A blockchain is a peer to peer tool that works something like an open ledger. Every participant in a certain network had access to the whole history of every "transaction"- whether it be financial as in the case of Bitcoin, or also general information.

A blockchain runs on a set of nodes, each of which may be under the control of a separate entity or organization. These nodes connect to each other in a dense peer-to-peer network, so that no individual node acts as a central point of control or failure - [https://www.multichain.com/blog/2017/05/blockchain-immutability-myth/ multichain.com]

• Blockchain architecture - [https://www.pluralsight.com/guides/blockchain-architecture pluralsight.com]
• How does blockchain work - [https://medium.com/@micheledaliessi/how-does-the-blockchain-work-98c8cd01d2ae medium]

Uses

Mkinsey recently analysed the state of industry and question:

Are there benefits to be accrued that justify the changes required in [[market infrastructure]] and [[data governance]]? - [https://www.mckinsey.com/industries/financial-services/our-insights/blockchains-occam-problem?cid=other-eml-nsl-mip-mck&hlkid=87d6eb5836364cbf94419c9121e01664&hctky=1273956&hdpid=7222d727-e2da-4c04-9730-b4982cb5b53f mckinsey.com]

To get there we see three key principles as minimum conditions for progress:

1. [[Start with a problem]]
2. [[Clear business case]]
3. [[Path to adoption]]

Transactions

Each node can generate and digitally sign transactions which represent operations in some kind of ledger or database, and these transactions rapidly propagate to other nodes across the network in a gossip-like way.

Each node independently verifies every new incoming transaction for validity, in terms of:

• (a) its compliance with the blockchain’s rules
• (b) its digital signature
• (c) conflicts with previously seen transactions

If a transaction passes these tests, it enters that node’s local list of provisional unconfirmed transactions (the “memory pool”), and will be forwarded on to its peers. Transactions which fail are rejected outright, while others whose evaluation depends on unseen transactions are placed in a temporary holding area (the “orphan pool”).

Blocks

At periodic intervals, a new block is generated by one of the “validator” nodes on the network, containing a set of as-yet unconfirmed transactions.

Every block has a unique 32-byte identifier called a [[hash]], which is determined entirely by the block’s contents. Each block also includes a timestamp and a link to a previous block via its hash, creating a literal “block chain” going back to the very beginning.

Just like transactions, blocks propagate across the network in a peer-to-peer fashion and are independently verified by each node.

To be accepted by a node, a block must contain a set of valid transactions which do not conflict with each other or with those in the previous blocks linked.

If a block passes this and other tests, it is added to that node’s local copy of the blockchain, and the transactions within are “confirmed”. Any transactions in the node’s memory pool or orphan pool which conflict with those in the new block are immediately discarded.

Applications

Blockchain uses-cases - [http://letstalkpayments.com/blockchain-use-cases-comprehensive-analysis-startups-invoved letstalkpayments.com]

Blockchains have many potential appplications, but the most appealing is in security. According to Satoshi Nakamoto's calculations, it is almost impossible to forge a blockchain transaction once the history has passed a certain threshhold of difficulty, because the computer power required to attack the system would have to be more than the combined computer power of every node in the network.

YOUTUBE 19QT8-i1Wf0 Coinscrum (Apr 2014) - The Concept of the [[Blockchain]]

Potential Applications

Blockchains have many potential appplications, but the most appealing is in security. According to Satoshi Nakamoto's calculations, it is almost impossible to forge a blockchain transaction once the history has passed a certain threshhold of difficulty, because the computer power required to attack the system would have to be more than the combined computer power of every node in the network.

Links

A distributed hash table (DHT) is a class of a decentralized distributed system that provides a lookup service similar to a hash table. Any participating node can efficiently retrieve the value associated with a given key. [https://en.wikipedia.org/wiki/Distributed_hash_table pull wikipedia]

• [[Block Chain]]

• [[Block Chain Technology]]

• Scalable privacy for every blockchain - [https://enigma.co/ enigma.co]