International Journal of Network Security, Vol.21, No.3, PP.501-510, May 2019 (DOI: 10.6633/IJNS.201905 21(3).17) 501 General Model for Secure Electronic Cash Scheme Dany Eka Saputra 1 , Sarwono Sutikno 2 , and Suhono Harso Supangkat 2 (Corresponding author: Dany Eka Saputra) Departement on Informatics, STMIK “AMIKBANDUNG” 1 Jl. Jakarta no 28, Kota Bandung, Jawa Barat, Indonesia School of Electrical Engineering, Institut Teknologi Bandung 2 Jl. Ganesha No 10, Kota Bandung, Jawa Barat, Indonesia (Email: dekastra@gmail.com) (Received Nov. 01, 2017; Revised and Accepted June 18, 2018; First Online Feb. 24, 2019) Abstract The vast variation of electronic cash scheme make it dif- ficult to compare a scheme with another. We propose a general model of electronic cash. The development of the model uses logical modeling based on Inenaga et al. model of money system. The model consists of three sub- model: the model of system, the model of process, and the model of property. The model of system describe the basic model of electronic cash data, entity, and form. The model of process enlist the common process found in elec- tronic cash scheme. The model of property describes the common property in electronic cash scheme, including se- curity property. We find that our model can be used as a base of security evaluation and covers wider variation of electronic cash scheme than the model in Inenaga et al. Keywords: Electronic Cash; Mathematic Modeling; Secu- rity Model 1 Introduction Comparing and choosing electronic cash schemes for an implementation requires great effort. Each scheme need to be reviewed to list its respective properties and choose the one that suits the implementation. However, two dif- ferent schemes may define a single property differently. This condition may complicate the effort to define the se- curity objectives of electronic cash and may hamper the security of the implementation. For example, Dreier et al. proposed a method to evaluate the security of electronic cash [9]. The works of Chen & Chou [7], and Wang et al. [28] also attempt to evaluate another existing schemes. However, the definition of forgery in [9] differs with the definition used in [7] and [28]. An attempt to design new electronic cash scheme face similar problem. Different definition of property and be- havior may lead to incorrect design. This condition may result in insecure scheme. Having standard definition or model of electronic cash and its property (including secu- rity property) greatly help the process of designing a new scheme or comparing schemes for implementation. Modeling a common definition of electronic cash de- mands quite an effort. A model usually represents certain aspect of an object. By observing the object for any pat- tern that represent the object’s properties, we can build a model of the object. In electronic cash, extracting those pattern is a challenging task. Due to the numerous scheme of electronic cash, we can find many variation of property and its definition. Under this condition, it is difficult to extract a common pattern. For a start, the electronic cash scheme can be divided into two paradigms: centralized and distributed electronic cash [26]. Both paradigms have different ways to describe and process electronic cash. Cannard-Gouget [2] explain four definition of anonymity, which is differs from the definition of anonymity in most of electronic cash scheme. Inenaga et al. propose a model of money system [15]. The model describes the general model of money system that can be used to model electronic cash. The model also describes the transfer model of electronic cash and the security property of electronic cash. However, the model only covers off-line electronic scheme. It does not model the electronic cash data creation process and does not consider the issuer of electronic cash as part of the system. The model lacks the generality needed to describe electronic cash system. We propose a new General Model of Electronic Cash. We take several concepts from Inenaga et al. and form a new model that covers wider range of electronic cash scheme. The model is build by using logical approach, so it can be used as a tool to design new scheme or to compare and evaluate existing scheme. The proposed model only covers the description of cen- tralized electronic cash. By using this paradigm, we refer electronic cash as a digital representative of cash that cre-