Version 2026-10-17b. Generate a random pad, then encrypt or decrypt. Everything runs locally in this page; nothing is sent anywhere.
Read this first. A one-time pad is only unbreakable if the pad is truly random, at least as long as the message, kept secret, used only once, and destroyed after use. Reusing a pad, even once, lets an attacker recover both messages.
Security instructions
Read these before you make or share a pad.
The pad is the entire secret. The math of a one-time pad cannot be broken, so all of your security rests on the key (the pad) itself.
Never reuse a pad. Each pad, and each page or stretch of key, is for one message only. Never use the same key material twice.
Destroy each page after use. Once a message is sent or read, burn that page.
Treat the pad like cash. If a pad is ever copied or intercepted, every message encrypted with it is exposed.
Deliver the pad physically. Hand it over in person, or mail it separately from the message so the two never travel the same route. For remote use, generate the pad on one machine and physically carry it to the other (a USB drive or a printed copy). Never send it over the network it is meant to protect.
Never email a pad. Don’t generate the pad on one computer and email it to the other. That puts the key on the same wire as the encrypted message, and the whole system collapses.
Know when a pad makes sense. If you can meet in person to swap a pad, you could usually swap the message in person too. A pad earns its keep when you need to communicate later, over distance, without meeting again.
Printable pad
Make paper pad sheets to print and hand over in person. Generated in this browser with crypto.getRandomValues; nothing is sent to any server.
250 groups = 25 rows of 10 groups per page (max 300 so a page fits on one sheet). Letters pads add a tabula recta reference page.
Using a paper pad. Both parties keep identical copies; use each page for one message only, then burn it. Cross off groups as you use them and never reuse a page. A pad generated on a screen is only as safe as the device and printer that made it: use a trusted, offline machine if it matters, don’t save the file, and clear this page when done.