Imagine first a user communicating with her bank over the Internet. When the bank receives a request to transfer $$1,000$ from the user$$s account to the account of some other user X$,$ the bank has to consider the following:

$1)$Is the request authentic? That is$,$ did the user in question really issue this request, or was the request issued by an adversary who is impersonating the legitimate user? $2)$ Assuming a transfer request was issued by the legitimate user, is the request received by the bank exactly the same as what was sent by that user? Or was, e$.$g$.,$ the transfer amount modified as the request was sent across the Internet?