File Encryption Tool

Last reviewed: 2026-07-13

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Encrypt or decrypt a file with a password, right in this browser - no upload, no app to install.

Key features

• Reads the file you choose with the browser FileReader and never uploads it to a server.
• Derives an encryption key from your password with WebCrypto PBKDF2 (250,000 rounds) plus a fresh random salt, entirely in the browser.
• Encrypts the file with AES-256 (WebCrypto AES-GCM) using a fresh random IV generated in the browser for every run.
• Decrypts a .enc file back to the original with WebCrypto AES-GCM when you supply the same password.
• Builds the protected copy as a downloadable file in the browser, with no server round-trip.

When to use it

Reach for it when you need to protect a single file with a password before storing or sharing it, and you would rather not upload the file or install an app. The file is opened locally in your browser and never leaves the device, so it suits sensitive documents you want to keep off any server.

Encrypt and decrypt

Action	You provide	You get back
Encrypt	Any file plus a password	A protected copy with a .enc extension
Decrypt	A .enc file plus the same password	The original file under its original name

Encrypting the same file with the same password twice produces two different .enc files, because a fresh random salt and IV are used every time - that is expected, not a bug.

Privacy

Everything runs in your browser: the file is read locally with FileReader, the key is derived from your password, and the encrypted or decrypted result is built as a download with no server round-trip. Your file and your password are never uploaded.

How the encryption works

The file is scrambled with AES-256 using a key derived from your password (PBKDF2, 250,000 rounds) plus a fresh random salt and IV every time. The .enc file carries a small 32-byte header - a tag plus that fresh salt and IV - in front of the scrambled data, and your original filename is encrypted inside the data too, so Decrypt can restore the exact filename without it ever being stored outside the encrypted file.

A wrong password, or a .enc file that was edited or corrupted, is refused with a plain error message instead of producing a broken or garbage file.

The tool works on any file type - text documents, spreadsheets, archives, images, or anything else. There is no file-type filter and no size limit set by this tool. Treat the downloaded .enc file as opaque: the original name, type, and all bytes are sealed inside, and decrypt restores them exactly.

What the password actually protects, byte by byte

Your password is never used as the key directly. It is stretched through PBKDF2 with 250,000 SHA-256 rounds against a fresh 16-byte random salt, and only the result is handed to AES-GCM-256 - so two people who pick the same password still get different keys, because the salt differs every run. The protected file is one container: a 4-byte tag, then the 16-byte salt, then the 12-byte random IV, and finally the ciphertext, which means the whole header costs exactly 32 bytes before your data begins. Because the 12-byte IV is regenerated every time, encrypting a 10 KB spreadsheet twice yields two byte-different .enc files of the same length - matching outputs would actually signal a broken IV, not a correct one. The original filename is packed, length-prefixed, inside the encrypted bytes, so Decrypt restores "report-q3.xlsx" rather than a generic name without ever writing that name to disk in the clear. If you paste the wrong password or a single byte of the .enc file was altered in transit, the AES-GCM authentication tag fails verification first and the tool shows a plain error instead of handing back a corrupted file - there is no password recovery path, so a lost password means the file stays sealed for good, by design.

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