Blockchain is a decentralized digital ledger that securely stores records across a network of computers in a way that is transparent, immutable, and resistant to tampering. Each "block" contains data, and blocks are linked in a chronological "chain."
A blockchain is a distributed database or ledger shared across a computer network's nodes. They are best known for their crucial role in cryptocurrency systems, maintaining a secure and decentralized record of transactions, but they are not limited to cryptocurrency uses. Blockchains can be used to make data in any industry immutable—meaning it cannot be altered.
Since a block can’t be changed, the only trust needed is at the point where a user or program enters data. This reduces the need for trusted third parties, such as auditors or other humans, who add costs and can make mistakes.
Since Bitcoin's introduction in 2009, blockchain uses have exploded via the creation of various cryptocurrencies, decentralized finance (DeFi) applications, non-fungible tokens (NFTs), and smart contracts.
Key Takeaways:
*Blockchain is a type of shared database that differs from a typical database in the way it stores information; blockchains store data in blocks linked together via cryptography.
*Different types of information can be stored on a blockchain, but the most common use has been as a transaction ledger.
*In Bitcoin’s case, the blockchain is decentralized, so no single person or group has control—instead, all users collectively retain control.
*Decentralized blockchains are immutable, which means that the data entered is irreversible. For Bitcoin, transactions are permanently recorded and viewable to anyone.
How Does a Blockchain Work?
You might be familiar with spreadsheets or databases. A blockchain is somewhat similar because it is a database where information is entered and stored. The key difference between a traditional database or spreadsheet and a blockchain is how the data is structured and accessed.
A blockchain consists of programs called scripts that conduct the tasks you usually would in a database: entering and accessing information, and saving and storing it somewhere. A blockchain is distributed, which means multiple copies are saved on many machines, and they must all match for it to be valid.
The Bitcoin blockchain collects transaction information and enters it into a 4MB file called a block (different blockchains have different size blocks). Once the block is full, the block data is run through a cryptographic hash function, which creates a hexadecimal number called the block header hash.
The hash is then entered into the following block header and encrypted with the other information in that block's header, creating a chain of blocks, hence the name “blockchain.”
Transaction Process
Transactions follow a specific process, depending on the blockchain. For example, on Bitcoin's blockchain, if you initiate a transaction using your cryptocurrency wallet—the application that provides an interface for the blockchain—it starts a sequence of events.
In Bitcoin, your transaction is sent to a memory pool, where it is stored and queued until a miner picks it up. Once it is entered into a block and the block fills up with transactions, it is closed, and the mining begins.
Every node in the network proposes its own blocks in this way because they all choose different transactions. Each works on their own blocks, trying to find a solution to the difficulty target, using the "nonce," short for number used once.
The nonce value is a field in the block header that is changeable, and its value incrementally increases with every mining attempt. If the resulting hash isn't equal to or less than the target hash, a value of one is added to the nonce, a new hash is generated, and so on. The nonce rolls over about every 4.5 billion attempts (which takes less than one second) and uses another value called the extra nonce as an additional counter. This continues until a miner generates a valid hash, winning the race and receiving the reward.
Fact: *Generating these hashes until a specific value is found is the "proof-of-work" you hear so much about—it "proves" the miner did the work. The sheer amount of work it takes to validate the hash is why the Bitcoin network consumes so much computational power and energy.
Once a block is closed, a transaction is complete. However, the block is not considered confirmed until five other blocks have been validated. Confirmation takes the network about one hour to complete because it averages just under 10 minutes per block (the first block with your transaction and five following blocks multiplied by 10 equals 60 minutes).
Not all blockchains follow this process. For instance, the Ethereum network randomly chooses one validator from all users with ether staked to validate blocks, which are then confirmed by the network. This is much faster and less energy intensive than Bitcoin's process.
Blockchain Decentralization
A blockchain allows the data in a database to be spread out among several network nodes—computers or devices running software for the blockchain—at various locations. This creates redundancy and maintains the fidelity of the data. For example, if someone tries to alter a record on one node, the other nodes would prevent it from happening by comparing block hashes. This way, no single node can alter information within the chain.
Because of this distribution—and the encrypted proof that work was done—the blockchain data, such as transaction history, becomes irreversible. Such a record could be a list of transactions, but private blockchains can also hold a variety of other information like legal contracts, state identifications, or a company's inventory. Most blockchains wouldn't "store" these items directly; they would likely be sent through a hashing algorithm and represented on the blockchain by a token.