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What threats does Skype face?

The Internet phone company's security chief takes stock of IM worms, encryption and other matters.

In late December, a security firm sent out an alert that a worm was spreading via Skype. It turned out to be a false alarm.

No worm has spread on Skype, and while security experts have painted a target on the popular Internet telephony application, its defenses have been pretty solid, according to the company's chief security officer, Kurt Sauer.

That's not to say there is no work to be done on security at Skype, part of eBay. The company is looking at integrating payment features, which obviously need securing, Sauer said. Also, Skype is in talks with security companies to provide add-ons to its software to secure text-based communications, he said.

Skype is often described as a boon for security because all calls are encrypted and there is no central server that could be targeted in a cyberattack. However, the application has also caused headaches for many IT administrators because it can find ways to make a Net connection despite strong firewall controls on corporate networks.

Sauer took a break from Skype security for an interview with CNET News.com, accompanied by Chief Operating Officer Michael Jackson.

Q: What do you do as chief security officer for Skype?
Sauer: I came to Skype three years ago. I came from Sun Microsystems, where I was doing work on peer-to-peer authentication. I came to audit the cryptography work that had been done in the Skype client as it existed. Since then, I've taken on the role of overseeing the security architecture of the Skype product family. That's grown into also dealing with incident response for security vulnerabilities. Since the acquisition by eBay, I also look at things like Sarbanes-Oxley compliance for security.

How significant a part of your job is dealing with security vulnerabilities in the Skype client?
Sauer: There are teams of people who are responsible for dealing with a lot of the nuts and bolts. Security of the architecture and where we're driving the product probably takes up about half my time. The other half is spent on compliance-related issues.

Do you see any exploitation of any security flaws in the Skype client? Have Skype users been under attack?
Sauer: We have not had any known exploitation of Skype vulnerabilities. Vulnerabilities divide themselves into different categories and we have not seen attack vectors in Skype's products that allow worms or viruses to replicate. Instead, they have tended to be one-off problems that can cause Skype to fail.

There have been several bugs related to the Skype URL, where clicking on a malicious link could cause a PC to be compromised. Were these issues all reported to you privately?
Sauer: Yes. I had experience with security vulnerability response work when I was at Sun. What I wanted to bring to Skype from that experience was transparent communication with vulnerability reporters.

I don't think that we're ever going to be able to say that we're done tinkering with how we ensure the quality of our software.

One of the ways that you can really piss off the security researcher community is to be completely opaque, not say anything back. Some researchers don't want to talk to you, but to the extent they want to engage in a dialogue, we try to do that.

If you look at the robustness of the Skype code, would you say it has become much better over the years you have been with the company?
Sauer: Close to three years ago we had problems in our quality assurance process. We were working on building code tests and unit testing to improve the quality of the code. Things that happened between a year and two years ago turned into a need for better organization of the actual code development. So now I've introduced a lot more peer review over software before it gets to the final release.

Processes to make sure the software gets out is as flawless as it can, you feel those have all been established now?
Sauer: I don't think there's any organization that can't learn. I don't think we are the perfect software engineering organization. With each level of additional control, there is a certain amount of cost and time. You have to make rational decisions about how much overhead you're willing to place in the product development cycle. I don't think that we're ever going to be able to say that we're done tinkering with how we ensure the quality of our software. But having peer review is actually one of the best defenses to bad code that you can have because people don't ever want to show crappy code to a co-worker.

Flawed code isn't the only way users could get hit. We've seen worms hit all the popular instant-message tools. Is that a threat for Skype, too?
Sauer: I haven't seen any. You can't send executable code through a chat. A lot of what IM clients are going through is figuring out how to properly protect users against things like attacks against browsers that are launched through links. To that extent, we're looking at how we can partner with companies like antivirus vendors.

Symantec and, I think, McAfee have products that do things like doing risk scoring for links. It would be a really interesting thing for us to allow for a third-party specialist application to be able to make risk assessments of things like link content to help users make informed choices. We're certainly in active discussions about how we could do that.

Some security experts have predicted that Skype could be used as a way for hackers to remotely control networks of compromised computers, botnets. Have you seen that happen?
Sauer: I haven't, but you can certainly use Skype for application-to-application messaging. I'm not going to say you can't do that, but we have not seen instances of that happening. We do think that the Skype client has sufficient controls to prevent things like auto spreading because of the current authorization model. For example, I can't send you a file unless you've authorized it.

Have you seen any proof-of-concepts of malicious software that targets Skype?
Sauer: We've had some security researchers share concepts of things in the past. They were just simple ideas that we agreed not to disclose.

Some folks see Skype itself as a security threat, especially in businesses with controlled environments. Skype can find its way outside of the corporate firewalls even if IT people try to hammer it shut. Is Skype a security threat?
Sauer: That's what the most recent copy of our network administrator guide and Skype 3.0 is all about. It's trying to provide controls that let IT administrators run their networks the way that they want to.

A lot of administrators have objected to users coming in and installing Skype on a desktop. One place like that is eBay, it was amusing when we had the acquisition.
A lot of administrators have objected to users coming in and installing Skype on a desktop. One place like that is eBay, it was amusing when we had the acquisition. I came out and popped in to talk to the IT people who where all stunned because they were trying to keep Skype out. eBay has been a really good learning opportunity for us about how a business that is not Skype would use Skype in their business. One of the things that eBay expressed was a strong desire to be able to push out policies and allow those policies to be.

You touched upon encryption, which people and even certain countries are concerned about because they want to control what kind of communication goes on. How do you deal with that, have you ever caved and given anybody the encryption keys to Skype?
Sauer: Since we don't have the encryption keys, therefore we can't give them to somebody.

So even you can't listen on my Skype calls?
Sauer: The way that Skype works is that the people who are communicating communicate on a secure channel between themselves with keys that are generated by them and not generated by Skype.

So the answer to the question--if even you can't listen on somebody's Skype calls--is...?
Sauer: What we say to that is that we provide a safe communications experience. I'm not going to tell you that we can or can't listen in to that.

And you don't provide government, or any agency or any company, a way that they could listen in on Skype conversations.
Sauer: We don't.

Skype is offering more paid services, such as SkypeOut for calls to regular phones. Recently I've heard complaints from Skype users who had their credit card payments declined, even though their card was good. Are you experiencing a fraud increase?
Sauer: Anybody who sells nontangible goods with value is a target for fraudsters. I've had friends of mine contact me about this very sort of thing. We don't publish how we do it, but it is our protection mechanism. I'm not going to tell you what our precise method of protecting credit cards is, but I will say that if you're going to use the same credit card on a bunch of accounts, it's probably not going to work.

Is there an increase in fraud? Is it a major concern for you?
Jackson: It's a concern because it's a pain in the ass. We have an antifraud algorithm to trap the people who are cheating us, but it traps a lot of good users as well. It is a very fine balance that does affect the business itself because we're declining a lot of good transactions and pissing regular users off.

Rounding out Skype and security, what is your major concern, what keeps you up at night?
Sauer: The thing that keeps me up at night is our future development activity. We have a lot of new initiatives. We talked about things like adding the ability to send money to Skype. These are new areas that bring with them new consumer risks, so we have to work closely within our engineering teams to make sure we have total buy-in on how we're going to do something so that we don't mis-engineer anything.