A provably secure signature and signcryption scheme using the hardness assumptions in coding theory

Signcryption is a cryptographic protocol that provides authentication and confidentiality as a single primitive at a cost lower than the combined cost of sign and encryption. Code-based cryptography, a likely candidate for post-quantum cryptography, provides an exciting alternative to number-theoretic cryptography. Courtois, Finiasz and Sendrier proposed the only practical code-based signature(CFS signature) at Asiacrypt 2001. But that signature scheme currently lacks a formal proof of security due to the existence of the high rate distinguisher proposed by Faugère et al. In this paper, we make use of an alternate keyconstruct for the CFS signature, and thus prove its existential unforgeability under chosen message attacks (EUF-CMA). Also, we propose a code-based signcryption scheme and prove its security. To the best of our knowledge, this is the first code-based, provably secure signature and signcryption scheme in literature.