Chapter 01

What is Blockchain Technology?

“The practical consequence […is…] for the first time, a way for one Internet user to transfer a unique piece of digital property to another Internet user, such that the transfer is guaranteed to be safe and secure, everyone knows that the transfer has taken place, and nobody can challenge the legitimacy of the transfer. The consequences of this breakthrough are hard to overstate.”

– Marc Andreessen

From a cruising altitude, a blockchain might not look that different from things you’re familiar with, say Wikipedia.

With a blockchain, many people can write entries into a record of information, and a community of users can control how the record of information is amended and updated. Likewise, Wikipedia entries are not the product of a single publisher. No one person controls the information.

Descending to ground level, however, the differences that make blockchain technology unique become more clear. While both run on distributed networks (the internet), Wikipedia is built into the World Wide Web (WWW) using a client-server network model.

A user (client) with permissions associated with its account is able to change Wikipedia entries stored on a centralized server.

Whenever a user accesses the Wikipedia page, they will get the updated version of the ‘master copy’ of the Wikipedia entry. Control of the database remains with Wikipedia administrators allowing for access and permissions to be maintained by a central authority.


Wikipedia’s digital backbone is similar to the highly protected and centralized databases that governments or banks or insurance companies keep today. Control of centralized databases rests with their owners, including the management of updates, access and protecting against cyber-threats.

The distributed database created by blockchain technology has a fundamentally different digital backbone. This is also the most distinct and important feature of blockchain technology.

Wikipedia’s ‘master copy’ is edited on a server and all users see the new version. In the case of a blockchain, every node in the network is coming to the same conclusion, each updating the record independently, with the most popular record becoming the de-facto official record in lieu of there being a master copy.


Transactions are broadcast, and every node is creating their own updated version of events.

It is this difference that makes blockchain technology so useful – It represents an innovation in information registration and distribution that eliminates the need for a trusted party to facilitate digital relationships.

Yet, blockchain technology, for all its merits, is not a new technology.

Rather, it is a combination of proven technologies applied in a new way. It was the particular orchestration of three technologies (the Internet, private key cryptography and a protocol governing incentivization) that made bitcoin creator Satoshi Nakamoto’s idea so useful.


The result is a system for digital interactions that does not need a trusted third party. The work of securing digital relationships is implicit — supplied by the elegant, simple, yet robust network architecture of blockchain technology itself.

Defining digital trust

Trust is a risk judgement between different parties, and in the digital world, determining trust often boils down to proving identity (authentication) and proving permissions (authorization). Put more simply, we want to know, ‘Are you who you say you are?’ and ‘Should you be able to do what you are trying to do?’In the case of blockchain technology, private key cryptography provides a powerful ownership tool that fulfills authentication requirements. Possession of a private key is ownership. It also spares a person from having to share more personal information than they would need to for an exchange, leaving them exposed to hackers.Authentication is not enough. Authorization – having enough money, broadcasting the correct transaction type, etc – needs a distributed, peer-to-peer network as a starting point. A distributed network reduces the risk of centralized corruption or failure.This distributed network must also be committed to the transaction network’s recordkeeping and security. Authorizing transactions is a result of the entire network applying the rules upon which it was designed (the blockchain’s protocol). Authentication and authorization supplied in this way allow for interactions in the digital world without relying on (expensive) trust. Today, entrepreneurs in industries around the world have woken up to the implications of this development – unimagined, new and powerful digital relationshionships are possible. Blockchain technology is often described as the backbone for a transaction layer for the Internet, the foundation of the Internet of Value. In fact, the idea that cryptographic keys and shared ledgers can incentivize users to secure and formalize digital relationships has imaginations running wild. Everyone from governments to IT firms to banks is seeking to build this transaction layer.

Authentication and authorization, vital to digital transactions, are established as a result of the configuration of blockchain technology.

The idea can be applied to any need for a trustworthy system of record.

Authored by Nolan Bauerle; images by Maria Kuznetsov


The leader in blockchain news, CoinDesk is a media outlet that strives for the highest journalistic standards and abides by a strict set of editorial policies. CoinDesk is an independent operating subsidiary of Digital Currency Group, which invests in cryptocurrencies and blockchain startups.

Chapter 02

How Does Blockchain Technology Work?

As stated in our guide “What is Blockchain Technology?”, there are three principal technologies that combine to create a blockchain. None of them are new. Rather, it is their orchestration and application that is new.

These technologies are: 1) private key cryptography, 2) a distributed network with a shared ledger and 3) an incentive to service the network’s transactions, record-keeping and security.

The following is an explanation of how these technologies work together to secure digital relationships.

Cryptographic keys

Two people wish to transact over the internet.


Each of them holds a private key and a public key.


The main purpose of this component of blockchain technology is to create a secure digital identity reference. Identity is based on possession of a combination of private and public cryptographic keys.

The combination of these keys can be seen as a dexterous form of consent, creating an extremely useful digital signature.

In turn, this digital signature provides strong control of ownership.


But strong control of ownership is not enough to secure digital relationships. While authentication is solved, it must be combined with a means of approving transactions and permissions (authorisation).

For blockchains, this begins with a distributed network.

A Distributed Network

The benefit and need for a distributed network can be understood by the ‘if a tree falls in the forest’ thought experiment.

If a tree falls in a forest, with cameras to record its fall, we can be pretty certain that the tree fell. We have visual evidence, even if the particulars (why or how) may be unclear.

Much of the value of the bitcoin blockchain is that it is a large network where validators, like the cameras in the analogy, reach a consensus that they witnessed the same thing at the same time. Instead of cameras, they use mathematical verification.

In short, the size of the network is important to secure the network.

That is one of the bitcoin blockchain’s most attractive qualities — it is so large and has amassed so much computing power. At time of writing, bitcoin is secured by 3,500,000 TH/s, more than the 10,000 largest banks in the world combined. Ethereum, which is still more immature, is secured by about 12.5 TH/s, more than Google and it is only two years old and still basically in test mode.

System of record


When cryptographic keys are combined with this network, a super useful form of digital interactions emerges. The process begins with A taking their private key, making an announcement of some sort — in the case of bitcoin, that you are sending a sum of the cryptocurrency — and attach it to B’s public key.



A block – containing a digital signature, timestamp and relevant information – is then broadcast to all nodes in the network.


A realist might challenge the tree falling in the forest thought experiment with the following question: Why would there be a million computers with cameras waiting to record whether a tree fell? In other words, how do you attract computing power to service the network to make it secure?

For open, public blockchains, this involves mining. Mining is built off a unique approach to an ancient question of economics — the tragedy of the commons.

With blockchains, by offering your computer processing power to service the network, there is a reward available for one of the computers. A person’s self-interest is being used to help service the public need.

With bitcoin, the goal of the protocol is to eliminate the possibility that the same bitcoin is used in separate transactions at the same time, in such a way that this would be difficult to detect.

This is how bitcoin seeks to act as gold, as property. Bitcoins and their base units (satoshis) must be unique to be owned and have value. To achieve this, the nodes serving the network create and maintain a history of transactions for each bitcoin by working to solve proof-of-work mathematical problems.

They basically vote with their CPU power, expressing their agreement about new blocks or rejecting invalid blocks. When a majority of the miners arrive at the same solution, they add a new block to the chain. This block is timestamped, and can also contain data or messages.

Here’s a chain of blocks:


The type, amount and verification can be different for each blockchain. It is a matter of the blockchain’s protocol – or rules for what is and is not a valid transaction, or a valid creation of a new block. The process of verification can be tailored for each blockchain. Any needed rules and incentives can be created when enough nodes arrive at a consensus on how transactions ought to be verified.

It’s a taster’s choice situation, and people are only starting to experiment.

We are currently in a period of blockchain development where many such experiments are being run. The only conclusions drawn so far are that we are yet to fully understand the dexterity of blockchain protocols.

More on this point in our guides “What are Applications and Use Cases for Blockchain Technology?” and “What is the Difference Between Open and Permissioned Blockchains?”


Authored by Nolan Bauerle; images by Maria Kuznetsov


The leader in blockchain news, CoinDesk is a media outlet that strives for the highest journalistic standards and abides by a strict set of editorial policies. CoinDesk is an independent operating subsidiary of Digital Currency Group, which invests in cryptocurrencies and blockchain startups.

Chapter 03

What Can a Blockchain Do?

Financial institutions have financed the disruption of countless industries over the last 30 years; they have an idea of what a revolutionary technology can do to static incumbents.

So, to stay ahead of change, banks have been proactive in setting up R&D labs, building test centers and establishing partnerships with blockchain developers to fully understand the revolutionary potential of the technology.

Financial institutions were the first to dip their feet in, but academia, governments and consulting firms have also studied the technology.

All of this work is, of course, in addition to what the entrepreneurs and developers are doing, either by finding new ways to use the bitcoin or ethereum blockchains, or else creating entirely new blockchains.

This has been going on for over three years now, and the results are starting to come in.

While some of the waters are still murky, this is what we know a blockchain can do:

Establish digital identity

As discussed in our guide “How Does Blockchain Technology Work?”, the identity component of blockchain technology is fulfilled through the use of cryptographic keys. Combining a public and private key creates a strong digital identity reference based on possession.

A public key is how you are identified in the crowd (like an email address), a private key is how you express consent to digital interactions. Cryptography is an important force behind the blockchain revolution.


As stated in our guide “What is a Distributed Ledger?”, blockchains are an innovation in information registration and distribution. They are good for recording both static data (a registry) or dynamic data (transactions), making it an evolution in systems of record.

In the case of a registry, data can be stored on blockchains in any combination of three ways:

  • Unencrypted data – can be read by every blockchain participant in the blockchain and is fully transparent.
  • Encrypted data –can be read by participants with a decryption key. The key provides access to the data on the blockchain and can prove who added the data and when it was added.
  • Hashed data – can be presented alongside the function that created it to show the data wasn’t tampered with.

Blockchain hashes are generally done in combination with the original data stored off-chain. Digital ‘fingerprints’, for example, are often hashed into the blockchain, while the main body of information can be stored offline.

Such a shared system of record can change the way disparate organizations work together.

Currently, with data siloed in private servers, there is an enormous cost for inter-company transactions involving processes, procedures and cross-checking of records.

Read more on this in our guide “What are the Applications and Use Cases of Blockchains?”.

Prove immutability

A feature of a blockchain database is that is has a history of itself. Because of this, they are often called immutable. In other words, it would be a huge effort to change an entry in the database, because it would require changing all of the data that comes afterwards, on every single node. In this way, it is more a system of record than a database.

Read more on this in our guide “What is the Difference Between a Blockchain and a Database?”.

Serve as a platform

Cryptocurrencies were the first platform developed using blockchain technology. Now, people have moved from the idea of a platform to exchange cryptocurrencies to a platform for smart contracts.

The term ‘smart contracts’ has become somewhat of a catch-all phrase, but the idea can actually be divided into several categories:

There are the ‘vending machine’ smart contracts coined in the 1990s by Nick Szabo. This is where machines engage after receiving an external input (a cryptocurrency), or else send a signal that triggers a blockchain activity.

There are also smart legal contracts, or Ricardian contracts. Much of this application is based on the idea that a contract is a meeting of the minds, and that it is the result of whatever the consenting parties to the contract agree to. So, a contract can be a mix of a verbal agreement, a written agreement, and now also some of the useful aspects of blockchains like timestamps, tokens, auditing, document coordination or business logic.

Finally, there are the ethereum smart contracts. These are programs which control blockchain assets, executed over interactions on the ethereum blockchain. Ethereum itself is a platform for smart contract code.

Blockchains are not built from a new technology. They are built from a unique orchestration of three existing technologies.


Read more on this in our guide “What are the Applications and Use Cases of Blockchain Technology?”.

Authored by Nolan Bauerle; images by Maria Kuznetsov


The leader in blockchain news, CoinDesk is a media outlet that strives for the highest journalistic standards and abides by a strict set of editorial policies. CoinDesk is an independent operating subsidiary of Digital Currency Group, which invests in cryptocurrencies and blockchain startups.

Chapter 04

What is a Distributed Ledger?


Ledgers, the foundation of accounting, are as ancient as writing and money.

Their medium has been clay, wooden tally sticks (that were a fire hazard), stone, papyrus and paper. Once computers became normalized in the 1980s and ’90s, paper records were digitized, often by manual data entry.

These early digital ledgers mimicked the cataloguing and accounting of the paper-based world, and it could be said that digitization has been applied more to the logistics of paper documents rather than their creation. Paper-based institutions remain the backbone of our society: money, seals, written signatures, bills, certificates and the use of double-entry bookkeeping.

Computing power and breakthroughs in cryptography, along with the discovery and use of some new and interesting algorithms, have allowed the creation of distributed ledgers.

In its simplest form, a distributed ledger is a database held and updated independently by each participant (or node) in a large network. The distribution is unique: records are not communicated to various nodes by a central authority, but are instead independently constructed and held by every node. That is, every single node on the network processes every transaction, coming to its own conclusions and then voting on those conclusions to make certain the majority agree with the conclusions.

Once there is this consensus, the distributed ledger has been updated, and all nodes maintain their own identical copy of the ledger. This architecture allows for a new dexterity as a system of record that goes beyond being a simple database.

Distributed Ledgers are a dynamic form of media and have properties and capabilities that go far beyond static paper-based ledgers. For more on this, please read our guide “What Can a Blockchain Do?” For now, the short version is they enable us to formalize and secure new kinds of relationships in the digital world.

The gist of these new kinds of relationships is that the cost of trust (heretofore provided by notaries, lawyers, banks, regulatory compliance officers, governments, etc…) is avoided by the architecture and qualities of distributed ledgers.

Our Wikipedia analogy in our guide “What is Blockchain Technology?” hints at the power of these new kinds of relationships.

The invention of distributed ledgers represents a revolution in how information is gathered and communicated. It applies to both static data (a registry), and dynamic data (transactions). Distributed ledgers allow users to move beyond the simple custodianship of a database and divert energy to how we use, manipulate and extract value from databases — less about maintaining a database, more about managing a system of record.

Authored by Nolan Bauerle; images by Maria Kuznetsov


The leader in blockchain news, CoinDesk is a media outlet that strives for the highest journalistic standards and abides by a strict set of editorial policies. CoinDesk is an independent operating subsidiary of Digital Currency Group, which invests in cryptocurrencies and blockchain startups.

Chapter 05

Why Use a Blockchain?


As the implications of the invention of have become understood, a certain hype has sprung up around blockchain technology.

This is, perhaps, because it is so easy to imagine high-level use cases. But, the technology has also been closely examined: millions of dollars have been spent researching blockchain technology over the past few years, and numerous tests for whether or not blockchain technology is appropriate in various scenarios have been conducted.

Blockchain technology offers new tools for authentication and authorization in the digital world that preclude the need for many centralized administrators. As a result, it enables the creation of new digital relationships.

By formalizing and securing new digital relationships, the blockchain revolution is posed to create the backbone of a layer of the internet for transactions and interactions of value (often called the ‘Internet of Value’, as opposed to the ‘Internet of Information’ which uses the client-server, accounts and master copy databases we’ve been using for over the past 20 years.)

But, with all the talk of building the digital backbone of a new transactional layer to the internet, sometimes blockchains, private cryptographic keys and cryptocurrencies are simply not the right way to go.

Many groups have created flowcharts to help a person or entity decide between a blockchain or master copy, client-server database. The following factors are a distillation of much of what has been previously done:

Is the data dynamic with an auditable history?

Paper can be hard to counterfeit because of the complexity of physical seals or appearances. Like etching something in stone, paper documents have certain permanence.

But, if the data is in constant flux, if it is transactions occurring regularly and frequently, then paper as a medium may not be able to keep up the system of record. Manual data entry also has human limitations.

So, if the data and its history are important to the digital relationships they are helping to establish, then blockchains offer a flexible capacity by enabling many parties to write new entries into a system of record that is also held by many custodians.

Should or can the data be controlled by a central authority?

There remain many reasons why a third party should be in charge of some authentications and authorizations. There are times when third-party control is totally appropriate and desirable. If privacy of the data is the most important consideration, there are ways to secure data by not even connecting it to a network.

But if existing IT infrastructure featuring accounts and log-ins is not sufficient for the security of digital identity, then the problem might be solved by blockchain technology.

As Satoshi Nakamoto wrote in his (or her) seminal work, “Bitcoin: A Peer-to-Peer Electronic Cash System”: “Merchants must be wary of their customers, hassling them for more information than they would otherwise need. A certain percentage of fraud is accepted as unavoidable.”

Private key cryptography enables push transactions, which don’t require centralized systems and the elaborate accounts used to establish digital relationships. If this database requires millions of dollars to secure lightweight financial transactions, then there’s a chance blockchains are the solution.

Is the speed of the transaction the most important consideration?

Does this database require high-performance millisecond transactions? (There is more on this point in our guide: “What is the Difference Between a Blockchain and a Database?”).

If high performance, millisecond transactions are what is required, then it’s best to stick with a traditional-model centralized system. Blockchains as databases are slow and there is a cost to storing the data – the processing (or ‘mining’) of every block in a chain. Centralized data systems based on the client-server model are faster and less expensive… for now.

In short, while we still don’t know the full limits and possibilities of blockchains, we can at least say the use cases which have passed inspection have all been about managing and securing digital relationships as part of a system of record.

Authored by Nolan Bauerle; images by Maria Kuznetsov


The leader in blockchain news, CoinDesk is a media outlet that strives for the highest journalistic standards and abides by a strict set of editorial policies. CoinDesk is an independent operating subsidiary of Digital Currency Group, which invests in cryptocurrencies and blockchain startups.

Chapter 06

How Could Blockchain Technology Change Finance?

This question has been asked by every futurist research lab in many of the largest banks, central banks, financial institutions, think tanks, consulting firms and government committees around the world.

R3CEV, a consortium effort financed by some of the world’s largest banks, is busy trying to answer this question. Goldman Sachs, McKinsey Consulting and Consumers’ Research have all written excellent reports on this question. The UK Government, the Senates of the US, Canada, Australia and the EU have all made inquiries along these lines.

Many startups also produce white papers concerning their particular innovation or use of blockchain technology, and often include the larger social question: “How this will change things?”

Much of this research underlines four major areas of change:

Infrastructure for cross-border transactions

The digital revolution has totally transformed media, as we all know. It’s had an effect in the finance industry as well. Of course, financial institutions use computers. They used them for databases in the 1970s and 1980s, they made web pages in the 1990s and they migrated to mobile apps in the new millennium.

But the digital revolution has not yet revolutionized cross-border transactions. Western Union remains a big name, running much the same business they always have. Banks continue to use a complex infrastructure for simple transactions, like sending money abroad.

The following infographic, prepared by Richard Gendal Brown, shows the infrastructure and intermediaries in cross-border banking that have been in place since the ’70s.

This architecture is the result of the finance industry using highly secured private databases. Digitization has meant we merely sort information into private databases much faster.

Blockchain technology allows for financial institutions to create direct links between each other, avoiding correspondent banking. R3’s principal product to date, Corda, aims at correspondent banking. Corda is a play on words incorporating ‘accord’ (agreement) and ‘cord’ (the straightest line between two points in a circle).

In Corda’s case, the circle is made up of banks who would use a shared ledger for transactions, contracts and important documents.


Brown used to work on IBM’s blockchain products, but has since moved over to work at R3CEV.

Competing financial institutions could use this common database to keep track of the execution, clearing and settlement of transactions without the need to involve any central database or management system. In short, the banks will be able to formalize and secure digital relationships between themselves in ways they could not before.

In the above representation, that means correspondent banking agreements and the RTGS could both be shortcutted.

Transactions can occur directly between two parties on a frictionless P2P basis. Ripple, a permissioned blockchain, is built to solve many of these problems.  

Digital assets as a class

Bitcoin created something unique: digital property.

Before bitcoin, ‘digital’ was not synonymous with scarcity. Anything digital could be copied with the click of a button. A quick look at the music industry and album sales tells this story convincingly.


But bitcoin did something new: it created uncopyable digital code.

So, for the first time since bits and bytes were invented, there was a way to own something digital that couldn’t be copied. This gave the digital code value. To this day, bitcoin’s value is based on the capacity of its blockchain to prevent double-spending and the creation of counterfeit coins.

With this in mind, bitcoin developers have pioneered coloured coins that can act as stock in a company. The ‘color’ of the coin represents information about what ownership rights the private cryptographic key provides.

After receiving SEC permission, online retail giant Overstock announced it would issue public shares of company stock on its tØ blockchain platform. We’ve also seen the advent of ‘initial coin offerings’ (ICOs) and ‘appcoins’ (cryptocurrencies native to an app that help fund development of the project).

These examples are only part of the story for blockchains in digital assets. They can be the asset, but blockchains can also be used to run the market itself.

Basically, these efforts are treating digital assets as a bearer instrument, which is a wide and dexterous application.

Governance and markets

This ability, however, extends beyond just recording transactions. Nasdaq, for example, was one of the first to build a platform enabling private companies to issue and trade shares using a blockchain.

Other developers are coding financial instruments that can be pre-programed to carry out corporate actions and business logic.

In 2016, a blockchain project called The DAO, running on the ethereum blockchain, was launched with the aim of emulating a crowdfunding market. Your percentage of contribution to the fund represented the percentage vote in how the total fund would be spent.

Regulatory reporting and compliance

Blockchains can serve as a fully transparent and accessible system of record for regulators. The can also be coded to authorize transactions which comply with regulatory reporting.

For example, banks have severe reporting obligations to agencies such as FinCEN. Every single time they authorize a transaction of more than $10,000, they must report the information to FinCEN, who stores it for use as an anti-money laundering database.

Clearing and Settlement

With paper-world trading, the time frame for clearing and settlement of a transaction is generally referred to as ‘T+3’ – that is, three days after the trade (T), the transaction is settled.

With blockchain technology, the entire lifecycle of a trade – execution, clearing and settlement – occurs at the trade stage. With a digital asset, trade is settlement, and the cryptographic keys and digital ownership they control can lower post-trade latency and counterparty risk.

Accounting and auditing

Whereas most databases are snapshots of a moment in time, blockchain databases are built from their own transaction history. They are a database with context, a history of itself, a self-contained system of record.

The implications for auditing and accounting are profound.

Authored by Nolan Bauerle


The leader in blockchain news, CoinDesk is a media outlet that strives for the highest journalistic standards and abides by a strict set of editorial policies. CoinDesk is an independent operating subsidiary of Digital Currency Group, which invests in cryptocurrencies and blockchain startups.

Chapter 07

What are Blockchain's Issues and Limitations?

There are treacherous passes in any technological revolution.

Some people in the blockchain industry have pointed out that blockchain has become overhyped, when, in reality, the technology has limitations and is inappropriate for many digital interactions.

But through research and development, success and failure, and trial and error, we’ve learned the current issues and limitations of blockchains.


Blockchain technology involves an entirely new vocabulary.

It has made cryptography more mainstream, but the highly specialized industry is chock-full of jargon. Thankfully, there are several efforts at providing glossaries and indexes that are thorough and easy to understand.

Network size

Blockchains (like all distributed systems) are not so much resistant to bad actors as they are ‘antifragile’ – that is, they respond to attacks and grow stronger.

This requires a large network of users, however. If a blockchain is not a robust network with a widely distributed grid of nodes, it becomes more difficult to reap the full benefit.

There is some discussion and debate about whether this a fatal flaw for some permissioned blockchain projects.

Transaction costs, network speed

Bitcoin currently has notable transaction costs after being touted as ‘near free’ for the first few years of its existence.

As of late 2016, it can only process about seven transactions per second, and each transaction costs about $0.20 and can only store 80 bytes of data.

There’s also the politically charged aspect of using the bitcoin blockchain, not for transactions, but as a store of information. This is the question of ‘‘bloating’ and is often frowned upon because it forces miners to perpetually reprocess and rerecord the information.

Human error

If a blockchain is used as a database, the information going into the database needs to be of high quality. The data stored on a blockchain is not inherently trustworthy, so events need to be recorded accurately in the first place.

The phrase ‘garbage in, garbage out’ holds true in a blockchain system of record, just as with a centralized database.

Unavoidable security flaw

There is one notable security flaw in bitcoin and other blockchains: if more than half of the computers working as nodes to service the network tell a lie, the lie will become the truth. This is called a ‘51% attack’ and was highlighted by Satoshi Nakamoto when he launched bitcoin.

For this reason, bitcoin mining pools are monitored closely by the community, ensuring no one unknowingly gains such network influence.


Because blockchain protocols offer an opportunity to digitize governance models, and because miners are essentially forming another type of incentivized governance model, there have been ample opportunities for public disagreements between different community sectors.

These disagreements are a notable feature of the blockchain industry and are expressed most clearly around the question or event of ‘forking’ a blockchain, a process that involves updating the blockchain protocol when a majority of a blockchain’s users have agreed to it.

These debates can be very technical, and sometimes heated, but are informative for those interested in the mixture of democracy, consensus and new opportunities for governance experimentation that blockchain technology is opening up.

Authored by Nolan Bauerle


The leader in blockchain news, CoinDesk is a media outlet that strives for the highest journalistic standards and abides by a strict set of editorial policies. CoinDesk is an independent operating subsidiary of Digital Currency Group, which invests in cryptocurrencies and blockchain startups.

Chapter 08

Hard Fork vs Soft Fork
bitcoin, forks

Last updated: 16 March, 2018

Forks, or the threat of them, seem to be an established feature of the cryptocurrency landscape. But what are they? Why are they such a big deal? And what is the difference between a hard fork and a soft fork?

A “fork,” in programming terms, is an open-source code modification. Usually the forked code is similar to the original, but with important modifications, and the two “prongs” comfortably co-exist. Sometimes a fork is used to test a process, but with cryptocurrencies, it is more often used to implement a fundamental change, or to create a new asset with similar (but not equal) characteristics as the original.

Not all forks are intentional. With a widely distributed open-source codebase, a fork can happen accidentally when not all nodes are replicating the same information. Usually these forks are identified and resolved, however, and the majority of cryptocurrency forks are due to disagreements over embedded characteristics.

One thing to bear in mind with forks is that they have a “shared history.” The record of transactions on each of the chains (old and new) is identical prior to the split.

Hard forks

There are two main types of programming fork: hard and soft.

A hard fork is a change to a protocol that renders older versions invalid. If older versions continue running, they will end up with a different protocol and with different data than the newer version. This can lead to significant confusion and possible error.

With bitcoin, a hard fork would be necessary to change defining parameters such as the block size, the difficulty of the cryptographic puzzle that needs to be solved, limits to additional information that can be added, etc. A change to any of these rules would cause blocks to be accepted by the new protocol but rejected by older versions and could lead to serious problems – possibly even a loss of funds.

For instance, if the block size limit were to be increased from 1MB to 4MB, a 2MB block would be accepted by nodes running the new version, but rejected by nodes running the older version.

Let’s say that this 2MB block is validated by an updated node and added on to the blockchain. What if the next block is validated by a node running an older version of the protocol? It will try to add its block to the blockchain, but it will detect that the latest block is not valid. So, it will ignore that block and attach its new validation to the previous one. Suddenly you have two blockchains, one with both older and newer version blocks, and another with only older version blocks. Which chain grows faster will depend on which nodes get the next blocks validated, and there could end up being additional splits. It is feasible that the two (or more) chains could grow in parallel indefinitely.

This is a hard fork, and it’s potentially messy. It’s also risky, as it’s possible that bitcoins spent in a new block could then be spent again on an old block (since merchants, wallets and users running the previous code would not detect the spending on the new code, which they deem invalid).

The only solution is for one branch to be abandoned in favor of the other, which involves some miners losing out (the transactions themselves would not be lost, they’d just be re-allocated). Or, all nodes would need to switch to the newer version at the same time, which is difficult to achieve in a decentralized, widely spread system.

Or, bitcoin splits, which has happened (hello, bitcoin cash).

Soft fork

A soft fork can still work with older versions.

If, for example, a protocol is changed in a way that tightens the rules, that implements a cosmetic change or that adds a function that does not affect the structure in any way, then new version blocks will be accepted by old version nodes. Not the other way around, though: the newer, “tighter” version would reject old version blocks.

In bitcoin, ideally old-version miners would realize that their blocks were rejected, and would upgrade. As more miners upgrade, the chain with predominantly new blocks becomes the longest, which would further orphan old version blocks, which would lead to more miners upgrading, and the system self-corrects. Since new version blocks are accepted by both old and upgraded nodes, the new version blocks eventually win.

For instance, say the community decided to reduce the block size to 0.5MB from the current limit of 1MB. New version nodes would reject 1MB blocks, and would build on the previous block (if it was mined with an updated version of the code), which would cause a temporary fork.

This is a soft fork, and it’s already happened several times. Initially, Bitcoin didn’t have a block size limit. Introducing the limit of 1MB was done through a soft fork, since the new rule was “stricter” than the old one. The pay-to-script-hash function, which enhances the code without changing the structure, was also successfully added through a soft fork. This type of amendment generally requires only the majority of miners to upgrade, which makes it more feasible and less disruptive.

Soft forks do not carry the double-spend risk that plagues hard forks, since merchants and users running old nodes will read both new and old version blocks.

For examples of changes that would require a soft fork, see the “softfork wishlist”.

You can follow CoinDesk’s news and updates on cryptocurrency forks here.

Authored by Noelle Acheson; Fork image via Shutterstock


The leader in blockchain news, CoinDesk is a media outlet that strives for the highest journalistic standards and abides by a strict set of editorial policies. CoinDesk is an independent operating subsidiary of Digital Currency Group, which invests in cryptocurrencies and blockchain startups.

Chapter 09

What is SegWit?
door, opening

Last updated: 22 February, 2018

SegWit (short for Segregated Witness) is a protocol upgrade that changes the way data is stored. It was activated on litecoin on May 10, 2017, and on bitcoin on 23 August, 2017.

Developer Pieter Wiulle first presented the idea at the Scaling Bitcoin conference in December 2015.

Many hailed it as a long-awaited solution to bitcoin’s scaling problem. The maximum block size in the main protocol is 1MB, which restricts the number of transactions bitcoin can process to approximately 7 per second. This was going to limit bitcoin’s potential growth, and prevent it from becoming a usable high-volume payment system.

While the upgrade does enable a greater number of transactions in bitcoin’s blocks, SegWit’s initial intention was to fix a bug in the bitcoin code called transaction malleability. This flaw allowed anyone to change small details that modified the transaction id (and the subsequent hash) but not the content. While not a critical problem for bitcoin, it prevented the development of more complex features such as second-layer protocols and smart contracts.

SegWit fixed transaction malleability by removing the signature information (otherwise known as the “witness” information) and storing it outside the base transaction block. With that, signatures and scripts can be changed without affecting the transaction id.

Slimming down

A side benefit that is taking on a much greater importance is that, without the signature information, the transactions weigh much less. This means that more can fit in a block, and bitcoin can process a greater throughput without changing the block size.

SegWit introduced a new concept called “block weight.” This is a mashup of the block size with and without the signature data, and is capped at 4MB, while the block size limit for the base transactions remains at 1MB. This means that the SegWit upgrade is compatible with the previous protocol, and avoids the need for a hard fork.

So, SegWit does not increase the block size limit, but it does enable a greater number of transactions within the 1MB blocks. The 4MB cap includes the segregated witness data, which technically does not form part of the 1MB base transaction block.

Building on top

Another big step forward made possible by SegWit is that it supports the development of second layer protocols, such as the lightning network. The malleability fix made any feature that relied on unconfirmed transactions less risky and easier to design.

The lightning network will further boost bitcoin’s transaction capacity by taking frequent, small transactions off-chain, only settling on the bitcoin blockchain when the users are ready.

SegWit activation also boosted development work on other features such as MAST (which enables more complex bitcoin smart contracts), Schnorr signatures (which would enable another transaction capacity boost) and TumbleBit (an anonymous top-layer network).

Not everyone's happy

Not everyone in the bitcoin community agrees that SegWit is the solution bitcoin has been waiting for. Some believe that it is a case of “kicking the can down the road,” and at best a temporary fix.

Resistance to SegWit was one of the factors behind the development of bitcoin cash, a fork of the bitcoin network which chose to implement a larger block size limit rather than rely on a new transaction structure.

Where are we?

In spite of the obvious advantages, the rollout of the upgrade is moving slowly. At pixel time, 14% of transactions were using the new format (you can follow the progress here).

The main reason is that many wallets have yet to add SegWit support. Some big names such as Trezor, Ledger, Electrum and Kraken have already done so. Coinbase – the largest wallet provider in terms of number of transactions – is working on it, and expects to implement the upgrade in early 2018. And the wallet attached to bitcoin’s most popular full node implementation, Bitcoin Core, is expected to roll out SegWit in the first quarter of 2018.

With the main bitcoin code also making SegWit-friendly adjustments, this could lead to an uptick in both usage and additional functionality experimentation. Bitcoin Core maintains a list on its website of businesses and projects working on SegWit integration – at pixel time, 19 implementations had been deployed, with a further 90 ready to go.

As more wallets embrace the upgrade, the percentage of transactions that use the SegWit structure will increase, and bitcoin fees should drop as blocks contain a greater number of transactions. Furthermore, the development of lightning and similar second layer protocols should get more of a boost, enhancing bitcoin’s scope and potential. This is unlikely to happen overnight – but the change is an important one, and represents a big step forward.

Authored by: Noelle Acheson; Image of door opening via Shutterstock


The leader in blockchain news, CoinDesk is a media outlet that strives for the highest journalistic standards and abides by a strict set of editorial policies. CoinDesk is an independent operating subsidiary of Digital Currency Group, which invests in cryptocurrencies and blockchain startups.