New micropayment schemes based on paywords

Abstract

This paper proposes three new micropayment schemes based on hashing and salting techniques. These schemes add significant features to the PayWord scheme proposed earlier by Rivest and Shamir. The scheme SPayWord introduces a salt into the payment process which makes the scheme more secure with smaller PayWords. The scheme UPayWord removes the constraint of the original PayWord scheme which requires a client to set the maximum number of PayWords in advance. The scheme PPayWord provides mechanisms for dealing with the loss of PayWords in communication thereby enabling successful verification of subsequent PayWords after the loss in a secure manner. The schemes presented in tiffs paper seem to be significant for use in practical off-line micropayment systems.