[VOIPSEC] Soft Phone Vulnerabilities

[Yaron Sheffer]

Hi Craig,

Although in principle I support the "open is more secure" argument, I have to add that you are only half-right on the specific case of GSM. In GSM the protocols are indeed open, but the crypto algorithms are (still!) secret. They have been reverse-engineered and then broken.

The situation is better for 3G (UMTS).

BTW, there are some underlying design issues even with UMTS ciphering (stream ciphers, encryption but no authentication) so I wouldn't be surprised to hear news on this front, too.

Thanks,
	Yaron 

> -----Original Message-----
> From: Craig Southeren [mailto:craigs at postincrement.com] 
> Sent: Friday, June 9, 2006 3:02
> To: Jon Callas; Voipsec at voipsa.org
> Subject: Re: [VOIPSEC] Soft Phone Vulnerabilities
> 
> On Thu, 8 Jun 2006 11:34:25 -0700
> Jon Callas <jon at pgpeng.com> wrote:
> 
> ..deleted
> 
> > Actually, that's been documented rather well. I understand 
> how Skype 
> > works much better than I understand how a Nokia 6230 tied 
> to Cingular 
> > works, network-wise.
> 
> I don't share your understanding.
> 
> We have *one* document on the internals of Skype that was 
> written by a team that had to reverse engineer the 
> information. That's all we have.
> It may be correct, or it may not - again we have no way of 
> knowing for sure.
> 
> GSM moble phones are written to interoperable specifications 
> that have been around for years, and have been implemented by 
> multiple vendors. If you want to know how any part of a GSM 
> network operates, just go and get the specification. It won't 
> be easy to understand (a GSM network is
> complicated) but the information is all available. The same 
> applies to a SIP network or a H.323 network.
> 
> > Nonetheless, you are correct in saying that we have much better 
> > knowledge of the details of GSM cryptography than we do of Skype's.
> > However, what we know about GSM crypto is that it's crap.
> 
> Thanks for proving my point!
> 
> The lack of security in GSM is well known because it was 
> proven by peer review. We have no way of knowing if the 
> security in Skype is crap because it can't be peer reviewed.
>  
> > My point is that the alternative to Skype -- a cell phone 
> -- doesn't 
> > have better security.
> 
> We also have no way of knowing if Skype is better than GSM :)
> 
> ..deleted
> 
> > I don't have the alternative of free software products. My 
> cell phone 
> > is not open software. I have far less knowledge of its 
> internals than 
> > I do of Skype.
> 
> This is due to a lack of research, not a lack of available 
> information.
> 
> > >  - no possible control by a network administrator of the 
> working of 
> > > the software[3].
> > >
> > 
> > Unlike those mobile phones?
> 
> The attributes of a GSM mobile network are well known because 
> they are based on public and interoperable standards. Given 
> sufficient time, anybody or company can create a GSM mobile 
> handset, or base station, and have it work with anybody 
> else's equipment. It might not be technically wonderful, but 
> everyone can find out how it works.
> 
> Skype is a closed standard. We have no idea if the protocol 
> is crappy or not, because it is not open. Obviously Skype has 
> licensed the protocol to other vendors, but also just as 
> obviously these vendors are prohibited from disclosing that 
> information.
> 
> ..deleted
> 
> > I think you're completely missing my point.
> > 
> > The point is that whatever we may not like about Skype, it is not 
> > worse and often better than the alternatives.
> 
> If you are are talking about the user experience, then I 
> agree with you.
> 
> If you are talking about the design of the system, then I 
> cannot agree with you because there is insufficient 
> information to make this evaluation.
>  
> > if you say that you're going to disallow Skype because it's doing 
> > stuff on the network that you don't control, I think that's silly, 
> > because if you ban Skype, they'll use a mobile phone. You have less 
> > knowledge and control on the GSM network, and the cryptography is 
> > known to suck so badly it can be broken in realtime.
> 
> And you know this because the GSM specs have been peer 
> reviewed and found lacking. For all you know, the Skype 
> protocol could be breakable in real-time too, making it just 
> as "crappy".
>  
> > If you're going to ban Skype because it's running on a PC 
> that could 
> > have malware, it ignores software issues on mobile phones 
> and software 
> > issues on other VOIP phones. We are switching our local 
> infrastructure 
> > over to Cisco VOIP phones, which are also at the bottom -- software.
> 
> Again, comparing apples and oranges.
> 
> Software running on a purpose-built appliance such as GSM 
> phone, or a Cisco Phone, or Skype handset for that matter, 
> will usually be more reliable than software running in the 
> wild ecosystem that is a general purpose PC. 
> 
> All of which has nothing to do with how secure Skype is :)
>  
> > If you're going to ban Skype because it's VOIP and VOIP is 
> inherently 
> > less secure than POTS, then that is the best reason I know 
> of to ban 
> > it. The argument has its own problems, but it's a better 
> argument than 
> > many I've heard.
> 
> I also agree this is a sensible argument. Many companies I 
> know of will not use VoIP unless it is over a known secure 
> transport such as IpSec or a private network. I certainly 
> make this clear to companies I do business with.
>  
> ..deleted
> 
> > If you're worried about the security of running Skpye on a 
> PC, it's a 
> > valid complaint, but it's a complaint applicable Gizmo, 
> EyeBeam, etc.
> > The problem isn't a *Skype* problem. it's a problem with 
> running VOIP 
> > on a PC.
> 
> The difference is that those networks are not claiming to be 
> secure and encrypted. Skype is - but they provide no means to 
> verify that claim cryptographically. The same argument 
> applies to any closed source VoIP network.
>  
> ..deleted
> 
> > So I'll repeat my question -- what are the problems with Skype that 
> > are unique to Skype? I have my answers to this question (which I 
> > haven't stated at all). I'm not a Skype fan. But I'm not an enemy, 
> > either. The more I see of it, the more I am willing to tolerate it, 
> > and that in itself makes grumpy because I think they should 
> just hire 
> > some people to come out with an Inside Skype book. Heck, they could 
> > present it at some $1000/day conference and I'd be there in 
> a heartbeat.
> 
> My problem with Skype is very simple. 
> 
> They claim to provide a secure network, but they provide no 
> means to verify that claim. Given that they also claim to be 
> peer to peer, there are reasons to doubt their claim to 
> security. They are using this claim to distinguish their 
> product from competitors, and naive users are believing them. 
> 
> I'll certainly not be trusting their claims of security until 
> I have them verified by peer review. Until then, I'll 
> continue to use Skype (or MSN, or Yahoo or unencrypted SIP or 
> unencrypted H.323) but not for anything that I would not say 
> over the PSTN or cell phone networks.
> 
> History shows that networks developed behind closed doors are 
> very rarely secure, and I strongly suspect that in the end 
> Skype will prove to have some similar flaw. 
> 
>    Craig
> 
> 
> --------------------------------------------------------------
> ---------
>  Craig Southeren          Post Increment ? VoIP Consulting 
> and Software
>  craigs at postincrement.com.au                   
> www.postincrement.com.au
> 
>  Phone:  +61 243654666      ICQ: #86852844
>  Fax:    +61 243656905      MSN: craig_southeren at hotmail.com
>  Mobile: +61 417231046      
> 
>  "It takes a man to suffer ignorance and smile.
>   Be yourself, no matter what they say."   Sting
> 
> 
> 
>