Previewing encrypted content on the web
This would be an extension to The Open Graph protocol.
A current problem with previews of web URLs is they require the server to know the exact contents of the URL and be able to provide a preview as a resource either inside a header or as a URL to an image. If the primary content at the URL were encrypted, no preview could be provided directly by the server.
What the server could provide is an encrypted preview which was encrypted with a symmetric key by the original creator using one of the standard algorithms provided by webcrypto. Then the browser/client could find the decryption key in the URL fragment (or prompt the user for it) to then facilitate the decryption of the preview content safely on device. This would provide a standard