Blockchain

Blockchain is a type of distributed ledger technology (DLT) in which transactions or other records are grouped into blocks and linked sequentially using cryptographic techniques. A blockchain is maintained by a network of computers according to a defined protocol for validating, recording, and synchronizing data.

Blockchain technology can be used to maintain shared records without relying on a single centralized database administrator. It is used in applications including cryptocurrencies, digital assets, smart contracts, payments, supply-chain management, and other forms of digital record keeping.

Structure

A blockchain generally consists of a sequence of blocks containing transaction or other data.

A simplified representation is:

${Block}_{n - 1} \to {Block}_{n} \to {Block}_{n + 1}$

Each block may contain:

transaction or other recorded data;
a timestamp;
information identifying the preceding block;
a cryptographic hash;
other information required by the particular blockchain protocol.

Blocks

A block is a collection of records that is added to the blockchain according to the rules of the underlying protocol.

Blocks commonly contain:

a set of transactions;
a reference to the previous block;
a timestamp;
a block identifier or hash;
consensus-related information.

The exact structure varies among blockchain systems.

Cryptographic hash

A cryptographic hash is a mathematical function that converts input data into a fixed-length output.

Blockchain systems can use hashes to link blocks and detect changes to previously recorded information.

A simplified relationship is:

$H_{n} = Hash ({Block Data}_{n})$

A block may also contain the hash of the preceding block:

${Block}_{n} = ({Data}_{n}, H_{n - 1})$

If previously recorded data is modified, the resulting hash can change, allowing the alteration to be detected by systems that verify the chain.

Distributed ledger

A blockchain is a form of distributed ledger. Instead of maintaining a single authoritative database on one computer, copies or relevant representations of the ledger can be maintained across multiple network participants.

The participants use the blockchain protocol to determine how transactions are validated and how the ledger is updated.

Nodes

A node is a computer or other system that participates in a blockchain network.

Depending on the protocol, nodes may:

maintain a copy of the ledger;
receive transactions;
validate transactions;
validate blocks;
relay information;
participate in consensus.

The responsibilities of nodes vary among blockchain networks.

Consensus mechanism

A blockchain requires a mechanism for participants to agree on the state of the distributed ledger.

Common consensus mechanisms include:

The consensus mechanism determines how transactions or blocks are validated and how the network resolves competing versions of the ledger.

Proof of work

Proof-of-work is a consensus mechanism in which participants perform computational work to compete for the opportunity to add new blocks to the blockchain.

In systems using proof-of-work, successful participants may receive protocol-defined rewards.

Bitcoin is an example of a blockchain-based system that uses proof-of-work.

Proof of stake

Proof-of-stake is a consensus mechanism in which participants known as validators commit or stake assets according to the rules of the network.

Validators may be selected to propose or validate blocks based on the protocol's rules.

Proof-of-stake generally requires substantially less direct computational energy for consensus than proof-of-work.

Transactions

A blockchain transaction is a digitally recorded operation submitted to a blockchain network.

Depending on the system, transactions may represent:

transfers of digital assets;
execution of smart contracts;
changes to recorded data;
other operations defined by the protocol.

A simplified transaction process is:

$Transaction \to Validation \to Block \to Blockchain$

Immutability

Blockchain systems are often described as providing immutability because altering previously recorded data can require modification of subsequent records and, depending on the consensus mechanism, agreement or control over a substantial portion of the network.

Immutability is therefore a property of the technical and economic design of a particular blockchain rather than an absolute guarantee that information can never be changed.

Some blockchain systems permit authorized changes or reversals through protocol mechanisms or governance processes.

Decentralization

Decentralization refers to the distribution of control, validation, or record keeping among multiple participants rather than concentrating these functions in a single authority.

The degree of decentralization varies substantially among blockchain networks.

A blockchain can therefore be distributed without being completely decentralized.

Public and private blockchains

Blockchain networks can be categorized according to access and governance arrangements.

Public blockchain

A public blockchain is generally accessible to a broad group of participants.

Participants may be able to:

view blockchain records;
submit transactions;
operate nodes;
participate in validation or consensus.

The exact permissions depend on the protocol.

Private blockchain

A private blockchain restricts participation to authorized entities.

Private blockchains may be used by organizations that require controlled access to a distributed ledger.

Permissioned blockchain

A permissioned blockchain restricts specified functions, such as transaction validation or network participation, to authorized participants.

Permissioned systems may be public to read, private to read, or otherwise configured according to the requirements of the application.

Smart contracts

A smart contract is a program deployed on a blockchain or related distributed system that executes according to predefined rules.

Smart contracts can be used to automate transactions and other operations.

Applications include:

decentralized finance;
digital assets;
token issuance;
automated payments;
decentralized applications.

A smart contract does not necessarily constitute a legally enforceable contract in the conventional legal sense.

Cryptocurrency

Blockchain technology is closely associated with cryptocurrencies.

Cryptocurrencies can use blockchains to record transfers and maintain a shared transaction history.

Bitcoin and Ethereum are prominent examples of blockchain-based systems, although their technical architectures and purposes differ.

Digital assets and tokenization

Blockchain systems can be used to create and transfer digital tokens representing different types of assets or rights.

Tokenization can involve:

digital-native assets;
claims on physical assets;
financial instruments;
access rights;
other forms of digital representation.

The legal status and ownership implications of a token depend on its design and the applicable jurisdiction.

Decentralized finance

Decentralized finance (DeFi) uses blockchain networks and smart contracts to provide or facilitate financial functions.

Applications can include:

lending;
borrowing;
trading;
asset exchange;
liquidity provision;
collateral management.

DeFi systems can operate without some traditional financial intermediaries, although they remain subject to technological, economic, and regulatory risks.

Supply-chain applications

Blockchain can be used to create shared records of transactions or events within supply chains.

Potential applications include:

tracking goods;
recording provenance;
verifying transactions;
monitoring movement of products;
coordinating information among participants.

The usefulness of a blockchain-based supply-chain system depends on the accuracy of information entered into the system.

Identity management

Blockchain technology can be used in some digital-identity systems to record or verify information about identity credentials.

Potential applications include:

credential verification;
decentralized identity;
authentication;
certification records.

Blockchain does not by itself guarantee that the underlying identity information is accurate.

Financial services

Financial institutions may use blockchain or related distributed-ledger technologies for:

payments;
securities settlement;
trade finance;
collateral management;
transaction recording;
digital assets;
reconciliation.

Potential benefits include shared records and automated processing, although integration with existing financial infrastructure can create technical and regulatory challenges.

Advantages

Potential advantages of blockchain technology include:

distributed record keeping;
transparency in systems where records are publicly accessible;
cryptographic integrity;
automated transaction processing;
reduced dependence on a single database administrator;
programmable transactions;
auditability.

The benefits depend on the architecture and purpose of the blockchain.

Limitations

Blockchain technology also has limitations, including:

scalability constraints;
transaction-processing costs;
energy consumption for some consensus mechanisms;
storage requirements;
interoperability challenges;
governance issues;
privacy concerns;
regulatory uncertainty;
irreversible transactions in some systems.

Blockchain is therefore not necessarily superior to conventional databases for every application.

Scalability

Scalability refers to the ability of a blockchain network to process increasing numbers of transactions while maintaining acceptable performance.

Public blockchains can face trade-offs among:

transaction throughput;
decentralization;
security;
latency;
operating costs.

Various approaches have been developed to address scalability, including changes to blockchain architecture and additional transaction-processing layers.

Security

Blockchain systems use cryptographic techniques and consensus mechanisms to protect the integrity of their ledgers.

However, blockchain applications can still be vulnerable to:

software vulnerabilities;
private-key theft;
compromised accounts;
smart-contract vulnerabilities;
consensus attacks;
fraudulent applications;
weaknesses in centralized services connected to the blockchain.

The security of a blockchain therefore depends on both the underlying protocol and the surrounding ecosystem.

Privacy

Blockchain transparency does not necessarily mean that users are personally identified.

Some public blockchains record transactions using addresses or other pseudonymous identifiers rather than conventional names.

However, transaction histories can sometimes be analyzed and linked to real-world identities through external information.

Privacy characteristics vary substantially among blockchain systems.

Governance

Blockchain governance refers to the mechanisms through which changes to a blockchain's protocol, rules, or operating parameters are proposed, evaluated, and implemented.

Governance may involve:

developers;
validators;
miners;
token holders;
network operators;
other stakeholders.

Different blockchain networks use different governance models.

Blockchain and databases

A blockchain and a conventional database can both store digital records, but they are designed for different requirements.

A conventional database is generally managed by a defined administrator who can modify records according to established permissions.

A blockchain distributes record validation and maintenance among network participants according to protocol rules.

Blockchain systems may therefore be useful where multiple parties require a shared record without relying entirely on a single controlling organization.

Importance

Blockchain is a significant development in distributed computing and digital record keeping. By combining cryptographic linking, distributed data storage, consensus mechanisms, and programmable transactions, blockchain systems can provide new ways to coordinate and record transactions among multiple participants. Its applications extend beyond cryptocurrencies to financial services, digital assets, supply chains, identity systems, and other areas requiring shared digital records.