Neither your files nor your password ever leave your device — 100% local processing

Encrypt Files with a Password

Lock any file with AES-256 into a .mtenc file, and unlock it with the password. Everything runs inside your browser.

⚠️ If you forget the password, the file cannot be recovered by any means. Keep it somewhere safe.
⚠️ Some files exceed 500MB. Processing happens in browser memory, so it may be slow or fail depending on your device.

0 B uploaded — this page has not sent your files to any server?

Private by design — encryption and decryption run on your device, right inside your browser. Neither your files nor your password are ever uploaded, and since we never see the password, we cannot decrypt your files either.How this differs from upload-based sites — most online archive tools upload your archive to a server, unpack it there, and promise to delete it after a while. If it is password-protected you have to hand over the password too, and until deletion your files are sitting on someone else's server. zipmoa has no upload step at all. The more sensitive the archive — bundled contracts, scanned IDs, a company backup — the more that difference matters.

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Lock a sensitive file so nothing opens it without your password

Contracts, scanned IDs and backups are exactly the files you don’t want readable if a USB stick goes missing or a cloud account is breached. This tool encrypts any file, whatever its format, with AES-256-GCM into a .mtenc file, and turns it back into the original on the same page when you enter the password. Neither the file nor the password leaves your browser.

A closer look

Encryption uses the standard cryptography built into your browser (WebCrypto). Your password is not used as the key directly. For every file a fresh 16-byte random salt is generated, and the password is run through PBKDF2-SHA256 310,000 times with it to produce a 256-bit key. That repetition is what makes guessing passwords one by one painfully slow for an attacker. AES-256-GCM then encrypts the contents and appends a 16-byte authentication tag; if the password is wrong, or even a single byte of the file has changed, the tag check fails and decryption is refused. Locking the same file twice with the same password gives two different results, because the salt and IV are random every time.

The .mtenc layout is published: the 6-byte marker MTENC1, the salt, a 2-byte name length, the original file name in UTF-8, a 12-byte IV, then the ciphertext. With the password, anyone can decrypt it using a standard crypto library, even if this site disappears. The important detail is that the original file name is stored unencrypted in that header so it can be restored, and the output is named “original name.mtenc”. The contents are hidden; the name is not. Encryption is not compression either: the result is larger than the original by exactly 52 bytes plus the file name’s length in bytes.

How to use it

When it helps

Papers on a USB stickLock contracts or ID scans before carrying them around, so whoever finds a lost stick sees nothing but file names.
A second lock on cloud backupsEncrypt before uploading, so a compromised cloud account doesn’t expose the contents.
Sending the file and password separatelyEmail the .mtenc and share the password by phone or another app. A leak on one channel isn’t enough to open it, and the recipient can decrypt on this same page.
Hiding names for a whole batchBuild a plainly named ZIP such as “files.zip” with Create ZIP, then encrypt that one ZIP; the names inside become part of the ciphertext.

Common snags

It says “Incorrect password.”This is what a failed GCM tag check looks like, and a typo is the most common cause, so check the keyboard language, Caps Lock and spaces at either end. A file that was truncated or damaged in transit produces the same message. When decrypting several files at once, the run stops at the file that fails, so add files locked with a different password separately.
I dropped a .mtenc and got the encrypt screen instead.The mode is chosen from the file extension. If an email or chat app stripped the trailing .mtenc, rename the file back to “original name.mtenc” and drop it again. Mixing regular files and .mtenc files in one selection triggers “Please select either regular files or .mtenc files, not both at once.”
Can it handle files of several hundred megabytes?The whole file is loaded into memory and encrypted in one pass, so the original and the result occupy memory at the same time. Files over 500MB trigger a warning, and depending on the device the job may be slow or fail. Process large files on a computer with plenty of RAM and other tabs closed.
Save all only downloaded one file.Save all starts the downloads one after another, about a third of a second apart, and some browsers first ask whether this site may download multiple files. Allow it and the rest follow; if they were blocked, press Save on each row instead.

Tip A forgotten password cannot be recovered, so store it in a password manager before you encrypt, and test-decrypt one file before deleting the original.

File Encryption FAQ

How secure is this?

Files are encrypted with AES-256-GCM, the same standard used by banks and governments. Your password is stretched into a key with PBKDF2 (SHA-256, 310,000 iterations), which makes brute-force attacks dramatically slower, and the GCM authentication tag detects any tampering. The final strength depends on your password though — use a long, unpredictable one.

Is the file format open? Can I decrypt without this site?

Yes — it is fully documented, not proprietary. The layout is MTENC1 magic (6 bytes) + salt (16 bytes) + filename length (2 bytes, big-endian) + original filename (UTF-8) + IV (12 bytes) + AES-256-GCM ciphertext (16-byte auth tag included). The key is PBKDF2-HMAC-SHA256 with 310,000 iterations. The original filename is stored in the header so it can be restored; the contents are fully encrypted. Anyone can implement this with a standard library such as WebCrypto or Python’s cryptography, so your files stay recoverable even if this site disappears — as long as you have the password. Without it, not even we can decrypt them.

What if I forget the password?

There is no way to recover the file. There is no master key, no backdoor, and nothing stored on any server — if the password is lost, the file cannot be recovered by any means. Keep your password somewhere safe.

Are my files uploaded anywhere?

No, nothing is ever sent anywhere. All encryption and decryption runs on your device, inside your browser — once the page is loaded, it even works offline. Neither files nor passwords leave your browser.