🚀 go-pugleaf

The poster asks about securing phone numbers and passwords on a distribution
(bootable) diskette.

It seems to me that this is ultimately a hopeless task.  Whether or not
the data is encrypted, it will eventually appear as clear text at the
COM1 port, and thus can be eavesdropped by a capable "cracker".

A better solution would be the use of a call-back system, whereby the user
dials the target computer, enters a password, and then hangs up.
If the caller is successfully authenticated, the computer will
dial the caller back at a pre-arranged phone number.  Even if the 
dial-in phone number and/or password is breached, the "cracker" would still
have to be physically located at the pre-arranged call-back phone.

This obviously costs more than a mere dial-in facility, but the poster
did say that his client was "security conscious".