Linking the key as the fragment identifier component (after a #) would prevent the server from seeing it, but still allow Javascript to have access to the key.

Linking the key as the fragment identifier component (after a #) would prevent the server from seeing it, but still allow Javascript to have access to the key. That way you can link encrypted content with a key, and have the server not know about it. This scheme has been deployed for at least one secure pastebin.