A processor with an elliptic curve cryptographic algorithm and a data processing method thereof are shown. Three elliptic curve cryptographic instructions are proposed in the instruction set architecture for key exchange between an initiator and a responder. The initiator device executes the first elliptic curve cryptographic instruction to generate a key pair (rA, RA). In addition to considering the first temporary public key RA, the responder device further takes the second temporary public key RB into consideration when executing the second elliptic curve cryptographic instruction to generate the responder-generated shared key KB. Based on the temporary private key rA, and the temporary public keys RA and RB, the initiator device executes the third elliptic curve cryptographic instruction to generate the initiator-generated shared key KA.