Leader track 🔗 · six sessions, no code
For anyone being asked to approve, fund or explain something built on a chain. What the mechanism actually is, what it guarantees, what it costs to defeat, who has to agree, what it cannot do for you, and how to decide whether you need one at all.
What a chain actually is
A hash, a link, and why that makes an edit visible. The Harbourgate register, six real blocks.
🔍 Leader session 2Tamper evident is not tamper proof
Edit a block and the check fires. Fix the hash and the failure moves one block along.
⛏️ Leader session 3What it costs to rewrite history
Mining as deliberate expense. The mean is known, and a single run tells you almost nothing.
🗳️ Leader session 4Who agrees, and how
Forks, longest chain, and why decentralised is a spectrum rather than a switch.
🚧 Leader session 5What a chain cannot do for you
It preserves what was written. It has no opinion on whether it was true.
🧭 Leader session 6Deciding whether you need one
Four questions, and the honest answer that a database with an audit log is often better.
Practitioner track 🏗️ · ten sessions, hands on
For the people who build and audit one. Hashing, blocks, breaking a chain deliberately, mining, the cost of a rewrite, Merkle proofs, signatures, consensus, smart contracts as a mechanism, and a capstone bench.
Hashing, hands on
SHA-256 as a function, its published test vectors, and why an implementation ships them.
🧱 Practitioner session 2Building the chain
Blocks, previous hashes, and the genesis convention of 64 zeros.
💥 Practitioner session 3Breaking the chain
Both stages of the tamper, and reading what verify actually reports.
⚒️ Practitioner session 4Mining
Nonces and difficulty, and measuring attempts properly instead of once.
🔁 Practitioner session 5The cost of a rewrite
Reforging from block 2, and what each extra zero buys.
🌳 Practitioner session 6Merkle trees
Prove one record belongs to a set of 1,024 by sending 10 hashes.
✍️ Practitioner session 7Signatures and identity
Who may add an entry, and why that question is answered outside the chain.
🤝 Practitioner session 8Consensus
Forks, the longest chain rule, and finality as a probability rather than a fact.
📜 Practitioner session 9Smart contracts, mechanically
Code that runs on the chain, and the guarantees that does not buy you.
🏗️ Practitioner session 10The chain bench
Build, tamper, mine, reforge and prove, all live in the page.
The whole thing on one page
Every idea in the course and the session that owns it. Click any node to jump there.
Three ways through
Everyone starts at session 1 of their track. These are the shortest useful routes if you cannot take all sixteen.
What is real here
The hash is a full SHA-256 written from the specification, not a stand-in. Every digest on every page comes out of it.
| The hash | Ships the three published SHA-256 test vectors and runs them, because a hash that is subtly wrong still produces plausible hex |
| The register | Six real blocks with real hashes, rebuilt in the page, tamperable in two different ways |
| Mining cost | Means over 500, 300, 120 and 150 trials, never a single run: at difficulty 3 the measured range is 40 to 17,343 attempts |
| No coins | No cryptocurrency, no price, no wallet, no token anywhere. Nothing here is investment advice |