Skype won't say if it decrypts VoIP calls

Network World - The encryption of Skype voice-over-IP (VoIP) phone calls might not be as secure as you think.

It's possible the company keeps keys so law enforcement authorities can decrypt encrypted VoIP phone calls, according to a report, but Skype won't say for sure one way or the other. (Compare IP PBXs.)

According to an online report, Austrian officials with legal authority to tap VoIP phone communications have no problem listening in on Skype calls, which are encrypted as a standard part of Skype service.

A Skype spokesman wouldn't say whether Skype keeps keys to decrypt calls. "Sorry, Skype does not comment on media speculation," said Skype vice president Chiam Haas.

It's virtually impossible to figure out for sure from independent research whether Skype keeps encryption keys or not, said David Endler, chairman of the Voice Over IP Security Alliance and senior director of security research at TippingPoint.

"No one has shown it publicly," he said. "Skype is a closed software package, essentially a black box." The company has on rare occasions allowed outside researchers to examine and verify the security of its encryption, but not whether the keys that can crack the encryption can be retrieved, he said.

To allay fears that the calls might not be secure from law enforcement, Skype should open its platform to evaluation by trusted, credible industry experts, he said.

Endler said it's equally difficult to know whether commercial VoIP vendors leave open the possibility of turning encryption keys over to law enforcement.

In the U.S., the Communications Assistance for Law Enforcement Act (CALEA) forbids requiring that vendors build in back-door decryption, said Jim Dempsey, vice president for public policy at the Center for Democracy & Technology. "CALEA expressly forbids requiring anyone to be able to decrypt anything," he said.

But that doesn't mean they don't build in key-retrieval anyway. Dempsey said there are no active proposals to force vendors to leave encryption back doors in their VoIP gear, but that could change. "Nothing in regulations is permanent," he said.

Endler said that attempts by researchers to learn more about how Skype works have been effectively blocked by measures put in place by Skype. "They've taken extreme measures to prevent reverse engineering of their client software," he said, more so than mainstream VoIP vendors.