What Is Blockchain?
A blockchain is a distributed digital ledger used to record transactions and other data across a decentralized peer-to-peer network. Another way to understand it is as a shared encrypted database that is duplicated across many computers and updated by the network.
It is part of the wider family of distributed ledger technologies. Instead of storing the record in one central database controlled by one authority, blockchain distributes the record across many nodes.
Distributed
Copies of the ledger are stored by many participants.
Peer-to-Peer
Nodes communicate directly across the network.
Secure
Cryptography protects data integrity and transaction ownership.
Transparent
Participants can verify the ledger state according to network rules.
The Blockchain Network
A blockchain network is a peer-to-peer decentralized network. Its participants are called nodes. A node may be a desktop computer, laptop, mobile device, server, mining rig or other electronic device that contributes resources to the network.
These nodes help maintain the network’s integrity and security. They store data, verify transactions and participate in the consensus process depending on the blockchain design.
Centralized Network
One central authority controls the main database or server.
Decentralized Network
Many peers cooperate to maintain the network and ledger.
Centralized Network vs Decentralized Network
In a centralized system, a central authority or server controls the main database and approves transactions. For example, when someone pays by credit card, the transaction usually requires approval from a bank or payment intermediary.
In a decentralized blockchain system, participants can transact directly according to the network rules. The system relies on cryptographic authentication, a decentralized network and a consensus mechanism to maintain trust and integrity.
Centralized Model
- One main point of control
- Users rely on a third party
- Possible single point of failure
- Data is controlled by the central operator
Decentralized Model
- Many nodes maintain the ledger
- Transactions follow consensus rules
- No single server controls the full system
- Cryptography protects data integrity
Decentralization reduces dependence on a single trusted intermediary and helps remove the single point of failure found in many centralized systems.
The Composition of Blockchain
A blockchain is made of a chronological chain of blocks. The first block is called the genesis block. Each later block is appended after the previous block, forming a chain.
Every node in the blockchain network can store or access a copy of the distributed ledger, depending on the network design and the role of the node.
The Block Structure
A block contains a block header and a list of transactions. The header stores important metadata, while the transaction list stores the data that will be added to the blockchain.
Block Header
Contains metadata such as previous hash, timestamp, nonce and other fields.
Transactions
Contains the transactions or records bundled into the block.
Block Height
The number of blocks before a particular block in the chain.
Nonce
A number adjusted by miners during Proof-of-Work mining.
Block Height
The block height of a block is the number of blocks that came before it. The genesis block has a block height of zero because no blocks precede it.
Nonce
A nonce is a value used by miners while solving a Proof-of-Work puzzle. Miners change the nonce to try to produce a valid block hash that satisfies the network difficulty target.
What Is Proof of Work?
In the Bitcoin network, miner nodes collect valid unconfirmed transactions into blocks. Miners then compete to solve a cryptographic puzzle before proposing the next block.
This process is called Proof of Work. It requires computing effort, which helps prevent spam and tampering because attacking the network would require significant resources.
Difficulty
Difficulty measures how hard it is to find a valid hash for a target. In Bitcoin, difficulty adjusts periodically so that blocks continue to be produced at the intended pace.
What Is Timestamping?
A timestamp records when an event occurred. In digital systems, timestamps are attached to digital data such as files, images, transactions and blocks.
Timestamping is important in blockchain because each block carries time information and refers to the previous block using cryptographic hashes. This creates a chronological record that is difficult to alter without detection.
What Is a Hash?
A hash is the output of a hash function. The function takes input data of any length and produces a fixed-length alphanumeric value. The input might be a document, spreadsheet, image, contract, transaction or block.
Important Properties of Hashing
- ✓A given input produces a predictable output of a specified length.
- ✓A tiny change in input produces a dramatically different hash.
- ✓For cryptographic hash functions, it is extremely difficult to infer the original input from only the hash.
- ✓Hashes help participants agree on the current state of the blockchain.
Hashing helps preserve blockchain integrity. If someone tampers with data in a block, the hash changes, and the network can detect that the block no longer matches the expected chain.
What Is a Digital Signature?
A digital signature is a cryptographic method used to prove authenticity, integrity and non-repudiation. In blockchain, digital signatures help prove that a transaction was authorized by the rightful owner.
Digital signatures use asymmetric cryptography. A user has a public key and a private key. The public key can be shared, while the private key must remain secret. Transactions are signed with the private key and verified with the public key.
Private Key
Used by the owner to sign a transaction or message. It must be kept secret.
Public Key
Used by others to verify that the signature matches the sender.
Signing
The sender creates a hash and signs it with the private key.
Verification
The receiver checks the signature using the sender’s public key.
Blockchain depends on hashing to protect the ledger state and digital signatures to prove transaction ownership.
Summary
- ✓Blockchain is a distributed digital ledger maintained by many nodes.
- ✓Decentralized networks reduce reliance on a single central authority.
- ✓Blocks are linked chronologically from the genesis block onward.
- ✓Proof of Work uses computing effort to secure the network and prevent abuse.
- ✓Hashing protects integrity, while digital signatures prove authorization.