P2P-CKKS: enhancing homomorphic encryption efficiency via dynamic power-of-two vector padding

Abstract The CKKS scheme supports secure approximate arithmetic on encrypted real-valued data, but its performance suffers when input vectors are not of power-of-two length. We propose Power-of-Two CKKS (P2P-CKKS), a variant that automatically pads input vectors with zeros up to the next power of two. This padding prevents overflow and other error conditions, enabling efficient Fast Fourier Transform (FFT) operations for polynomial arithmetic. Our experiments show that P2P-CKKS maintains the same accuracy as the original data while substantially improving computational efficiency. Importantly, even when inputs are already powers of two, P2P-CKKS matches or exceeds the execution speed of standard CKKS. In our tests, P2P-CKKS achieved a 100% success rate across all examined vector sizes, demonstrating robust scalability. These results suggest that adaptive zero-padding is a straightforward but effective strategy for improving the efficiency of encrypted computation.