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Merkle tree

A hashed summary of transactions stored in the header of a block in a blockchain distributed ledger. Transaction data are recursively hashed twice using the SHA256 cryptographic algorithm until there is only one hash value remaining, known as the "Merkle root." The root is very small in size and can be quickly processed to determine if a transaction resides within the block. For example, 16 transactions in a block produce a 128-byte Merkle path, but 65,535 transactions take up only 512 bytes. See blockchain.




Blockchain Headers
The Merkle root is stored in the headers of the blocks in the blockchain.






blockchain

The underlying architecture of Bitcoin and other financial systems. The blockchain is a distributed ledger that provides verifiable proof of a transaction. There is no central repository. The blockchain is replicated on many nodes dedicated to that platform.

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/private key pairs, only Bitcoin owners can transfer their coins, but the authenticity of the transactions can be verified by anyone. The date and amount of coins transferred are transparent but not the parties involved in the transaction. 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 the financial world. See ICO, Bitcoin mining, Bitcoin, Litecoin and Ethereum.




The Blockchain
Blocks are chained together by storing the hash of the header of the previous block. The block linking is what prevents transactions from being modified or refuted. The Merkle root is a hashed summary of transactions that is used for quick verification (see Merkle tree). See cryptographic hash function.






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