The invention pertains to the field of encrypt protocol technology, in particular pertains to a secure key exchange protocol which can calculate online efficiently, can repudiate, can not be forged. The environment and the method for realizing the protocol is: the public key of the user 'A' is that A is equal to ga, and the DH key component is that X is equal to gx; The public key of the user 'B' is that B is equal to gb, and the DH key component is that Y is equal to gy. The user 'A' verifies that the user 'A' simultaneously know a and x through Bcx+eaYda+fx; The user 'B' verifies that the user 'B' simultaneously know b and y through Aeb+dyXcb+fy. The input inclusion protocol of hash function c, d, e and f implements all relevant public information each time, the input and output mutual nesting and influence. In order to improve the efficiency of online calculation, the input of c does not include Y, the input of d does not include X, e is 1 or 0. The protocol is capable of fulfilling the different needs and the priorities of users to key exchange such as the efficiency of online calculation, repudiatability, security which can not be forged, denial-of-service-attack proof, internal-situation-leakage proof, and explicit or implicit identity and key confirmation.