alt Hacker NewsWhen comparing two ciphertexts A,B a FHE sorting function will output a sorted pair of two new ciphertexts:
E.g. FHE_SORT(A,B) -> (X,Y)
where Dec(X)<Dec(Y)
But without decoding, there's no way of knowing whether X (or Y) comes from A or B.
Source: II. D of https://eprint.iacr.org/2015/995.pdf
It’s not that simple. The client has to send the server the comparison function.
To do anything practical the server usually needs to provide the client with gigabytes of per-client-key encrypted seed data.