The cipher is strong. The key derivation is the weak link.

AES-256 has no known practical attack against it. But an encrypted ZIP is not protected by AES alone — it is protected by whatever key your password turns into, and the ZIP format dictates how that happens. The WinZip AES standard this tool implements derives the key with PBKDF2-HMAC-SHA1 at 1,000 iterations and a 16-byte random salt. That iteration count was fixed when the format was written and has never been raised, because raising it would break every ZIP tool already shipped.

For comparison, this site's File Encrypter uses 200,000 iterations. Both use AES-256; the difference is that guessing a password costs an attacker 200 times more work there than here.

The practical consequence is that password length matters more for a ZIP than almost anywhere else. Short or dictionary-based passwords can be tested at enormous speed against a 1,000-iteration derivation. A long passphrase cannot be, no matter how cheap each guess is. This tool enforces a six-character minimum — treat that as a floor the format allows, not as a recommendation.

Which programs can actually open the result

This catches out more people than the encryption ever does. Neither operating system's built-in archive handler supports AES ZIPs — both implement only the legacy ZipCrypto scheme, which is old enough to be broken with widely available tools. Someone who double-clicks your file and gets an error will usually conclude it is corrupt rather than that they need different software. Tell the recipient which program to install before you send it.

The file names are not encrypted

AES encrypts the contents of every entry in the archive. It does not encrypt the ZIP central directory, so anyone holding the file can list what is inside — names, uncompressed sizes and timestamps — without ever knowing the password. A file called Q3-redundancies-final.xlsx has already given away most of what matters.

If the names themselves are sensitive, rename them before you build the archive, or reach for full-file encryption instead: the File Encrypter produces an opaque .enc container with no readable structure at all.

What an encrypted ZIP does not do

It protects a file at rest and as an email attachment. It does not protect the unencrypted original still sitting in your Downloads folder, it does not prove who sent the archive, and it does nothing at all if the password travels in the same email thread as the file. Encryption here happens entirely in your browser — the files and the password never reach a server — but that guarantee ends the moment the archive leaves your machine.

Send the password through a different channel from the file: a phone call, a message on another app, or a password-manager share. To take protection back off an archive you own, use Remove ZIP Password.