Paper 2016/1157

NewHope without reconciliation

Erdem Alkim and Léo Ducas and Thomas Pöppelmann and Peter Schwabe

Abstract

In this paper we introduce NewHope-Simple, a variant of the NewHope Ring-LWE-based key exchange that is using a straight-forward transformation from Ring-LWE encryption to a passively secure KEM (or key-exchange scheme). The main advantage of NewHopeLP-Simple over NewHope is simplicity. In particular, it avoids the error-reconciliation mechanism originally proposed by Ding. The explanation of his method, combined with other tricks, like unbiasing the key following Peikert's tweak and using the quantizer $D_4$ to extract one key bit from multiple coefficients, takes more than three pages in the NewHope-Simple paper. The price for that simplicity is small: one of the exchanged messages increases in size by $6.25%$ from $2048$ bytes to $2176$ bytes. The security of NewHopeLP is the same as the security of NewHope; the performance is very similar.