How and with what help to create a secure exchanger?

Question

Encryption

Good afternoon!
there was an interesting idea to organize a secure (encrypted) data transfer between clients via the Internet. (under clients I mean a client application or an accompanying tool).
The procedure is as follows: User P1 creates a file to be viewed by user P2. This file must be uploaded (sent\moved) in encrypted form to a certain storage location (server), so that P2 can take this encrypted file from there. At the same time, the exchange between P1 - the server must be via a secure protocol, and from the server to P2 too. Thus, we transmit encrypted data in an encrypted channel.
Roughly, you can encrypt a file into a container (with any available programs for encrypting into a container), then make an FTP server with encrypted disks and exchange via FTPS. But all this, in my opinion, is not very "Usable" for users.
Tell me who knows what similar solutions, developments?
Free solutions are preferred. but I will also consider commercial ones for an affordable price (not cloud ones).
Perhaps someone knows an article with the implementation of the same FTPS.

Answer 1

"Everything is stolen before you."
Synology has such a solution - like a private cloud, so we change documentation with contractors.

Answer 2

There are many ready-made solutions, but all of them are based on trust to one degree or another .
For example, if you make such an application yourself, then ordinary users will have a question about trusting you. Where is the guarantee that when secret service agents or a mafia boss come to you, you will not sell them your project with giblets? I'm talking about torture in general.
After all, you, as the future "curator" of such a service, have a great opportunity to roll out an application update in which you weaken encryption, add holes or even outright trojans to your application.
Well, if we are talking about advanced users, then they do not need such applications, because there are enough simple tools for encrypting files.
PS And where did you get the idea that the idea is interesting? At first glance, it looks like a bicycle.

Answer 3

Encrypting data and traffic (channel) together does not make much sense - double encryption will not add much security. It will be enough to implement one of the encryption options.
If the server is "secure", i.e. it is in a safe place, untrusted people do not have access to it, then it makes no sense to encrypt the data. Use VPN to access the server - all traffic transmitted over VPN will be encrypted. Data is not limited to files - any traffic transmitted over VPN will be encrypted. Encryption will occur automatically, the user will only need to establish a VPN connection.
If the server is not secure (for example, VPS in the cloud), then it makes sense to encrypt data, while the channel may be open. To encrypt files, you can use anything, for example, an archiver with support for strong encryption, or the same PGP, etc. In this case, the user will need to take additional steps to encrypt/decrypt files. And you also need to organize and maintain a public key infrastructure (PKI) so that clients can generate keys.