STE WILLIAMS

Microsoft Patent Points to Snooping

A new Microsoft patent points towards Skype becoming equipped for lawful interception, which could be important as the service grows up to challenge traditional telcos.

The patent was filed back in 2009, but granted last week and picked up by Computerworld. Titled “Legal Intercept”, it covers one way in which a VoIP-based communications system might enable a call to be intercepted and covertly recorded, naming Skype as one of the services to which it could be applied.

Microsoft bought Skype back in May, but only received approval for the deal in June – so hasn’t had much time to do anything with the VoIP leader. Skype is hugely successful, with 170 million registered users, but it’s been very secretive about its protocols and security, refusing interoperability and asking users to just trust in Skype for their security.

That won’t wash in the real world, and neither will denying governments the right to listen in on their citizens. Most of us accept that security forces need to occasionally tap into phone lines, hopefully with suitable judicial oversight, but Skype’s apparent reluctance to permit such taps has resulted in rumours of secret deals and government-backed attacks on the cryptography used to protect Skype calls.

The patent describes how client, or network, software can be surreptitiously alerted that incoming and/or outgoing calls are to be monitored for a specific user. Such calls are then copied (packet by packet) to the monitoring server without the user being aware. The patent suggests the interception software could be placed in a NAT or router, but also incorporated into the VoIP client itself.

India has made it clear that Skype risks being kicked out of the country unless it sorts out some sort of lawful intercept capability, and other countries will be quick to follow India’s lead. So if Microsoft wants to see Skype spreading around the world then it will need to have just what’s described in the Legal Intercept patent.

Citizens aghast that their VoIP calls could be intercepted might be annoyed, but they’d be better off petitioning their governments, rather than raging against the companies trying to obey the law.

  • 29/06/2011
  • adm

Linguists Use Sounds to Bypass Skype Crypto

Decryption is difficult and computationally expensive. So what if, instead of decrypting the content of a message, you found a correlation between the encrypted data and its meaning – without having to crack the code itself?

Such an approach has been demonstrated by a group of University of North Carolina linguists working with computer scientists on encrypted Skype calls. While their research paper only managed to partially recover conversations, an encryption scheme that leaks even some of the data it’s meant to protect is no longer secure.

It works like this: spoken English has a set of known – and quite settled – rules for its phonetic grammar.

For non-linguists, this means the order in which we can and cannot put different sounds together. The “ds” sound, or phoneme, at the end of sounds is fairly common at the end of English words, but doesn’t occur at the beginning.

Systems like speech-to-text converters use these rules to break strings of sounds into individual words; they match sounds against a dictionary of legal phoneme combinations and map these into words. What the researchers discovered is that encryption leaves a pattern that can be subjected to this kind of analysis – without decrypting the data.

When you encode spoken English for VoIP using (in the case of Skype) CELP (code excited linear projection), you will end up with patterns in the data that match the patterns in the sounds. In particular, those patterns end up being reflected in the size of the data frame: the more complex the sound that’s being encoded, the larger the frame, resulting in a correlation between frame size and the original sounds spoken.

When the data created by CELP is encrypted, it retains the original frame size – and that means that even encrypted Skype data will retain the correlation between the size of the data frame and the original phonemes.

The technique gets another helping hand: at least some of the time, boundaries between sounds correspond to sudden changes in frame size, hinting at the difference between “Han Solo” and “Hans Solo”.

The researchers mapped the size of encrypted data frames in the Skype stream back to likely patterns of phonemes, and used that mapping – which they called “Phonetic Reconstruction” – to reconstruct the call, without decrypting the data.

So how well does it work? Not so well that we should all abandon Skype tomorrow. However, the researchers noted that if an encryption scheme is to be considered secure, “no reconstruction, even a partial one, should be possible; indeed, any cryptographic system that leaked as much information as shown here would immediately be deemed insecure.”

Bigger phoneme-word dictionaries (covering more dialects and languages) and faster processing would improve the accuracy of this kind of analysis.

Source

  • 02/06/2011
  • adm

Skype Vulnerability Gives Remote Access to Mac OSX Systems

Mac users running Skype are vulnerable to self-propagating exploits that allow an attacker to gain unfettered system access by sending a specially manipulated attachment in an instant message, a hacker said.

“The long and the short of it is that an attacker needs only to send a victim a message and they can gain remote control of the victim’s Mac,” Gordon Maddern of Australian security consultancy Pure Hacking blogged on Friday. “It is extremely wormable and dangerous.”

The vulnerability, which Maddern said isn’t present in the Windows or Linux versions of the popular VoIP program, was confirmed by Skype spokeswoman Brianna Reynaud, who said a fix will be rolled out next week. Its disclosure comes the same week that researchersdiscovered a new crimekit that streamlines the production of Mac-based malware. It also comes as new malware surfaced for Apple’s OS X that masquerades as a legitimate antivirus program.

Reynaud said there are no reports that the Skype vulnerability is being actively exploited.

Maddern said he stumbled on the critical flaw by accident.

“About a month ago I was chatting on skype to a colleague about a payload for one of our clients,” he wrote. “Completely by accident, my payload executed in my colleagues skype client. So I decided to test another mac and sent the payload to my girlfriend. She wasn’t too happy with me as it also left the her skype unusable for several days.”

He then set out to write proof-of-concept attack code that used payloads borrowed from theMetasploit exploit framework. The result: a Skype exploit that allows him to remotely gain shell access on a targeted Mac. Because it’s sent by instant messages, it might be possible to force each infected machines to send the malicious payload to a whole new set of Macs, causing the attack to grow exponentially.

Maddern didn’t say what interaction is required on the part of the victim, and he didn’t immediately respond to an email seeking clarification. His blog post says he notified Skype of the vulnerability more than a month ago, and that he will withhold specific details until a patch is released to prevent malicious attacks.

According to a post on the Skype Security blog that was published a few hours after this story went live, a hotfix for the vulnerability was released in mid April.

“As there were no reports of this vulnerability being exploited in the wild, we did not prompt our users to install this update, as there is another update in the pipeline that will be sent out early next week,” Skype’s Adrian Asher wrote.

He added:

This vulnerability, which they blogged about earlier today, is related to a situation when a malicious contact would send a specifically crafted message that could cause Skype for Mac to crash. Note, this message would have to come from someone already in your Skype Contact List, as Skype’s default privacy settings will not let you receive messages from people that you have not already authorized, hence the term malicious contact.

 

  • 08/05/2011
  • adm