4Privacy App (opens in new tab)

It sounds like they are making the claim that they can revoke access to data immediately, but they say you don't need to store the content on-device. I looked up "key displacement" and can't find any immediate references, though I'm not an expert.

My understanding is that if I acquire a ciphertext encrypted with key v1, I will always be able to decrypt it. Any "asynchronous" protocol will have this problem, right? I can be revoked access if I need a piece of the key from a trusted party or if that v1 of the ciphertext can be guaranteed deleted, but caching old versions of keys and files means I will always retain access to the versions of files I ever had access to.

Could someone with a bit more understanding shed some light on this?

I really wish they got more into the nuts and bolts of what this is in terms of the end user.

Some of the screenshots have things mentioned like passport / drivers license. However it also sounds more like a collaboration tool with chat and image sharing.

I suppose time will tell, but I think it would have been wise to explain more before asking for money as that was a bit of a turn off for me.

I am really interested in this in general, I just don't know if I can make my people use yet another privacy-focussed app.

This is not strictly for communication I know but if there is any collaborative component, it will be a tough sell to convince others (esp. in the US). Most people have gotten tired of this and just don't care, it is quite frustrating.

Looks like the key contribution is the idea of being able to revoke access to data.