Key Recovery Attack on Rank Quasi-Cyclic Code-based Signature Scheme

Rank Quasi-Cyclic Signature (RQCS) is a rank metric code-based signature scheme based on the Rank Quasi-Cyclic Syndrome Decoding (RQCSD) problem proposed by Song et al. in [2]. Their paper was accepted in the 22nd International Conference on Practice and Theory of Public Key Cryptography (PKC 2019). They have also shown that RQCS is EUF-CMA in the random oracle model. This short paper describes how to recover the secret key in RQCS with practical simulations. Our experimental results show that we are able to recover the secret key of RQCS in less than 41 seconds for all the proposed schemes at 128-bit, 192-bit and 256-bit security level.