An interactive client-server authentication system and method are based on Random Partial Pattern Recognition algorithm (RPPR). In RPPR, an ordered set of data fields is stored for a client to be authenticated in secure memory. An authentication server presents a clue to the client via a communication medium, such positions in the ordered set of a random subset of data fields from the ordered set. The client enters input data in multiple fields according to the clue, and the server accepts the input data from the client via a data communication medium. The input data corresponds to the field contents for the data fields at the identified positions of the random subset of data fields. The server then determines whether the input data matches the field contents of corresponding data fields in a random subset.