Hi,
maybe it is not that kamailio related question, but I dont know any other place with such good voip professionals ;) I have kamailio and mediaproxy. Clients are BudgetTone 200 (Grandstream) and CSipSimple. I am forcing clients to use SRTP but it does not support adding any certificate on both sides. SRTP call is working fine.
The question is, in this case, is man-in-the-middle attack possible? Maybe I should study SRTP more, but basically, if there are no certificates, there is no method how to be 100% sure that the media goes directly between clients. Is it true?
Thanks for response, Mino
Hi, If you are using SRTP your conversations will be encrypted, so nobody could eavesdrop it. Only if your Kamailio was compromised they could be eavesdropped.
I think you are confusing SRTP (media) with signaling (SIP). You should implement SIP over TLS too, it makes no sense to use SRTP without encrypt signaling. If not, it could be possible to sniff conversations with a MiTM but, anyway, I don't know any tool which supports it.
Here I speak a bit about VoIP encryption, I think it could help you: http://nicerosniunos.blogspot.com.es/2011/08/voip-eavesdropping-counter-meas...
Best regards.
2012/11/27 Mino Haluz mino.haluz@gmail.com
I forgot something, with Kamailio default configuration media goes always directly between clients. Moreover, if you want to be sure that any endpoint is who it says to be you should use client side autentication for SIP protocol. TLS module documentation clears how to do it.
http://kamailio.org/docs/modules/devel/modules/tls.html
2012/11/27 Jesús Pérez Rubio jesus.perez@quobis.com
Ok so what I understand from the document - there are in fact only these possibilities, how to be sure there is not Mitm.
1) To use ZRTP for media encryption with SIP TLS (in case proxy is compromised, attacker can not still decrypt ZRTP even though it goes through the proxy) 2) To use IPSec for media between the clients (can be SIP or SIPS, does not matter) if media goes directly between clients 3) To use SRTP with other key management (MIKEY, SDES) ?
When using these ways, audio could be decrypted
1) SRTP with SIP (keys are exchanged in SDP, so if they are not encrypted, SRTP loses its sense) 2) SRTP with SIPs (if the proxy is hacked, SIPs packet are decrypted on proxy and SDP payload can be seen, and SRTP packets can be decrypted)
Right?
On Tue, Nov 27, 2012 at 11:21 PM, Jesús Pérez Rubio jesus.perez@quobis.comwrote:
Right, there is an error in de doc with SDES sorry, the only options are first two. You could even encrypt at codec level and there are some other ways to encrypt networking communication at lower levels, but these two are the most reasonable solutions.
2012/11/28 Mino Haluz mino.haluz@gmail.com
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Jesús Pérez Rubio -
Mino Haluz