Аннотация
In this paper, we describe valid and invalid bitcoin transactions. Bitcoin is one of the most widespread currencies in the network, which can be used to perform purchases and transactions among nodes. Because of its digital feature, it can undergo some problems and attacks such as double spending (DS), Denial of Service(DoS), packet sniffing and so on. One of the most common challenges is double spending. DS implies spending a balance of given cryptocurrency more than once, viably making a difference between the spending record and the sum of available cryptocurrency. It is suggested that it can be prevented by including Timestamp server, which adds precise time data that is never repetitive. In this paper, the given solution was implemented using Java platform. The experiment results show the progress in preventing DS of bitcoin as soon as we connected the TSA server.