What encryption actually is, in plain words.

I’ve read the word “encrypted” on more apps than I can count, and most of the time it tells you almost nothing. Here’s what it really means, the way I’d explain it to a friend. Every app you use will tell you your data is encrypted. It’s on the login screen, the pricing page, the little padlock in the corner of the browser. And because it’s on everything, it’s stopped meaning much. I’ve spent more time on that one word than I’d care to admit, building a notes app where it actually has to be true, so here’s how I think about it. No maths. No padlock pictures. Underneath, encryption is an old and simple idea. You take a message, turn it into nonsense nobody can read, and make sure only the right person can turn it back. That’s the lot. Everything after that is detail about how good the nonsense is, and who’s allowed to undo it. The whole thing in one sentence Encryption takes something readable and mixes it into a mess that means nothing on its own. A matching key turns the mess back into the original. No key, and the mess stays a mess. The readable version is called plain-text. The mixed version is called cipher-text. That’s the entire vocabulary you need to know. Encryption turns plain-text into cipher-text, decryption is turning it back. A note is just text until you scramble it Say you’ve got a note on your phone, “dentist Thursday, 3pm”. Stored as it is, anyone who gets at the file reads it straight off. A thief with your unlocked phone. An app you handed too many permissions to. A company keeping a copy on its servers. All of them see “dentist Thursday, 3pm”. Encrypt it and that same note might sit on the disk as 9f2ac1b0e7..., a run of characters that means nothing. The appointment is still in there, in the sense that the right key brings it back, but on its own it tells a snoop nothing. Not the time, not the day, not that it was ever about a dentist. People reach for a padlock to explain this and I’ve never liked it. A padlock just stops you getting to the thi