Bitcoin

The case used in this module

Each module tells its own made-up Brindlecove story, so details can differ from one module to the next.

Key words

Double-spending

Paying with the same digital money twice. Bitcoin was designed to stop it without a bank in the middle.¹²

Hash

The result of scrambling any amount of data into a short, fixed-size output.³

Proof of work

Finding a number that makes a block's hash start with enough zeros. It takes many guesses to find, and one check to confirm.¹

Mining

Spending computing power to process transactions, secure the network and add the next block, in return for a reward.⁴²

Block subsidy

The new bitcoin a miner may create in a block. It started at 50 BTC and has been 3.125 BTC since April 2024.²⁵

Halving

The cut in half of the block subsidy every 210,000 blocks, roughly every four years.⁵⁶

Satoshi (sat)

The smallest unit of bitcoin. 100,000,000 sats make 1 BTC.⁴⁷

UTXO

Unspent transaction output: an amount of bitcoin waiting to be spent. A wallet's balance is the total of its UTXOs.⁸

Change output

The part of a transaction that sends the leftover back to the sender, because inputs can't be partly spent.⁷⁸

Fee rate

A transaction's fee divided by its size, usually in sats per virtual byte (sat/vB).⁹¹⁰

Mempool

A node's queue of transactions waiting to be added to a block.¹⁰

Lightning Network

A network of two-party payment channels. Payments move off the main chain, and only opening and closing a channel go on it.¹¹¹²