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 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 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 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.