To encrypt and decrypt files you need at least two private keys. Private key files in Ecedehey are self-contained HTML files that does encryption and decryption for you.
Ecedehey is completely browser-based and client side, no data is sent to the server. It solely relies on the WebCrypto API. You can even save this HTML page to your computer and open it with your preferred browser, to do the creation of private keys offline. Read more about it in the blog post.
Please note that this is built for educational purposes and has not been reviewed by any security expert. Do not rely on it for sensitive files.