30 Jul
2014
30 Jul
'14
10:22 a.m.
On 30/07/14 06:37, Muhammad Shahzad wrote:
Humm, no reply so far, may be because my email was
very long and no
body bothered to read it all. Anyways, here is the shorter more direct
version of it. (including kamailio dev list, since question is rather
technical).
Is it possible to implement a custom SIP transport in Kamailio script
file i.e. kamailio.cfg. The purpose is to allow experimentation with
custom encryption algorithms such as this,
https://github.com/mshary/itv
What we need is a couple of functions, one to receive incoming raw /
encrypted data received on SIP socket, which then can be parsed /
decrypted in kamailio.cfg (using e.g. LUA or PERL language modules
etc.) and afterwords feed to kamailio for usual processing (as if it
was normal / plain-text sip data received on sip socket). The second
function to do the opposite, it receives the normal / plain-text sip
data that is ready to be sent out from kamailio's core, encrypts it
and then send it out to actual destination.
In case above is not possible. Can i do it in kamailio's native code?
Any hooks / example code for reference?
If you look at encrypting sip messages,
look at topoh module. You can
write a replacement for its hooks. Topoh is practically decoding the
headers and then lets the pure SIP message go through config file
execution. Before sending, it encodes the headers and then let it go to
the network.
This is something that should be rather straightforward to do if you are
familiar with C code.
You mentioned that using TLS can still reveal patters of being sip. You
have to think here of ways to obfuscate even in your case of a new
encryption method. What can be matched here:
- periodical registrations - you can have the client (or even the
server) to use different expires times for each registration
- size of packages, specially if user IDs are the same or similar length
(e.g., say everyone uses a 10 digit id), practically no matter who is
calling who, the size will be pretty much the same because most of the
phones I have seen so far use same set of headers. Here you can add
random custom headers for each packet. I haven't checked the proposed
encryption algorithm (some use random blocks implicitly to pad the
data), but eventually you can add random data before and after the
packet that you strip (and re-add) in topoh-replacement module
The other option of having a totally different protocol than SIP should
be possible as well. But you need to re-implement a lot (like location,
authentication, ...). Look at msrp module for an example. This may need
to touch core code a bit.
Of course, in both cases, the client application has to be developed as
well. Perhaps still easier if going for first option, by reusing some
open source sip client and adding the encapsulation/decapsulation layer
when receiving/sending to network.
Cheers,
Daniel
Many thanks and kind regards for your help.
On Mon, Jul 28, 2014 at 2:38 AM, Muhammad Shahzad
<shaheryarkh(a)gmail.com <mailto:shaheryarkh@gmail.com>> wrote:
Hi,
As the mobile voip is getting more and more popular these days,
there has been a strong opposition from GSM operators against
mobile voip apps. They often use tactics like blocking voip ports,
or detect and block voip traffic and in some cases restricting udp
traffic altogether to very low upload and download speeds. See
below link for some details,
http://www.linphone.org/eng/blog/linphone-over-3g.html
While not all the problems can be solved right now (especially the
limiting udp traffic, since RTP always uses udp transport) I was
wondering if we can at least handle the sip related problems. The
most important of them is SIP traffic detection. While some forks
would suggest using TCP/TLS to encrypt SIP traffic, it has a few
problems, e.g.
1. It requires somewhat high resources on mobile devices, so many
low-end android phones simply can't use it.
2. There is possibility that encryption signature may identify it
as SIP traffic. There exists firewalls (often deployed in middle
eastern countries) which have huge database of encryption
signatures and patterns which although may not decrypt the sip
packet but at least identify it as sip packet and block it.
Also with rough agencies of evil empires spying over millions of
users worldwide makes the current encryption standards pretty much
pointless, at least in terms of user privacy and network security.
So there is a strong need to experiment with new ideas and
concepts to regain internet freedom. Some of such ideas are,
1. Convert sip traffic which is plain text to binary format just
before transmitting it and revert it to plain text upon reception.
2. XOR the sip traffic (pretty much same as binary sip).
3. Use some very lightweight but effective / non-standard
encryption algorithm, e.g.
https://github.com/mshary/itv
All these ideas require that SIP server such as Kamailio is able
to adopt to these, preferably with minimal or no change in native
code. The NoSIP module seems an interesting module in this regard.
It provides all traffic it thinks is not the SIP traffic to
configuration script, where we can do our own parsing and do
whatever we want with it. I have two questions about this,
1. If parsed message is SIP, we can we send it back to kamailio
core to get it processed as if it is a normal SIP message received
by kamailio?
2. Can this module or any other module available in kamailio, that
can provide us full sip packet that is about to be transmitted
over sip socket, so we can "encode" it just before it is sent to
next hop?
I know this would be like writing a SIP transport in kamailio
script which would be very tough if not impossible to implement in
native core. But it will really help in winning the modern mobile
voip challenges.
Thank you.
--
Daniel-Constantin Mierla - http://www.asipto.com
http://twitter.com/#!/miconda - http://www.linkedin.com/in/miconda