Homomorphic Encryption - Cloud Computing compatible with Privacy

Suppose that you want to delegate the ability to process your data, without giving away access to it. Craig Gentry at the IBM T.J. Watson Research Center shows that this separation is possible.

He describes a fully homomorphic encryption scheme that keeps data private, but that allows a worker that does not have the secret decryption key to compute any (still encrypted) result of the data, even when the function of the data is very complex. 

In short, a third party can perform complicated processing of data without
being able to see it. Among other things, this helps make cloud computing compatible with privacy.

http://crypto.stanford.edu/craig/easy-fhe.pdf