Private simultaneous messages based on quadratic residues

Private Simultaneous Messages (PSM) model is a minimal model for secure multiparty computation. Feige, Kilian, and Naor (STOC 1994) and Ishai (Cryptology and Information Security Series 2013) constructed PSM protocols based on quadratic residues. In this paper, we define QR-PSM protocols as a generalization of these protocols. A QR-PSM protocol is a PSM protocol whose decoding function outputs the quadratic residuosity modulo p of what is computed from messages. We design a QR-PSM protocol for any symmetric function f: { 0 , 1 } ⁿ→ { 0 , 1 } of communication complexity O(n²) . As far as we know, it is the most efficient PSM protocol for symmetric functions since the previously known best PSM protocol was of O(n²log n) (Beimel et al., CRYPTO 2014). We also study the sizes of the underlying finite fields F_p in the protocols since the communication complexity of a QR-PSM protocol is proportional to the bit length of the prime p. We show that there is a prime p≤ (1 + o(1)) N²2 ^2N-2 such that any length-N pattern of quadratic (non)residues appears modulo p (and hence it can be used for general QR-PSM protocols), which improves the Peralta’s known result (Mathematics of Computation 1992) by a constant factor (1+2)2 .