Hwang and Ku introduced a concept of reparability feature into key distribution protocol.In this paper

the key distribution protocol

proposed by Hwang and Ku

is analyzed.This paper also presentes security problems in Hwang and Ku's protocol

and furthermore

the argument on whether the protocol has the perfect reparability feature.So

an improved reparable key distribution protocol is proposed in this paper

which solves these security problems.A method

hiding the duplicated event markers

is also proposed and is applied in the protocol to successfully solve the perfect reparability problem.