A blockchain is a ongoing growing list of records, called blocks, which are linked and secured using cryptography. Each block contains a cryptographic hash of the previous block,a timestamp and transaction data. If we talk about design then, in blockchain, the modification of the data is not allowed. It is "an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way".For use as a distributed ledger, a blockchain is typically managed by a peer-to-peer network collectively adhering to a protocol for inter-node communication and validating new blocks. Once recorded, the data in any given block cannot be altered retroactively without the alteration of all subsequent blocks, which requires collusion of the network majority.