I have a CKKS ciphertext containing [a, b, c, d] and I want to get these 4 ciphertexts : [a, a, a, a]; [b, b, b, b]; [c, c, c, c]; [d, d, d, d].
Is there a more efficient way than repeating the following process for each slot:
- multiplying it with a binary mask [1, 0, 0, 0] to obtain [a, 0, 0, 0]
- (rotate & add) 3 times each the multiplied ciphertext to get [a, a, a, a]
I was advised to look at multiplication with a specific polynomial, do you have some ideas ?
Thank you in advance
NB: I called it ciphertext extension as I didn't came up with a more precise term.. :/