The present invention relates to a secure transmission method and apparatus, particularly to a security control method for a data transmission process and a software protection apparatus using the same, where data transmitted between a computer running protected software and the software protection apparatus is in a cipher-text form, and thus a plain text does not appear in a communication line during the whole process. Moreover, since a random number is involved for scrambling and the data is encrypted, hence commands sent from the protected software to and those returned from the software protection apparatus change constantly even when the same command is sent from the sending end. In this way, it will be more difficult for a cracker to crack, thus securing the transmission of private confidential data.