You're going to encrypt publicly accessible sensitive data with a 9 digit number ? This is not even close to the current level of security. You don't get to make millions of guesses when some dumb website or clerk requires your SSN to do something.
To decrypt data you get to guess over and over again. An SSN would be a terrible key for that.
To decrypt data you get to guess over and over again. An SSN would be a terrible key for that.