> Note that if provided with the plaintext of a username known to be in use, Signal can connect that username to the Signal account that the username is currently associated with. However, once a username has been changed or deleted, it can no longer be associated with a Signal account.
The "no longer associated", I will need to get Signal word for that, right. (You cannot cryptographically prove something was deleted, right.)
You shouldn't need to cryptographically prove that an old username is unavailable. You should be able to simply send a request to Signal servers asking if it's available and receive "no" as a response.
You'd have to take their word that this wouldn't change, though.
> Note that if provided with the plaintext of a username known to be in use, Signal can connect that username to the Signal account that the username is currently associated with. However, once a username has been changed or deleted, it can no longer be associated with a Signal account.
The "no longer associated", I will need to get Signal word for that, right. (You cannot cryptographically prove something was deleted, right.)
But it's good enough I guess