Electronic cash is an electronic payment protocol which prototect user's privacy. For the privacy protection, anonymity and unlinkability is important. Anonymity is the most important property for user's privacy. But linkability is as much important as anonymity. If linkability can not be prevented, attackers can grasp the consumption pattern of electronic cash user. And what is much worse is that if some techniques such as data mining are applied, the identy of electronic cash user, the flow of electronic cash, or the source of income can be revealed. Most of the electronic cash protocols proposed in the early times were inefficient. To solve this problem, divisible electronic cash protocols were proposed. But, these protocols also had the problem of linkability. Thus, electronic cash protocols with unlinkability are needed to be proposed. In this thesis, an electrnic cash protocol is proposed which enhances user's privacy protection by providing unlinkability. The unlinkable protocol is devised using keyed hash chain. Besides, proposed protocol is devisible, is atomic and satisfies general requirements of electronic cash. This protocol also provides scalability and efficiency in managing electronic cash systems.