CKKS multiply experimental feature doesn't work correctly when integrated with SEAL

[Tomas Gonzalez Aragon]

When trying to integrate the HEXL experimental features into SEAL, I found that it's not giving me the correct results.
I'm not sure if I'm doing something wrong or if there is an error in the CKKS multiply implementation of HEXL.

How to reproduce:

git clone https://github.com/tgonzalez89-intel/SEAL.git
git checkout hexl-ckks-mult-bug
./build.sh
cd build/bin
./sealtest

Observe that the tests fail.

You can run git diff 3.7.2 to observe the changes I made to SEAL in order to integrate HEXL's CKKS multiply.

[Jose Rojas Chaves]

Hello @tgonzalez89-intel I have debugged test CKKSEncryptNaiveMultiplyDecrypt in SEAL and I found out that the HEXL method is not working fine when operand1 and operand2 are a pointer to the same ciphertext. The same thing should be happening in CKKSEncryptSquareRelinDecrypt where in place multiplication is also called in the following way:

evaluator.multiply_inplace(encrypted, encrypted);

Thanks for spotting this. We will be fixing this on HEXL.

[Tomas Gonzalez Aragon]

Created PR with fix (#98)