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Innovative encryption scheme secures cloud

Posted: 13 Jun 2013 ?? ?Print Version ?Bookmark and Share

Keywords:homomorphic encryption? cloud computing? functional-encryption scheme? garbled circuit?

Researchers from MIT's Computer Science and Artificial Intelligence Laboratory, together with colleagues at the University of Toronto and Microsoft Research, have revealed an encryption scheme that takes advantage of homomorphic encryption. The technology, seen as having the potential to secure cloud computing, allows a Web user to send encrypted data to a server in the cloud, which would process it without decrypting it and send back a still-encrypted result.

Homomorphic encryption ensures that the server has no idea what the search term is or which records match it. As a consequence, however, it has no choice but to send back information on every record in the database. The user's computer can decrypt that information to see which records matched and which didn't, but then it's assuming much of the computational burden that it was trying to offload to the cloud in the first place.

Known as a functional-encryption scheme, it allows the cloud server to run a single, specified computation on the homomorphically encrypted result!asking, say, "Is this record a match?" or "Is this email spam?"!without being able to extract any other information about it.

"This is a very, very general paradigm," said Shafi Goldwasser, the RSA professor of electrical engineering and computer science, one of the paper's co-authors and, together with her fellow MIT professor Silvio Micali. "Say we're talking about the surveillance cameras of the future, which come up with encrypted images. Why would we want to do that? It's a question of liberty versus safety. If you're looking for a suspect, you might be interested in doing some computations on an encrypted image, to match to the subject. Another possibility would be a medical database, where all the information is encrypted and... someone [runs] a drug study on those blood samples!but just that drug study, nothing else. Our result is in some sense the first result showing that you can do this very generally."

Joining Goldwasser on the paper are Raluca Ada Popa, a graduate student in the department of electrical engineering and computer science, her advisor, associate professor Nickolai Zeldovich, and Yael Kalai of Microsoft Research and Vinod Vaikuntanathan of the University of Toronto, both of whom did their graduate work at MIT with Goldwasser.

The researchers built their functional-encryption scheme by fitting together several existing schemes, each of which has vital attributes of functional encryption, but none of which is entirely sufficient in itself. The first of those is homomorphic encryption.

Another is what's known as a garbled circuit, a technique developed in the mid-1980s and widely used in cryptography. A garbled circuit lets a user decrypt the result of one cryptographically protected operation on one cryptographically protected data item!say, "Is this record a match?" The problem is that, if the garbled circuit is used on a second data item!"How about this record?"!the security breaks.

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