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Add "Byzantine Fault Tolerance" (#25519)

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Alvin Tan
2018-12-17 20:53:53 -05:00
committed by Christopher McCormack
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guide/english/blockchain/index.md
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---
title: Blockchain
---
## Blockchain
## Blockchain
> "Is a decentralized database that stores a registry of assets and transactions across a peer-to-peer network. Is basically a public registry of who owns what and who transacts what. The transactions are secured by cryptography, and over time, that transaction history gets locked in blocks of data that are then cryptographically linked together and secured. This creates an immutable, unforgeable record of all the transactions across this network. This record is replicated on every computer that uses the network."
>
> --Bettina Warburg<sup>1</sup>
@ -28,24 +28,23 @@ The words block and chain were used separately in Satoshi Nakamoto's original pa
As of 2016, blockchain 2.0 implementations continue to require an off-chain oracle to access any "external data or events based on time or market conditions to interact with the blockchain."
### Types of Blockchains
Blockchains can be broadly classified into two categories -
1. Permissionless, public blockchains - these are not controlled by any single company or person. The blockchain is accessible to anyone to participate in. Bitcoin and Ethereum are examples of permissionless blockchains. Consensus is arrived at by participating miner nodes in the network, who perform certain actions (Proof-of-Work) and are rewarded for helping to maintain the state of the distributed ledger. Anyone interested can become a miner and participate in the consensus building process.
2. Permissioned blockchain - these are typically owned by a single party, or by a consortium of organizations. The participants in the network, along with their roles in the network, are pre-determined. These kinds of blockchains are implemented by enterprises who are looking to improve efficiencies across business processes that span multiple parties. Examples of permissioned blockchain platforms would be Ripple, Corda, Quorum and Hyperledger. [Hyperledger](https://www.hyperledger.org) is an open source project run by [The Linux Foundation](https://www.linuxfoundation.org/projects/), and is a set of frameworks and tools which can be used to build permissioned blockchain networks. Of the frameworks available, Hyperledge Fabric has gained a level of maturity required for production level blockchains.
### Bitcoin
Bitcoin’s main problem to solve was to achieve distributed consensus while remaining a decentralized system. Distributed consensus is essentially the idea that all the nodes that make up the network must come to a collective agreement without the use of a centralized control. In Bitcoin, the nodes are agreeing on exactly which transactions present on the network are valid. This is difficult in many ways, one of which is the potential for n number of nodes to be malicious and not want to follow
the consensus of the other nodes. Bitcoin has the benefit of being able to incentivize its nodes to “follow the rules” through rewards and transaction fees because it is a currency system.
### Byzantine Fault Tolerance
Imagine the scenario where there is an empire and there are three generals with their respective armies at different positions. All of them must attack in order to win the fight or they can choose to retreat. Their only means of communications are through pigeon posts. But there is a problem, the generals can't trust each other or ensure that the message has not been corrupted along the way. How do they solve this problem? Blockchain essentially does so by listening to information broadcasted by other people, reaching to a consensus of which information is deemed true. As such, this model asssumes that the amount of "traitors" do not exceed more than 1/3 of the entire network.
#### Sources
1. [Bettina Warburg, "How the blockchain will radically transform the economy", TED Talks, December 8, 2016](https://youtu.be/RplnSVTzvnU?t=213)
2. [Depository Trust and Clearing Corporation, "Embracing Disruption: Tapping the Potential of Distributed Ledgers to Improve the Post-Trade Landscape", DTCC, 2016]
(https://hub.digitalasset.com/hubfs/Industry%20Reports/dtcc-embracing-disruption.pdf?t=1539879453546)
3. Brian Curran, "What is Practical Byzantine Fault Tolerance? Complete Beginner’s Guide", October 21, 2018 (https://blockonomi.com/practical-byzantine-fault-tolerance/)
##### More information
* [Bitcoin Whitepaper by Satoshi Nakamoto](https://bitcoin.org/bitcoin.pdf)