Summary Learning edx about Blockchain
A blockchain is a specific form or subset of distributed ledger technologies, which constructs a chronological chain of blocks, hence the name 'block-chain'. A block refers to a set of transactions that are bundled together and added to the chain at the same time. In the Bitcoin blockchain, the miner nodes bundle unconfirmed and valid transactions into a block. Each block contains a given number of transactions. In the Bitcoin network, miners must solve a cryptographic challenge to propose the next block. This process is known as 'proof of work', and requires significant computing power.
Timestamping is another key feature of blockchain technology. Each block is timestamped, with each new block referring to the previous block. Combined with cryptographic hashes, this timestamped chain of blocks provides an immutable record of all transactions in the network, from the very first (or genesis) block.
A block commonly consists of four pieces of metadata:
- The reference to the previous block
- The proof of work, also known as a nonce
- The timestamp
- The Merkle tree root for the transactions included in this block.
The Merkle tree, also known as a binary hash tree, is a data structure that is used to store hashes of the individual data in large datasets in a way to makes the verification of the dataset efficient. It is an anti-tamper mechanism to ensure that the large dataset has not been changed. The word 'tree' is used to refer to a branching data structure in computer science, as seen in the image below. According to Andreas M. Antonopoulos, in the Bitcoin protocol,
"Merkle trees are used to summarize all the transactions in a block, producing an overall digital fingerprint of the entire set of transactions, providing a very efficient process to verify whether a transaction is included in a block."
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