A multivariate based threshold ring signature scheme

In Sakumoto et al. (CRYPTO 2011, LNCS, vol 6841. Springer, Berlin, pp 706–723, 2011), presented a new multivariate identification scheme, whose security is based solely on the MQ-Problem of solving systems of quadratic equations over finite fields. In this paper we extend this scheme to a threshold ring identification and signature scheme. Our scheme is the first multivariate scheme of this type and generally one of the first multivariate signature schemes with special properties. Despite of the fact that we need more rounds to achieve given levels of security, the signatures are at least twice shorter than those obtained by other post-quantum (e.g. code based) constructions. Furthermore, our scheme offers provable security, which is quite a rare fact in multivariate cryptography.