An improved key distribution protocol with perfect reparability

This paper handles the problem on reparability of key distribution protocols, whose concept was introduced by Hwang and Ku (1995). Two reparable key distribution schemes, which were proposed by Hwang and Ku, are analyzed and their security defects are pointed out, which caused the discussion on whether there can be perfect reparability suitable for implementation. Not agreeing with these authors about the result they got, this paper proposed an improved key distribution protocol, which removes security defects mentioned. Especially, a new method, concealing the repeat of event marker is proposed. This method gives the protocol perfect reparability without making the protocol complex and does not increase the computation much.