Blockchain · Crypto · Fintech

1 · Cryptographic hashing — SHA-256

A hash function takes any input and returns a fixed-size fingerprint. Even a one-bit change in the input completely changes the output — this is the avalanche effect. Type below and watch the digest update live.

Try flipping a single letter and watch ~50% of the output bits flip — that's why hashes work for fingerprinting blocks and detecting tampering.

2 · Digital signatures — ECDSA

Crypto-wallets don't store coins — they store a private key that can sign messages. Anyone with your public key can verify the signature, but only you could have made it. This demo uses real ECDSA on the P-256 curve via the browser's WebCrypto.

3 · Merkle trees

Each block commits to its transactions through a Merkle root — a single hash that summarises hundreds of transactions. Change any leaf and the root changes, which lets light clients verify membership cheaply.

4 · The block chain

Each block stores the hash of the previous block, forming a chain. Edit any block's data and every block downstream is invalidated — the chain turns red. Re-mine to repair it (and notice how expensive an attacker's job becomes).

5 · Proof of work — mining a single block

Miners try nonces until SHA-256(block) < target. Watch the search live. Doubling the leading-zero count makes the work ~16× harder.

6 · The UTXO model (Bitcoin)

Bitcoin doesn't track balances — it tracks unspent transaction outputs. To pay, you consume whole UTXOs as inputs and create new UTXOs as outputs (one to the recipient, one back to yourself as change).

7 · Bitcoin forks & upgrades

Forks happen when the rules change. Soft forks tighten rules and stay backward-compatible; hard forks are incompatible and split the chain. Click each event to learn what happened.

8 · Wallets & Ethereum addresses

An Ethereum address is derived from a private key by: privKey → secp256k1 pubKey → keccak256(pubKey)[12:] → 0x.... This demo uses a P-256 stand-in for browser-native crypto, but the pipeline is identical.

9 · The Ethereum account model

Unlike Bitcoin's UTXO model, Ethereum has two kinds of accounts:

• EOA — Externally Owned Account, controlled by a private key. Has balance & nonce.
• Contract — code lives at the address. Has balance, nonce, code, and storage.

10 · Gas & fees (EIP-1559)

Every EVM operation costs gas. Post-EIP-1559, the user pays (baseFee + priorityFee) × gasUsed; the baseFee is burned, the priority fee ("tip") goes to the validator.

11 · The EVM — opcode walker

The Ethereum Virtual Machine is a stack machine. Step through a tiny program that computes (3 + 4) × 2 and watch the stack.

12 · Solidity — deploy & call a contract

This is a JavaScript-backed simulation of the Counter contract you'd write in Remix. Deploy it, call the functions, watch the state and gas cost.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract Counter {
    uint256 public count;
    address public owner;

    constructor() { owner = msg.sender; }

    function increment() external { count += 1; }
    function decrement() external {
        require(count > 0, "underflow");
        count -= 1;
    }
    function reset() external {
        require(msg.sender == owner, "not owner");
        count = 0;
    }
}

13 · ERC-20 fungible tokens

The ERC-20 standard defines six functions every fungible token must support. The two killer features that enable DEXes & DeFi are approve and transferFrom — they let a contract pull tokens from you only up to a pre-approved allowance.

14 · NFTs — ERC-721

Each tokenId is unique and points to off-chain metadata (image, traits) usually pinned on IPFS. Ownership is on-chain; the art lives elsewhere.

15 · Automated Market Maker (Uniswap V2)

A constant-product market maker holds two assets and enforces x × y = k. Big trades move the price more — that's slippage. The 0.3% fee is added to the pool, paying the LPs.

16 · Layer-2 rollups

Rollups execute transactions off-chain and post only a compressed state-root to L1, amortising one expensive L1 tx over hundreds of L2 txs. Optimistic rollups assume validity and allow a 7-day fraud-proof window. ZK rollups attach a zero-knowledge validity proof — finality is instant.

17 · Bitcoin halving & supply schedule

Every 210 000 blocks (~4 years) the coinbase reward halves. The geometric series converges to the famous 21 million BTC cap.

13 · Consensus — Proof of Work vs Proof of Stake

Ethereum's "Merge" cut energy use by ~99.95% by swapping PoW for PoS in 2022.