An extension is probably not needed. JavaScript and local storage allow you to do this kind of stuff. Proton Drive and Mail accomplish this without an extension.

I think you can get away with using the web crypto apis and storing the private key in indexeddb. If you want users to be able to change devices or recover after blowing away their client storage, allow the user to download their private key and save it to a password manager.

I mean no offense by this at all, but I wouldn’t because it would indicate a poor understanding of cryptography to me as a user. Either that or being intentionally misleading. In either case, probably unsafe for the user. There does not need to be an extension to encrypt content such that the server never has access to it. It can be encrypted and sent to the host with a key the server never possesses.

You're saying you don't want users to have to trust the website code that the server offers. So why would the user trust the extension instead?

is this asking too much from users?

Installing a browser extension for one site? From usability point of view, how is that any different than installing an app for each service/company?

I wouldn't, but obviously there seems to be many people who install an app for everything.

I wouldn't install a browser extension over an app. And I probably wouldn't install a browser extension for a web app.

I've read the thread. Your argument for an extension is to make it open source, why couldn't your front end code be open source instead?

If what you're building is worth the hassle of installing the add-on and viewing the content, I suppose. There's not many programs people use PRIMARILY for security. You wouldn't use a note program that has audited security if you can't save notes, for instance.

Can you derive the private key from the password? Like PBKDF2 or something. I guess it's what most E2E sites do. I wouldn't install anything unless it was for work and involved me receiving money.

Well I heard that safety is always a compromise between convenience and security. I think this would only make sense if you have a provider that you can trust now to provide a clean extension, but you can't trust to not do a rugpull or be forced by agents to suddenly implement a vulnerability. But that is basically specifically targeting you or your group. So this is already incredibly niche.

For most people, you either trust or you don't, and preferably you only trust a server in a neutral country like Switzerland. If you make it too complicated you diminish the usefulness of the service.

I believe it would be far more secure to have a native linux app written in e.g. rust to do all this. For an encrypted messenger for example.

What? Lol no. And a site like that probably shouldn't have signatures. Something like Bernstein authenticators would be way preferable.

In part that sounds like what zeronet did, but that was static p2p websites. User content was signed and distributed by the user. But the code of the website could block and filter the user content. Everything was handled by client-side javascript basically

No, as there's no use case for me.

Not all data that I share is sensitive. Server stored stuff, unencrypted is fine for me.

As for other sorts of sensitive stuff, Signal works perfectly fine for me.

This is a recipe for blindly hosting CSAM.

Checkout cryptpad, it may inspire you ideas on how to implement an app to hold user-encrypted contents

If you want it to work, I think you'll need to start with a group of trusted contacts who run it because they know you and want to use what you've built.

If it really solves some problems, word will spread out from there.

If it's a solid extension which could be used by other websites, and it's explained clearly like in your post by the website which needs it, then probably yes.

Hell no. I don't install any extensions for any reason other than uBlock and a pw manager. Just because you say "trust me, bro" doesn't make your extension secure or privacy - focused.

Https already encrypts content during transit. Just use login/password/totp/passkey.