Blockchain is a record (database) that continues to grow, called a block, which is connected and secured using cryptographic techniques.
Each block usually contains a cryptographic hash from the previous block, a timestamp, and transaction data. By design, blockchain is resistant to data modification. Blockchain is an open distributed ledger that can record transactions between two parties efficiently and in a way that can be verified and permanent. For its use as a distributed ledger, blockchain is usually managed by a peer-to-peer network collectively by following certain protocols for communication between nodes and confirming new blocks. Once recorded, data in a block cannot be changed retroactively without changes to subsequent blocks, which requires the consensus of the majority of the network.
Blockchain is designed from the beginning to be secure (secure by design) and is an example of a distributed computing system with high Byzantine Fault Tolerance (BFT). Decentralized consensus can be achieved with blockchain. This makes blockchain suitable for recording events, medical records, and other record management activities, such as identity management, transaction processing, evidence documentation, food traceability, and voting.
Blockchain was created by Satoshi Nakamoto in 2008 and is used as a ledger for public transactions of Bitcoin cryptocurrency. The invention of the blockchain for bitcoin makes it the first digital currency that can overcome the double-spending problem without the need for a trusted or centralized authority. This bitcoin design has also inspired other applications.
