Foundational · v0
What Is a Blockchain?
A database thousands of strangers maintain together, where no one can quietly edit the past — the substrate all of DeFi runs on.
TradFi →A shared, tamper-evident ledger
01 · Concept — what problem does it solve?
Every financial system needs a ledger — a record of who owns what. Normally one trusted party (a bank) keeps it. A blockchain removes that party: it is a ledger replicated across thousands of independent computers, where transactions are batched into blocks that are cryptographically chained together, so altering an old record breaks every block after it visibly. The result is a database no single entity controls and no one can rewrite — trustless by construction. That property is the entire foundation DeFi is built on.
02 · Mechanics
- Blocks & the chain: each block holds a batch of transactions, a timestamp, and the hash of the previous block. Change anything in the past and the hash chain no longer matches.
- decides which new block is valid:
- Proof of Work (Bitcoin): miners burn energy solving a puzzle to earn the right to add a block. Secure, slow (~7 tx/s), energy-hungry.
- Proof of Stake (Ethereum, since 2022): validators lock up ETH as collateral and are chosen to propose blocks; misbehavior is slashed. ~99.9% less energy.
- Immutability: rewriting history needs majority control of the network's work or stake — economically absurd on a large chain.
- : users pay a fee in the chain's native coin (ETH, BTC) to get a transaction included; the fee floats with demand.
03 · Formulas
block_N.prev_hash == hash(block_N-1) // the link that makes tampering visible
// attack cost: control > 50% of hashpower (PoW) or stake (PoS)
// Ethereum 2026: ~897k validators, ~38.9M ETH staked (~32% of supply)
// Ethereum gas: often well under $0.20 for a simple transfer
04 · Edge cases & risks
- "Blockchain = unhackable" is wrong: the ledger is tamper-evident, but the things on top — smart contracts, bridges, and user keys — get exploited constantly. The base layer being secure does not make the application layer safe.
- Decentralization is a spectrum: a chain with ten validators is barely more trustless than a database. Real security needs hundreds to thousands of independent ones.
- Public vs. permissioned: "enterprise blockchains" with one admin keep the buzzword but drop the trustless property — they are just databases with extra steps.
- Irreversibility: there is no undo and no support line. A confirmed transaction is final.
Connected concepts