Sending a file only the right person can open

Email isn’t private: messages sit in mailboxes and backups for years, and a wrong address sends a file to a stranger. When a file holds personal, financial or medical details, lock it with a password before it leaves your computer, so a copy in the wrong place is useless without the password. The file is locked in your browser and isn’t uploaded.

Take care with secrets. This runs only in your browser: what you enter isn't uploaded, stored or put in a link, and the page is built so that it can't send it anywhere else. Your browser's extensions and other software on your device can still see what's on screen, so use a device you trust and real secrets only when you need to. Disconnecting from the internet once the page has loaded gives the most protection. Use is at your own risk: see the terms.

1. Choose a password worth using

A file sent by email can be attacked at leisure, so the password needs to be strong, not just long enough for a website. In the Password Generator, a Passphrase of words (XKCD) of five or six words is strong and easy to read out over the phone.

2. Lock the file

In Encrypt / Decrypt, type the Password, then under File choose the file and Encrypt file. It downloads a copy with .enc added to its name, scrambled with AES-256. Send that copy and keep the original. For a short message rather than a file, paste it under Text and Encrypt text gives text you can paste into an email.

If the file is a PDF, there’s a gentler way: Protect / Unlock PDF with Protect it with a password puts an Open password on the PDF itself (AES-256), so the person opens it in their usual PDF reader, typing the password, with nothing else to install. Keep the original, as a forgotten password can’t be recovered. Steps 3 and 4 apply as they are, except that the file keeps its .pdf name.

3. Send the password another way

A password in the same email as the file protects nothing. Send it by a different route: a text message, a call, or a chat app, so someone who gets one doesn’t get the other. Agree it in advance if you send files to the same person often.

4. How they open it

Tell them which tool you used. They open the same Encrypt / Decrypt page, type the password and choose Decrypt file: it downloads the original. Someone who prefers not to use a website can use the openssl command shown under The same on the command line, on a Mac or Linux as it comes, or on Windows with OpenSSL installed. The Iterations must match on both sides; leave it at 600,000 unless you’ve agreed otherwise.

A wrong password usually gives an error, but about once in 256 tries it gives a file of garbage instead, and the format can’t tell whether the file was changed on the way. To be sure, run the original through Hash / Checksum before you send it and give them its SHA-256 with the password; they paste it under Expected hash after decrypting.

A forgotten password can’t be recovered, so keep the original until they’ve confirmed it opens.