On 7 Feb 2008, at 00:36, Tilghman Lesher wrote: > On Tuesday 05 February 2008 09:22:29 Cavalera Claudio Luigi wrote: >> Hello, >> I'm doing some research concerning iax encryption, I haven't find any >> clients (softphones or hardphones) which implement so I have not >> tested >> it yet. >> >> There was also this message on asterisk-security mailing list >> http://archives.free.net.ph/message/20070507.101933.222987b2.en.html >> which got no answers and this makes me think that this iax >> encryption is >> not much interesting for the community. >> >> Anyway, in iax specification there is this statement: >> "Only the data portion of the messages are encoded." >> >> Which are the consequences of this, is it true as stated on >> http://www.voip-info.org/wiki/view/IAX+encryption >> that >> "The calling/called numbers are still passed in the clear over >> encrypted >> IAX, so you are still vulnerable to traffic analysis." >> ? >> >> If it's true how to deal with this? >> Would you consider media payload encryption enough? >> Maybe it's better to just forget about iax encryption and consider >> some >> more general approach like using openvpn >> http://www.voip-info.org/wiki/view/IAX_OpenVPN ? >> >> This half-encrypted iax encryption doesn't make much sense to me, >> therefore I think there's probably something I'm >> missing/misunderstanding. > > Is it important for you to conceal that a call was made from abc to > xyz on > thus-and-such a date? Or do you merely need to conceal the content > of a > call? You can already do traffic analysis and figure out that a call > occurred, just not what the endpoints are (even if you encrypted the > entire > link). The only way to get around that is to continuously send > random garbage > through the pipe at the same rate and consistency as would occur > with a real > IAX2 call. And the endpoints are only as specific as the systems on > either > end choose to make them. If you used some system of src/dst > obfuscation, you > could conceal even that information, though repeated calls to various > destinations could still be paired and correlated. > > IAX2 encryption is designed to obscure the same information as is > obscured > when you encrypt a call over the PSTN -- the content is protected, > but the > existence of such a call is not. Remember that a potential attacker > will > always choose the weakest link, and will probably attack the audio > stream > at a different location, if she cannot listen to the IP stream > directly (such > as a true wiretap on an analog endpoint or breaking into one of the > two > machines involved in the encryption). The idea is to make the IAX2 > link > unattractive as a potential target of wiretapping (whereas before it > would > have been the most obvious choice), thus forcing the attacker to > choose a > different attack scenario. > > -- > Tilghman > > ________________________
Also if you _really_ care about concealing the dialed number you can do it just fine. The simplest way is to have a single exten that takes _all_ encrypted calls, then once the call is up, dial 'onwards' with DTMF, the DTMF frames would be encrypted. In fact IAX kinda supports this at the protocol level (although I don't know of a working implementation apart from the iAXy perhaps, but that doesn't do crypto...). The NEW frame doesn't _have_ to contain a dialed number, the digits can be sent later (I forget the frametype), but later means within the encrypted session :-) Tim. _______________________________________________ -- Bandwidth and Colocation Provided by http://www.api-digital.com -- asterisk-users mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users