To provide a system for secure electronic commerce, which is applied to the environment of online transaction via the Internet and an enterprise network and in which secure electronic commerce can be executed by encrypting and decrypting transaction data by joining together verification and a hardware serial number, when network transactions are executed by a point to point communication protocol, and to provide a method therefor.

Any one of the client devices has a unique hardware serial numbers. Accordingly, even if someone else finds the public key and the private key of a user, the verification and operations of encryption and decryption cannot be executed to the transaction data, since the hardware serial number of a device used by that other person is different from the hardware serial number of the device of the user.