These are also the years when Burning Man became the craziest festival in the world. There used to be something called the Suicide Club in San Francisco. It was a group of crazy kids doing crazy things, like climbing the Golden Gate Bridge. Several of them went one to create other crazy events around the Bay Area. One of them, Mary Grauberger, was organizing one of those "human-potential" events: once a year, during the summer solstice in june, she was inviting her friends to a beach party in San Francisco. During her beach part of 1986 two of her friends, Larry Harvey and Jerry James, burned the effigy of a man. It became a tradition for that beach party. At the same time the Suicide Club had evolved into the Cacophony Society, another semi-legal organization that was organizing strange events for young people. People like Dan Kottke, who had been Steve Jobs' best friend during his college years and helped him start Apple, remember fondly the Cacophony Society. In 1990 Kevin Evans and John Law of the Cacophony Society invited Harvey to transplant the burning ritual to the Black Rock Desert in northern Nevada. Kevin Evans was an artist, one of the several artists who had joined the Cacophony Society. Burning Man became a festival, a festival of artistic sculptures in the desert that are burned at the end of the festival. Today, Burning Man is the most famous festival in the USA. It was started by a carpenter and two jobless Cacophony members. Originally it was famous for sex and drugs, but now it is famous for the way it self-organizes in the middle of the desert and for the colossal artistic sculptures, some of which move (a legacy of the Survival Research Laboratories, another unique movement of the 1980s in San Francisco that focused on shows of machines destroying each other).

The history of P2P begins outside the Bay Area in Boston. In june 1999 Shawn Fanning invented a system to distribute mp3 files over the Web, Napster. This system allowed people all over the world to share music files. But this was illegale and the music industry eventually forced Napster to stop doing it. Nonetheless, Napster had invented a new technology, Peer-to-Peer (P2P); and proved its potential. Napster inspired a new generation of P2P services, most of them used to share music illegally, like Kazaa in Estonia and BitTorrent in San Francisco. These hackers, like Bram Cohen of BitTorrent, became heroes of the counterculture for defying the giant corporations of the music industry.

We are getting closer to Bitcoin. Let me backtrack to explain where Cohen came from. In 2000 a former Yahoo scientist Jim McCoy started EGBT (Evil Geniuses for a Better Tomorrow) to work on MojoNation, a different kind of P2P platform. He was inspired by videogames to solve the problem of "Agoric computing", which was a serious topic of computer science for the purpose of improving large-scale computation. The "mojo" was a cybercurrency, but it was not used to buy and sell things: it was used to provide balanced and secure computation for a network. MojoNation was a fascinating application of concepts of economics applied to optimization of computers. In 2001 SUN, that at the time was a major power in the Internet world (SUN originated Java, that still today powers the Web), introduced a similar open-source project, XTA (Juxtapose). Bram Cohen worked with Jim McCoy. That's where he learned the technology that he used to create BitTorrent, that became the most popular P2P platform. Another EGBT alumnus, Zooko Wilcox-O'Hearn, turned MojoNation into Mnet. So the concepts of cybercurrecy and P2P had been joined.

In 2009 this cypherpunk Satoshi Nakamoto introduced the digital currency Bitcoin, based on a P2P model, the first successful currency not to be printed by a government.

(See here for speculation on his real identity)

Bitcoin was implemented as a "dark net". The extropian Hal Finney became the first person to ever receive a bitcoin. Just like the previous P2P systems, Bitcoin was based on very sophisticated technology, and in this case on very sophisticated mathematics. From an engineering point of view, Bitcoin's main achievement was that the system was capable of creating copies that could not be copied.

In 1992 Cynthia Dwork (IBM's Almaden labs in San Jose) published "Pricing via Processing or Combatting Junk Mail" in which she conceived computational processing as a "cost" to make "spam" email very expensive, and therefore discourage spammers. In 1997 Adam Back in Britain published "hashcash", a method to use cryptographic hash functions on a network to achieve that "cost" for spammers. Again, the intent was to discourage abuse of email, but Back de facto invented a method to control processes a network with no need for a central authority. Also in 1997 Nick Szabo published the paper "Formalizing and Securing Relationships on Public Networks" that described a distributed trust model.

A mathematical model for "cryptocurrencies" was first described in 1998 by the mysterious Chinese mathematician Wei Dai on the "cypherpunks" forum. His idea was simple: let everybody have a record of every transaction, so that noone can cheat the others. This idea creates an anonymous and distributed system in which the community guarantees "trust", not the central government. Bitcoin shifts the power from the central government to a P2P network. Wei Dai says that he was inspired by "The Crypto Anarchist Manifesto" written in 1992 by Tim May, an early employee at Intel. At the same time, the extropian Nick Szabo proposed a cybercurrency called "bit gold". He conceived a sophisticated way to prevent people from spending twice a cybercurrency, a way to avoid that people can make copies. When we were rehearsing a presentation, the Chinese interpreter Wang Yang, who is usually hired to translate my talks in China, said that the system invented by Szabo sounds like something from a videogame. She was right. Szabo's model is indeed reminiscent of videogames and fantasy movies: there are masters assigning "difficult tasks" to novices; if the novices succeed, they become masters. In 1997 Szabo realized the value of his idea: he described how cryptocurrencies could be used to implement "smart contracts" on the Internet. The "difficult tasks" were a variation on the "proof of work" method employed by anti-spam software since the 1992 to fight email spammers. The "proof of work" method has a long mathematical tradition. It has yielded Hashcash and the family of "secure hash algorithms", which are recognized by the US government.

That's it. Now you have the complete recipe for creating Bitcoin: you need some crazy religious cult, some quasi-gangsters on the Internet, mathematicians who borrow ideas from economics and from videogames, some military software, and a group of individuals who are willing to risk jail.

In 2016 Craig Wright, a computer security expert based in Australia with a PhD in theology, confessed to be the real Satoshi Nakamoto but not everybody is convinced. I donÎéÎ÷t believe it. First of all, the cypherpunk forum was born in Santa Cruz, south of Silicon Valley (founded by Tim May, a former Intel employee) and everything about bitcoin has happened on that forum. Second, Wright worked with Dave Kleiman, based in Florida, a paraplegic and a computer security expert who died a horrible death, alone and poor, in 2013. Maybe Satoshi Nakamoto is dead, and Wright knows that he is deadÎíÎõ

My guess is that governments will learn to love the blockchain and smart contracts. Ironically, they may use the blockchain for the exact opposite reason that it was created: every transaction gets recorded, and every contract is self-executed, which means that governments can keep track of all transactions and can tax all transactions and don't even need tax collectors because the tax is collected automatically on the blockchain. Governments will learn to twist blockchain technology so that it becomes a technology of absolute and incorruptible transparency. And, talking of corruption, blockchain can also be used to fight corruption because it contains a record of everything that has happened and a simple algorithm can detect suspicious transactions.

Even before Bitcoin became famous, the success of peer-to-peer models had generated a lot of enthusiasm in the counterculture. Ori Brafman's "Starfish And The Spider" (2007) and Yochai Benkler's "The Wealth of Networks" (2007) publicized the notion of "decentralized autonomous organizations" (DAOs) and Michel Bauwens published the "Peer-to-peer Manifesto" (2008). Bitcoin realized their dreams. Bitcoin is not just a cybercurrency: it is a method to reinvent government bureaucracy without the bureaucrats.

Bitcoin's "blockchain" mechanism is the real revolution. The blockchain technology allows a network of computers to make changes to a global record without the need for a central authority. The blockchain is a ledger shared by all the computers of the network, and its technology makes it impossible to spend the same money twice (no counterfeits). You can use it for the "smart contracts" that Szabo envisioned. In theory, you can create a society in which there is no need for central authorities of trust. Today, trust is guaranteed by something like the national bank (run by the government) or the title company (the agency that certifies who owns a house). Blockchain creates trust through an algorithm. Any form of peer-to-peer contract (whether selling a house or renting a car) can be made safer through blockchain. Smart contracts (which, ultimately, are mathematical formulas) represent patterns of interaction in society. Philosophically speaking, this is a major revolution: every contract in human societies can be reduced to a math problem. Computers had reduced contracts to data stored in a database, but "smart contracts" are more than just the record of an agreement: they include an algorithm that needs to be calculated in order to verify the validity of the contract and that then automatically executes the contract. The smart contract is more than data: it consists of data AND a math problem.

Politically speaking, it is an even bigger revolution. If blockchain is adopted for "smart contracts", what is the function of governments? Today we use police, trials and prisons not only for violent crimes but also for people who violated contracts. If computer algorithms can maintain "order", what is the function of police, justice and prisons? Decentralization had historically meant chaos, but blockchain is a system based on decentralization that actually guarantees order. It sounds like a contradiction, but its technology is basically order enforced through chaos. It is also much more secure than government databased and corporate databases, because the security of a transaction is guaranteed by all the computers in the network. The blockchain technology is much more than a method to manage a virtual currency: it is a digital record keeper that does not require intermediaries/middlemen and cannot be distorted/hijacked.

In 2014 the first wedding via blockchain was celebrated in the USA. I am not sure how if they can ever divorce!

Avalon (China, 2012, later renamed Canaan Creative) was the first company to manufacture ASIC mining chips. 21 Inc (San Francisco, 2013) introduced an embeddable bitcoin mining chip in 2013 and then the first computer with native hardware and software support for Bitcoin in 2015. In 2015 BitFury (San Francisco, 2011) introduced a "green" ASIC chip capable of delivering a minimum computing power of 100 gigahash per second. Bitcoin mining hardware started popping up all over the world.

Bitcoin is neither the first nor the only cryptocurrency. In 2016 Cryptsy, the largest "altcoin" exchange, listed dozens of them. Some, like Omni/Mastercoin, introduced by JR Willett in 2013, use the same blockchain as bitcoin. Others, like Litecoin (created by former Google engineer Charles Lee in 2011, second for market capitalization in 2015) and Primecoin/PPCoin/Peercoin (all created by an anonymous "Sunny King" in 2012) employed different "proof of work" algorithms. Sunny King devised an algorithm called Proof of Stakes (PoS) to reduce the energy consumption of mining, a "green" alternative to Proof of Work. PPCoin/Peercoin s "green" was the first cryptocurrency to implement PoS and in 2013 it evolved into Primecoin. Also in November 2013 a person known only as BCNext launched NXT, the second cryptocurrency based on POS (a platform to build financial applications). In 2014 Jae Kwon launched Tendermint, that improved PoS with Byzantine Fault Tolerant (BFT) consensus. When in 2008 Satoshi Nakamoto invented the blockchain, he had de facto solved an old mathematical problem, known as distributed Byzantine Fault Tolerant (BFT) consensus. The problem had originally been raised by the SIFT project at SRI in 1978 in the context of airplane safety. The problem had been solved theoretically in 1999 by Miguel Castro and Barbara Liskov at MIT, but Nakamoto solved practically it for a virtually infinite network like the Internet. Jae Kwon's breakthrough was to improve the blockchain with a number of mathematical tricks. He achieved the same level of security guaranteed by Bitcoin's Proof-of-Work system but without the need for massive computation. The result was a new theory of distributed consensus, and in fact within a few years a number of new consensus algorithms based on BFT have appeared: starting with Vlad Zamfir's Casper the Friendly Ghost (2015).

Another popular cryptocurrency is Ripple. Jed McCaleb was the original founder of OpenCoin with the goal of creating a bitcoin network that didn't rely on mining. The project was renamed Ripple after Chris Larsen joined it. It is unusual because it is based on a trust graph, not a blockchain.

Then there is the usual avalanche of startups. Andrew Cook founded his Cook Investment Firm in Chile in 2011, when he was 20 years old, and today it is the world's largest bitcoin investment fund. CoinBase, founded in San Francisco in 2012, offers a bitcoin marketplace and a platform for bitcoin payments. Epiphyte (2013) offers banking for crypto-currencies. Circle (2013) allows users to send bitcoins to friends and family. NextBank (2015) aims to become the first all-bitcoin institution. Quickcoin (2014) integrates a bitcoin wallet with Facebook to send bitcoins as messages. BitShares (2013) offers financial services (including exchange and banking) on a blockchain. BitShares was developed by Daniel Larimer in 2013 using a new consensus algorithm, delegated Proof of Stake (dPoS) instead of proof of work. Larimer built Graphene, an open-source blockchain implementation in C++ that has been used also in other applications like Steemit. In 2016 CoinCloud, a trader of bitcoin for cash, installed a "bitcoin machine teller" in Menlo Park.

SolarCoin, a nonprofit organization founded in 2014 by Nick Gogerty, is a digital currency that rewards solar electricity generation.

And the blockchain is already being used for applications outside fintech. For example, Gems, launched in 2014 by Daniel Peled in Israel, uses the bitcoin blockchain to implement a social messenger (therefore a "decentralized" social messenger). Skuchain, founded in 2014 in Mountain View by Srinivasan Sriram, has applied the blockchain to the supply chain of manufacturing. An example of how blockchain technology can help track (and record) a supply chain is about the food that we buy at the supermarket: we have no idea where the ingredients came from. Ripe.io, founded in 2017 in San Francisco by Raja Ramachandran, uses blockchain technology and the Internet of Things to transform the digital food supply chain. This technology gives users the ability to learn more about the quality of their food, where it was produced, and more. Additionally, farmers can use this technology to automate internal processes and meet market demands around growing high quality and sustainable products. Proof of Existence (2014), Factom (Texas, 2014) and Empowered Law (Chicago, 2015) offer notary Service to register documents. MedVault wants to record medical information on the bitcoin blockchain, and Factom partnered with medical-services provider HealthNautica to do the same thing.

Steemit is a platform for publishers launched in 2016 by Ned Scott and Dan Larimer (of BitShares fame). The Steem blockchain produces tokens (steems) that users gain for posting, discovering, and commenting on content. Authors are rewarded with steem when their content is liked by users. Curators are rewarded with steem for discovering content that becomes popular. In December 2017 Steem token was ranked 32nd of 1,358 cryptocurrencies. Steem's market capitalization reached a peak of $1.6 billion before collapsing down to 17 million in March 2017.

Stellar, founded by Ripple's founder Jed McCaleb in 2014, is a non-profit open-source platform for micro-payments designed for the developing world. It augments the Ripple consensus algorithm with a method developed by David Mazieres at Stanford University, the Federated Byzantine Agreement. Ripple allows banks and multinational corporations to make international payments. Stellar allows individuals to trade money directly with each other.

Tron, launched in September 2017 by Justin Sun Tron (still a student at Hupan University in China), connects content creators with ordinary users (by January 2018 it had a market capitalization of over $16billion and it was preparing to launch its own blockchain and become a competitor of Ethereum). In 2018 Tron announced the "TRON Arcade" fund to encourage game developers to develop blockchain-based games. Ripple responded with a similar fund in 2019 in collaboration with a brand new startup, Forte, a blockchain gaming startup just launched in San Francisco by Kevin Chou (who was formerly the founder of mobile game startup Kabam in Vancouver).

The blockchain can also be used for "Initial Coin Offerings" (ICOs) to invest in new projects. When you buy the digital currency of an ICO, It is not the same as buying a startup's share after an IPO because the digital currency does not give you voting power on the project: it only gives you a share of the profit. You can use this system to create a venture capital firm, like Blockchain Capital did; or to fund an incubator for blockchain projects, like Adel did; but it can really be any project. Storj, for example, allows computer users to buy and sell storage: when you offer storage on your computer to others, you earn storj coins, and when you need storage on other people's computer you have to pay them storj coins.

Initial coin offerings raised $11.8 billion between January and May of 2018, almost double the total for the whole of 2017. The big ICOs were Telegram’s for $1.7 billion and EOS's for $4 billion.

Monegraph and Ascribe deal with intellectual property. The blockchain can help artists and writers protect their work from copyright infringement.

Each consensus algorithm answers a simple question: who should produce the next block of updates to apply to the blockchain?

Proof of stake replaces miners with validators. These have a power that is proportional to the amount of coins they own. The advantage is that it takes a lot less power. Cardano, Qtum, Pivx, BitConnect and Stratis use PoS. But the problem is the same: richer users get richer faster.

Proof of importance takes into consideration not only your stakes but also how often you transact with others, and with whom, how active you are.

Delegated Proof-of-Stake and traditional Proof-of-Stake stand to each other like direct democracy stands to representative democracy. In delegated PoS, every participant that owns coins is allowed to vote for delegates. The delegates who get the most votes are the ones who earn the right to validate transactions and create new blocks, and make money out of it. Clearly, this is similar to the presidential elections in the USA. Lisk, EOS, Steem, BitShares and Ark use delegated Proof of Stake.

Codius, invented in 2014 by Stefan Thomas and Evan Schwartz in San Francisco, is another general platform for smart contracts. Blockchain technology can be used to track the history of all sorts of information and securely: nobody can tamper with information encoded in the blockchain. Any kind of peer-to-peer contract can be implemented as a (secure and unbreakable) blockchain application. And removing the middleman (the notary public, the home-ownership registration company, the car registration office, etc) can save money and time in almost every sector.

You completely change society when you reduce every contract in human society to a math problem. Today it takes a specialist to verify a contract and usually the proof is some kind of official (and expensive) certificate. In a future driven by blockchain, we will simply perform a search operation, just like today we search with Google or Baidu for some information, and we will simply email the "certificate" that we found with that search. Sorry for the attorneys, but there will be no need for filing patents or wills. And note that the technology is almost entirely open-source: anybody can contribute to progress in blockchain technology, and no company owns the rights on blockchain.

The future of bitcoin is smart contracts, the future of smart contracts is... almost infinite. Here is why. Ethereum doesn't store massive data within the blockchain itself. It uses an additional component (originally Swarm, later cancelled, now IPFS). Ethereum consists of three main blocks: contracts (the "decentralized logic"), IPFS (the "decentralized storage") and Whisper (a "decentralized" messaging system, still under development). IPFS stands for InterPlanetary File System, invented by Juan Benet in 2015. All data on IPFS are perpetually recorded online via P2P distribution. IPFS provides an encrypted address for each piece of information. The level of security if very high: a piece of information in IPFS cannot be manipulated. So far it sounds just like boring database management but in practice... the IPFS protocol can replace HTTP, the protocol that carries the entire Internet! It doesn't end here. Ethereum is "Turing-complete", a technical term that means: it can implement any program. Ethereum can become the "world computer" of the future...

A recent competitor of Ethereum is Dfinity, developed by Dominic Williams since 2015. It is a virtual computer of potentially unlimited capacity, similar in concept to Ethereum. All dapps built for Ethereum will be able to run on Dfinity. You can write software to run on Dfinity by using the Motoko programming language. Dfinity is proposing to extend the Internet via an Internet Computer Protocol (ICP) that connect data centers around the world.

A traditional application is centralized, meaning that its software runs from one specific computer, the so-called "server". You typically access it from your own computer or smartphone. A traditional application is made of routines that access databases. A decentralized application (a dApp) is made of smart contracts that access the blockchain, which is a decentralized P2P network. Compared with traditional applications, smart contracts are the computations that we perform on the database. Legal contracts are written in legal language. Smart contracts are written in software. Smart contracts are a series of instructions, written in "solidity", the programming language of Ethereum: when the first set of instructions are done, then execute the next function and after that the next etc. Each step is recorded by all the nodes in the Ethereum network. Each step in a smart contract is a transaction and has a cost that is measured in "gas". The price of gas is paid in "ether". Ether measures the market value, gas measures computational use.

Each dApp has its own native currency, which is called a token. Once you are inside the dApp, you use its token, just like inside a movie theater you use a movie ticket. You bought the movie ticket with money. The equivalent of your money is ether, that allows you to buy all sorts of tokens, the equivalent of movie tickets. The creator of a dApp must create the dApp's own token: a token can be created on a website like the Token Factory or written from scratch in solidity. Initially you, the creator, own all the tokens. Then you sell tokens for ether. to the people who want to transact with you. The price of a token depends on supply and demand. At that point you govern your own monetary policy. You create your private economy. That's tokenomics.

Originally, each dApp had its own token, incompatible with the tokens of other DAPPs. A smart contract working with several dApps had to deal with the complexity of using different tokens, but then Ethereum came up with a standard to make tokens compatible with each other. Almost all smart contracts in 2017 were based on an Ethereum standard, ECR20. A token is a cryptocurrency with a special purpose because it implements a contract. Before ECR20 they were not compatible. Now almost all tokens are based on ECR20 and therefore are compatible.

There are other ways to exchange tokens. Bancor, launched by an Israeli team in 2017, is an alternative exchange for tokens: it converts any token to any other token in the Bancor network with no counterparty and at automatically calculated price, based on a simple arithmetic formula. To be accepted by Bancor, your token needs to be a "smart" toke: a token with a smart contracts built inside it. All tokens in the Bancor network can be converted to and from the BNT, Bancor Network Token. When it was introduced, Bancor's ICO passed the DAO as the biggest ICO of all time ($152m); but its valuation crashed almost immediately.

In August 2017, when Bitcoin was collectively valued at $47 billion, a new split took place. The original blockchain can only have one megabyte of data added to it every 10 minutes. Bitcoin Cash, mainly implemented by Amaury Sechet, uses blocks that can be as large as eight megabytes. Bitcoin Cash was officially born when block number 478559 was mined. The opponents of the split argued that a larger block made mining even more problematic, requiring more powerful hardware, and therefore helping usher in monopolies. There was already a huge environmental cost in mining bitcoins: in 2017 bitcoin mining consumed about one billion dollars a year in electricity.

There are two fundamental solution to the limitations of the blockchain . The first one is to increase the block size, and that was the Bitcoin XT fork; but this means that all the computers on the bitcoin network must install a new version at the same time! The other solution is to keep the same block size (1 megabyte) but to increase the volume of transactions fitting into a block: that was the so-called "segregated witness" (SegWit) optimization invented by Pieter Wuille in 2015 and adopted in 2016. In 2017 Jeff Garzik proposed another solution, the "Segwit2x fork": increase the block size to two megabytes in addition to SegWit optimization.

In 2017 the skyrocketing transaction fees of bitcoin led to another split: Bitcoin Cash (BCH), promoted by evangelist Roger Ver as "more spendable" than Bitcoin (BTC), split from Bitcoin (BTC). BCH introduced a blocksize limit of 8Mbytes allowing for about 2,000,000 transactions per day (versus Bitcoin’s blocksize limit of 1 Mbyte allowing for about 250,000 transactions per day) and therefore lower transaction fees. But in November 2018 another war flared up, this time inside the BCH camp, with Jihan Wu’s Bitmain (the largest manufacturer of mining equipment in 2018, based in Beijing, that also controlled the BTC.com and Antpool mining pools) and Haipo Yang's cryptocurrency exchange ViaBTC (also based in China) fighting against Craig Wright's new startup nChain (based in London) and billionaire Calvin Ayre's CoinGeek (a mining pool based in the USA, also the largest pool of BCH miners at the time of the fork). In theory their argument was over a technical issue (variously known as "canonical ordering of transactions", "lexical ordering" and "pre-consensus") and over the blocksize (that nChain planned to raise to 128 Mbytes). The Chinese had adopted the protocol Bitcoin ABC (that eventually extended the blocksize to 32 Mbytes), while nChain announced the introduction of a new protocol, Bitcoin SV (for "Satoshi's Vision"). In practice, many suspected a power struggle between the Chinese and the Westerners.

There are also concerns about the independence of Bitcoin. Sure: Bitcoin is run by the crowd. But some factors can make it very vulnerable to government decisions. For example, in 2017 Bitcoin de facto depends on China because the majority of bitcoin miners are located in China. The bitcoin miners in China are basically laundering money: they spend Chinese currency to pay for cheap Chinese electricity that allows them to make bitcoins that can be turned into dollars abroad. In September 2017 the Chinese government banned "initial coin offerings". What if the Chinese government decides to crack down on bitcoin mining? What happens to Bitcoin if overnight most of the miners of the world go out of business?

Dash, that was born as Xcoin and Darkcoin when it was launched in 2014 by Evan Duffield, protects your privacy by using Gregory Maxwell's "coinjoin" technique (2013) that mixes a transaction with many others to hide its information. In 2017 its market cap increased 8,000%. Dash was innovative in many ways. First of all, it introduced a second-tier network ("masternodes"): only 45% of the block rewards go to "miners", 45% go to the masternodes, and 10% is taken as a sort of tax to fund the budget. That budget is the second and major innovation. Dash was born out of frustration that no decision was easy within the Bitcoin community. Dash was designed to have built-in governance: masternodes can vote and take decisions quickly. Therefore in August 2015 Dash introduced the first decentralized governance system, the Dash Budget System. In January 2016 the masternodes voted quickly to extend the size of the block to 2 megabytes, something that the Bitcoin community never agreed to do. (There are even plans to increase the Dash blocksize to 400 megabytes). In 2017 Dash started a collaboration with Arizona State University, the "Blockchain Research Lab".

In March 2015 Japanese hackers launched NEM, which is almost a fork of NXT. NEM, whose currency is XEM, uses a "proof of importance" method: it assigns an importance score to every account on its blockchain, and it rewards accounts proportionally to how actively participate. Instead of "mining", NEM has "harvesting": it still results in adding transactions to the blockchain in exchange for a financial reward, but this time the "importance" of the participant makes a difference. Other innovations include: multisignature accounts, encrypted messaging, and especially the Eigentrust reputation system. The EigenTrust algorithm was developed in 2015 at Stanford by Sep Kamvar, Mario Schlosser and Hector Garcia-Molina. Since the "proof of importance" method was the PhD thesis of Makoto Takemiya, we thought that Takemiya was the founder, and he behaved like he was, but then the other founders expelled Takemiya, who went on to found the startup Soramitsu in 2016 that then won a contract with a central bank in Asia.

Governance is also the reason that Tezos was launched in 2017 by Arthur and Kathleen Breitman (who collectively used the pseudonym LM Goodman when they wrote the white paper in 2014). Texos introduces democracy in the blockchain: your voting power power is proportional to the tokens that you hold. It launched with a delegated proof-of-stake algorithm but even that can be submitted to a democratic vote.

Managing a blockchain is not trivial so now some companies are beginning to offer "blockchain-as-a-service": Azure by Microsoft, Ardor by Jelurida, founded by Petko Petkov (a core developer of NXT) and Lior Yaffe, and Stratis, founded by Chris Trew in Britain, a platform for dapps written in C# that make use of the Microsoft .NET framework.

In 2015 Sergio Demian Lerner launched DagCoin, the first block-less coin based on a method called " directed acyclic graph". There are no miners and there are no blocks in a DAG. Users confirm each other's transactions through their own transactions. Each user that transacts becomes automatically the equivalent of a Bitcoin miner. Because there are no blocks, there is no blocksize issue.

None of these coins is well suited for micro-transactions. A Bitcoin transaction doesn't make sense if the amount involved is very small. Therefore in 2016 group of hackers created Iota, which is basically a lightweight version of Bitcoin designed for micro-transactions. However, Iota is significantly different from Bitcoin and all the blockchain technologies because it uses a "directed acyclic graph" (or DAG), known as a "tangle", instead of a blockchain. The white paper of the tangle was written by Serguei Popov but Iota's founders are probably many. Its creators market it as platform for "the Economy of Things", for creating an autonomous machine economy.

Greg Meredith developed the Rchain technology for a decentralized social media platform called Synereo but then spun off Rchain in 2016 as a general-purpose platform for smart contracts capable of processing 40,000 transactions per second. Rchain too uses a directed acyclic graph of blocks (blockDAG) rather than a blockchain.

The DAG was also used in Ethereum for its "proof of work" algorithm: a DAG is generated for each "epoch" (every 30,000 blocks) according to a complex algorithm that combines Vitalik Buterin's Dagger algorithm and Thaddeus Dryja's Hashimoto algorithm.

There are so many variations, all of them introduced in less than five years, that the expression "blockchain technology" has already become obsolete. Now it is better to talk about "distributed ledger technology" or DLT. The only thing that they have in common is that all DLT systems provide an immutable record of all transactions.

We really have to separate bitcoin and blockchain. Bitcoin is a virtual currency that has no owner. It is struggling to become a mainstream form of money because we contradict ourselves: we like the fact that there is no "central bank" but at the same time we don't believe in its future because... there is no central bank. Governments obviously don't like bitcoin (and virtual currencies in general) because transactions in bitcoins avoid taxes (and can easily be used for criminal activities). My guess is that eventually the governments of developed countries will find a use for bitcoin (or some variation of bitcoin) when they find a way to tax bitcoin transactions. There is also a general feeling that bitcoin could be useful in unstable countries where the government is weak or the local currency is not trusted by the people. If a country with these problems has a population equipped with smartphones, it would make sense that people trust bitcoin better than their country's currency.

Bitcoin may rise or decline, but, regardless, the blockchain industry is vibrant. This phenomenon is no longer about a virtual currency. This is potentially a revolution in the way society works. I am confident that the technical limitations of blockchain will be solved. In fact, there are already multiple proposals. And i am confident that governments will eventually appreciate the benefits of using a blockchain (or some modified version of blockchain technology) to record transactions and getting rid of unnecessary bureaucracy (that often translates into corruption and bribes). The resistance to adopting blockchain for recording transactions will be more conceptual than technical. Ultimately, the blockchain is a database, and it sounds weird that the entire world will work on just one database. We will probably end up with different blockchains, and then a way to make them communicate.

In 2016 the Linux Foundation started the Hyperledger Project to advance blockchain technology. Read the list of the companies that have joined this project: IBM, Accenture, Intel, Fujitsu, Hitachi, ... Hyperledger was launched in 2014 by Dan O'Prey and Daniel Feichtinger, and it was basically Ripple with the pratical Byzantine Fault Tolerant (BFT) consensus method. In 2015 DAH acquired simultaneously Hyperledger and a Java-based reimplementation of Bitcoin. In 2016 DAH donated the whole package to the Linux Foundation.

Within the blockchain industry, there is a lot of interest for Ethereum, which is rapidly becoming the most interesting blockchain platform. The critics say that Ethereum, is not designed for distributed computing. Ethereum is designed for consensus. The blockchain was designed to avoid cheating: it was not designed to be the backend of a distributed system. This is all true, but Ethereum was born just a few years ago. The open-source Ethereum community has time to fix these problems. Meanwhile, Consensus Systems (ConsenSys), founded by Martin Koeppelmann and Joseph Lubin in New York in 2014, provides a platform to build Custom "decentralized applications" ("dapps") for blockchain ecosystems on top of Ethereum. There are already "dapps" that people can use, like Spritzle/HitFin, an Ethereum-based app for trading financial derivatives.

Ethereum is one of the so-called "Bitcoin 2.0 technologies" for developing decentralized applications ("dapps"): Ethereum, Counterparty, Maidsafe, Rootstock, Tauchain... The Counterparty platform (created in 2014 by Chris DeRose) is like Ethereum but it uses the Bitcoin blockchain. The platform includes a protocol that allowes Counterparty nodes to communicate with each other via the Bitcoin blockchain and a native currency (XCP). Swarm, formed by Joel Dietz in 2014 in Palo Alto, is an incubator of Counterparty projects. Storj, formed in 2014 by Shawn Wilkinson in Georgia, is a distributed peer-to-peer encrypted cloud storage (similar to Dropbox but distributed, like Swarm/IPFS but running on Counterparty instead of Ethereum)

There has been much criticism of Ethereum (after its DAO was hacked) but also some success stories. For example, in 2017 a branch of United Nations used Ethereum to help the Syrian refugees in Jordan.

The biggest problem of blockchain technology is scalability. In 2017 Visa managed 1667 transactions per second, Paypal managed 193 transactions per second, Bitcoin managed just 3-4 transactions per second, and Ethereum managed 20 transactions per second.

There are other platforms for easy decentralization of applications: Eris was founded in 2014 in New York by two lawyers, and markets itself as a "universal blockchain platform" because it can clone Ethereum, Bitcoin and many other blockchains. They think that the blockchain is just like a database, and each user should have its own. Etherparty, founded in 2015 in Los Angeles, and based on Ethereum, is cloud-based: no programming required for developing dapps.

Each "coin" is an economy of scale. For example, Filecoin, a blockchain project created by Protocol Labs in San Francisco (founded in 2014, by Juan Benet, inventor of IPFS), allows one to earn filecoins for hosting files: many of our devices have unused storage, and you can become a Filecoin miner (rewarded with filecoins) if you offer that storage to others.

The smart contract is the simplest form of decentralized automation. A decentralized application is a smart contract with an unlimited number of participants. By definition, these are applications that have no server: the blockchain (which is distributed all over the network) serves as the "backend". There is no centralized intermediary like in the business applications that run on Oracle or SAP backends.

One important precursor of the decentralized world was MaidSafe, invented in 2006 in Britain by David Irvine. It used concepts of volunteer-computing to decentralize the Internet: the storage came from disk space "donated" by volunteers on the Internet (most of the hard-disk space that exists on all the personal computers of the world is not used) connected via peer-to-peer protocols. No central servers, no central databases, and lots of encryption to protect the data. The goal was to build "a safe Internet". The name means: MAID (Massive Array of Independent Disks) SAFE (Secure Access For Everyone). When you store data on MaidSafe, the data are broken down into tiny chunks, heavily encrypted, and then randomly distributed around the world. Only the owner can reassemble and decrypt these chunks MaidSafe does not use blockchain, it uses a different way to provide security, but the general concept is very similar. The difference is that transactions are not stored in a blockchain: there are literally no traces left of a transaction, except at the two parties involved. MaidSafe's network is based on SafeNet: a super-secure platform that decentralizes all the services currently available on the Internet (messaging, email, social networks, data storage, video conferencing, etc). SafeNet makes the Internet work without any need for servers and databases. The beauty of the SafeNet is that a user can log into any computer of the network and the computer becomes "her" computer: her data, her applications, her profile. When she logs out, no trace of her work is left behind. The fans of MaidSafe see it as the final solution to the problems of identity theft and surveillance. Governments probably see it as a nightmare, because it would also protect criminals and terrorists.

Since the invention of the state, society can be defined by one property: contracts are legally binding. This actually means all sorts of imperfection in the system. The interpretation of the law is flexible. A judge in California and a judge in Arizona can read the same law in two different ways. A trial is often decided by the rhetorical power of the defense attorney, regardless of whether the defendant is guilty or innocent. A contract based on the blockchain is not legally binding, it is technologically-binding. Software inexorably executes the contract. The auto-executing software replaces lawyers, courtrooms, judges and prisons. There is no need for a legal system if the world moves to smart contracts. So you can use smart contracts to build DAOs, "decentralized autonomous organizations". A DAO is an unmanned organization (no office, no staff) that runs under the control of an incorruptible algorithm. The algorithm is, in turn, implemented in an open-source software that can be "audited" (verified, controlled) publicly. DAOs are autonomous; DAOs are self-enforcing; DAOs have no central control.

Bitnation, started in 2014 by Susanne Tarkowski Tempelhof, is a platform to create DAOs. Her motto is "Create Your Own Nation In 140 Lines Of Code". A DAO provides the same services that traditional governments provide, but in a decentralized way: there is nobody in control of those services. After "Do It Yourself" software and "Do It Yourself" biotech, now we have D.I.Y. governments.

Decentralization has historically meant chaos, but blockchain is a system based on decentralization that actually guarantees order. It sounds like a contradiction, but its technology is basically order enforced through chaos. It is also much more secure than government databased and corporate databases, becuse the security of a transaction is guaranteed by all the computers in the network.

Things are happening so fast that there is a new term and a new concept every month. Now the world of DAOs is also talking about the "Distributed Collaborative Organization". The term was introduced in 2014 by Primavera De Filippi (Harvard University) and Houman Shadab (New York Law of School): they proposed a way to integrate blockchain-based distributed organizations (DAOs) with the existing legal system.

One reason for the success of online fintech was the Great Recession of 2008-11. Small businesses were not able to get loans from traditional banks, and this created an opportunity for alternative banks and for crowd-based (P2P) financing. The first beneficiaries were non-bank lenders such as OnDeck (New York, 2007), Kabbage (Atlanta, 2009) and Funding Circle (London, 2010).

P2P is again the protagonist here. Two companies founded in 2006 in San Francisco pioneered peer-to-peer (social) lending: Prosper and LendingClub, both providing marketplaces for lending that match those who want to borrow money with people who want to lend money. They represent the marriage of fintech, P2P and the sharing economy.

Automated financial advisory has been legitimized by the success of Betterment, founded in 2008 in New York, and Personal Capital, founded in 2009 in Redwood City. It is not surprising that financial advisors have been replaced by machines because they were already using machines. The financial investments are largely based on algorithms. It was just a matter of making those algorithms available to the public directly. Now they are competiting on algorithms.

Fintech is also attacking the venture capitalists. There are platforms that collect money from individuals to fund startups. This was pioneered by EquityNet (founded in Arizona in 2005), that offered a social network for investors and entrepreneurs, and in 2011 two startups for equity crowdfunding opened in San Francisco: CircleU and Wefunder. but investment by random individuals in private businesses was not legal in the USA until very recently, so it has not taken off. England, instead, has success stories like Crowdcube (2011) and Seedrs (2012), Israel became a major center of fintech in the 2010s thanks to its strong credentials in cybersecurity, big data and artificial intelligence. Israel lives in a dangerous place, surrounded by hostile neighbors and two civil wars. By coincidence, the military technology that Israel has developed to defend itself, i.e. for "security", is almost exactly what you need in fintech. In fact, several of Israel's fintech startups had their roots in 8200, the elite agency of the Israeli army that spies the world and makes sure nobody spies Israel. TechCrunch estimates that in 2015 there were more than 300 cybersecurity companies operating in Israel, accounting for about 10% of the global market, and more than 400 fintech startups on the Internet offering services for payments, crowdfunding, lending, insurance, wealth management, fraud detection, etc. and many were already experimenting with blockchain technology. Major Western banks established research labs in Israel. For example, in 2013 Citibank opened its Citi Innovation Lab in Tel Aviv, not in Silicon Valley.

Same story for peer-to-peer insurance platforms: Berlin-based Friendsurance (2010) and London-based Guevara (2014) came before New York-based Lemonade (2015). If you want to meet the innovators of fintech, you have to travel somewhere else.

The USA is not the best place for financial experiments. Britain is far ahead of the USA in fintech because of the different laws. When the stock market crashed in 1929, a lot of ordinary families lost money, so the USA came up with specific rules and regulations to protect ordinary investors. In those days there were no startups. When the world of startups exploded in the 1990s, the USA was unprepared: it had rules that made it illegal for ordinary people to invest in startups. In Britain, instead, there were just ethical principles. In the 1990s it was easier for Britain to introduce laws specifically designed for the age of the Internet. For example, equity crowdfunding has been fully legalized in the USA only in 2015. To this day, the USA is not a friendly country for financial innovation because so many laws protect the individual, i.e. the government intentionally discourages individuals from speculation. The USA doesn't want another crisis like 1929 or 2008 when millions of citizens lose their money. Any financial innovation is carefully scrutinized by the US government. Only biotech is more scrutinized than fintech. So it is not surprising that Britain and Israel are ahead of the USA.

In 2017 not only Bitcoin passed the landmark of $10,000 but Wall Street entered the picture. Australian Stock Exchange became the first global market to use the blockchain technology. The contractor was Digital Asset Holdings, founded in 2014 in New York by Sunil Hirani and Don Wilson. Hirani had previously founded the financial firms Creditex (1999), sold to InterContinentalExchange in 2008 for more than half a billion dollars, and TrueEX (2010). In 2015 Digital Asset hired as CEO another veteran of Wall Street, Blythe Masters, who was at J.P.Morgan Chase for 27 years. That's when the spree of acquisitions began: in 2015 they acquired Hyper, founded in 2014 by Daniel Feichtinger and Dan O'Prey in San Francisco, and Bits of Proof, founded in Hungary by Tamas Blummer, and in 2016 they acquired another San Francisco startup, Blockstack.io, founded in 2015 by Peter Shiau and others, and Elevance Digital Finance, founded in Switzerland by Vincent Peiker in 2014.

It is also unpredictable which technology succeeds. Billpoint started two years before PayPal, offering the same kind of person-to-person service and it was backed by eBay, Wells Fargo and Visa (what else do you want in order to succeed? the biggest online marketplace, one of the biggest banks and one of the biggest credit-card companies), but nobody remembers them. In 2002 Pay By Touch had a technology that allowed users to pay with a swipe of their finger on a biometric sensor. Pay By Touch went out of business in 2007. You will not find an easy explanation for why it failed. Today we have fingerprint scanning on Apple and Samsung smartphones. Fujitsu and ZTE are about to introduce retina scanning. Why did Pay By Touch fail? When it comes to financial applications, there are just too many human factors involved, and it is really difficult to predict what will succeed.

Fintech has to continue tapping into the power of the "crowd". The financial world used to be a fortress open only to very rich people. Ordinary people were only allowed to give their money or borrow money, both actions that make the financial institutions rich. Ordinary people had no way to benefit from the process itself, from the investment that the bank makes with your money. Things have changed in the age of the "crowd". The three big crowdfunding platforms (Kickstarter, Indiegogo, and GoFundMe) are already funding more innovation than all venture capitalists combined. I don't think that the same will happen any time soon to lending and insurance, because of all the regulations that are involved, but, thanks to P2P technology, for the first time there is a chance for the "crowd" to dispossess the big financial institutions. Capitalism's future is not the capitalist but the common person. P2P is the most important revolution in fintech since the invention of the credit card.

NEO (called Antshares until June 2017) is the Chinese response to Ethereum. NEO is developed and maintained by is an open source community called City of Zion. NEO is a different kind of blockchain technology for digitizing assets and automating smart contracts. NEO and Ethereum are aiming are competing to become the platforms of choice for DApps (Decentralized Applications), ICOs (Initial Coin Offerings), and smart contracts. In 2017 Ethereum still owned the market for DApps, and almost every ICO was built on Ethereum's ERC20 standard. NEOX is NEO's equivalent of Ethereum's ERC20. For example, Nex (built on NEO's NEOX) is an ICO developed by City of Zion to build a platform for payment solutions. NEO and Ethereum are two ways to create a smart economy in which physical assets such as houses, cars and diamonds will become digital entities and proof of ownership will be stored in the blockchain.

Ethereum uses Bitcoin?'s Proof of Work, which may soon become outdated if people switch to Proof of Stake (PoS). The advantage of PoS is that it solves the problem of excessive energy use: it takes virtually no energy to run PoS?.

NEO, instead, uses Delegated Byzantine Fault Tolerance (that they published in 2016). What this means is that NEO can process transactions much faster than Ethereum. Every node in the Ethereum space participates in the validating process, whereas NEO limits the "voting rights" to bookkeepers, a group of selected members who in practice maintain the network for everybody. Of course, this also means that NEO is not fully decentralized because its governance is concentrated in a few dozen bookkeepers (who happens to be mostly members of NEO's team).

Ethereum launched the Enterprise Ethereum Alliance, an open source blockchain initiative for linking Ethereum with the traditional business world. Members include BP, HP, Toyota, MasterCard, Microsoft, Intel. In 2014 NEO's founders Da HongFei and Erik Zhang founded a company called OnChain whose platform, DNA (Decentralized Network Architecture), introduced in 2016, links their blockchain technology with Chinese businesses and government. So NEO provides the public blockchain (the equivalent to the original blockchain) whereas OnChain's DNA provides private blockchains for businesses. OnChain partnered with Microsoft (called Legal Chain?) to digitize and secure signatures with blockchain technology; with the Japanese Ministry of Economy, Trade and Industry, with Alibaba to provide secure on the cloud; with China's vast conglomerate Fosun Group to integrate blockchain technology and traditional business; and with several regional governments of China to develop public services and digital identity.

Now that blockchain technology has become popular, it would be nice if it were easy to build blockchain applications. Lisk was started in 2016 by Max Kordek and Oliver Beddows to make it easier for developers to develop blockchain applications. It is also an open-source project, which means that Lisk is available for free, and it is written in JavaScript, a very popular programming language.

Eos.io, launched in 2017 by Dan Larimar of BitShares and Steemit fame, is an open-source project to create a platform that provides all the services to scale up a dapp. Ethereum is a decentralized supercomputer, EOS is an operating system. In January 2018 it had a market capitalization of $6 billion.

Cardano, launched in 2017 by Ethereum's cofounder Charles Hoskinson, is an open-source project that introduced a more robust proof-of-stake algorithm (ouroboros). It is designed by a global team of academics and its team includes lawyers and regulators to make sure that it integrates and complies with the financial world. Its coin is called ada. Cardano wsa called the "Ethereum of Japan" because 95% of the participants in the Initial Coin Offering (2015) were from Japan. In January 2018 it enjoyed a $31 billion market capitalization. Cardano is fundamentally a combination of Ripple (payments) and Ethereum (smart contracts). Quote from their marketing material: "the best of Bitcoin (store of value), Litecoin (cheap, fast p2p transactions), and Ethereum (smart contracts) into one coin". It is written in Haskell (a functional language, not object-oriented like Java) and in Plutus (a Haskell for smart contracts). It has a layered architecture: a PoS -based cryptocurrency called the Cardano Settlement Layer (CSL) which handles transactions (like Bitcoin or Ripple), and a set of protocols called the Cardano Computation Layer (CCL), which handles smart contracts (like Ethereum).

Now that we have more than one blockchain (and they are all incompatible with each other) we will need cross-chain integration: Ark's SmartBridge and NEO's NEOX are tentative steps in that direction, to let people transact across different blockchains. Today, if you want to go from one blockchain network to another one, you need to trade one coin for the other, which can be annoying if your application has to go back and forth betweek the two networks. Ark was specifically created (in 2016 by a group including Fran‡ois-Xavier Thoorens, Mike Doty, Lars Rensing, Scott McPherson, and Rok Cernec) to link the various competing blockchain networks. Ark has rapidly developed in a competitor of Ethereum, a full-fledged platform for smart contracts. Like NEO, Ark too is based on Delegated Proof of Stake and claims very fast transactions. In 2017 ARK was incorporated in France because one of its goals is to be a legal business entity, compliant with the laws and regulations of a state (in this case, France). Their ambitious roadmap is at https://ark.io/roadmap

Several platforms were born to solve the problem of anonymity: Bitcoin isn't anonymous at all because the whole network sees a transaction and who is transacting. If they know the physical person behind an account, they know every transaction that that person carried out.

Zcash, launched in 2016 by Wilcox, is the outcome of the Zerocash project, which is based on an extension for privacy of the Bitcoin blockchain proposed in 2014 by Mathew Green, a John Hopkins University professor (the original paper had an international cast of authors: Eli Ben-Sasson, Alessandro Chiesa, Christina Garman, Matthew Green, Ian Miers, Eran Tromer, and Madars Virza). All information about transactions is encrypted. Its method is based on the "zero-knowledge proof": a zero-knowledge proof or protocol allows a "prover" to assure a "verifier" that they have knowledge of a secret without revealing the secret itself. Zero-knowledge proofs allow you to prove that you know something without revealing what it is. Zero-knowledge proofs were first conceived in 1985 by Shafi Goldwasser, Silvio Micali, and Charles Rackoff of MIT in their paper "The Knowledge Complexity of Interactive Proof-Systems" (1985). Later other MIT scientists (Manuel Blum, Paul Feldman, Silvio Micali) develop non-interactive zero-knowledge proof. In 2017 the market-cap surpassed $1 billion. The critics accuse Zcash of being a "corporate coin": it is funded by a corporation (there is no company behind Bitcoin, Ethereum, etc) and the donor list to the Zerocash project includes DARPA, the Air Force Research Laboratory, Office of Naval Research. Also note that it is possible to add ZCash as a sidechain to the Bitcoin blockchain.

Monero (whose name means simply "coin" in Esperanto) was launched in 2014 and was born out of Bytecoin, a failed coin whose creator is still unknown today. It uses the CryptoNote protocol, published in 2013 by Nicolas van Saberhagen, and in 2017 it adopted Gregory Maxwell's Confidential Transactions algorithm (2015). Monero obscures sender, recipient and amount of every transaction. Because it is so good at privacy, it was dubbed "the drug dealer's cryptocurrency of choice" by a Wired journalist.

ZCash later switched to a method called Groth16, developed in 2016 by Jens Groth who in 2010 had published an influential paper on what he called NIZK (for "non-interactive zero knowledge"). Groth16 is a zero-knowledge SNARK and Zcash was the first major application of the concept of a zk-SNARK (SNARK stands for "succinct non-interactive argument of knowledge"), a concept first introduced in 2011 by Alessandro Chiesa of MIT in collaboration with scientists of Tel Aviv University, (Nir Bitansky, Ran Canetti and Eran Tromer) in another influential paper ("From extractable collision resistance to succinct non-interactive arguments of knowledge, and back again", 2011). These zk-SNARKs are proof constructions in which a prover can prove knowing some information (e.g. a secret key) without disclosing that information to the verifier, and, in fact, in the case of non-interactive ones like Groth16, with no interaction between prover and verifier. In a zero-knowledge proof the prover proves to the verifier that a statement is true without revealing any information other than the validity of that statement. I convince you that i am right by telling you only that I am right, but you know that there is a proof that I am right. That's why Zcash transactions are so "anonymous": Zcash uses zk-SNARKs to verify transactions, i.e. revealing nothing about the transaction other than it's valid. The "non-interactive" zero-knowledge proofs such as Groth16 have the further advantage that the proof consists of a single message sent from prover to verifier, i.e. they are also optimization methods. Zero-knowledge proofs are also used to compress a large blockchain into only a much smaller one and to condense many Ethereum transactions into a single proof. Two ways have been developed to use zk-SNARKS: "transparent setup" (Fractal, Halo, SuperSonic-CG) and "universal setup" (Sonic, Marlin, SuperSonic-RSA, Plonk). Groth16 was chosen by Zcash because it was the fastest and smallest known zk-SNARK. It is non-universal. The "universal" kind was invented by Sonic (introduced in January 2019 by Mary Maller and Sean Bowe), but it was slow. Plonk (introduced later in 2019 by Aztec's scientists Zac Williamson and Ariel Gabizon) is universal and fast. Then Sonic's authors created Marlin, an improvement over Sonic. The year 2019 witnessed an avalanche of new zk-SNARK protocols. In February 2020 Aztec (founded by Tom Pocock and Zachary Williamson in 2017), which uses Zcash-based technology, introduced confidential tokens in Ethereum, i.e. created a privacy network on the Ethereum blockchain.

An alternative to the zk-SNARK is the zk-STARK ("zero-knowledge scalable transparent arguments of knowledge"), introduced in 2018 by Eli Ben-Sasson at Technion in Israel ("Scalable, transparent, and post-quantum secure computational integrity", 2018). The difference is simple: zk-SNARK proofs require a trusted party or parties to initially setup the zero-knowledge proof system, whereas zk-STARK proofs don't require a trusted setup. However, there is a price to pay for using zk-STARK proofs: the size of the proofs can be much bigger.

Indirectly this minority exposed the second major way to hack a blockchain. If a cryptocurrency is "cheap", some miner could purchase enough mining power to acquire 51% of the mining. If that happens, this miner can rewrite the history of the blockchain. This is called the "51% hack". In January 2019 this is precisely what happened in Ethereum Classic: a hacker gained control of the majority of this cryptocurrency's mining and started rewriting the transaction history (they created a fork overriding the previous history). If you do this, you can spend twice the same amount of that cryptocurrency. This, so far, has only happened to cryptocurrencies that use proof of work as their protocol for verifying transactions. The first cases were detected in 2018 but only the attack on Ethereum Classic made the headlines. Why did it take so long for hackers to carry out a "51% attack"? Probably because the "hashrate marketplaces", that rent computing power to miners, have become more popular. If you have enough money, you can rent a lot of mining power on these marketplaces, especially during times when the main miners are resting their computers (for example, when the cryptocurrency is losing value and it's not worth mining it).

Libra is part of a movement towards bringing the blockchain to the smartphone. In 2019 the most famous project after Libra was Celo. Rene Reinsberg in Switzerland founded cLabs in 2017 and started development of Celo with the goal of creating a blockchain-based mobile payment. Like Libra, Celo uses a "stablecoin", a coin pegged to traditional assets (like the US dollar), and, just like in Libra, there are no "miners". Celo is basically Libra done by someone who is not Facebook, and therefore less intimidating. Mobile payment have been popularized by many smartphone apps but they didn't use blockchain technology before Celo. To achieve its goal, cLabs needs to create an "ultralight" client that can run on cheap phones, and that's Celo. The technical problem that Celo is trying to solve is that the size of a blockchain increases exponentially. Given the size of Bitcoin's blockchain in early 2020, a phone needed to download approximately 47 megabytes of data to perform a Bitcoin transaction. And in order to perform an Ethereum smart contract, the size of the data to download was 4.4 gigabytes. Even more on a proof-of-stake network. The concept is not new: Satoshi Nakamoto's original Bitcoin paper talks about light client protocols ("simple payment verification"). Solution proposed previously that would make it possible to verify the entire blockchain from a smartphone (that would create "simplified payment verification" or SPV wallets) include: NiPoPoW, aka "non-interactive proofs of proof-of-work" (developed in 2016 by Aggelos Kiayias at the University of Athens in Greece), and Flyclient (developed in 2018 by Benedikt Bunz from Stanford and Lucianna Kiffer from Northeastern University while interning at Visa under Mahdi Zamani) for proof-of-work networks, as well as Coda (developed in 2018 by Izaak Meckler, who studied cryptography at UC Berkeley, and Evan Shapiro, who studied robotics at Carnegie Mellon University) for proof-of-stake networks. Celo uses a proof-of-stake consensus algorithm, and wants to simplify the Ethereum mechanism too. In order to communicate with the Ethereum blockchain, the Ethereum user must use a blockchain client, also called "node". The most popular clients before Celo were Geth and Parity. Technically speaking, Celo is a fork of Geth. Celo's native unit of accounting is the cryptocurrency Celo gold, equivalent to ether in Ethereum. Plumo is the light client protocol for the Celo proof-of-stake network.

Another advantage of Libra and Celo is that they will provide the user with a "digital identity", a way to build up a "credit score" that can be used to apply for loans. Both Libra and Celo target the "unbanked" population, the population that does not have a bank account.

The method used by Nakamoto is now called “blockchain” and is the sum of all those methods developed in the 1990s to create trust without having to rely on a central authority. A central authority (laws, police, justice, bank, and so on) does not exist in the cyberworld of the Internet. Bitcoin was a currency, but it was also a lot more: its underlying blockchain technology was a new way to run a society without a central authority. Satoshi Nakamoto left the Bitcoin project almost immediately after release 0.2 (December 2009), co-written with Martti Malmi, a student at the Helsinki University of Technology who was interestested in decentralized cybercurrencies. Nakamoto's last posted something in December 2010 (except for posting in 2014 a short sentence "I am not Dorian Nakamoto" to dispel a magazine story). Hal Finney added some code to the original code soon after the publication of the white paper when the code was posted on the website Sourceforge. Malmi, who was the first person to sell bitcoins for dollars (5,000 bitcoins for 5 dollars), left too in 2011 and the project moved to the open-source repository Github (coincidentally created the same year that Nakamoto developed Bitcoin) and since then it has been developed by a community of volunteers. Gavin Andresen, formerly a virtual-reality expert at Silicon Graphics in Silicon Valley, joined in 2010 and in 2012 started the Bitcoin Foundation in Boston (established with a large donation by Silicon Valley-based anarchist and bitcoin evangelist Roger Ver, who in 2011 had created the first major online store accepting bitcoin payments and previously had been jailed for selling explosives on eBay).

The identity of Nakamoto has remained a mystery probably because someone has been lying a lot. Satoshi stopped communicating in 2013. Craig Wright (based in Australia), a long-time subscriber to the cypherpunks mailing list, and his long-time friend Dave Kleiman (a computer security analyst based in Florida), have been identified as the most likely candidates, and Wright himself publicly announced to be Nakamoto in 2016. However, the "proof" that he offered was quickly refuted by the community. He had childishly manipulated some files. Not only did he fake the proof, but he didn't even realize that it would take just a few days for Bitcoin experts to find out the truth. He acquired the reputation of being a congenital liar. Wright doesn’t even seem to have adequate C++ programming skills. (In the process, he indirectly disgraced Gavin Andresen, one of the few who was fooled by Wright’s fake proof). A few weeks later, cypherpunk Phil Wilson (from New Zealand), who never met the other two in person, claimed to have written most of the original code after joining the duo in mid-2008. Some believe Wilson, some don’t (Martti Malmi doesn’t). Wilson has no proofs because (he claims) he deleted all his bitcoin files and coins in 2011 for fear of a police investigation. Dave Kleiman died in 2013. Hal Finney died in 2014.

Joseph Vaughn-Perling claims that Wright introduced himself as Satoshi Nakamoto back in 2005, three years before the Bitcoin paper was published. Uyen Ngyuen said in 2015 that Wright is Nakamoto.

Is the identity of Nakamoto important? It will be on the first of January 2020. If Craig Wright and Phil Wilson told the truth, there is a Tulip Trust that contains one million bitcoins mined by Wright and Dave Kleiman. According to the trust contract, Wright is not able to touch that money until that day. On that day, if the fund exists, he or whoever owns it can dump one million bitcoins on the market. Many people think that everything Wright said is false. His nickname is “faketoshi”. A post on a bitcoin website called him “a liar who has a strong financial motive to claim Satoshi's identity provides bogus proof”. His financial motivation could be that this fund allows him to borrow money for his businesses. He cannot touch the money of this fund but he can tell investors “I will repay you in 2020”. The problem is that any serious investor would be skeptic about the contract of this trust: it looks like it was not written by a lawyer, it looks like it was written by an amateur.

However, the Tulip Fund could exist, and even if Craig Wright is not Nakamoto, Wright could own the rights to sell it. So part of the story could be true even if the other part is not true. In early 2018 Kleiman's brother Ira sued Wright, accusing him of basically stealing Kleiman's bitcoins. According to the lawsuit, Wright forged and back-dated the fund's contract after Kleiman’s death. Therefore it seems like Kleiman's own brother has found evidence that Wright has indeed the power to sell those bitcoins.

Many details still don't make sense, whichever version you believe. To start with, if Kleiman owned such a large fortune of bitcoins, why did he never cash any of it? Kleiman died poor, sick and lonely a few months after signing that contract (if it is real) that kept the bitcoins locked until 2020. In 2011 Kleiman and Wright set up a company, W&K Info Defense Research whose address was Dave Kleiman’s house in Florida. In October 2012 Wright, Kleiman and a 20-year old Vietnamese girl named Uyen Nguyen living in Los Angeles also opened another company, CO1N. The Tulip trust is first mentioned in September 2011 by Kleiman. A document names Uyen Nguyen as the "Tulip Trading Trust trustee" as appointed by Dave Kleiman in October 2012. It is not clear how Nguyen became such a close confident of Kleiman and Wright; and what is the relationship between the "Tulip trust" and W&K in both of which she has key roles. In 2014, after the death of Kleiman, this Nguyen reopened W&K, which many interpret as "Craig Wright via Uyen Nguyen took over the company", but then she closed it again in 2017. What for?

Update of 2021: Nothing relevant happened in January 2020, except that Wright's version of the facts became less and less credible. In May 2021 Wright's wife Ramona Ang, identifying herself as the trustee for the Tulip Trust, sued Ira Kleiman accusing him of destroying the electronic data that give access to the funds of the Tulip Trust, yet another twist in Wright's story. The 2018 lawsuit (Ira Kleiman demanding that Wright releases the bitcoins mined with the deceased Kleiman) will go to trial in November 2021, and everybody expects Wright to get into a mountain of legal troubles.