ABSTRACT
This chapter gives a detailed discussion about the El Gamal signatures providing its formal construction and security proofs. It discusses the RSA signature schemes. The chapter presents blockchain as an application of hash function and public-key encryption. The digital signature is used to allow the nearby nodes to verify that the transaction is originated from a valid and trusted node within the blockchain network. This consensus algorithm used in bitcoin is proof of work, which is used to approve the transaction. Smart contract inspired still works under the same blockchain framework wherein the transactions are validated by peer nodes and agreed through the consensus algorithm. Consortium blockchain may assign different roles to the participating nodes in hierarchical form. Consortium blockchain lies between private and public blockchain: it is fully decentralized but the number of participating nodes is limited. For instance, the participating nodes are divided into validating and transaction nodes, in which only validating nodes involved in consensus process.
