New Micropayment Schemes Based on PayWords

This paper proposes three new micropayment schemes based on hashing and salting techniques. These schemes add signiicant 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 UP-ayWord 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 veriication of subsequent PayWords after the loss in a secure manner. The schemes presented in this paper seem to be signiicant for use in practical oo-line micropayment systems.