Toward Authenticating the Master in the Modbus Protocol

The power systems relying on the Modbus protocol for distributed control render their facilities vulnerable since there is no security consideration in the protocol. An intruder, without being authenticated, may harm the system by issuing malicious commands. This letter presents a cryptographic scheme that aims to enhance the Modbus protocol with authenticity, in which it is infeasible for an attacker to maliciously forge as the master. Applying the concept of hash chains, the proposed design bases its security on the one-way property of cryptographic hash functions. Also, one compression function is devised to reduce the storage overhead to $O(1)$ in terms of slave storage. Therefore, authenticity is achieved at low storage cost in the proposed scheme.