Key Concepts in Blockchain: Hashing, Blocks, and Nodes

 🔐 1. Hashing

Definition: Hashing is the process of converting data into a fixed-length string of characters using a cryptographic algorithm (e.g., SHA-256).


✅ Key points:

A hash is unique to the input data (like a digital fingerprint).


Even a tiny change in input produces a completely different hash.


Hashing ensures data integrity — if the data is altered, the hash changes.


Example:

plaintext

Copy

Edit

Input: "Hello"

SHA-256 Hash: 185f8db32271fe25f561a6fc938b2e264306ec304eda518007d1764826381969

In blockchain, hashing is used:


To link blocks securely.


To verify transactions and data integrity.


📦 2. Blocks

Definition: A block is a container that holds a list of transactions and some metadata (like timestamp, previous hash, etc.).


✅ Structure of a block:

Block Header:


Hash of the previous block


Timestamp


Nonce (used in mining)


Block Body:


List of transactions


Blockchain = Chain of Blocks

Each block references the hash of the previous block.


This chaining makes the blockchain tamper-proof — altering one block breaks the chain.


🌐 3. Nodes

Definition: Nodes are computers that participate in the blockchain network.


✅ Types of nodes:

Full Node: Stores the entire blockchain and validates transactions and blocks.


Lightweight (SPV) Node: Stores only part of the blockchain; relies on full nodes for validation.


Miner Node: Special nodes that validate transactions and add new blocks to the chain (via mining or staking).


Role of nodes:

Maintain the network by validating and propagating transactions.


Reach consensus on the state of the blockchain.


Ensure decentralization — no single entity controls the blockchain.


🔄 Summary

Concept What It Does Why It Matters

Hashing Converts data to a fixed string Ensures data security and integrity

Blocks Store transaction data Form the backbone of the blockchain

Nodes Run the network Keep the system decentralized and secure


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