nickgallick Blockchain Fundamentals
Core Concepts
How It Works
A blockchain is an append-only linked list of blocks. Each block contains a hash of the previous block. Changing any past block invalidates all subsequent hashes — this is immutability.
Consensus
| Mechanism | How | Used By | Trade-off |
|---|---|---|---|
| Proof of Work | Miners solve puzzles | Bitcoin | Secure but energy-intensive |
| Proof of Stake | Validators stake tokens, slashed if dishonest | Ethereum | Efficient, ~99.95% less energy |
| Proof of Authority | Trusted validators | Private chains | Fast but centralized |
Key Numbers
| Metric | Ethereum L1 | Base (L2) | Bitcoin |
|---|---|---|---|
| Block time | ~12s | ~2s | ~10min |
| TPS | ~15 | ~1000 | ~7 |
| Finality | ~12min | ~minutes | ~60min |
| Gas cost | $$$ | $ | N/A |
The EVM (Ethereum Virtual Machine)
- Stack-based VM executing smart contract bytecode
- Every node runs the same computation → deterministic consensus
- Storage is EXPENSIVE: writing 32 bytes costs
20,000 gas ($0.50-$50) - Memory is cheap. Design accordingly: compute at read time, store minimally
- No floating point. All math is integer. Use fixed-point (amounts in wei, not ETH)
Key Concepts for Developers
Wallet: public/private key pair. Address = identity. Private key = NEVER expose.
Transaction: signed message. Contains: to, value, data, gas limit, gas price.
Smart Contract: code at a blockchain address. Immutable once deployed.
ABI: JSON describing contract functions/events. The "API spec."
Events/Logs: cheap data emission (vs storage). Frontends listen to these.
Token Standards
| Standard | Type | Use Case |
|---|---|---|
| ERC-20 | Fungible tokens | Arena Coins (interchangeable units) |
| ERC-721 | NFTs | Badges, trophies (each unique) |
| ERC-1155 | Multi-token | Batch of different items (mixed badges) |
L1 vs L2
| Layer | Examples | Cost | Speed | Security |
|---|---|---|---|---|
| L1 | Ethereum mainnet | $$$ | Slow | Maximum |
| L2 Optimistic | Optimism, Base, Arbitrum | $ | Fast | Ethereum (fraud proofs) |
| L2 ZK | zkSync, Starknet, Polygon zkEVM | $ | Fast | Ethereum (validity proofs) |
For new projects: ALWAYS build on L2. Base (by Coinbase) is the current default — low fees, high throughput, Ethereum security.
Optimistic vs ZK rollups:
- Optimistic: assume valid, fraud proofs if challenged. 7-day withdrawal delay. Easier to build.
- ZK: cryptographic proof of validity. No delay. Harder to build. Better long-term scaling.
What Goes On-Chain vs Off-Chain
| On-Chain (expensive, permanent, verifiable) | Off-Chain (cheap, fast, mutable) |
|---|---|
| Token balances (Arena Coins) | User profiles |
| Badge ownership (NFTs) | Challenge descriptions |
| Challenge results (hash) | Full transcripts |
| ELO snapshots (end of season) | Real-time leaderboards |
| Reputation scores | Session data |
Rule: Store the minimum needed for verification on-chain. Everything else stays in Supabase.
Sources
- ethereum/solidity documentation
- OpenZeppelin/openzeppelin-contracts
- Ethereum.org developer documentation
- Vitalik Buterin's "Endgame" L2 vision
Changelog
- 2026-03-21: Initial skill — blockchain fundamentals