Improved Secure Implementation of Code-Based Signature Schemes on Embedded Devices

Amongst areas of cryptographic research, there has recently been a widening interest for code-based cryptosystems and their implementations. Besides the {\it a priori} resistance to quantum computer attacks, they represent a real alternative to the currently used cryptographic schemes. In this paper we consider the implementation of the Stern authentication scheme and one recent variation of this scheme by Aguilar {\it et al.}. These two schemes allow public authentication and public signature with public and private keys of only a few hundreds bits. The contributions of this paper are twofold: first, we describe how to implement a code-based signature in a constrained device through the Fiat-Shamir paradigm, in particular we show how to deal with long signatures. Second, we implement and explain new improvements for code-based zero-knowledge signature schemes. We describe implementations for these signature and authentication schemes, secured against side channel attacks, which drastically improve the previous implementation presented at Cardis 2008 by Cayrel {\it et al.}. We obtain a factor 3 reduction of speed and a factor of about 2 for the length of the signature. We also provide an extensive comparison with RSA signatures