Review and classification of electronic cash research

Electronic cash research has been done for at least 3 decades. On that period, there have been many researches resulting in various schemes and forms of electronic cash. This paper is reviewing some researches on that period and classify the research based on the basic science used in the research. A number of 43 papers is classified into 4 categories: protocol engineering, information security, cryptography, and system engineering. The result of this paper is information in research opportunity in electronic cash research.