Bitcoin from Scratch

Eighteen chapters. No libraries. From a single byte to a network running across several machines.

Everything uses only the Python standard library. No Bitcoin libraries, no black-box APIs, no “just copy this for now, you’ll understand later.” Every term you’ve heard (hash, public key, signature, block, mining, consensus, UTXO, Merkle tree, Script) becomes code you wrote yourself before it is allowed to carry that name.

This book argues one thing¶

The genuinely original part of Bitcoin is not the cryptography. It is everything else.

Satoshi’s building blocks were almost all borrowed: digital signatures (Diffie–Hellman / RSA, 1976–77), proof-of-work (Adam Back, 1997), hash time-stamp chains (Haber–Stornetta, 1991), the idea of a decentralized ledger (Wei Dai / Nick Szabo, 1998), and the first serious attempt at digital cash (David Chaum, 1982).

What he invented was how to build a bank with no manager out of those bricks.

That claim is easy to say and hard to prove, so this book counts it. Every chapter ends with a ledger: of the code you just wrote, which lines are cryptography, and which are systems design, consensus, game theory, or economics. By chapter 18 the tally speaks for itself.

The bricks are borrowed. The house is original.

Start here: Prologue: Borrowed Bricks, an Original House

Contents¶

Part I · Bricks: the cryptographic floor¶

Ch	Title	What you build by hand
1	Bytes, Hashes, Commitments	`sha256()`, and `commit()` / `verify()`: a guessing game nobody can cheat
2	Finite Fields, Elliptic Curves, Public Keys	Hop around a curve mod 97, derive a public key, then brute-force it back
3	Digital Signatures	Real ECDSA, then count how many times `priv` appears inside `verify`

Part II · Retracing the ancestors¶

Ch	Title	What you build by hand
4	The Hash Time-Stamp Chain	Haber–Stornetta’s chain; edit one old block and watch everything after it break
5	Proof-of-Work	Hashcash-style mining, and a lesson about luck that most books skip

Part III · The house: building a chain¶

Ch	Title	What you build by hand
6	Transactions and Double-Spending	A UTXO ledger, and your first problem cryptography cannot solve
7	Blocks and Longest-Chain Consensus	The rule that settles double-spends: this chapter contains zero cryptography
8	Incentives and Issuance	Block rewards, halving, 21 million: making the machine run itself
9	Forks and Upgrades	Changing the rules with nobody in charge

Part IV · Surviving the long run¶

Ch	Title	What you build by hand
10	Fees and Difficulty Adjustment	Two negative-feedback loops that keep the system steady
11	Merkle Trees and Efficient Verification	Prove a transaction is in a block without downloading the block
12	Mempool, Fee Market, Confirmations	RBF, CPFP, reorgs: why your transaction is stuck
13	Switching to the Real Curve	Swap the toy curve for the one Bitcoin actually uses

Part V · Toward real engineering¶

Ch	Title	What you build by hand
14	The Script VM	Spending conditions are not a database field; they are a running program
15	Wallets and HD Key Trees	How twelve words grow a thousand addresses
16	Hardware Signing	Why the private key lives in a room with no network cable
17	A Multi-Node Network	Run your chain across several machines and watch them converge
18	Why Script Is Deliberately Weak	How loops, global state, and one bad opcode could kill every node

Appendices¶


A	The cryptography map: roads this book does not take (encryption, zero-knowledge proofs, MPC)
B	Why a quantum computer breaks public keys but not hashes
C	CHECKSIG vs CSFS: same lamp, different piece of paper

One thread¶

bytes → hash → commitment → finite field → elliptic curve → public key → signature → chain → mining → transactions → consensus → incentives → upgrade coordination → efficient verification → the real curve → mempool and confirmations → Script → wallets → hardware signing → a real network → the limits of the script engine

Later chapters reuse functions you wrote in earlier ones. Read in order.

This book argues one thing¶

Contents¶

Part I · Bricks: the cryptographic floor¶

Part II · Retracing the ancestors¶

Part III · The house: building a chain¶

Part IV · Surviving the long run¶

Part V · Toward real engineering¶

Appendices¶

One thread¶

Other ways to read it¶