A blockchain is a growing list of records, called blocks, that are linked together using cryptography.[1][2][3][4] Each block contains a cryptographic hash of the previous block, a timestamp, and transaction data (generally represented as a Merkle tree). The timestamp proves that the transaction data existed when the block was published in order to get into its hash. As blocks each contain information about the block previous to it, they form a chain, with each additional block reinforcing the ones before it. Therefore, blockchains are resistant to modification of their data... Blockchains are typically managed by a peer-to-peer network for use as a publicly distributed ledger, where nodes collectively adhere to a protocol to communicate and validate new blocks... The blockchain was invented by a person (or group of people) using the name Satoshi Nakamoto in 2008 to serve as the public transaction ledger of the cryptocurrency bitcoin.[3] The identity of Satoshi Nakamoto remains unknown to date. The invention of the blockchain for bitcoin made it the first digital currency to solve the double-spending problem without the need of a trusted authority or central server... Cryptographer David Chaum first proposed a blockchain-like protocol in his 1982 dissertation... Nakamoto improved the design in an important way using a Hashcash-like method to timestamp blocks without requiring them to be signed by a trusted party and introducing a difficulty parameter to stabilize rate with which blocks are added to the chain.



  • public blockchain: bitcoin, ethereum
  • private blockchain: permissioned
  • hybrid
  • sidechain: A sidechain is a designation for a blockchain ledger that runs in parallel to a primary blockchain.[133][134] Entries from the primary blockchain (where said entries typically represent digital assets) can be linked to and from the sidechain; this allows the sidechain to otherwise operate independently of the primary blockchain (e.g., by using an alternate means of record keeping, alternate consensus algorithm, etc.).[135]

There are already several blockchain interoperability solutions available.[137] They can be classified in three categories: cryptocurrency interoperability approaches, blockchain engines, and blockchain connectors. The IETF has a recent Blockchain-interop working group that already produced the draft of a blockchain interoperability architecture.

May'2014: Minimum Viable Blockchain, by Ilya Grigorik. The block chain is agnostic to any "currency". In fact, it can (and will) be adapted to power many other use cases. As a result, it pays to understand the how and the why behind the "minimum viable block chain".

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