Homomorphic encryption: Answers

Having considered the questions raised in the homomorphic encryption tutorial, let’s share our answers.

Diagram of homomorphic encryption process by David Butler

1. The third party gets to see the medical data. This may be okay if they can be trusted, but it is not ideal that anyone else is able to see the data. There is also another problem with this method. When the data is decrypted by the third party it is all in one place and not encrypted and thus vulnerable to being hacked — this situation is not ideal.
2. FHE requires one to be able to compute additions and multiplications on ciphertexts. PHE allows for one of these operations to be performed on the ciphertexts or another subset of functions, but not all functions. There are more encryption schemes that achieve PHE, however it is not always enough to only be able to compute one operation on ciphertexts, as it greatly limits what functions can be computed.

This article was written by David Butler, one of the course creators and teachers at Oxbridge Inspire. David is studying for a PhD at the Alan Turing Institute in London.

If you enjoyed this article, you might consider coming to our course in Cambridge this summer on the Mathematics behind Cryptography.