Popularization and acceptance of electronic commerce mainly depend on the following properties：security，atomicity，privacy and anonymity．There are no electronic commerce protocols appropriate forelectron－ic transactions ofphysicalgoods in which three properties are needed：security，atomicity and privacy．An elec－tronic commerce modelis suggested in this paper．The modelis named ELCwhich simulates L／Cin internationaltrade．Then a secure and atomic electronic commerce protocolis proposed．Finally the protocolis analyzed foritsstrength and correctness by proving the desired properties using BAN style logic in the presence of an intruder．