Intermediate Algebra (The Math Lab, 1985)

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#1034 - The Math Lab - Intermediate Algebra is a math eduware by Charles W. Avery and Charles B. Barker, from Cupertino, California, published in 1984/1985.

What is pretty funny is that I was telling DiskBlitz about my current crack. He asked which title it was. I answered and he then asked if I was using his .a2r file for my crack. It was not: while DiskBlitz was imaging his copy, I was cracking the title from my own original disk.

Disk structure
The disk seems to be a DOS 3.3 double-sided disk. When one boots it, the sound is familiar. An analysis with Locksmith Fast Disk Backup shows that the disk is on-disk protected.

Protection type
An analysis with the bitcopier of Copy II + shows that the protection lies in a change of the epilog markers of the address field: D5AA96 ABFF (instead of DEAA)
A further analysis shows data on T23. An extra disk? A nibble count or check? Let's see...

How to copy
Boot my copy disk.
Launch Advanced Demuffin 1.4
Press P to bypass boot
Enter the monitor
B98B:18 60 EA
Press ctrl-Y to return
Copy both sides

How to crack
The boot program is XMGPRT on both sides. The file contains the check of the nibbles on disk. If the disk is an original one, it launches the HELLO file, otherwise it crashes.
Boot my copy disk
Launch Copy II Plus
Change boot program from XMGPRT to HELLO on both sides.


The disk images are available at http://www.brutaldeluxe.fr/crack/

Reboot and... enjoy,

LoGo
7/2020

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That is the XMGPRT file where the on-disk check lies: