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Blockchain Fundamentals

This section builds the blockchain data structure from its individual parts, before treating it as a financial system, treat it as what it fundamentally is: blocks of data, linked by hashes, secured by proof-of-work, with a deterministic rule for resolving disagreements. Everything here is protocol-agnostic groundwork for the deep, Bitcoin-specific treatment that follows in the next section.

What you need to know first

Cryptography (specifically hash functions and Merkle trees) and Distributed Systems (specifically consensus and the CAP theorem). This section combines both directly: a blockchain is a cryptographic data structure operated under a distributed consensus protocol.

Chapters

  1. Blocks: the header/body split, and why it exists
  2. Block Headers: all six fields of Bitcoin's 80-byte header, with a verified serialization example
  3. Transactions: the UTXO model versus the account model, as a general design choice
  4. Hashes and Block Linking: why altering an old block requires redoing every block after it
  5. Merkle Roots: the header field that commits to every transaction in a block
  6. Genesis Blocks: the necessary, hardcoded exception to trustless verification
  7. Block Height: absolute position versus confirmation count
  8. Block Time: the propagation-delay tradeoff behind Bitcoin's ~10-minute target
  9. Chain Reorganizations: why they're routine, and when they become serious
  10. Consensus Rules: the distinction between consensus rules and policy rules
  11. Fork Choice: cumulative proof-of-work, precisely, not just "longest chain"
  12. Permissionless vs Permissioned Networks: why not every "blockchain" offers the same guarantees

Build one

Reading about a data structure only goes so far. examples/simple-blockchain/ is a small, runnable TypeScript implementation that builds up, module by module, everything covered in this section: blocks, hash linking, Merkle roots, a basic proof-of-work search, and tamper-detection validation. It is explicitly not production-grade or Bitcoin-compatible, see that project's README for exactly what it omits and why, so its simplicity isn't mistaken for a claim about what real security requires.

Next

Continue to Bitcoin, where this same data structure gets its full, deep treatment: real transaction formats, real mining economics, real script-based spending conditions, and everything else that turns this chapter's abstractions into the network actually running today.