Patent ID: 6886102

Claim:
A method for determining whether a sender seeking to send a message to a receiving computer system via a network is an authorized sender, comprising: receiving from the sender a request to communicate; selecting a number N 1 ; calculating a hash value for the number N 1 using a predetermined cryptographic hash function; sending the hash value to the sender; receiving from the sender a second number N 2 ; calculating a hash value for the number N 2 using the predetermined cryptographic hash function; comparing the hash value for the number N 1 with the hash value for the number N 2 ; and processing a message received from the sender if at least a prescribed nonzero number of bits of the hash value for the number N 1 match the corresponding bits of the hash value for the number N 2 ; wherein the number N 2 is determined by an authorized sender by using the predetermined cryptographic hash function to search for a number (N 2 ) such that at least the prescribed nonzero number of bits of the hash value for the number N 2 match the corresponding bits of the hash value for the number N 1 .