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This article was posted to the Usenet group alt.hackers in 1995; any technical information is probably outdated.


Article: 7386 of alt.hackers
From: (Terje Mathisen)
Newsgroups: alt.hackers
Subject: Re: YKYBPMTLW
Date: 15 Feb 1995 11:18:06 GMT
Organization: Hydro Data, Norsk Hydro (Norway)
Lines: 52
Approved: Yes!
Message-ID: 3hsnte$
Reply-To: (Terje Mathisen)
X-Newsreader: IBM NewsReader/2 v1.02
Status: RO

In <>,
(Andy Dingley) writes:
>> Using my ancient Amstrad PCW8256
>One of my parent's neighbours lost the password to their accounts computer
>last w/e, an old PC1512. I happened to be around, so got dragged over
to fix
>it. I had one of my own PCs sitting nearby, with all the file-hacking
tools I
>could want, but unfortunately only a 3.5" drive and no LapLink
cable. I
>*could* have made up a serial cable I guess, but instead I used DEBUG to
>write a hex->ASCII filter and started TYPEing recent files through
that and
>MORE. I soon found a mis-spelt version of what looked like the right
>password, and sure enough, we were in.
>OK, I cheated 8-) I wrote it in tiny C on my machine, printed a listing of
>the OBJ and used that as a guide when flying DEBUG. I'll leave the
>assembler-from-memory to people like Vik Olliver. 8-)


Here's what I wrote last night, sitting at the console of a NetWare V4.02
file server, which I was going to upgrade to 4.1:

The problem was that the server had a monochrome vga crt but was running in
color mode, making it impossible to see which of several options was
selected in the upgrade menues, so I wrote down the following script:

 mov ax,7
 int 10
 int 20

and hand-assembled that into

  b8 07 00
  cd 10
  cd 20

which became 184 7 0 205 16 205 32 in decimal.

The only thing remaining was to use an editor that allowed zero bytes
in "text" files to generate a 7-byte program.  Running
this program in autoexec.bat tells the install program to use a color
set compatible with a monochrome display.

(No, I didn't have debug available, that would have been a lot easier ;-)

-Terje Mathisen (include std disclaimer) <>
"almost all programming can be viewed as an exercise in caching"

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