Notes on CP/M 3 Password Protection
by A.G.H. Sibley
The CP/M 3, or CP/M-Plus, operating system for 8080/Z80 machines provides two
levels of password protection, namely a disk restriction and a file protection system.
Exactly how the passwords are stored in an encrypted form and how the
programmer may access these areas to decode the password, in the event of a loss
of memory faculties, is explained below.
In order to use password and date time stamping of files, a CP/M 3 utility,
INITDIR.COM, is run to reorganise the directory area. This creates space in the
disk directory for the date/time stamping and passwords but at the expense of
halving the number of directory entries. The area which is created is known as the
Extended File Control Block, XFCB.
Label XFCB construction
If the directory area on a disk (which has been label stamped) is examined using a
suitable utility like DU.COM, then the following should be seen:
DISK UTILITY v8.6
Universal Version under CP/M 3.1
Type ? for help
Type X to exit