v1.4.1: The "not sure what to use? Generate a strong one" note now disappears as soon as there's a password in the field, typed or pasted, instead of sitting there once you've already got one.
v1.4.0: Added a "Remove" button per file and a "Clear all" button. A batch that mixes new files to encrypt with already-encrypted files to decrypt now pauses processing with an explanation, since those almost always need different passwords, instead of silently applying one password to both. There's also a link to the Password Generator, in a new tab, if you'd rather not make one up.
v1.3.1: The "someone sent you an encrypted file" banner now changes its message once a file is actually dropped in, instead of still telling you to drop it in after you already have.
v1.3.0: The sharing instructions are now always shown in a visible, read-only text box, not just copied to the clipboard. The "someone sent you a file" banner and dropzone now also react to a file being recognized as encrypted the moment it's dropped in, not only when arriving through the special decrypt link. You can also arrive here with a password already filled in from the Password Generator's handoff button.
v1.2.0: Encrypted files now start with a short, unencrypted, human-readable note pointing back to this tool, so a file that gets separated from its instructions still explains itself if opened directly. Everything after that note stays fully encrypted.
v1.1.0: Added a decrypt-mode link (?mode=decrypt) with clearer on-page instructions for recipients, and a "Copy sharing instructions" button for whoever sent the file.
v1.0.0: Initial release. Password-protect any file with AES-256-GCM, or decrypt a file this tool made.
Lock any file behind a password before you send it somewhere you don't fully trust: email, cloud storage, a USB stick you're handing over. The file never leaves your device, and neither does your password.
How this actually works
Your password is run through PBKDF2 (600,000 rounds of SHA-256) with a random salt to produce a key, then your file is encrypted with AES-256-GCM, the same building blocks used by password managers and full-disk encryption. This page loads no outside code at all to do it: everything here comes from the Web Crypto API already built into your browser. There is no way for us, or anyone, to recover a file if the password is lost. There's no backdoor and no reset link, so keep the password somewhere safe. Every encrypted file also starts with a short, plain-text note pointing back to this page, readable even in a text editor, in case the file ever gets separated from your instructions. That note reveals nothing about what's inside; everything past it is fully encrypted.
Someone sent you an encrypted file? Drop it in the box below, then type in the password they gave you through a separate message or call, not this same link.
This file was already encrypted with this tool. Enter the password below, the one you were given through a separate message or call, not this same link, then click "Process all files" to decrypt it.
Click to choose files or drag them here
Plain files get encrypted; files this tool already encrypted (.mrjenc) get decrypted
Password
If you forget this password, the encrypted file cannot be recovered by anyone, including us. There's no backdoor and no reset.
Send the password a different way than the file itself: a text, a call, a separate app. If either one gets intercepted alone, it's useless without the other.
This batch has both new files to encrypt and already-encrypted files to decrypt. Since they almost certainly need different passwords, processing is paused. Remove the files you don't want to handle right now (or click "Clear all"), process the rest, then add the others back afterward.