Would be possible to have a one-time view key where it would expire after one use or a specific time has been reached? We assume that this is using the blockchain thus it cannot be modified. What I have known so far is, this is not possible because an encrypted data would still be viewed by the key after it has been viewed or after some time has elapsed. Perhaps some expert here can share some ideas about how to make this work. The only thing that I could think is implementing this using a third party application (a server as an authentication system which is not a really good solution).