// learn · episode 04 · season finale
Wallets, keys & signatures
Episode 3 showed how the network agrees on history. Last question: what does it mean for a coin in that history to be yours? The answer is a number. This page uses real cryptography — actual ECDSA key generation, signing, and verification in your browser (the P-256 curve; Bitcoin and Ethereum use its cousin secp256k1 — same mathematics, same lessons). Nothing you do here leaves the page.
01 · the key
Your key is just a number
No account. No username. No registration. Ownership starts with nothing more than a random number so large that no one else will ever pick it.
your private key — 256 bits, freshly generated
generating…
how big is 2²⁵⁶?
About 1.2 × 10⁷⁷ possible keys — within shouting distance of the ~10⁸⁰ atoms in the observable universe. Nobody guesses yours. Nobody brute-forces it either (you saw why in episode 1). Security is bigness.
honesty corner
This key was generated in your browser and never leaves the page. Treat real ones like toothbrushes: never share, never reuse. Whoever knows the number is the owner — the chain can't tell the difference.
02 · the pipeline
Key → address: one way only
You never show anyone that number. What you show the world is the end of a one-way pipeline: the private key produces a public key, and hashing the public key produces your address. Walking backwards up this pipeline is the same impossibility you met in episode 1.
private key — SECRET
generating…
public key — shareable
…
address — public, on-chain
…
Real chains differ only in the last step — Ethereum hashes with keccak-256, Bitcoin with SHA-256 then RIPEMD-160 — and use the secp256k1 curve instead of our P-256. Same shape, honestly simplified.
03 · the act of ownership
Sign & verify
Owning the key would mean nothing if you couldn't prove it without revealing it. That's what a signature does — and you're about to make a real one.
This is the whole trick of ownership: the private key stays secret, yet anyone can check your claim using only the public key. When a wallet app "sends crypto", this is all it really does — sign a message saying so, and broadcast it for the miners of episode 3 to bury under confirmations.
04 · the hard truth
Lose the key, lose everything
Everything you've built this episode hangs on one number. The scariest property of this system is also its most honest one: nobody can save you. Go ahead — experience it safely.
private key
∅ gone. not misplaced — gone.
the sober numbers
Estimates suggest millions of bitcoin sit at addresses whose keys are lost — hard drives in landfills, passwords taken to graves. The standard mitigation is a seed phrase: 12–24 ordinary words that encode the key, easy to write down, easy to store. But that only moves the question: where do those words live, and who can find them when you're gone? That's not a technology problem. It's an inheritance problem.
season complete
You've touched every load-bearing part
Fingerprints that can't be faked, chained into a history that can't be quietly rewritten, agreed on by strangers, owned through numbers only you know. That's a blockchain — no magic left, just mathematics you've now used with your own hands.
One thread runs through this whole series: keys don't survive their owners by default. Digital assets that outlive their owners need a succession plan.
That's the problem I work on →