Encrypt File
Encrypt any file with a password using AES-256-GCM in your browser. Handles huge files; decrypt anytime here. Free and private — nothing is ever uploaded.
- No upload — 100% private
- Instant, on your device
- Free, no sign-up
- Works offline once loaded
How it works
How to use Encrypt File
Drop one or more files (any type, any size). They stay on your device.
Type a strong password twice — or click “Generate strong password” and save it in your password manager.
Click “Encrypt file”. You get report.pdf.mstbx, which is unreadable without the password.
To open it later, come back, switch to Decrypt, drop the .mstbx file and enter the same password.
Why use it
Why use our Encrypt File tool
AES-256-GCM with a slow key
Your password is stretched with PBKDF2-SHA-256 (600,000 rounds, random salt) into a 256-bit key, so guessing passwords is painfully slow for attackers.
Built for big files
Files are encrypted in 4 MB pieces read straight from disk. In Chrome and Edge the result can be written directly to a file, so multi-gigabyte videos and backups work.
Tamper detection
Every piece carries an authentication tag tied to its position. A changed byte, swapped pieces or a cut-off download are detected instead of producing a silently broken file.
Strength meter and generator
See how guessable your password is as you type, or generate a random 20-character password and copy it in one click.
Nothing leaves your device
Encryption uses your browser's built-in Web Crypto. No upload, no account, no server — the page even works offline once loaded.
FAQ
Frequently asked questions
How does the encryption work, in plain words?
Your password is mixed with a random salt and run through PBKDF2-SHA-256 600,000 times to make a 256-bit AES key. The file is split into 4 MB pieces and each piece is locked with AES-256-GCM using its own unique nonce. Each piece also gets a tag proving it hasn't been altered, moved or dropped, and the last piece is marked as last, so a shortened file is caught too.
What if I forget the password?
The file is gone for good. There is no back door, reset link or master key — that is what makes it secure. Store the password in a password manager and test decrypting before you delete the original.
How do I open a .mstbx file?
Come back to this page (or the Decrypt File page), drop the .mstbx file and type the password. The original file, with its original name, is restored on your device. Bookmark the page — it works offline too.
Is the file name hidden?
The original name, type and date are stored encrypted inside the file and restored when you decrypt. The .mstbx file itself is named like report.pdf.mstbx, so rename it to something neutral before sharing if the name is sensitive. The approximate size is always visible.
Can I encrypt several files or a folder at once?
Yes. Each file is encrypted separately with the same password, or tick “Put all files in one ZIP, then encrypt it” to get a single .mstbx that also hides how many files there are and their names.
Is it safe to encrypt files before uploading them to the cloud?
That's a great use. Google Drive, Dropbox or email only ever see the encrypted .mstbx, so even a leaked account doesn't expose the contents — as long as your password is strong and kept separately.
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