Blockchain Fundamentals

1. What is a Blockchain?

At its core, a blockchain is a distributed digital ledger. Unlike a traditional database controlled by a single entity (like a bank or a technology company), a blockchain is maintained by a network of computers (nodes) distributed across the globe.

Every time a transaction occurs, it is mathematically verified by the network, grouped into a "block," and cryptographically chained to the previous block. This creates an unalterable, chronological history of data.

2. Consensus Mechanisms

Since there is no central authority, the network must agree on the validity of transactions. This agreement is achieved through consensus mechanisms:

• Proof of Work (PoW): Used by Bitcoin. "Miners" compete to solve complex cryptographic puzzles to validate blocks and secure the network. It requires massive computational power.
• Proof of Stake (PoS): Used by Ethereum. "Validators" lock up (stake) their own cryptocurrency as collateral to validate blocks. It is significantly more energy-efficient than PoW.

3. Cryptography & Hashing

Blockchains rely heavily on public-key cryptography. Every user has a Public Key (an address others can send assets to) and a Private Key (a secret password used to authorize transactions). Never share your private key.

Furthermore, each block contains a unique cryptographic identifier called a hash. If anyone tries to alter a previous block, the hash changes, invalidating all subsequent blocks and alerting the entire network to the tampering attempt.