Portable Secret

Portable Secret is a lightweight technique, more of a demonstrated hack than a maintained product, for sharing encrypted content without requiring the recipient to install any special software. It was created to let its author securely exchange documents by email with a family member who could not reasonably be expected to learn PGP, age, or a similar encryption tool.

A 'Portable Secret' is simply an HTML file containing an encrypted payload and a small amount of JavaScript that calls into the browser's built-in Web Cryptography API. Anyone with a reasonably modern browser can open the file and, if they know the password, decrypt the secret inside, even completely offline, since the file has no external dependencies and can be carried on something like a USB drive.

The author describes use cases such as storing sensitive private keys or two-factor recovery codes, and keeping accessible copies of important documents like a passport photo that remain available even if all trusted devices are lost. The project is explicitly presented as a neat trick rather than a polished product, with the source code and creator tool provided mainly as a demonstration, and a more full-featured product called PrivacyProtect.dev was later built on the same idea by someone else. It is written in HTML and JavaScript and released under the MIT license.