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 tlie 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 i is known as the
Extended File Control Block, XFCB. – Lo
Label XFCB construction
oy ON BR
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
00 00534554 20202020 20434F4D 00000051 *.SET COM. ..Q*
10 02030405 06070000 00000000 00000000 *..... eee eee eeee
20 20544553 54202020 20202020 81440000 * TEST © De.
30 64646464 75757575 12070000 12070000 *dddduuuu........
40 00444154 45202020 20434F4D 00000016 *.DATE COM....
50 08090000 00000000 00000000 O0000000 *... cee ec ec eevee’
60 00444952 20202020 20434F4D 00000072 *.DIR COM...xr*
70 OAOBOCOD OEOF1011 00000000 O0000000 *... cece cece cee e®