Hello, everyone,

I am new to Homomorphic Encryption and try to use HElib to implement a complex neural convolutional network. Retrieving an
entry on the certain position of the cipher text vectoris a very common and useful operation. It can be implemented by multiplying a zero-one vector, but very expensive.

I read Shai Halevi's paper Algorithms in HElib which discussed zero-fill shift. The paper gave me the feeling that the shift operation can be achived with a lower cost.

I found HElib really provided zero-fill shift operation, so a masking can be achieved by two shifts and one rotation, i.e., suppose position is i (zero-based), shift left i, shift right n-1, and rotate right n-1-i. However, the experimental code I wrote showed the shift operation is more expensive both in noise budget (like multipication) and speed (like rotation).

So, is there a cheap method to do zero-one masking in HElib? Or do I have any misunderstanding?

Thank you very much,

Steven