Author Archives: Martyn Davies

About Martyn Davies

Martyn is Principal Consultant for Weird Crater, a telecom and software consultancy.

VoIP Phone Vulnerabilities

At the IP’06 event in London recently, I heard Tom Cross of Internet Security Solutions present on VoIP Security, and some of types of threats to VoIP phones.  Those of you that have listened to the Bluebox Podcast will have heard Dan York, Jonathan Zar and Shawn Merdinger talk about the threats to phone handsets before.  Some of these devices ship from the factory in an unsafe state, with security holes like remote configuration backdoors and TFTP servers running on the phone.  Often if there are usernames and passwords they can be weak combinations like ‘1’ and 1′ or ‘root’ with no password.  Often users do not know that these back doors are open, and the software does not force you to change from default or factory passwords.

The cost of not closing these security holes is that someone could remotely hack into the phone, and once in control of the phone could trace or record phone calls; mount a denial-of-service attack such as repeatedly reboot the phone; or hijack the phone in order to make calls at your cost.  So Tom’s advice was to make sure that VoIP phones are not accessible to the Internet, so they can’t be attacked from outside.

In many ways the PBX is a dinosaur these days, since it is solving problems we no longer have.  For example VoIP phones have built in dialling directories, so we don’t need a special abbreviated dialling system inside the company; VoIP softphones can have their own voicemail functionality, so we don’t need the PBX to do that.  Also traditionally, the PBX has been the device that shares out and manages the expensive, limited resources, the telco trunk lines, and increasingly PBXes don’t need to do that either, often sitting just on a LAN or LANs.  However, thinking about Tom’s words, the security aspect is a whole new reason to buy PBXes, as any device that can limit the exposure of SIP phones to attack is going to be of benefit.

 

 

 

All Quiet On The Western Front

I just stumbled across an interesting article about the use of VoIP in the battlefield. Looking at it from a security point-of-view, you can see that they have all the problems of civilian VoIP, but the consequences of failure could be much higher.

To take some examples: A successful denial-of-service attach could disable battlefield communication; Defeating the encryption system could result in eavesdropping, and the gathering of strategic intelligence; Failures in authentication could result in an enemy posing as your troops, inserting their own disinformation, or perhaps they could make accredited troops fail to attach to the voice network. Network hijacking could also be a problem, where they piggyback on your network to use its resources and equipment to pass their own data.

Certainly a lot of threats to counter. I’ve heard it said that military technology is 10 years ahead of civilian technology. I’m hoping that’s true in this case, and that there’s a lot of good stuff that we can benefit from in the next few years.

Just Plain Cuckoo

According to news in PC Pro magazine, authorities in Switzerland have come up with an unorthodox plan to tackle call tapping of Skype and other VoIP users.  VoIP calls can be end-to-end encrypted, which means that tapping on the Internet itself is often not practical.  For example Skype use an undisclosed encryption algorithm and key exchange system.  Phil Zimmermann’s Zfone employs perfect secrecy so that the conversation cannot even be listened to later offline when the encryption key has been obtained.

So the Swiss plan?  Tap the calls on the PC, by means of installing some kind of trojan to tap into the audio stream before it is encrypted.  It would be installed either by the authorities or remotely by the ISP.

Now, this is a daft idea on so many different levels that it’s hard to know where to begin.  In an ordered society like Switzerland you could expect a high level of compliance with this kind of procedure.  Unfortunately, the ones that won’t comply (for example malevolent hackers; gangsters; terrorists) are probably the ones that you are most interested in gathering intelligence about.  Secondly, it’s a gift for criminals, since if you leave a backdoor open, the PC already compromised, then someone will likely exploit this for criminal purposes.

With the right software in place, audio could be relayed in from elsewhere, allowing criminals to make calls “on your phone”, possibly implicating you in a crime.  Similarly, audio could be relayed out, so that those outside the government service could tap your phone, a boon to tabloid newspapers and blackmailers.

Finally, in a world of ever more mobile users, is this approach even practical?  Mobile users with GPRS in their phone or PDA can connect to the Internet without even touching a Swiss ISP.  Crime doesn’t necessarily stop at borders these days, couldn’t criminals just be in and out of the country before the G-Man sneaks some tapping software onto their laptop?

 

 

Talk to the Hand

We’ve written here before about Phil Zimmermann’s Zfone and the ZRTP protocol, but what exactly does an encrypted phone call sound like?  Well, here is a sample, captured with Wireshark and converted to MP3 for your audio pleasure with Goldwave.

Now, if only Mr. Schwarzenegger can find a way to apply the same encryption to all of his MP3 recordings… 

 

Hello Mom, I’m a Fake

It’s with some gloom that I look at these new services that use VoIP technology to fake your Caller ID. The first one I came across was FakeCaller, but others like Telespoof are arriving every day.

FakeCaller presents itself as a bit of fun (and ominously has a ‘pranks’ tab at the top of the welcome page, although no content there as yet). The notice at the bottom of the page suggests that you shouldn’t use it for harassment and stalking, or use foul language in the voice messages you send. But I ask you, what legitimate purpose could there be for a system that allows you to lie about your name and caller ID, and sent a computer speech message down the phone when they answer?

Telespoof think that their customer base is those who lie as part of their everyday work, even down to how you appear on the phone. I would have thought that simply restricting the display of your number (as you can on most cellular and landline systems these days by entering a code) would be enough. Perhaps that mean anonymous in a more insidious way, i.e. anonymous even to law enforcement and security forces.

I’m not sure how we got into this situation that VoIP telcos should be able to ‘opt out’ of the caller ID system, but overnight the whole concept of caller ID has become useless and unreliable. When I received a sales call from a company selling satellite TV warranties recently, they gave me the hard sell, suggesting that my Sky box was out of warranty and likely to fail at any minute. Small matter that I don’t have a box, but occasionally they must hit someone that does. Such a company could have no restraint in lying about their name and caller ID if it helped to close a sale.

This all just means more opportunities for mis-selling, phishing, faking, defrauding and otherwise messing with people, and I can’t see how anyone could be in favour of it.

Double Ending

Martin Geddes recently reflected on the use of Skype as a tool for recording podcasts with two people in different locations.  This is a technique that is used on many podcasts now, including Blue Box, the VoIP Security Podcast.  But as Geddes says, sometimes the quality is not all it should be, and it would be useful to be able to record in top quality, and in some way transmit this out-of-band, while using the inferior, real-time audio between the two podcasters.  Sometimes this technique (called double-ending, or a “double ender”) is done manually today in podcasting and in radio: each person records their end of the conversation locally, then the files get spliced together at the end to make a broadcast quality programme.  The telephone call only needs to be good enough for the two people to understand each other while the interview is taking place.

But adding double-ending functionality in Skype has interesting possibilities, apart from the podcasting one.  In some areas human speech needs to be understood by less tolerant parties than humans, for example in the areas of automatic speech recognition, or speaker verification.  Given that VoIP streams can be of cellphone quality (or lower), it could be useful for a computer system to be able to play back a passage of speech it was having trouble with.  For example, a speaker verification system might listen to the live VoIP speech, perhaps match with a certainty of 20%, then after a few tens or hundreds of milliseconds it could try again using extra hi-fidelity information that came in while it was processing the first time.  Much better than forcing the user to re-speak their passphrase over and over until the computer figures it out.

On the subject of Dan York (of Blue Box) and Martin Geddes, you can almost see them in this photograph from Fall VON.  York is moving at speed, presumably in order to eclipse Geddes.

Schneier Honoured

Catching up on my reading, I see that Dr Dobb’s Journal honoured crypto guru Bruce Schneier in their April edition with an excellence in programming award.  I’ve been a fan of DDJ since I first came across the magazine in the 1980’s, and (with my software developer hat on) once even had the thrill of contributing to DDJ.

Congratulations, Bruce, coming from one of the World’s top-rank developer publications, I think this is an accolade to really enjoy.Â