Sealed Message
Lock a message with a passphrase. Only someone with the same passphrase can open it.
A different version of this page is available. You are still using the saved one.
Only matters when sealing. Opening detects the style.
How this works
- Everything happens inside this page on your device. The page itself is blocked from using the network, so nothing you type can be sent anywhere. The only network use is fetching this page's own files from this same address.
- Your passphrase is stretched into a key with PBKDF2 (600,000 rounds of SHA-256), and the message is locked with AES-256-GCM. Both come from your browser's built-in encryption.
- Each sealed message carries its own tamper check. If any part of it is changed or missing, it will refuse to open. The check covers one message, not a conversation: it cannot tell you that nothing was left out or sent twice. Newer sealed messages record when they were sealed, and that time is shown when you open them.
- A wrong passphrase and a damaged message look the same to the page. It cannot tell you which one happened.
- Agree on the passphrase in person or on a call, never in the same chat as the sealed text. Four or more random words make a strong one.
- Sealed text hides what you said. It does not hide that you sent something, and anyone can recognise it as sealed text.
- Use Safari, Chrome or Firefox itself. The browsers built into apps such as Messenger and Instagram can read what is typed into any page they show, so this page refuses to work inside them.
- Nothing you type is saved. Closing or clearing the page removes it.
- When opened from a web address, the page keeps a copy of itself on your device. Later visits use that copy, even with no connection, and a change published by the site's owner is only used after you choose it. This guards against accidents and outages. It cannot guard against whoever controls the website, who could replace this page. For anything that matters a great deal, use a copy of the page kept on a computer.