Hide unused coefficients after inner products

[naure]

Following #81

After the polynomial product, only some coefficients contain the desired outputs, that is the inner products. Other coefficients may reveal information about input, which should be removed before decryption or further processing.

One way to do that is to add a blinding polynomial, with zeros at the location of outputs, and random coefficients at the locations to hide. Find the locations here in accumulate_inner_products(…).

Tasks

• Generate the blinding polynomial.
• Encrypt it.
• Add it to the ciphertext of outputs.