Secure, User-controlled Data

Estimated reading time: 4 minutes

Wang developed an interface that displays a Sieve user’s data items as a list and allows the user to create and label icons that represent different attributes. Dragging a data item onto an icon assigns it that attribute. At the moment, the interface is not particularly user friendly, but its purpose is to show that the underlying encryption machinery works properly.

Blind manipulation

Key homomorphism is what enables Sieve to revoke an app’s access to a user’s data. With key homomorphism, the cloud server can re-encrypt the data it’s storing without decrypting it first — or without sending it to the user for decryption, re-encryption, and re-uploading. In this case, the researchers had to turn work that was largely theoretical into a working system.

“All these things in cryptography are very vague,” Wang says. “They say, ‘Here’s an algorithm. Assume all these complicated math things.’ But in reality, how do I build this? They’re like, ‘Oh, this group has this property.’ But they don’t tell you what the group is. Are they numbers? Are they primes? Are they elliptic curves? It took us a month or so to wrap our heads around what we needed to do to get this to work.”

Of course, a system like Sieve requires the participation of app developers. But it could work to their advantage. A given application might provide more useful services if it had access to data collected by other devices. And were a system like Sieve commercially deployed, applications could distinguish themselves from their competitors by advertising themselves as Sieve-compliant.

“Privacy is increasing in importance and the debate between Apple's iPhone encryption and the FBI is a good example of that,” says Engin Kirda, a professor of electrical and computer engineering at Northeastern University. “I think a lot of users would appreciate having cryptographic control over their own data.”

“I think the real innovation is how they use attribute-based encryption smartly, and make it usable in practice,” Kirda adds. “They show that it is possible to have private clouds where the users have real privacy control over their data.”