SIP 
> 
> 
> Hi,
> 
> I'm not quite sure, which working group fits best for this 
> question, thus I'm starting with the SIP WG ;-)
> 
> When SIP and SRTP are used in conjunction, an appropriate
> key management is necessary for SRTP. Within the MSEC WG 
> MIKEY has been defined, which is thought to be used (also) 
> for SRTP. 
> 
> MIKEY and an related draft (draft-ietf-msec-MIKEY-DHHMAC-
> 01.txt) offer 4 different key management methods based on:
> - pre-shared secrets
> - public key encryption
> - Diffie Hellman protected with signatures
> - Diffie Hellman protected with pre-shared secrets
> 
> When MIKEY and SRTP are to be used in a SIP environment, 
> what would be a suitable choice out of the four options?
> 
> I'm not sure if the pre-shared secret pased methods are 
> suitable, since this would assume, that all users who want to 
> communicate need to exchange a shared secret before. Well, this 
> could be done by puting a shared secret in the SIP message and 
> securing this by S/MIME, but then MIKEY would be protected by 
> symmetric methods, although asymmetric technology was used to 
> secure the shared secret transport, namely S/MIME. One could 
> also use the certificates and private keys to secure MIKEY 
> right from the beginning. 
> 
> There might be scenarios where the symmetric case is 
> appropriate, but I'm not sure if this is a rather general case.
> 
> Is MIKEY generally considered for key management in SIP or will 
> this rather be done using draft-baugher-mmusic-sdpmediasec-
> 00.txt secured by S/MIME?
> 
> The usage of MIKEY and SRTP is especially interesting in 
> conjunction with other multimedia protocols like H.323. Voice 
> encryption and associated key management could be performed 
> across the different signaling protocols.
> 
> Was there already a discussion related to this question, which 
> I may be missed? 
> 
> Regards
>         Steffen
> 
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