An authentication method for authenticating a wireless power transmitter to a wireless power receiver includes receiving a SSP value, an ID, and a random number RND from a wireless power receiver; determining an index based on the RND; choosing a base code from a set of base codes according to the index; determining a secure code from the base code, the index, the RND, the SSP value, and the ID; and transmitting the secure code to the wireless power receiver. A further method includes receiving a secure code from the wireless power transmitter; retrieving an index from the secure code; determining a base code from a set of base codes according to the index; calculating a second secure code; and authenticating the wireless power transmitter by comparing the secure code and the second secure code.