Financial Cryptography

Rumours of Skype + SSL breaches: same old story (MITB)

Skype is the darling child of cryptoplumbers, the application that got everything right, could withstand the scrutiny of the open investigators, and looked like it was designed well. It also did something useful, and had a huge market, putting it head and shoulders of any other crypto application, ever.

Storms are gathering on the horizon. Last year we saw stories that Skype in China was shipping with intercept plugins. 3 months ago I was told by someone who was non-technical that the German government was intercepting Skype. Research proved her wrong ... and now leaks are proving her right: Slashdot reports on leaked German memos:

James Hardine writes "Wikileaks has released documents from the German police revealing Skype interception technology. The leaks are currently creating a storm in the German press. The first document is a communication by the Ministry of Justice to the prosecutors office, about the cost splitting for Skype interception. The second document presents the offer made by Digitask, the German company secretly developing Skype interception, and holds information on pricing and license model, high-level technology descriptions and other detail. The document is of global importance because Skype is used by tens or hundreds of millions of people daily to communicate voice calls and Skype (owned by Ebay, Inc) promotes these calls as being encrypted and secure. The technology includes interception boxes, key forwarding trojans and anonymous proxies to hide police communications."

Is Skype broken? Let's dig deeper:

[The document] continues to introduce the so-called Skype Capture Unit. In a nutshell: a malware installed on purpose on a target machine, intercepting Skype Voice and Chat. Another feature introduced is a recording proxy, that is not part of the offer, yet would allow for anonymous proxying of recorded information to a target recording station. Access to the recording station is possible via a multimedia streaming client, supposedly offering real-time interception.

Nope. It's the same old bug: pervert your PC and the enemy has the same power as you. Always remember: the threat is on the node, the wire is safe.

In this case, Mallory is in the room with you, and Skype can't do a darn thing about it, given that it borrows the display, keyboard, mike and speaker from the operating system. The forthrightness of the proposal and the parties to the negotiations would be compelling evidence that (a) the police want to infect your PC, and (b) infecting your PC is their preferred mechanism. So we can conclude that Skype itself is not efficiently broken as yet, while Microsoft Windows is or more accurately remains broken (the trojan/malware is made for the market-leading Microsoft Windows XP and 2000 only, not the market-following Linux/MacOSX/BSD/Unix family, nor the market-challenging Vista).

No change, then. For Skype, the dream run has not ended, but it has crossed into that area where it has to deal with actual targetted hacks and attacks. Again, no news, and either way, it remains the best option for us, the ordinary people. Unlike other security systems:

Another part of the offer is an interception method for SSL based communication, working on the same principle of establishing a man-in-the-middle attack on the key material on the client machine. According to the offer this method is working for Internet Explorer and Firefox webbrowsers. Digitask also recommends using over-seas proxy servers to cover the tracks of all activities going on.

MITB! Now, normally we make a distinction between demos, security gossip, rumours and other false signals ... but the offer of actual technology by a supplier, with a hard price, to a governmental intercept agency indicates an advanced state of affairs:

The licensing model presented here relates to instances of installations per month for a minimum of three months. Each installation of the Skype Capture Unit will cost EUR 3500, SSL interception is priced at EUR 2500. A one-time installation fee of EUR 2500 is not further explained. The minimum cost for any installation on a suspect computer for a comprehensive interception of both SSL and Skype will be EUR 20500, if no more than one one-time installation fee are required.

This is the first hard evidence of professional browser-interference of SSL website access. Rumours of this practice have been around since 2004 or so, from commercial attacks, but nobody dared comment (apparently NDAs are stronger than crimes in the US of A).

What reliable conclusion can we draw?

• the cost of an intercept is 2500 and climbing.
• the "delivery time" taken is a month or so, perhaps indicating the need to probe and inject into Windows.
• MacOSX and Linux are safe for now, due to small market share and better security focus
• Vista is safe today, for an unknown brew of market share, newness and "added security" reasons.
• Skype itself is fine. So install your Skype on a Mac (if human) or a Linux box (if a hardcore techie).

Less reliably, we can suggest:

• All major police forces in rich countries will have access to this technology.
• Major commercial attackers will have access, as well as major criminal attackers.
• Presumably the desire of the police here is to not interfere with ordinary people's online banking, which they now can do because most banking systems are still stuck on dual factor (memo to my bank: your super-duper advanced dual factor system is truly breached by the MITB).
• Nor, presumably, do they care about your reading of this blog nor wikileaks, both being available in cleartext as well. Which means the plan to install *TLS/SSL everywhere to protect all browsing* is still a good plan, and is only held up by the slowness at Apache and Microsoft. (Guys, one million phishing victims every year beg you to hurry up.)
• Police are more interested in breaching the online chat of various bad guys. So, SSL email and chat forums, Skype chat and voice.

Of course the governance issue remains. The curse of governance says that power will be used for bad. When the good guys can do it, then presumably the bad guys can do it as well, and who's to say the good guys are always good? People who have lots of money should worry, because the propensity for well-budgetted but poorly paid security police in 1st world countries to manipulate their pensions upwards is unfortunately very real. Get a Mac, guys, you can afford it.

In reality, it simply doesn't matter who is doing it: the picture is so murky that the threat level remains the same to you, the user: you now need to protect your PC against injection of trojans for the purpose of attacking your private information directly.

Final questions: how many intercepts are they doing and planning, and did the German government set up a cost-sharing for payoffs to the anti-virus companies?

Posted by iang at January 29, 2008 05:46 PM | TrackBack