A company wants to transmit data over the telephone, but it
is concerned that its phones may be tapped. All of its data
is transmitted as four-digit integers. It has asked you to
write a program that will encrypt its data so that the data
may be transmitted more securely. Your script should read a
four digit integer entered by the user in a prompt dialog
and encrypt it as follows: Replace each digit by (the sum of
that digit plus 7) modulus 10. Then swap the first digit
with the third, and swap the second digit with the fourth.
Then output XHTML text that displays the encrypted integer.