IMPROVEMENT OF HARN DIGITAL SIGNATURE FOR DIFFIE-HELLMAN PUBLIC KEYS

Recently, Ham proposed a digital signature for Diffie-Hellman public k eys without using a one-way function (Electron. Lett., 1997, 33, (2), pp.125-126). In the Letter, the authors show that Ham's digital signat ure is not secure enough to withstand the Nyberg-Rueppel attack. That is, an adversary who discloses one session key can obtain all the othe r session keys subsequently distributed by the same key exchange proto col. An improvement to Ham's digital signature that can overcome the w eakness stated above is also proposed.