To be fully homomorphic the code has to be such that a third party can add and multiply numbers that it contains without needing to decrypt it. In other words they can change the data by working with just the encrypted version. This may sound like magic but a fully homomorphic scheme was invented in 2009 by Craig Gentry. This was a step in the right direction but the problem was that it is very inefficient and computationally intensive. Since then there have been a number of improvements that make the scheme practical in the right situations
Now Victor Shoup and Shai Halevi of the IBM T J Watson Research Center have released an open source (GPL) C++ library, HElib as a Github project https://github.com/shaih/HElib. The code is said to incorporate many optimizations to make the encryption run faster.
Homomorphic encryption has the potential to revolutionize security by allowing operations on data without the need to decrypt it."
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