Faster Spiral: Low-Communication, High-Rate Private Information Retrieval

Private information retrieval (PIR) enables a client to retrieve a specific element from a server’s database without disclosing the index that was queried. This work introduces three improvements to the efficient single-server PIR protocol Spiral. We found that performing a modulus switching towards expanded ciphertexts can improve the server throughput. Secondly, we apply two techniques called the composite NTT algorithm and approximate decomposition to Spiral to further improve it. We conduct comprehensive experiments to evaluate the concrete performance of our protocol, and the results confirm an approximately 1.7 times faster overall throughput than Spiral.