SCORE: A SlotToCoeff Optimization for Real-Vector Encryption in CKKS

We present SCORE, a modified version of the SlotToCoeff operation tailored to encrypted real vectors in the CKKS scheme, where SCORE stands for “SlotToCoeff Optimization for Real-Vector Encryption”. This approach accelerates CKKS bootstrapping algorithms that employ the SlotToCoeff operation as their final step, provided the inputs are encryptions of real vectors. We demonstrate its utility through proof-of-concept implementations for two such algorithms: the conventional bootstrapping algorithm and the SPRU algorithm. Our results indicate notable performance gains of up to 2× compared to the original formulations of the algorithms.