We propose a cheap micropayment scheme based on reasonable requirements. It is flexible in the sense that many security options are possible depending on the policy of the involved participants. We avoid large data storage, heavy computations. The scheme is software based for the user and hardware based for the service provider. Possibilities of having software-based solution for both are also presented. 1 Introduction In the forthcoming years or even months, it is anticipated that electronic payments over secure networks are going to expand rapidly. The definition of the SET protocol (see [4]) by a group of credit cards providers is a definite sign of this expected growth. Among the variety of payment schemes that have been proposed recently, several address the very specific question of micropayments (see [1, 2, 6]). Such payments arise in the context of the Internet when an individual user is browsing around and wish to access resources for which a small payment appears adequ...