Key management is the crucial part of cyber security defense in the smart substation. Difficulties in designing the key management scheme are balancing security and efficiency

combing with communication characteristics and security requirements of the smart substation. After analyzing the message security requirements and feasibility of Needham-Schroeder key management scheme applied in the smart substation

a key management scheme of smart substation based on the improved NSSK protocol is proposed. The detailed flow and solutions to the issues of generation

distribution

update

and destructionoy of the key are provided. And the key security

anti-forgery attacks

anti-middle attacks

anti-replay attacks

forward and backward security

operation and transmission time costs of the scheme are analyzed. The validity of the key management scheme is judged by the BAN logic. The analyzing results show that the key management scheme proposed has good resistance to the attacks above and lower computation and transmission time cost

satisfying the requirements of cyber security in the smart substation.