algo-blockchain-basicslisted

# Blockchain Fundamentals ## Overview A blockchain is a distributed, append-only ledger where blocks of transactions are cryptographically linked. Each block contains: transactions, previous block hash, timestamp, and nonce. Consensus mechanisms (PoW, PoS, BFT) ensure agreement without a central authority. Trade-off: decentralization vs performance. ## When to Use **Trigger conditions:** - Evaluating whether blockchain is appropriate for a use case - Designing systems requiring distributed trust, immutability, or transparency - Understanding blockchain architecture for integration or development **When NOT to use:** - When a trusted central authority exists and works well (use a database) - When performance (thousands of TPS) is the primary requirement - When data privacy requires deletion capability (blockchain is append-only) ## Algorithm ``` IRON LAW: Blockchain Is Useful ONLY When You Need TRUSTLESS Consensus If participants trust each other (or trust a central authority), a traditional database is faster, cheaper, and simpler. Blockchain's value proposition is: untrusted parties can agree on state without an intermediary. If trust already exists, blockchain adds overhead with no benefit. Ask: "Who doesn't trust whom?" before choosing blockchain. ``` ### Phase 1: Input Validation Assess use case against blockchain decision criteria: multiple untrusting writers? Need for immutability? No trusted central party? Public verifiability required? **Gate:** At least 3 of