We investigate the security of the cryptocurrency Bitcoin and deal with both the security principle of this new type of currency and the associated security risks for end users.

This paper deals with attacks on the payment network itself, such as DoS attacks, Sybil attacks, the 51% attack in its various forms, and game-theoretic attacks, as well as risks for the end user when using Bitcoin in everyday life and problems with their privacy and the risks that a decentralized system entails. A decentralized system is in its nature transparent to all participants, and it can be assumed that governments, intelligence agencies and criminals also try to gain influence here.

The aim of this paper is to find out how Bitcoin compares to traditional centralized payment systems in terms of security and whether new attacks and problems emerge with the decentralization, which could undermine the network or reveal the pseudonymous payment participants.