-------------Magic Slate 80------------
A 4am crack                  2017-02-09
-------------------. updated 2020-07-04
                   |___________________

Name: Magic Slate 80-column
Version: 1.4
Genre: productivity
Year: 1987
Credits: Donna Stanger, Paul Elseth
Publisher: Sunburst Communications
Platform: 80-column Apple //e or later
Media: single-sided 5.25-inch floppy
OS: custom
Previous cracks: none
Similar cracks:
  #1004 Magic Slate 40
  #1003 Magic Slate 20

                   ~

               Chapter 0
 In Which Various Automated Tools Fail
          In Interesting Ways


COPYA
  fails on first pass

Locksmith Fast Disk Backup
  unable to read track $01

EDD 4 bit copy (no sync, no count)
  works

Copy ][+
  disk presents a ProDOS catalog

                 --v--

CATALOG DISK            SLOT 6  DRIVE 1
/MAGIC.SLATE.80


   NAME           TYPE  BLKS  MODIFIED

   MS              SYS    32  16-JUL-87
   MS.CONFIG       SYS     3  <NO DATE>
   MS.EDIT80       SYS    74  26-AUG-87
   MS.PRINT80      SYS    53  09-JUL-87
   MS.UTILS80      SYS    38  22-JUL-87

BLOCKS FREE:65    USED:215   TOTAL:280

PRESS [RETURN]

                 --^--

Copy ][+ nibble editor
  T01 has no structure at all, no data,
  just sync bytes and scattered nibbles

                 --v--

   COPY ][ PLUS BIT COPY PROGRAM 8.4
(C) 1982-9 CENTRAL POINT SOFTWARE, INC.
---------------------------------------

TRACK: 01  START: 1800  LENGTH: 3DFF

4CF8: FF FF FF FF FF FF FF FF   VIEW
4D00: FF FF FF FF FF FF FF FF
4D08: FF FF E4 FF FF FF FF FF
4D10: FF B9 FF FF FF FF FF E4
4D18: FF FF FF FF FF D5 BE EC  <-4D1D
4D20: F4 F4 F4 F4 F4 F4 FF FF
4D28: FF FF FF FF FF FF FF FF
4D30: FF FF FF D2 D2 D2 FF FF  FIND:
4D38: FF FF FF FF FF FF FF FF  D5

---------------------------------------

  A  TO ANALYZE DATA  ESC TO QUIT

  ?  FOR HELP SCREEN  /  CHANGE PARMS

  Q  FOR NEXT TRACK   SPACE TO RE-READ


                 --^--

Disk Fixer
  T00 has standard ProDOS bootloader
  and disk catalog (see Copy ][+ above)
  but the disk does not sound or look
  like ProDOS when it boots.
  No way to read T01.

Why didn't COPYA work?
  Track $01 is missing/unreadable

Why didn't Locksmith FDB work?
  probably a runtime check that ensures
  that track $01 is missing/unreadable

EDD worked. What does that tell us?
  No half or quarter tracks, because I
  didn't even try to copy those. There
  is definitely a run-time protection
  check of some kind, but it's probably
  just checking that track $01 is
  unreadable.

Next steps:

  1. Search disk for common elements of
     a run-time protection check
  2. If that fails, trace the boot
  3. If that fails, I dunno, go feed
     the ducks or something

                   ~

               Chapter 1
        In Which We Get Lucky,
     To The Detriment Of The Ducks


On the theory that some code on disk is
trying to access track $01, and thus
noticing if it's unexpectedly readable,
let's enumerate some of the ways that
could happen:

- Reading a file that is mapped to the
  unreadable track $01. Copy II+ "disk
  map" shows there are no files mapped
  to track $01, so let's rule that out.
  In fact, the first file suspiciously
  skips over the track altogether:

                 --v--

DISK MAP                SLOT 6  DRIVE 1
/MAGIC.SLATE.80/MS

   TRACK           1               2
   0123456789ABCDEF0123456789ABCDEF012

S0 ..****.............................
EE ..****.............................
CD ..****.............................
TC ..****.............................
OB ..****.............................
RA ..****.............................
 9 ..****.............................
 8 ..****.............................
 7 ..****.............................
 6 ..****.............................
 5 ..****.............................
 4 ..****.............................
 3 ..****.............................
 2 ..****.............................
 1 *.***..............................
 F *.***..............................

   USE ARROW KEYS TO MAP OTHER FILES

                 --^--

- Issuing a ProDOS MLI "raw block read"
  and checking the return code. This is
  a popular technique under ProDOS,
  partly because it can be adapted to
  work on 3.5-inch and 5.25-inch disks.
  But I'm not sure if this disk is
  really full ProDOS or if it just uses
  the ProDOS disk structure for
  convenience. At any rate, a sector
  search for "20 00 BF" (a JSR to the
  standard ProDOS MLI entry point)
  yields precisely zero results, so...

- Manually seeking to the track and
  looking for a nibble sequence. There
  is no explicit support for "seeking
  to a particular track" unless you're
  calling ProDOS internals. Without
  calling into ProDOS, this technique
  would require low-level disk access
  (turning on the drive and hitting the
  right stepper motors and whatnot).
  Here are some possibilities:

  "BD 89 C0" (LDA $C089,X)   ; drive on
  "AD E9 C0" (LDA $C0E9)     ; drive on
  "BD 80 C0" (LDA $C080,X)   ; stepper

And lo! A search for "BD 89 C0" yields
several results.

                 --v--

------------- DISK SEARCH -------------

------------- DISK SEARCH -------------

$00/$0E-$A7   $03/$04-$2C   $05/$0A-$68
$18/$03-$2F


             PRESS [RETURN]

                 --^--

- T00,S0E is part of PRODOS (although I
 think it's called "MS" on this disk).

- T05,S0A appears to be legitimate RWTS
  code of some sort. (The existence of
  "LDA $C08A,X" nearly is a strong
  indication of legitimacy; RWTS code
  needs to deal with both drives, but
  copy protection routines rarely work
  on anything but drive 1.)

- T18,S03 is similarly unsuspicious.

That leaves T03,S04. And that is a
different kettle of nibbles altogether.

                   ~

               Chapter 2
     A Different Kettle of Nibbles


The routine containing "LDA $C089,X"
appears to start at offset $14:

                 --v--

T03,S04
----------- DISASSEMBLY MODE ----------
; save flags
0014:08             PHP

; prevent interrupts
0015:78             SEI

; not sure what this does
0016:84 46          STY   $46
0018:84 47          STY   $47
001A:20 00 08       JSR   $0800
001D:A9 08          LDA   #$08
001F:85 46          STA   $46
0021:A9 00          LDA   #$00
0023:85 47          STA   $47
0025:85 42          STA   $42
0027:20 00 08       JSR   $0800

; turn on drive motor manually
002A:A6 07          LDX   $07
002C:BD 89 C0       LDA   $C089,X
002F:BD 8E C0       LDA   $C08E,X

; set up Death Counter
0032:A0 00          LDY   #$00
0034:84 08          STY   $08
0036:C8             INY
0037:D0 04          BNE   $003D
0039:E6 08          INC   $08

; if Death Counter hits 0, fail
003B:F0 1F          BEQ   $005C

; match nibble sequence "D5 BE EC"
003D:BD 8C C0       LDA   $C08C,X
0040:10 FB          BPL   $003D
0042:C9 D5          CMP   #$D5
0044:D0 F0          BNE   $0036
0046:BD 8C C0       LDA   $C08C,X
0049:10 FB          BPL   $0046
004B:C9 BE          CMP   #$BE
004D:D0 F3          BNE   $0042
004F:BD 8C C0       LDA   $C08C,X
0052:10 FB          BPL   $004F
0054:C9 EC          CMP   #$EC
0056:D0 EA          BNE   $0042

; restore flags, clear carry, and exit
0058:28             PLP
0059:18             CLC
005A:90 02          BCC   $005E

; restore flags, set carry, and exit
005C:28             PLP
005D:38             SEC

; turn off drive motor on the way out
005E:BD 88 C0       LDA   $C088,X
0061:60             RTS

Pretty straightforward. We're looking
for a non-standard nibble sequence that
doesn't normally exist. But it does
exist on track $01 -- I saw it earlier
in the Copy II Plus nibble editor. The
caller expects the carry flag to be
clear on success or set on failure
(like DOS and ProDOS conventions).

If I change the failure path at offset
$5C to match the success path at offset
$58, the caller will always think the
protection check succeeded. In other
words, change the "SEC" to a "CLC".

T02,S0D,$5D: 38 -> 18

Quod erat liberandum.

                   ~

               Changelog


2020-07-04

- typos

2017-02-09

- initial release

---------------------------------------
A 4am crack                    No. 1005
------------------EOF------------------
