Voice of VOIPSA

This was a question I asked at the recent VON conference in San Jose, CA. Of course we talk a lot here about VoIP Security, but actually if we take a step back, is VoIP itself any longer a meaningfully separate concept? The thing is that technology moves on, and maybe some people care whether they are connected via cable or ADSL, but pretty much, the average Joe is happy that “broadband” is magic that provides fast Internet. Today there’s still talk about “WiFi” as a distinct technology, but WiMax, LTE and mobile broadband (EVDO, UMTS etc) are on the rise, and within a couple of years, we’re all likely to have forgotten which technology we’re using to connect to the Internet.

So my thesis is that IP is so very intrinsic to the nature of all telecoms today, that it’s probably not even worth using “Vo” any longer. Why should I say that? Well firstly, SS7, the mainstay of today’s international telecoms network, in many cases uses IP to carry the signalling traffic, using the protocol family known as Sigtran. In traditional telecoms, media and signalling has long been split, with SS7 connecting the calls, and a parallel network of E1/T1 links carrying the voice calls. The long established estrangement of media and signalling continues into the NGN world, with signalling now mostly meaning SIP, and the media usually RTP, but there is still a world of choice. When SS7 meets SIP we can often find ISUP (the call control protocol most widely used by telecoms incumbents) being tunnelled using protocols like SIP-I and its twin (in the iron mask) SIP-T. In the “legit” SS7 community we find that BICC (Bearer Independent Call Control) allows us to connect calls in a way familiar to all fans of ISUP, and yet the calls themselves don’t need to be 64k bearer channels any more, but can also be the IP-friendly RTP streams.

This is not a fashion, but simply an evolution. Today, when telcos federate, it is largely using traditional TDM lines, and traditional SS7 protocols. But this is changing: it’s very cheap and convenient to interconnect using Sigtran, and there is much talk about how to connect calls using “codec free” operation: that is, to pipe the audio unchanged from end to end, to optimize audio quality and bandwidth usage. The GSM Association are promoting a system called IPX, which will allow mobile carriers to interconnect using IP, such that not only signalling and media are seamlessly interconnected (via a private intranet), but also settlement data will automatically be exchanged, so that every telco knows what they owe to every other party.

If I may press my point further, in many projects the traditional TDM core is being removed in favour of a big SIP router surrounded by a ring of session border controllers (SBCs). One major factor in these projects is that the customers are still today 80/20 connected via traditional E1/T1 or SS7 networks, which means that part of the magic is a media gateway that knows how to talk both SS7 and SIP. So SIP networks have TDM customers, and your Granny may already be using IP without even knowing it.

So does VoIP exist? When IP is such a fundamental tool in what we know as “legacy” telco networks, perhaps it does not. Consequently does VoIP Security exist? Well as we’ve often discussed here at the VoIPSA blog before, when you start moving voice traffic over your IP network, then you have all the voice system vulnerabilities plus all the IP vulnerabilities that just arrived at your doorstep. Perhaps actually the truth is that nearly all voice is already VoIP, so VoIP security is not just an enterprise concern, but is actually a core issue for every telco on the planet.

For some weeks, Alec Saunders, ace blogger and iotum founder has been running a podcast experiment via Facebook. Iotum have created a free conference call application on Facebook (which works rather well in fact), and to showcase its use Alec and friends use the conference facility to record a daily podcast show called Squawkbox, talking about topical news in tech.

Today’s show was on the subject of voice phishing, a favourite topic of some of our friends here at VOIPSA. In fact, VOIPSA board members Dan York and Jonathan Zar (also the Blue Box Podcast team) were on Alec’s call today. So if you’ve time to give it a listen, it’s an interesting discussion, and it can be found here.

The UK’s National Codes Centre recently ran a competition for amateur codebreakers to try their hands on breaking one of the original WW2 codes (Lorenz Cipher) using modern PC hardware. The National Codes Centre at Bletchley Park (known as “Station X” during the war) is a museum and heritage site for early computing as well as codebreaking. In a nice irony, the winner of the competition was a German programmer, Joachim Schueth, who ran his software on a 1.4 GHz laptop with NetBSD as the O/S, beating the original Colossus codebreaker by a factor of hours. The original Colossus could break the code in 3 hours and 15 minutes, whereas Schueth’s code took just 46 seconds.

On the performance difference, Schueth himself said: “My laptop digested ciphertext at a speed of 1.2 million characters per second – 240 times faster than Colossus. If you scale the CPU frequency by that factor, you get an equivalent clock of 5.8 MHz for Colossus. That is a remarkable speed for a computer built in 1944. Even 40 years later many computers did not reach that speed. So the Cipher Challenge would have been very much closer had it taken place 20 years ago.” That’s right, not GHz, but MHz. The original Colossus was not so much a Pentium, but rather a Z80.

At Bletchley Park, they have a working Colossus which was lovingly rebuilt over many years by a team of enthusiasts, with help from some of the original designers. The Colossus MKII can be seen working by visitors to Bletchley Park.

Bletchley Park is the UK’s mecca for people interested in the history of code breaking, and in particular the codes of World War 2. Bletchley Park (in WW2 known as “Station X”) was the home of the code breakers, and where early computing pioneers like Alan Turing worked on the science of breaking cyphers.

This week, a team of volunteers led by Tony Sale completed a 14 year project to rebuild Colossus, one of the code-breaking computers used at Bletchley Park. After the war the machines were dismantled and even the plans destroyed by order of the military, so the Colossus had to be painstakingly remembered and reconstructed, with the help of some of the original engineers that built it. Tony Sale has had a long association with Bletchley Park, and also with remembering and rebuilding the most important antique computers in the British history of computing.

Although the Colossus was somewhat single-minded in its operation, its use of valves as electronic switches paved the way for the general-purpose computers of the 1940s and 50s, and of course the work they did at Bletchley paved the way for the use of encryption technologies that we use today in data and voice applications across the Internet.

Link: Silicon.com report on the Colossus rebuilt.

Some time back we reported here about the Pena/Moore case, where a duo stole VoIP services and then sold them on to third parties, who thought they were buying a legitimate service. Pena went on the run, and I believe is still missing. The techie of the duo, Robert Moore is now off to prison. Information Week have an interview with him here.

Skype is certainly taking some punishment recently. Today the news broke that someone has let loose a worm that uses the Skype API to send a chat message to your Skype contacts. The chat message includes a link which (if the user clicks on it) will download the w32/Ramex.A virus, which in turn infects their PC, and will visit their Skype friends. Obviously, this is a big concern for anyone with a user base as large as Skype’s, since even a small percentage of users that click on the link can cause wide distribution.

More: Skype Blog

Just to show that VoIP security is not all about SIP, researchers Himanshu Dwivedi and Zane Lackey from iSEC Partners have produced some interesting material on vulnerabilities in IAX, which they just presented at the recent Black Hat conference. IAX (pronounced eeks) as you may know, is a proprietary protocol often used to connect together Asterisk servers for the purposes of call routing. Implementors say that it is simpler than SIP, and also tunnels through firewalls better than SIP, thanks to a ‘VPN like’ approach that tunnels signalling and media together down the same pipe.

iSEC came up with a number of novel attacks including exploiting authentication problems with the use of MD5 hashes; man-in-the-middle and DoS. They have a very nice paper here that describes their attacks in detail, and they have also made available some code (in Python) that you can use for your own experimentation.

Not stopping at IAX, they also had a go at the granddaddy of VoIP protocols, H.323, and have published a couple of attack tools there too. It’s enough to keep you busy all Summer long.

More: Black Hat USA 2007 abstracts
iSECPartners

Day two opens with a keynote from Jonathan Rosenberg, one of Henning Schulzrinne’s early collaborators on SIP. Rosenberg went on from Columbia University to Dynamicsoft, later Cisco Systems where he is now a Fellow. Rosenberg is still active in IETF work related to SIP, and was principal author of NAT traversal techniques, STUN and ICE.

Rosenberg touched on many topics in his presentation on the challenges for IP telephony, but of course one of the challenges he talked about was SPIT or voice SPAM. He said that one basic decision point is whether you know the caller or not. As long as we have strong identity on VoIP networks, it’s possible to keep a white list of permitted callers. Then the problem becomes how to enroll people on to that list in the first place.

Safely letting in people that you don’t know opens the field to a whole range of different techniques. Some that he mentioned include: consent and reputation systems; CAPTCHAs; computational puzzles and payments at risk. Some of these he outlined as more promising than others, but the point is that this problem is not solved yet, and in fact is an ongoing discussion in the IETF and elsewhere.

Day one of IPTComm brings a whole raft of VoIP Security topics: Saverio Niccolini of NEC Philips spoke about a holistic approach to VoIP intrusion detection and prevention, including the use of a “honeypot” to draw attacks away from the true telephony service to a dummy that can help in analsysis of attacks. Jens Fiedler of Fraunhofer Fokus spoke about VoIP Defender, a prototype system that allows the dynamic analysis of SIP traffic, with realtime generation of filter rules, then applied back to the signalling traffic. Ali Fessi (Univ. of Tuebingen) spoke about CoSIP, and attempt to marry traditional SIP servers with a P2P SIP approach, with the aim of improving resilience to system failures or DoS attack. Humberto Abdelnur (INRIA) described Kiph, a stateful SIP fuzzer. Rather then the approach taken by the PROTOS toolset, KIF is SIP-specific, and understands not just the grammar, but also to some extent the context and behaviour of SIP, in order to better test for vulnerabilities in SIP-based products. Finally Ge Zhang (Fraunhofer FOKUS) spoke about DoS attacks to VoIP, based on attacks to the DNS server, which of course the SIP Proxy depends upon for its function. He also described some limited defences against this threat.

Interestingly, Henning Schulzrinne told us in his opening remarks that our host, Columbia University NY, recently experienced its own SPIT (Internet Telephony SPAM) attack, with someone accessing the Proxy, and “war dialling” a lot of IP phone extensions. There have been few real-life examples of this so far, but you can see that large IP communities, like universities, are likely to attract such attacks.

Reading recently about Snom releasing a new phone with IPSec VPN capabilities started me thinking about the incredible processing power that embedded devices have these days.  It wasn’t so many years ago that IP phones couldn’t offer encryption due to the high CPU demands, but as each passing month goes by, the clock rates go up, new CPUs come out, while the prices go down.  Nokia advertised their new N95 smartphone recently, proclaiming that this is “what the computer has become”, and this is actually true.  The navigation computer on the Apollo moon missions had to be loaded and reloaded several times during the trip, as it only had an 8k memory to store navigation programs in.  Famously, their computer crashed several times on the first moon landing, due to data overload from the radar telemetry.  Those guys would have been happy to have a modern PDA on board, with thousands of times more power than their humble machine.

Since these phones have more power, we expect the devices to do much, much more, and the devices can suffer from feature-itis, where all kinds of bells and whistles are added, not because they are needed, but because we can do it, and cheaply.  So far from getting a device that is “just a phone”, we get all kinds of extraneous features, many of which have security implications, and in fact vulnerabilities.  Ask the average cellphone user, and you will probably find that they only know about 5% of the functions available to them, and they probably didn’t even read the (usually thin) handbook that came with it.  This is also true for VoIP phones, which normally come packed with other non-VoIP services like TFTP, FTP, LAN capture, embedded web server, network time service, and so on.  A lot of these features can be exploited when passwords are left at factory default, which they commonly are.

If we are going to make all the phones into fully-functional computers, then from a security point of view we need to make sure that each device is properly audited, and hardened, and patch-managed.  Many enterprises are not yet ready for what the computer has become.