[VOIPSEC] What methods of encrypting SIP signaling are out there *other than* TLS encryption?

[dan_york at Mitel.com]

VOIPSEC readers,

Question for the list... someone recently asked me if there were methods 
of encrypting SIP *other than* TLS-encryption (SIPS) in common usage? 

I pondered that for a bit but I couldn't honestly think of any other 
implementations that I have heard about recently (in the open standard 
world - there are of course always proprietary encryption schemes).  I 
recall some people doing some work with S/MIME-encrypted SIP, but I don't 
remember that going anywhere (am I wrong?).  All the vendors, SBCs, 
firewalls, etc. that I could think of use TLS-encrypted SIP as the method 
of securing SIP signaling.  (Well, okay, I do remember hearing of someone 
nailing up an IPSec VPN between the set and the IP-PBX and routing all SIP 
and voice over the IPSec VPN, but for me IPSec seems a wee bit too 
heavyweight.)

Are there other SIP encryption mechanisms out there that I'm forgetting?

Note that I am talking about *SIP* signaling encryption and NOT about SRTP 
encryption.  I'm well aware of all of the various SRTP encryption 
mechanisms.

Thanks,
Dan

-- 
Dan York, CISSP
Dir of IP Technology, Office of the CTO
Mitel       http://www.mitel.com
dan_york at mitel.com +1-613-592-2122
PGP key (F7E3C3B4) available for 
secure communication