Solving the Rank Decoding Problem Over Finite Principal Ideal Rings

The rank decoding problem has been the subject of much attention in this last decade. This problem, which is at the base of the security of public-key cryptosystems based on rank metric codes, is traditionally studied over finite fields. But the recent generalizations of certain classes of rank-metric codes from finite fields to finite rings have naturally created the interest to tackle the rank decoding problem in the case of finite rings. In this paper, we show that some combinatorial type algorithms for solving the rank decoding problem over finite fields can be generalized to solve the same problem over finite principal ideal rings. We study and provide the average complexity of these algorithms. We also observe that some recent algebraic attacks are not directly applicable when the finite ring is not a field due to zero divisors. These results could be used to justify the use of codes defined over finite rings in rank metric code-based cryptography.