On the security of the Okamoto-Tanaka ID-based key exchange scheme againstactive attacks

As far as the knowledge of authors, the rigorous security of Okamoto-Tanaka identity-based key exchange scheme nas shown in [4] for the first time sin ce its invention. However, the analysis deals with only the passive attack. In this paper, we give several models of active attacks against the scheme and show the rigorous security of the scheme in these models. We prove sev eral relationships among attack models, including that (1) breaking the sch eme in one attack model is equivalent to breaking the RSA public-key crypto system and (2) breaking the scheme in another attack model is equivalent to breaking the Diffie-Hellman key exchange scheme over Z(n). The difference of the complexity stems from the difference of the timing of dishonest part y's sending out and receiving messages.