Apple says it has end-to-end encryption for iMessage and FaceTime communications, but users should not interpret that as providing an ironclad defense against government snooping.
Apple made the disclosure late Sunday in releasing the number of user-information requests made by U.S. authorities, including intelligence agencies, from December through May. In releasing the figures, Apple joined Facebook, Google and Microsoft, which have taken similar steps to ease customers' privacy concerns.
The need to soothe customer jitters followed the revelation that the National Security Agency (NSA) was gathering massive amounts of customer data, including email and chat messages, from Internet companies as part of a wide-ranging surveillance program meant to catch terrorists.
Apple's privacy protection appeared to go further than rivals, because of the company's claim that "there are certain categories of information which we do not provide to law enforcement or any other group because we choose not to retain it."
"For example, conversations which take place over iMessage and FaceTime are protected by end-to-end encryption so no one but the sender and receiver can see or read them," the company's statement said. "Apple cannot decrypt that data."
Apple customers concerned with government spying should not take comfort in the protection the company provides. That's because under the Communications Assistance for Law Enforcement Act (CALEA), Apple "must provide law enforcement access tools," said Chris Hoofnagle, director of Information Privacy Programs at the University of California, Berkeley.
"Additionally, there are export control considerations -- some encryption cannot be exported to certain countries," he said.
Apple won't provide security experts with details of its encryption architecture, so what it means by "cannot decrypt" data is unclear, said Matthew Green, assistant research professor and cryptography expert at Johns Hopkins University, said.
"Some people are arguing that they can't do it [decrypt], and other people are saying they could do it if they wanted to, but they have policies in place that won't let them do that stuff," Green said. "There are a lot of questions as to what exactly they mean."
No matter how Apple designs iMessage, its messaging service, and FaceTime, the Skype-like voice over IP service, there has to be keys for encrypting and decrypting the information flowing between senders and receivers.
A possible scenario is that each Apple device has its own private and public key, the latter of which is accessible to Apple, but can only encrypt data. When someone wants to send a text message, that person's device gets the public key of the recipient's device. The key is used to encrypt the information, which only the receiving device can decrypt.
Under a court order, Apple could easily gain access to the communications by issuing a different public key, Green said. "At the stage where the person says I want to send a message to you, Apple has to be trusted to actually hand that person your public key, and not the public key of the FBI."
Another scenario would be to have each device with its own private keys for encrypting and decrypting data, so Apple would not hold anything. However, since people can set up iMessage or FaceTime on multiple Apple devices, there is nothing stopping the company from using a customer's credentials to set up the services on another computer to intercept communications, Green said.
Also unclear is how Apple uses iCloud backup. If iMessages are stored on a cloud server, then it is possible law enforcement could get access through that computer, Green said.
Bottom line, while end-to-encryption sounds good, it does not mean communications cannot be intercepted.
"They built something [iMessage] that's very easy to use, but unfortunately, doesn't provide you with bulletproof privacy," Green said. "So I'm kind of waiting for Apple to maybe give some clarification about what they do."