Software authorization system and method

A software authorization system has a server end and a user end. A software authorization method includes acquiring a software identification code of a protected software when the user end downloads the protected software from the server end; transmitting the software identification code and an inherent user identification code to the server end; acquiring a first key and main key by the server end according to the user identification code and the software identification code, respectively, so as to generate a second key by operating the main key and the first key and transmit the second key to the user end; restoring the main key by the user end with the second key combined with the first key; and decrypting the protected software by the main key. Therefore, the protected software is hard to be decrypted.