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Definition: blockchain

The underlying architecture of Bitcoin and other electronic financial systems. The blockchain is considered to be the most secure way of storing transactions. Instead of a central repository and single point of failure or fraud, the blockchain is a ledger replicated on hundreds of computers (even thousands depending on the system) that provides verifiable proof of a transaction between sender and receiver. The blockchain is continuously maintained by the invested parties, which may provide only verification or be in business to obtain fees (see Bitcoin mining).

Using Bitcoin as the example, blocks of transactions are created when parties exchange coins, one block approximately every 10 minutes. All the blocks are linked (see illustration below). By using public key cryptography, only Bitcoin owners can transfer their coins, but the authenticity of the transaction can be verified by anyone. The date and amount of coins are transparent but not the two parties involved. See public key cryptography.

Not Just for Bitcoin
Because the blockchain algorithm provides a robust list of rightful ownership, both the public and private sectors are using or exploring blockchain technologies for digital currencies other than Bitcoin as well as applications such as contracts, fundraising and title registration. By recording transactions without a middleman, performance is improved, and not having a central point of attack means greater security. In addition, transactions cannot be reversed or altered. As a trusted protocol, proponents claim that blockchain systems will eventually revolutionize every aspect of finance. If so, it is a massive amount of technical complication being added to the world. See ICO, Bitcoin and cryptocurrency.

The Blockchain - One-Way Linkage
Blocks are chained together by storing the hash of the header of the previous block. This prevents transactions from being modified or refuted. If a transaction within a block were altered, the link to the subsequent block would be broken. The Merkle root is a hashed summary of transactions that is used for quick verification (see Merkle tree). See cryptographic hash function.