A method for authenticating the identity of a client device that is attempting to establish a communications link with a remotely located system server over a network. The method involves initially generating a unique registration ID code by inputting information pertaining to hardware characteristics of the client device itself, and a network address of the client device, into a cryptographic hash function. The hash function generates the unique registration ID hash code and presents it to the system server. The system server uses this registration ID hash code to authenticate the identity of the client device making the call. The system server then generates a pseudo random number (PRN), and transmits it to the client device. The PRN is used the next time the client device makes a call to the system server to generate a unique, client-side hash code, which is used by the system server to authenticate the identity of the client device.