Merge branch 'master' into gh-pages
This commit is contained in:
Jeff Parsons
commit
ec22af0da0
11 changed files with 196 additions and 29 deletions
106
_posts/2017-08-11-dbase-iii-copy-protection-revisited.md
Normal file
106
_posts/2017-08-11-dbase-iii-copy-protection-revisited.md
Normal file
|
|
@ -0,0 +1,106 @@
|
|||
---
|
||||
layout: post
|
||||
title: dBASE III Copy Protection Revisited
|
||||
date: 2017-08-11 10:00:00
|
||||
permalink: /blog/2017/08/11/
|
||||
---
|
||||
|
||||
One of the earliest tasks I remember tackling on an IBM PC was a basically a favor for my father-in-law, Tom Estelita.
|
||||
In 1984, he had purchased a copy of dBASE III and had become frustrated by its copy-protection. The previous version,
|
||||
dBASE II, had no such protection, which probably added to his frustration. At the time, he was running his own tiny
|
||||
software company, Radix 2 Software, and he certainly wasn't interested in redistributing dBASE III -- he just wanted to
|
||||
be able to back-up his software and switch between a handful of machines without the hassle or worry of relying on a
|
||||
single fragile copy-protected diskette.
|
||||
|
||||
At that time, my day job was writing PDP-11 application software, but I really wanted to learn more about the IBM PC,
|
||||
and I had done work for Tom in the past (writing BASIC accounting software on CP/M-based machines), so he made me a
|
||||
deal: he would loan me a floppy-based IBM PC and some IBM reference manuals, in exchange for attempting to crack dBASE
|
||||
III's copy-protection.
|
||||
|
||||
I have no recollection of how feasible I thought this challenge was, but I'm sure I jumped at the opportunity.
|
||||
Perhaps my thinking was that, after all, it's just software, so how hard could it be. In any case, I apparently took
|
||||
the challenge very seriously, because I also made a lot of notes.
|
||||
|
||||
I recently found [those notes](/docs/personal/#dbase-iii-copy-protection), along with copies of the
|
||||
[dBASE III disks](/disks/pcx86/apps/other/dbase3/1.0/) used. Unfortunately, all the disks contained was my *patched*
|
||||
(unlocked) version of `DBASE.EXE`, and for the sake of a complete archive, I wanted the *unpatched* (locked) version as
|
||||
well. Fortunately, my patching notes also show all the original bytes, so I reproduced the original file by reversing
|
||||
the patching process, using PCjs:
|
||||
|
||||
Loading /disks/pcx86/apps/other/dbase3/1.0/DBIII-100-UNLOCKED.json.......
|
||||
FDC: Mounted diskette "dBASE III 1.0 (Unlocked)" in drive A
|
||||
|
||||
A>dir
|
||||
|
||||
Volume in drive A has no label
|
||||
Directory of A:\
|
||||
|
||||
DBASE EXE 112720 9-28-84 3:46p
|
||||
DBASE OVL 147456 6-26-84 5:36p
|
||||
HELP DBS 53760 6-26-84 5:36p
|
||||
ASSIST HLP 15223 6-26-84 5:37p
|
||||
READ ME 4224 6-26-84 5:37p
|
||||
CONFIG SYS 22 6-26-84 5:37p
|
||||
6 File(s) 15360 bytes free
|
||||
|
||||
A>ren dbase.exe dbase.tmp
|
||||
|
||||
A>b:debug dbase.tmp
|
||||
-d 5f4 l4
|
||||
08FF:05F4 25 39 4F 45 %9OE
|
||||
-e 5f4
|
||||
08FF:05F4 25. 39.e3 4F.c4 45.eb
|
||||
-d a44
|
||||
08FF:0A44 2D 26 AB 36-38 06 9C 17 1A 54 A5 4B -&+68....T%K
|
||||
08FF:0A50 E8 41 4C E0 AF 68 0B 07-6E 07 80 16 1B B6 BF B7 hAL`/h..n....6?7
|
||||
08FF:0A60 4C 6B C2 39 26 DC 97 BF-3B CE C0 EB 4F BB B3 C2 LkB9&\.?;N@kO;3B
|
||||
08FF:0A70 27 A6 90 75 F4 AF 68 93-DF 62 43 CD B7 65 AD 34 '&.ut/h._bCM7e-4
|
||||
08FF:0A80 11 B0 85 93 29 A2 9B A4-42 74 A6 84 24 7C 17 4C .0..)".$Bt&.$|.L
|
||||
08FF:0A90 7B 5E F9 2C 66 0E 4E 27-B4 2F 50 4E 9C 76 CE D6 {^y,f.N'4/PN.vNV
|
||||
08FF:0AA0 DB 51 21 D1 2C 4B 3B 73-48 EE 8E 6A 9C D7 E2 4F [Q!Q,K;sHn.j.WbO
|
||||
08FF:0AB0 FA B6 10 24 28 A0 45 C8-50 36 9A 5E 9F C4 A1 EC z6.$( EHP6.^.D!l
|
||||
08FF:0AC0 A2 51 AA B8 "Q*8
|
||||
-e a44
|
||||
08FF:0A44 2D.b0 26.5e AB.e6 36.af
|
||||
08FF:0A48 38.1e 06.f1 9C.41 17.31 1A.73 54.59 A5.c1 4B.a4
|
||||
08FF:0A50 E8.0e 41.cd 4C.63 E0.fe AF.c1 68.39 0B.0b 07.62
|
||||
08FF:0A58 6E.60 07.93 80.be 16.cf 1B.08 B6.f8 BF.4e B7.56
|
||||
08FF:0A60 4C.53 6B.d3 C2.5d 39.4f 26.a3 DC.9a 97.ae BF.14
|
||||
08FF:0A68 3B.c4 CE.7b C0.dc EB.e4 4F.ee BB.45 B3.f9 C2.ab
|
||||
08FF:0A70 27.3f A6.15 90.56 75.3d F4.5b AF.a3 68.a1 93.20
|
||||
08FF:0A78 DF.ad 62.98 43.be CD.02 B7.c8 65.63 AD.df 34.c3
|
||||
08FF:0A80 11.e0 B0.2f 85.26 93.af 29.31 A2.29 9B.40 A4.4f
|
||||
08FF:0A88 42.86 74.98 A6.90 84.fc 24.d6 7C.76 17.e3 4C.e5
|
||||
08FF:0A90 7B.f1 5E.61 F9.08 2C.8a 66.20 0E.f7 4E.37 27.64
|
||||
08FF:0A98 B4.4f 2F.e2
|
||||
-w
|
||||
Writing 1B850 bytes
|
||||
-q
|
||||
|
||||
A>ren dbase.tmp dbase.exe
|
||||
|
||||
A>dir
|
||||
|
||||
Volume in drive A has no label
|
||||
Directory of A:\
|
||||
|
||||
DBASE EXE 112720 8-11-17 9:51a
|
||||
DBASE OVL 147456 6-26-84 5:36p
|
||||
HELP DBS 53760 6-26-84 5:36p
|
||||
ASSIST HLP 15223 6-26-84 5:37p
|
||||
READ ME 4224 6-26-84 5:37p
|
||||
CONFIG SYS 22 6-26-84 5:37p
|
||||
6 File(s) 15360 bytes free
|
||||
|
||||
saving diskette /disks/pcx86/apps/other/dbase3/1.0/DBIII-100-UNLOCKED.json...
|
||||
|
||||
I haven't examined this patch again (yet), but I will admit that it seems rather lengthy. Usually one strives for
|
||||
a very small, surgically precise patch that's more on the order of 3 or 4 bytes, but we have to remember that I wasn't
|
||||
very familiar with either the IBM PC or the 8088 instruction set at this point -- this was also a learning exercise.
|
||||
|
||||
And who knows, maybe Vault Corporation (the company that Ashton-Tate used to provide the copy-protection logic for
|
||||
dBASE III) wrote such sophisticated code that it was impossible to defeat so simply. However, experience suggests
|
||||
that's unlikely.
|
||||
|
||||
*[@jeffpar](http://twitter.com/jeffpar)*
|
||||
*Aug 11, 2017*
|
||||
Loading…
Reference in a new issue