Decrypt a file with its passphrase

Files in the MXENC version 1 container written by this site's Encrypt a file tool: AES-256-GCM, key from PBKDF2-HMAC-SHA-256 with the salt and iteration count stored in the file header, data in authenticated chunks with the original name, size and modified date encrypted inside. The byte layout is documented on the Encrypt a file page. Other encrypted formats (7-Zip, GPG, age, encrypted ZIPs) are not read here.

The first chunk fails its authentication check and the file is reported as "the passphrase is wrong, or the file was altered". Nothing is downloaded for that file. There is no hint, no limit on attempts and no lockout, because everything runs on your device; there is also no way to recover a forgotten passphrase.

Every chunk carries a 16-byte authentication tag that also covers the chunk's position and whether it is the last one. A flipped byte, a missing chunk, chunks in the wrong order or extra data at the end make decryption stop with a message naming the problem, so a downloaded file is always exactly what was encrypted.

The encrypted file is read into memory and the decrypted data is assembled in memory, so the practical limit is your device's memory. Deriving the key takes about a second per file on a laptop because of the 600,000 rounds recorded in the header; that delay is deliberate.

No. It exists so that your passphrase never leaves your device, so it runs only in your browser and is not offered on our API.

No. The page loads a small script into your browser and every operation runs on your device. You can check this yourself in the browser's network panel: after the page has loaded there are no upload requests. Closing the tab discards the file.

No. These basic tools are free, have no limits set by us and store nothing on our servers. The practical limit is your device's memory for very large files.

Nothing you open or type. While the tab is open, the tool pages keep a short list of the steps taken in it, in the tab's session storage: the step (page opened, started, succeeded, first success, used again or failed), the tool's name, the time, how many files were used and, for a failure, an error code; never a file name, the contents of a file or your text. It holds at most the latest 200 steps, and the browser deletes it when the tab closes. The page never sends it. Where a Report a problem button is shown, you can attach the last 20 steps to your report; nothing is attached unless you tick that box. In local storage the page keeps only choices you made: a Light or Dark theme until you choose System again, the language you picked with the EN / 中文 switch if it differs from your browser's language, and this tool in your recently used list if you switched that list on at the tools page.