Encrypt & decrypt files
Password-protect any file with AES-256. It never leaves your device.
How it works
- 01Drop any file. Files ending in .rndr open in decrypt mode automatically.
- 02Choose a strong password and type it twice.
- 03Download the encrypted .rndr file. Decrypt it here later with the same password.
Questions
›How strong is the encryption?
Files are encrypted with AES-256-GCM using your browser's built-in Web Crypto. The key comes from your password through PBKDF2-SHA256 with 600,000 iterations and a random salt, which makes every password guess slow. The real weak point is the password, so use a long one: four or more random words works well.
›What if I forget the password?
The file can't be recovered. There is no reset, no back door and no copy on our side, because nothing was ever sent to us. Keep the password in a password manager.
›Is there a size limit?
No limit from us. Files are encrypted in 4 MB chunks, so even very large files work. In Chrome and Edge, files over 200 MB are written straight to disk as they are processed; other browsers build the result in memory, so the practical limit there is your device's RAM.
›What is the .rndr format? Am I locked in?
It's simple and documented, so any developer can write a decrypter. A 60-byte header: "RNDR", version (1), KDF id (1 = PBKDF2-HMAC-SHA256), 2 reserved bytes, iterations (uint32), chunk size (uint32), 16-byte salt, 12-byte nonce, and a 16-byte key check (first half of SHA-256 of "RNDR key check" + key). Then chunks of AES-256-GCM ciphertext with a 16-byte tag. Chunk i uses the nonce with its last 4 bytes XORed with i, and authenticates the header + i (uint32) + a final-chunk flag byte, so missing, reordered or cut-off chunks are detected. All integers are big-endian; the password is UTF-8 in NFC form.
›Does it hide the file name?
The contents are encrypted, but the file is named after the original (report.pdf becomes report.pdf.rndr) so you can tell your files apart. Rename it before sharing if the name itself is sensitive; decryption doesn't depend on it.
›Are my files uploaded anywhere?
No. Your files are processed on your own device by your browser. They never touch our servers, so there are no upload waits, no size caps from us, and nothing to delete afterwards.