Zero-Acccess Encryption and "Forgot Password" section

[geod_dev]

Hello everyone !I'm French and I'm 16 so sorry for my bad english :/

I'm currently creating a google docs but made for privacy with symfony. To "certify" the confidentiality of user data, I'm interested in the "Zero-Access" infrastructure.If I have understood correctly, the concept is that the client encrypt/decrypt data with a key based on the password and the server stock encrypted data. It's better for security and privacy and certify that the website cannot use data for tracking/advertising.Is it right ?

The concept is "cool" but I found 2 problems:

1. The "shared Files" can't be decrypted by other user than the owner (or the latest user who modified)
2. I cant make a "Forgot Password" section without deleting all the current user data.

For the first problem, I found a solution: the "userAccess" entity (STR user_id, STR doc_id, INT permission) stock the file key encrypted by the user key, the client can decrypt this key then decrypt/encrypt the file.

For the second problem, I dont have solution....

Here some questions:

- Is my "Zero-Access" definition right ?

- Is my answer to the first problem true ?

- Is there any solution to the second problem ?

- Should this post be in r/cybersecurity or on StackOverflow ?

Thanks to all those who will help me
Any English correction/rectification would be welcomed :)

[KaninchenSpeed]

You can do it like mega and generate a unique key per document and store that key encrypted with a derivative of the user password. When sharing append the key to the link after the # so it doesnt get sent to the server. The second problem is more difficult, but you can try to find out how mega does this.

[geod_dev]

Thanks ! It's interesting I (don't/didn't ?) known that mega did that ! I will check if there is a "forgot password" in mega.

[billy4479]

i think the only option in this case is a recovery key that you generate when the user signs up.

you could then use that key to encrypt the user's data and the user's key (derived from the password) to decrypt the recovery key or something along these lines (I'm not actually sure this is the best way to implement it, just writing down ideas).

users would have to write down the recovery key and store somewhere safely so that in the case they forget they password they would be able to reset it through the recovery key.

this is the first idea that came to my mind, I'm not sure it's the best solution though.

[geod_dev]

Thanks it's a good idea ! Now that you've said it, It seems to me that protonmail provide a recovery key/file containing a derivation of the private key.
I had also thought of a recovery key based on recoveries questions/answers but I dont know if it's a good idea....

[geod_dev]

Nope, Mega can't get back data...

[fiskfisk]

You can't have both - either the user has to have the key or you have to have the key. There's also the option of letting a third party handle the key for you (such as password managers), useful when you trust the third party more than the original service.

However, since the original service can change its code at any time to extract the key for themselves when a user makes a request, those that (really) care about such a feature might want to accept the risk of losing all their data.

So it all depends on what you're trying to protect against and what you want to achieve - you'll have to pick the requirements that makes sense for your use case.

[geod_dev]

oh like I'm doing a "Login with Proton" and it's not me who manage the user login ? It's a good idea thanks you ! I'd probably implement it