End-to-end encryption ensures that only you and the person you’re chatting with can access your messages. The messages (and files) are encrypted on your device with a key that is only shared between you and the recipient.
Only the designated person can decrypt and read the message. Even if messages are transmitted though Crypho's servers, there is no way for anyone to decrypt and read them, as the keys are only available to the end users.
This is also the case with shared files.