Your bank needs to know who you are. Bitcoin doesn't. No ID, no name, no account. And yet, no one can spend your bitcoins for you. How?
A Bitcoin transaction relies on three objects you need to clearly distinguish. None is worth much alone: it's together that they prove ownership.
Click on each element. You'll see how it all fits together.
Let's get practical.
Interact with the elements below to see how private keys, public keys and signatures work together:
You've seen that the public key is calculated from the private key through a one-way operation. That calculation has a name: derivation. It's the 'toothpaste tube' effect: once it's out, it doesn't go back in.
No known method can derive the private key from the public key. And forging a valid signature without the right private key would take longer than the age of the universe, even harnessing every computer on the planet.
It's like a lock: anyone can verify that a key opens the door, but only whoever holds the right key can use it.
This mechanism completely changes the logic of ownership.
In the classical world, you must prove your identity to access an account. In Bitcoin, you only need to prove you control the right key.
Ownership then becomes a cryptographic proof, not a declaration.
Back to the coin graph: each one is locked by a key, and spending it means proving you own it.
In Bitcoin, owning means proving you hold the key.
One last question remains: how is all this actually presented to the user in real life?
More concretely, how are these keys stored, how is an address generated, and most importantly, what exactly is a wallet?
Next chapter: .