Since the keys are what users of our money will use to prove which money is theirs, and do stuff like sending it somewhere, they’re obviously very important to save well and keep them a secret from everybody else.
The logical next step once you get your keys, would be to write them down. But take a look at this key:
378bc5e22fc9fc02b41af8dd943e794f70576634b6223f3eba7ea76efe2c4400
Now take a look at this one and see if you can spot the problem:
378bc5e22fc9fc02b4laf8dd943e794f70576634b6223f3eba7ea76efe2c4400
Do you see it? There’s only one character changed. A 1 for a lower case l. This may look trivial, but with that single change, they’re totally different keys, they’d unlock very different wallets, and there’s no way to know which one is the wrong character, if any, or how many. No way.
So we have a problem. It’s very hard to write down these keys we created without making mistakes. And a tiny mistake as bad as a big mistake. It’s perfect or nothing. And if the keys are very difficult to write without errors, people are going to do insecure things to save them, like taking photos of the keys (which could be easily found on a device, have no encryption, could be automatically uploaded or shared without noticing it) or copy and pasting the keys on a text file somewhere. Even worse. We need to do something.
The solution is to translate from computer to human, from a meaningless string of characters, to a list of words. We’re better with words. We know that “food” is correct, and “fuod” is not. For example, our original key encoded into words would be:
nouns older lids rodent pumpkins railway wiggle mailed hoax waking evenings nocturnal oozed buckets germs gearbox gauze neon update axis macro syndrome madness magically rodent
How is this possible? Because we have a smaller number of characters than we have of words. But the important thing is that now users can write down a reasonably short list of words, all of them very different from each other, and with that have a perfect manual copy of their key. It’s easier to count the words to see if you’re missing one, and if you write down a mistake, it’s pretty easy to spot it.