---High School Math Competency Series-- -----------------Part I---------------- A 4am crack 2016-04-12 --------------------------------------- Name: High School Math Competency Series Part I Version: 1.0 Genre: educational Year: on-disk title screen says 1982 disk label says 1984 Author: Celia Keenholtz Publisher: Microcomputer Workshops Media: single-sided 5.25-inch floppy OS: DOS 3.3 Previous cracks: none Identical cracks: #670 Return to Reading: The Lion, The Witch, and The Wardrobe #669 Return to Reading: The Hobbit #668 Return to Reading: Tom Sawyer #667 Return to Reading: Charlotte's Web #623 The Magic String #528 Creatures of the Nights #527 Birds #521 Introduction to Counting #510 KidWriter 1.0 #468 Reading Fun: Beginning Consonant Sounds #456 Adding Fractions #437 Word Master #412 Math Class Level 5 ~ Chapter 0 In Which Various Automated Tools Fail In Interesting Ways COPYA immediate disk read error Locksmith Fast Disk Backup unable to read any track EDD 4 bit copy (no sync, no count) no errors, but copy grinds on boot Copy ][+ nibble editor modified address epilogue "AF FF FF" odd-numbered tracks (1, 3, 5...) also have a modified address prologue ("D4 AA 96") Disk Fixer ["O" -> "Input/Output Control"] set Address Epilogue to "AF FF FF" -> even-numbered tracks readable T00 looks like a DOS 3.3 RWTS set Address Prologue to "D4 AA 96" -> odd-numbered tracks also readable T01 readable. Also T03, T05, T07... T11 looks like a DOS 3.3 disk catalog T01,S09 -> startup program is "HELLO" Why didn't COPYA work? modified prologue and epilogue Why didn't Locksmith FDB work? modified prologue and epilogue Why didn't my EDD copy work? I don't know. Maybe a nibble check during boot? Next steps: 1. capture RWTS with AUTOTRACE 2. convert disk to standard format with Advanced Demuffin 3. patch RWTS to read demuffin'd disk 4. find the nibble check & bypass it 5. declare victory(*) (*) Take a nap. ~ Chapter 1 Bit Math Is Best Math [S6,D1=original disk] [S6,D2=blank disk] [S5,D1=my work disk] ]PR#5 ... CAPTURING BOOT0 ...reboots slot 6... ...reboots slot 5... SAVING BOOT0 /!\ BOOT0 JUMPS TO $08F0 CAPTURING BOOT1 ...reboots slot 6... ...reboots slot 5... SAVING BOOT1 SAVING RWTS ]BLOAD BOOT0,A$800 ]CALL -151 *801L . . all normal until... . 084A- 4C F0 08 JMP $08F0 *8F0L 08F0- A9 AA LDA #$AA 08F2- 85 31 STA $31 08F4- A9 00 LDA #$00 08F6- 8D F1 B6 STA $B6F1 08F9- 4C 00 B7 JMP $B700 I've seen this before. The RWTS uses zero page $31 to check the second byte of the address (or data (or both)) prologue (or epilogue (or both)). *BLOAD RWTS,A$2800 *FE89G FE93G ; disconnect DOS *B800<2800.2FFFM ; move RWTS into place *B944L ; routine to read address prologue B944- A0 FC LDY #$FC B946- 84 26 STY $26 B948- C8 INY B949- D0 04 BNE $B94F B94B- E6 26 INC $26 B94D- F0 F3 BEQ $B942 B94F- BD 8C C0 LDA $C08C,X B952- 10 FB BPL $B94F ; find prologue nibble #1 B954- 4A LSR B955- C9 6A CMP #$6A B957- D0 EF BNE $B948 B959- BD 8C C0 LDA $C08C,X B95C- 10 FB BPL $B959 ; find #2 B95E- C5 31 CMP $31 <-- ! B960- D0 F2 BNE $B954 B962- A0 03 LDY #$03 B964- BD 8C C0 LDA $C08C,X B967- 10 FB BPL $B964 ; find #3 B969- C9 96 CMP #$96 B96B- D0 E7 BNE $B954 Well this just answers a whole slew of questions at once. The code to find prologue nibble #1 explains how this disk can read its odd-numbered tracks (with non-standard address prologue "D4 AA 96"). Normal address prologue byte 1 is $D5. In binary: $D5 = 1101 0101 After LSR: 0110 1010 = $6A Odd-numbered tracks use $D4 instead. In binary: $D4 = 1101 0100 After LSR: 0110 1010 = $6A So this code will match either prologue and work on both odd and even tracks. Furthermore, RWTS code is time-critical between reading the last bit of one nibble and reading the first bit of the next. If it's too fast or too slow, it will get out of phase (because the disk spins independently of the CPU). Compare DOS 3.3 (cycle count in margin) B94F- BD 8C C0 LDA $C08C,X B952- 10 FB BPL $B94F B954- C9 D5 CMP #$D5 | 2 B956- D0 F0 BNE $B948 | 2 * B958- EA NOP | 2 B959- BD 8C C0 LDA $C08C,X B95C- 10 FB BPL $B959 (*) on the time-critical path, this branch is not taken, so always 2 ...and this disk's RWTS: B94F- BD 8C C0 LDA $C08C,X B952- 10 FB BPL $B94F B954- 4A LSR | 2 B955- C9 6A CMP #$6A | 2 B957- D0 EF BNE $B948 | 2 * B959- BD 8C C0 LDA $C08C,X B95C- 10 FB BPL $B959 Despite being more "flexible" (matching $D5 or $D4), this disk's RWTS uses the same number of bytes of code and runs in the same number of cycles. Nice. Furthermore, look at this code to match nibble #2 of the address prologue: *B959L B959- BD 8C C0 LDA $C08C,X B95C- 10 FB BPL $B959 B95E- C5 31 CMP $31 <-- ! B960- D0 F2 BNE $B954 There's zero page $31, initialized at $BB00 during boot. Solution: an IOB module that Advanced Demuffin calls before calling the original disk's RWTS. (Read the docs on my work disk.) ~ Chapter 2 In Which We Attempt To Use The Original Disk As A Weapon Against Itself *C500G ... ]CALL -151 ]BLOAD ADVANCED DEMUFFIN 1.5 ; standard Advanced Demuffin setup ; (unchanged) 1400- 4A LSR 1401- 8D 22 0F STA $0F22 1404- 8C 23 0F STY $0F23 1407- 8E 27 0F STX $0F27 140A- A9 01 LDA #$01 140C- 8D 20 0F STA $0F20 140F- 8D 2A 0F STA $0F2A ; initialize zero page used by the RWTS 1412- A9 AA LDA #$AA 1414- 85 31 STA $31 ; call RWTS 1416- A9 0F LDA #$0F 1418- A0 1E LDY #$1E 141A- 4C 00 BD JMP $BD00 *BSAVE IOB $31,A$1400,L$FB *BRUN ADVANCED DEMUFFIN 1.5 ["5" to switch to slot 5] ["R" to load a new RWTS module] --> At $B8, load "RWTS" from drive 1 [press "I" to load a new IOB module] --> load "IOB $31" from drive 1 ["6" to switch to slot 6] ["C" to convert disk] --v-- ADVANCED DEMUFFIN 1.5 (C) 1983, 2014 ORIGINAL BY THE STACK UPDATES BY 4AM =======PRESS ANY KEY TO CONTINUE======= TRK:................................... +.5: 0123456789ABCDEF0123456789ABCDEF012 SC0:................................... SC1:................................... SC2:................................... SC3:................................... SC4:................................... SC5:................................... SC6:................................... SC7:................................... SC8:................................... SC9:................................... SCA:................................... SCB:................................... SCC:................................... SCD:................................... SCE:................................... SCF:................................... ======================================= 16SC $00,$00-$22,$0F BY1.0 S6,D1->S6,D2 --^-- ]PR#5 ... ]CATALOG,S6,D2 C1983 DSR^C#254 152 FREE *A 002 HELLO *B 003 RBOOT *B 005 RLOAD *A 007 MENU *A 003 HRCG/INIT *T 002 START INIT *R 012 HRCG *A 054 WHOLENOS *A 066 FRACTIONS *A 044 DECIMALS *A 035 BASPERC *A 033 PRIMES *A 022 INTEGERS *A 035 ALGEBRA *B 005 ASC2 *B 014 LOGO.PAC *B 002 UNPACKER ]RUN HELLO ...hangs... ]PR#5 ...hold down key during boot so Diversi-DOS doesn't relocate to the language card... ]RUN HELLO,S6,D2 ...works... OK, it doesn't like Diversi-DOS 64K, but it is able to boot from a third- party disk. That's good news. The reason I always do this is to see whether there are any runtime checks for subtle differences in the original DOS. If the program runs after booting from a third-party disk, I can eliminate a whole range of possible secondary protections. [S6,D1=demuffin'd copy] ]PR#6 ...works... Wait, what? ~ Chapter 3 In Which We Angrily Investigate Why We Suddenly Have A Working Copy [S6,D1=mysteriously working copy] [S5,D1=my work disk] ]PR#5 ]BLOAD RWTS,A$2800 ]CALL -151 *FE89G FE93G *B800<2800.2FFFM *B944L . . all weirdness accounted for, until... . ; find epilogue byte #1 B98B- BD 8C C0 LDA $C08C,X B98E- 10 FB BPL $B98B B990- C9 DE CMP #$DE ; if found $DE, immediately exit with ; a "success" status (clear carry bit) B992- F0 0A BEQ $B99E ; if not $DE, do... this thing B994- 48 PHA B995- 68 PLA B996- BD 8C C0 LDA $C08C,X ; Note: no BPL loop here! It only reads ; the data latch once. B999- C9 08 CMP #$08 B99B- B0 A5 BCS $B942 B99D- EA NOP B99E- 18 CLC B99F- 60 RTS It's looking for a timing bit after the first epilogue byte. It doesn't even care what the first epilogue byte was, as long as it wasn't $DE. This RWTS will accept two different address prologues, "D5 AA 96" or "D4 AA 96". It will also accept two different address epilogues, "DE" or anything- other-than-DE-followed-by-a-timing-bit. Why didn't the EDD copy work? EDD preserved the original prologue epilogue but not the timing bits. The prologue checker (at $B944) finds "D5 AA 96" (even-numbered tracks) or "D4 AA 96" (odd-numbered tracks). But the epilogue checker's first compare (at $B98B) didn't match because the first epilogue byte was still the original value ($AF), and its second compare (at $B999) didn't match because there was no timing bit after the first byte. There was never any separate nibble check; the structure of the disk itself is designed to foil nibble copiers. Why did the demuffin'd copy work? Advanced Demuffin wrote out the data from each sector onto a standard disk that uses "D5 AA 96" prologue and "DE AA EB" epilogue. The RWTS always matches "D5 AA 96" and doesn't care that it never sees a "D4 AA 96" for a prologue. The epilogue checker always matches "DE" and never checks the timing bit. Thus, no RWTS patches are necessary. Quod erat liberandum. --------------------------------------- A 4am crack No. 671 ------------------EOF------------------