Blockchain

Blockchain

A blockchain is an append-only digital ledger storing a set of time-ordered transactions grouped in blocks that are linked together using cryptographic hashes.

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The history of transactions on the blockchain, including all transactions made by each address, is permanently open and visible to everyone. However, the identity of person operating a particular node is pseudo-anonymous. New addresses can be easily created on the blockchain without necessarily linking to an individual’s name. For example, if the Bitcoin or Ethereum address of an individual is discovered it becomes trivial to find all transactions performed with that address with tools such as Bitcoin block explorer or Etherscan.

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The history of transactions on the blockchain, including all transactions made by each address, is permanently open and visible to everyone. However, the identity of person operating a particular node is pseudo-anonymous. New addresses can be easily created on the blockchain without necessarily linking to an individual’s name. For example, if the Bitcoin or Ethereum address of an individual is discovered it becomes trivial to find all transactions performed with that address with tools such as Bitcoin block explorer or Etherscan.

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Private & permissionedPermissioned blockchains are different from public blockchains because the nodes allowed to participate in the network are restricted in some way. Projects developing private or permissioned blockchains include JPMorgan's Quorum, Multichain, R3, EWF, B3i, and many others.

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In September 2017 the Swiss city of Zug announced intent to release an app to secure its citizens personal identity on the blockchain and associate it with a crypto address. Citizens would register independently on the app and then would be verified by city officials. The linking of a traditional personal centralized identity with a decentralized crypto-address is one initiative intended to improve digital identity. It is intended as a digital passport on the blockchain that could be used for various services such as e-voting. Zug is part of what is known as crypto valley, a region in Switzerland known for attracting decentralized and crypto entrepreneurship due to its crypto-friendly legislation.

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The Monetary Authority of Singapore released a report announcing project Urbin, a report outlining plans for increased usage of blockchains in Singapore.

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Russia has plans to release a cryptographic version of their national currency, and are calling it cryptoruble. The cryptoruble cannot be mined; and will be controlled and maintained by central Russian authorities.

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The International Monetary Fund (IMF) and Christine Lagarde have spoken publicly about the potential of cryptocurrency and the possibility for an IMF based coin.

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A blockchain is a type of distributeddigital ledger ledger where transactions grouped into blocks are replicated across a network of participants. Blockchains arecan enable a decentralized, andledger system of transactions which do not rely on any central authority or trusted third parties for transaction validation. All participants in the peer-to-peer network are known as nodes, and maintain a full record of all transactions on the blockchain communicating directly following a protocol that forms a distributed consensus on the next valid block in the chain.

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Early work on cryptographically secure chains with timestamps was done by Haber and Stornetta including their 1991 paper “How to Time-Stamp a Digital Document". Building upon their previous work, Haber, Stornetta and Bayer published “Improving the Efficiency and Reliability of Digital Time-Stamping", which incorporated consideration of costs and benefits of three methods of digital timestamping including; linear linking, random witness, and merkle trees. Massias, Avila, and Quisquater extended this work to reduce the trust requirements for these digital timestamps.

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In 2004, Hal Finney combinedcreated ideasand implemented reusable proofs of work (RPOW) drawing inspiration from Adam Back's hashcash. Key innovations also came from Wei Dai’s's b-money and Adam Back’s hashcash to create his reusable proof of work tokens. Nick Szabo’s utilizes these ideas for timestamped proof of work to create a string of distributed property title registry for Bit gold.. Finally, inIn 2008, an individual, or group of individuals, released the bitcoin whitepaper under the name Satoshi Nakamoto and Bitcoin became the first successful implementation of a secure decentralized blockchain solving the double spend problem for a digital currency.

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Blockchains are decentralized peer-to-peer networks with a shared append-only ledger maintaining a consensus through a protocol. The unique characteristics of blockchains make them potentially transformative for a variety of industries requiring secure online transactions. They have the potential to solve a fundamental problem of digital trust whereby two individuals can perform almost any arbitrary transaction without a centralized trusted authority approving their transaction. Financial transactions are a natural starting place for blockchain technology, however, with the development of smart contract technology numerous applications can be adopted such as voting, supply chain, electronic health records, estate and property records, and much more.

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Each full node on the network replicates a history of all transactions on the blockchain. In addition to full nodes, some blockchains allow for other type of nodes like lightweight or spv nodes — which may contain only specific portions of the blockchain. The size of the blockchain increases over time which increases the capacity requirements to run a full nodes. This an important parameter for decentralized blockchain networks as increasing blockchain size comes with increased cost of storage for each user. The implications of trade-offs between blockchain size and numerous other factors has been a topic of significant debate within the bitcoin and cryptocurrency communities.

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Alex Dean
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Academic papers

Author
Title
Link

Alex Roehrs, Cristiano Andréda Costa, Rodrigo da Rosa Righi

OmniPHR: A distributed architecture model to integrate personal health records.

https://www.ncbi.nlm.nih.gov/pubmed/28545835

Cynthia Dwork, Moni Naor

Pricing via Processing or Combatting Junk Mail

http://www.wisdom.weizmann.ac.il/~naor/PAPERS/pvp.pdf

Daisuke Ichikawa, Makiko Kashiyama, Taro Ueno

Tamper-Resistant Mobile Health Using Blockchain Technology

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5550736/

Jesse Yli-Huumo, Deokyoon Ko, Sujin Choi, Sooyong Park, and Kari Smolander

Where Is Current Research on Blockchain Technology?-A Systematic Review.

https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/27695049/

Kurt Fanning David P. Centers

Blockchain and Its Coming Impact on Financial Services

https://onlinelibrary.wiley.com/doi/full/10.1002/jcaf.22179

Selena Ahmed & Noah ten Broek

Food supply: Blockchain could boost food security

https://www.nature.com/nature/journal/v550/n7674/full/550043e.html

Tim k. Mackey, Gaurvika Nayyar

A review of existing and emerging digital technologies to combat the global trade in fake medicines

https://www.ncbi.nlm.nih.gov/pubmed/28349715

Timothy Nugent, David Upton, Mihai Cimpoesu

Improving data transparency in clinical trials using blockchain smart contracts

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5357027/

Tsung-Ting Kuo Hyeon-Eui Kim Lucila Ohno-Machado

Blockchain distributed ledger technologies for biomedical and health care applications

https://academic.oup.com/jamia/article-lookup/doi/10.1093/jamia/ocx068

Xiao Yue, Huiju Wang, Dawei Jin, Mingqiang Li, Wei Jiang

Healthcare Data Gateways: Found Healthcare Intelligence on Blockchain with Novel Privacy Risk Control

https://link.springer.com/article/10.1007%2Fs10916-016-0574-6

Zachary Baynham-Herd

Technology: Enlist blockchain to boost conservation

https://www.nature.com/nature/journal/v548/n7669/full/548523c.html

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Each block in the blockchain contains a timestamp, some transactional data, and cryptographic hash link to the previous block. This creates a time-ordered chain of links from the genesis block to the most recent block that cannot be altered retroactively without alteration of all subsequent blocks, requiring a majoritycollusion collusionof a large portion of the network.

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Cryptographic hash functionsCryptographic hash functions are a key component of every blockchain. Common hash functions are MD5, SHA1, SHA2, SHA3. Hash functions convert data of any size into a digital string of a specific length called a hash. An example MD5 hash:

Alex Dean
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Documentaries, videos and podcasts (+2 rows) (+6 cells) (+146 characters)
Further reading

Author
Title
Link

Leslie Lamport, Robert Shostak, and Marshall Pease

The Byzantine Generals Problem

https://people.eecs.berkeley.edu/~luca/cs174/byzantine.pdf

Vlad Zamfir

Against on-chain governance

https://medium.com/@Vlad_Zamfir/against-on-chain-governance-a4ceacd040ca

Alex Rampell

Decrypting crypto, from bitcoin and blockchain to ICOs

https://a16z.com/2017/12/08/summit-crypto-alex-rampell/

Chris Berg, Sinclair Davidson, and Jason Potts

Basic primer on blockchain — ledger basics, why it matters

https://medium.com/@cryptoeconomics/the-blockchain-economy-a-beginners-guide-to-institutional-cryptoeconomics-64bf2f2beec4

Dhruv Bansal

Why it’s hard to “get” bitcoin: the blockchain spectrum

https://blog.unchained-capital.com/blockchain-spectrum-806847e1c575

Ed Felten

Blockchain: what is it good for? — including smart contracts

http://freedom-to-tinker.com/2018/02/26/blockchain-what-is-it-good-for/

Fred Ehrsam

Blockchain governance — design components, approaches, suggestions

https://medium.com/@FEhrsam/blockchain-governance-programming-our-future-c3bfe30f2d74

Fred Ehrsam

Funding the evolution of blockchains

https://medium.com/@FEhrsam/funding-the-evolution-of-blockchains-87d160988481

Joel Monegro

Fat protocols

https://www.usv.com/blog/fat-protocols

Kathleen Breitman

The myth of the irrational token holder — why blockchain governance doesn’t fit squarely into any existing model

https://medium.com/@kathleenbreit/the-myth-of-the-irrational-token-holder-c12438709afd

Luke Duncan

Thoughts on governance and network effects

https://blog.aragon.one/thoughts-on-governance-and-network-effects-f40fda3e3f98

Marco Iansiti and Karim Lakhani

The truth about blockchain — framework for adoption to help big company executives understand state of development; strategic investments; challenges, resources, processes to facilitate adoption

https://hbr.org/2017/01/the-truth-about-blockchain

Mark Miller and K. Eric Drexler

The Agoric papers series

https://e-drexler.com/d/09/00/AgoricsPapers/agoricpapers.html

Preethi Kasireddy

What do we mean by “blockchains are trustless”?

https://medium.com/@preethikasireddy/eli5-what-do-we-mean-by-blockchains-are-trustless-aa420635d5f6

Steven Johnson

Beyond the bitcoin bubble

https://www.nytimes.com/2018/01/16/magazine/beyond-the-bitcoin-bubble.html

Vitalik Buterin

Notes on blockchain governance

http://vitalik.ca/general/2017/12/17/voting.html

Documentaries, videos and podcasts

Title
Date
Link

How the U.S. government used blockchain to fight fraud

Oct 26, 2016

https://youtu.be/507wn9VcSAE

Khan Academy

May 1, 2013

https://youtu.be/0WiTaBI82Mc

Alex Dean
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Further reading

Author
Title
Link

Mohit Mamoria

WTF is the blockchain? — understanding the problem it solves before defining it

https://hackernoon.com/wtf-is-the-blockchain-1da89ba19348

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Introduction

A blockchain is a type of distributed ledger where transactions grouped into blocks are sharedreplicated across a network of participants. Blockchains are decentralized and do not rely on any central authority or trusted 3rd party for validation of transactions. All participants in the peer-to-peer network, known as nodes, maintain a full record of all transactions on the blockchain and communicate directly following a protocol to form a distributed consensus on the next valid block in the chain.

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Academic papers

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Author
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Alex Roehrs, Cristiano Andréda Costa, Rodrigo da Rosa Righi

OmniPHR: A distributed architecture model to integrate personal health records.

https://www.ncbi.nlm.nih.gov/pubmed/28545835

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Transaction signature scheme from the bitcoin whitepaper.
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Blockchain

A blockchain is an append-only digital ledger instoring whicha set of time-ordered transactions madegrouped in bitcoinblocks or another cryptocurrencythat are recordedlinked chronologicallytogether andusing publiclycryptographic hashes.

Article

Each block in the blockchain contains a timestamp, some transactional data, and cryptographic hash link to the previous block. This creates a time-ordered chain of links from the genesis block to the most recent block that cannot be altered retroactively without alteration of all subsequent blocks, requiring a majority collusion of the network.

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Bitcoin whitepaper released

The Bitcoin whitepaper by Satoshi Nakamoto describes the Bitcoin blockchain.

Efficient broadcast time-stamping

Benaloh and de Mare publish Efficient Broadcast Time-Stamping, which also describes techniques on digital time-stamping and ordering of documents.

Improved reliability and efficiency of digital time-stamps

Bayer, Haber, and Stornetta's paper examines and improves upon the resource usage of the Haber and Stornetta's previously proposed time-stamping. The links between time-stamped documents use cryptographic hashes, the grouping of the documents into blocks to reduce the amount of hash pointers required, and the organization of the links into a tree structure called a merkle tree. Additionally, they add research on secure names for bit-strings in a subsequent paper.

Early research on time-stamping digital documents

Haber and Stornetta's paper describes a digital notary type procedure allowing businesses to verify the date at which a document was created. The documents are linked together with digital timestamps such that it is infeasible for users to alter the date on the document. Each user time stamps their document as well as the previous document in the chain with a digital signature only they can provide, then broadcasts it to the network. Bitcoin uses a similar data structure for its digital ledger, and Satoshi Nakamoto references this paper in the bitcoin whitepaper.

Merkle Tree data structure is proposed

Ralph Merkle's 1980 paper on Protocols for Public Key Cryptosystems first describes the what is now known as the Merkle Tree, a data structure in the form of a tree of cryptographic hashes. This structure allows for a large amount of data to be verifiably stored in an efficient manner, a crucial aspect of blockchain architecture.

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A blockchain is a type of distributed ledgerdistributed ledger where transactions grouped into blocks are shared across a network of participants. Blockchains are decentralized and do not rely on any central authority or trusted 3rd party for validation of transactions. All participants in the peer-to-peer networkpeer-to-peer network, known as nodes, maintain a full record of all transactions on the blockchain and communicate directly following a protocol to form a distributed consensus on the next valid block in the chain.

...

Each block in the blockchain contains a timestamptimestamp, some transactional data, and cryptographic hashcryptographic hash link to the previous block. This creates a chain of links from the genesis block to the most recent block that cannot be altered retroactively without alteration of all subsequent blocks, requiring a majority collusion of the network.

...

In 2004, Hal FinneyHal Finney combined ideas from Wei Dai’s b-money and Adam BackAdam Back’s hashcash to create his reusable proof of work tokens. Nick SzaboNick Szabo’s utilizes these ideas for timestamped proof of work to create a string of distributed property title registry for Bit goldBit gold. Finally in 2008 an individual or group of individuals released the bitcoin whitepaper under the name Satoshi Nakamoto. Bitcoin was the first successful implementation of a secure decentralized blockchain solving the double spend problem for a digital currency.

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Currently, most blockchains currently utilize consensus protocols with proof-of-work. Proof-of-workProof-of-work requires nodes to compete for a financial reward by solving complex computational puzzles and win the privilege of mining the next block in the chain. The Proof-of-workProof-of-work protocol was originally developed to deter denial of service attacks and is designed such that the majority of computation power or hashpowerhashrate controls has control of the network. Adversarial nodes must compete against the totality of hashpowerhashrate of all non colluding nodes in order to defraud the system. An adversarial majority node would also potentially favor generating new coins over attempting to undermine the system and the validity of their proportion of the network.

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Consensus emerges from independent verification of each transaction by each full node on the network. Blocks are added to blockchains by mining nodes at different intervals depending on the how the protocol determines validity of blocks and the participants ability to create those new blocks. Nodes then verify the new blocks and construct the chain. Nodes then select which blockchain they prefer, typically based on cumulative proof of work demonstrated on the longest chain, and a consensus emerges. Note that there are many alternative consensus mechanisms under active development that result in blockchains or distributed ledgers with vastly different properties. Some of these consensus mechanisms rely on differing protocols like proof-of-stakeproof-of-stake (dPoS, Casper, Ourobouros, etc), proof-of-capacity, proof-of-coin age, proof-of-burn, proof-of-authority and many more.

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Transactional logic on blockchains can be simple, such as the transactions of value in bitcoin, to arbitrarily complex code called smart contractsmart contracts employed in EthereumEthereum and other blockchains.

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The history of transactions on the blockchain, including all transactions made by each address, is permanently open and visible to everyone. However the identity of person operating a particular node is pseudo-anonymous. New addresses can be easily created on the blockchain without necessarily linking to an individual’s name. For example if the bitcoinBitcoin or ethereumEthereum address of an individual is discovered it becomes trivial to find all transactions performed with that address with for example tools such as Bitcoin block explorer or Etherscan.

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Disagreements within blockchain communities on changes to the blockchain protocol have resulted in significant controversy, most famously the bitcoin block size debate resulting in the Bitcoin CashBitcoin Cash hardfork. Other controversial hard forks include the Ethereum hard fork due to The DAO vulnerability and hack, resulting in the blockchain Ethereum ClassicEthereum Classic blockchain.

Edits on 25 Oct, 2017
Alex Dean
Alex Dean edited on 25 Oct, 2017
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In 2004, Hal Finney combined ideas from Wei Dai’s b-money and Adam Back’s hashcash to create his reusable proof of work tokens. Nick Szabo’s utilizes these ideas for timestamped proof of work to create a string of distributed property title registry for Bit gold. Finally in 2008 an individual or group of individuals released the bitcoin whitepaper under the name Satoshi Nakamoto. BitcoinBitcoin was the first successful implementation of a secure decentralized blockchain solving the double spend problem for a digital currency.

Edits on 18 Oct, 2017
Alex Dean"added academic papers"
Alex Dean edited on 18 Oct, 2017
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Research examining the role of blockchain in healthcare, conservation, and other biological fields is increasing as shown by the increasing academic papers being released.

Academic papers

Author
Title
Link

Alex Roehrs, Cristiano Andréda Costa, Rodrigo da Rosa Righi

OmniPHR: A distributed architecture model to integrate personal health records.

https://www.ncbi.nlm.nih.gov/pubmed/28545835

Daisuke Ichikawa, Makiko Kashiyama, Taro Ueno

Tamper-Resistant Mobile Health Using Blockchain Technology

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5550736/

Jesse Yli-Huumo, Deokyoon Ko, Sujin Choi, Sooyong Park, and Kari Smolander

Where Is Current Research on Blockchain Technology?-A Systematic Review.

https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/27695049/

Selena Ahmed & Noah ten Broek

Food supply: Blockchain could boost food security

https://www.nature.com/nature/journal/v550/n7674/full/550043e.html

Tim k. Mackey, Gaurvika Nayyar

A review of existing and emerging digital technologies to combat the global trade in fake medicines

https://www.ncbi.nlm.nih.gov/pubmed/28349715

Timothy Nugent, David Upton, Mihai Cimpoesu

Improving data transparency in clinical trials using blockchain smart contracts

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5357027/

Tsung-Ting Kuo Hyeon-Eui Kim Lucila Ohno-Machado

Blockchain distributed ledger technologies for biomedical and health care applications

https://academic.oup.com/jamia/article-lookup/doi/10.1093/jamia/ocx068

Xiao Yue, Huiju Wang, Dawei Jin, Mingqiang Li, Wei Jiang

Healthcare Data Gateways: Found Healthcare Intelligence on Blockchain with Novel Privacy Risk Control

https://link.springer.com/article/10.1007%2Fs10916-016-0574-6

Zachary Baynham-Herd

Technology: Enlist blockchain to boost conservation

https://www.nature.com/nature/journal/v548/n7669/full/548523c.html

Alex Dean"added forks image"
Alex Dean edited on 18 Oct, 2017
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