Toru Kambayashi

Secure authenticated key exchange with revocation for smart grid

Using cryptographic technologies to provide security solutions in smart grid is extensively discussed in NISTIR 7628 [1] and IEC 62351 standards series [2]. Both series identify cryptographic key management for Intelligent Electronic Devices (IEDs) communication as one of the most important issues. In this paper, considering the system constraints and the security requirements in the smart grid, we propose an authenticated key exchange scheme with revocation by exploiting a well-known cryptographic protocol: Broadcast encryption [3], [11], [12] using a media key block(MKB) [15]. Furthermore, we show that our scheme is efficient in comparison with the PKI-signature based Internet Key Exchange(IKE) protocol, [4], [8] in terms of the following points of view: (1) communication cost; (2) compuation cost; (3) device revocation cost. The comparison results show that our scheme is efficient and cost-effective in most cases for devices and systems in smart grid.

Global optimization by center-concentrated sampling

The simulated annealing method is one of the probabilistic methods for optimization which attract much attention. The simulated annealing process can be analyzed as a time inh~ mogeneous Markov chain (or process), Several estimations of the convergence rate of the Markov chain (or process) are known. The estimations are, however, very small when the temperature becomes low. The author introduces a novel Markov process for continuous optimization. This Markov process is proved to converge rapidly when the temperature is low, provided some condition holds for the sampling density, a structural factor of the Markov process. The author offers an algorithm for simulation of the process, and some numerical experiments are carried out. The theoretical arguments and the results of the experiments show that annealing is not essential to such a probabilistic approach to continuous optimization.