Abstract. In a variant of the electronic cash protocol, an electronic coupon protocol, a withdrawn coin is divided into many sub-coins whose face values are fixed in advance, and the sub-coins are only used in payments. The original coin is called ticket and the sub-coins are called sub-tickets. The electronic cash protocol should satisfy not only the anonymity that the payer cannot be traced from the payments, but also the unlinkability. The unlinkability means that anyone cannot determine whether payments were made by the same payer. If the unlinkability does not hold, tracing the payer from one payment leads to tracing the payer from all his/her payments, and the link between the payments also facilitates the de-anonymization. In the previously proposed electronic coupon protocol, payments of sub-tickets derived from the same ticket are linkable. Since the complete anonymity of payments facilitates fraud and criminal acts, the electronic cash protocols should equip the revocation of the anonymity. In this paper, an electronic coupon protocol is proposed, where all payments are unlinkable but the anonymity of the payments can be revoked.
This paper discusses the problems and basic principles in the design of the algebraic language ASL/*. composed of a context-free grammar and a set of (conditional, in general) axioms, and specifies the set of expressions and the congruence relation on the set. The set of expressions and the syntax of each expression are specified by the context-free grammar. The congruence relation on the set of expressions is defined as the minimal equivalence relation, which satisfies the axioms and is closed under the "operations," i.e., the substitution into a "subexpression." The value of an expression and the concept of the realization are defined based on the congruence relation. The "projection" is a special case of the conditional axiom, which is a facility to include only the expressions satisfying the specified syntactical condition. Projection is useful for including primitive functions and procedures with parameter passing of call-by-value in a text, and also for description of a specification of a realization in a simple way.A text of ASL/* is ISSN0882-1666 18 7 10007-00 1 1 $7.5010 0 1987 Scripta Technica, Inc.
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