Blockchain is simply a decentralized peer-to-peer distributed ledger technology. A block in a blockchain is a collection of data and its transaction is propagated by using a flooding protocol called gossip protocol. Once the transaction is validated it is included in a block and is passed on to the network. The blocks in a blockchain is linked cryptographically to other blocks in chronological order where the link is a hash pointer and thus makes a chain where each chain consists of its own unique data and the identity of the previous block. Hence even if the data in a particular block is disturbed or changed, the cryptographic data of the same passed on to the next block of the chain will remain the same and thus will break the chain. The first block in the blockchain is called genesis block.