Finding a consensus is the major challenge of a decentralized, nonhierarchical network that consists of unknown and therefore untrusted nodes. The blockchain technology provides an automatic consensus algorithm that confirm the consensus between all participants of the blockchain system in every stage of the blockchain process.
Blockchain was firstly used as the basis of the bitcoin payment system. Bitcoin provides a decentralized payment system and an associated cryptocurrency. All transactions are completed between two entities and without participation of third parties (e.g., financial institutes). In this context, the blockchain technology is used to create a list of all transactions that took place. These transactions are grouped into blocks. Each block is appended to an existing block so that a chain is constructed that cannot be modified afterwards.
We are investigating the security of blockchains. The main focus is on the detection of possible attacks and respective protection measures. Furthermore, they work on the scalability of blockchains, the improvement of consensus algorithms and zero-knowledge proof systems.