Blockchain

Computers can share a big list.

This list keeps track of things. It links new parts to old parts. It is like a long chain. This helps keep the list safe. It is hard to change the list. A person named Satoshi Nakamoto made a special version. It was made for a digital money called bitcoin. Many computers work together to keep the list right. This way, no one can cheat the system. It is a very clever way to use computers.

A blockchain is a digital list of records. These records are kept in groups called blocks. Each block is linked to the one before it. This forms a long chain of data.

Blocks stay safe using something called a cryptographic hash. A hash is a special code that identifies a block. Each new block holds the code from the previous block. This links them together in a set order. If someone tries to change an old block, the codes will not match. They would have to change every block that comes after it. This makes the list very hard to change.

Many computers work together to manage the chain. This is a peer-to-peer network. This means no single computer is the boss. Instead, all computers follow a consensus algorithm. This is a set of rules to agree on new blocks.

A person named Satoshi Nakamoto created a famous blockchain in 2008. It was made for bitcoin. Bitcoin was the first digital money to solve the double-spending problem. This problem happens when someone tries to spend the same money twice. The blockchain makes sure each unit of value is moved only once.

A blockchain is a digital ledger used to keep track of records. You can think of a ledger as a shared list of information. Instead of one person holding the list, it is spread across a huge network of computers. This is called a distributed ledger. Each new group of records is called a block. These blocks are joined together in a specific order. This creates a long, continuous chain of data.

This system works using a special tool called a cryptographic hash. A hash is a unique code that represents the information in a block. Each new block contains the hash from the block that came before it. This creates a digital link between them. Because of these links, the data is very hard to change. If someone tries to change an old block, the hashes will no longer match. They would have to change every single block that follows to fix it. To make these changes, the whole network must agree through a consensus algorithm. This is a set of rules that the computers follow to stay in sync.

People have been working on these ideas for a long time. In 1982, a scientist named David Chaum wrote about a way to build trusted systems. Later, in 1991, Stuart Haber and W. Scott Stornetta described a secure chain of blocks. They wanted to make sure document timestamps could not be changed. In 1992, they added Merkle trees to the design. This helped the system work faster by grouping many certificates into one block.

A major breakthrough happened in 2008. A person or group using the name Satoshi Nakamoto created the first decentralized blockchain. Nakamoto used this to launch bitcoin, the first digital currency. This design solved the "double-spending" problem. This is when someone tries to spend the same digital money twice. Bitcoin uses a system called proof-of-work to add new blocks. In August 2014, the bitcoin blockchain reached a size of 20 GB. By 2024, that size grew to over 600 GB.

Blockchains are now used for many things beyond just money. Some people use them as a "payment rail" to move value. There are also private blockchains made for businesses to use. While most people know about public ones, some argue that private ones can be very secure too. You can see how this works by looking at how we use digital files today. Usually, we trust one big company to hold our data. A blockchain changes this by letting many computers share the job. This makes the system very strong and hard to break.

A blockchain is a decentralized, distributed digital ledger used to record information. It consists of growing lists of records called blocks that are securely linked together through cryptographic hashes. A hash is a unique digital code that represents the data within a block. Because each block contains the hash of the previous block, they form a continuous chain. This structure is often described as a linked list data structure. This technology is significant because it allows participants to verify and audit transactions independently. It also removes the ability to infinitely reproduce a digital asset. This ensures that each unit of value is transferred only once, solving the double-spending problem.

The mechanism of a blockchain relies on a specific sequence of steps to maintain integrity. First, a batch of valid transactions is collected into a block. These transactions are encoded into a Merkle tree, where data nodes act as leaves. Once the block is ready, it is digitally signed and assigned a cryptographic hash. This block then includes the hash of the block that came before it. This process links the new block to the entire history, all the way back to the very first block, known as the genesis block. If anyone tries to alter a block, they must change every subsequent block to make the hashes match again. To accept such changes, the entire network must reach a consensus.

Blockchains function through a peer-to-peer (P2P) computer network. Instead of relying on a central authority, many different computers, called nodes, manage the ledger. These nodes collectively follow a consensus algorithm protocol to add and validate new blocks. There are different ways to achieve this consensus. For example, bitcoin uses a proof-of-work system, which requires significant computation to add blocks. Other systems use proof-of-stake, where validators are chosen to propose new blocks. Some advanced protocols, like the Casper protocol used in Ethereum, aim for absolute finality. This means a block is irreversibly committed once a supermajority of validators approves it. In other systems, users rely on probabilistic finality, where the confidence in a block grows as more blocks are built on top of it.

The history of blockchain technology spans several decades of cryptographic research. In 1982, cryptographer David Chaum proposed a blockchain-like protocol in his dissertation. In 1991, Stuart Haber and W. Scott Stornetta described a method for a cryptographically secured chain of blocks. Their goal was to create a system where document timestamps could not be tampered with. In 1992, they and Dave Bayer added Merkle trees to improve efficiency. This allowed multiple document certificates to be collected into a single block. Under their company, Surety, they have published document certificate hashes in The New York Times weekly since 1995. In 2008, a person or group using the pseudonym Satoshi Nakamoto conceptualized the first decentralized blockchain. Nakamoto introduced a difficulty parameter to stabilize the rate at which blocks are added.

Satoshi Nakamoto implemented this design in 2009 as the core component of bitcoin. This was the first digital currency to solve the double-spending problem without a central server. The scale of the bitcoin blockchain has grown massively over time. In August 2014, the bitcoin blockchain file size reached 20 GB. By 2024, the size of the bitcoin blockchain exceeded 600 GB. While the terms "block" and "chain" were used separately in the original 2008 paper, the single word "blockchain" became popular by 2016. The technology has seen varying levels of adoption. In 2016, financial services saw a 13.5% adoption rate. However, in 2018, Gartner found that only 1% of CIOs had adopted blockchain within their organizations.

Blockchains can be categorized by how they are accessed and managed. Public or permissionless blockchains are open to everyone and are often decentralized. These are widely used for cryptocurrencies. In contrast, private or permissioned blockchains are proposed for specific business uses. Some experts argue that permissioned chains can be more secure if they are carefully designed. However, others have criticized the marketing of private blockchains without proper security models. There is also a risk of centralization as these systems grow. As the computer resources required to process larger amounts of data become more expensive, the system may become less decentralized. This can lead to a "51% attack," where one entity gains control of more than half the network to manipulate records.

Modern blockchain design is often viewed through several functional layers. The bottom layer is the infrastructure, which consists of the physical hardware. Above that is the networking layer, which handles node discovery and information propagation. The consensus layer manages how the network agrees on the truth. The data layer contains the actual blocks and transactions. Finally, the application layer can include smart contracts or decentralized applications. Because of this layered structure, blockchain is considered a type of payment rail. It is a distributed computing system with high Byzantine fault tolerance, meaning it can function correctly even if some parts of the system fail or act dishonestly.