Abstract: By analyzing typical authentication schemes, especially S/KEY schemes in one time password, a new authentication protocol COTP is proposed.Different from other one time password protocols, it gives the algorithm of chaotic scramble sort table and applies the scramble sort algorithm instead of real iteration times in the log on process.Gives the idea of encrypting to the seeds of protocol, theoretical analysis and computer simulation demonstrate that the COTP can resist little numbers attack, replay attack, internal attack and encryption seed and the times of iteration for transform, that realizes authentication between client and server.