Newsgroups: comp.sys.mac.apps
Path: utzoo!utgpu!watserv1!watnow.waterloo.edu!jlee
From: jlee@watnow.waterloo.edu (Johnny Lee)
Subject: Re: Compactor - A reason not to use
Message-ID: <1991Jan15.062305.4215@watserv1.waterloo.edu>
Sender: daemon@watserv1.waterloo.edu
Organization: University of Waterloo
References: <41470@nigel.ee.udel.edu> <draphsor.663638212@elaine5.stanford.edu> <sbXsa0600aw356gogZ@andrew.cmu.edu>
Date: Tue, 15 Jan 91 06:23:05 GMT
Lines: 36

In article <sbXsa0600aw356gogZ@andrew.cmu.edu> vd09+@andrew.cmu.edu (Vincent M. Del Vecchio) writes:
>
>I disagree somewhat with your interpretation.  I believe that Bill Goodman
>would be more than willing to disclose header-type information for
>incorporation into programs like FileList and CatStuff; this information should
>not be hard to deduce anyway and disclosing it doesn't give an advantage to
>your competitors.  On the other hand, in light of what I have heard about his

It wasn't that hard. One just needs to get a decent sampling of Compactor
archives and one doesn't have to be Sherlock Holmes to deduce 99% of all
the fields. Actually, the information that Mr. Goodman sends out doesn't
seem to reveal the Compactor-specific information, i.e. Compressed lengths,
location of compressed data.

>negotations with CompuServe, he seems to be reluctant to disclose the actual
>compression format with which the files in the archive are compressed or
>decompressed (typically, the filenames, orig. and compressed sizes, etc. of the
>compressed files are stored in plaintext (uncompressed) in the data fork of the
>archive file).  Perhaps a good way to put it would be to say that the archive
>format is known, but the compression format is still not.
>

From a preliminary look at the resulting archives, Compactor seems to use
a couple of types of compression including run-length encoding. I've never
heard any stories about reverse-engineering a compressed file, but
it should be nice late-night fodder.

Compactor is a nice Mac archiving program, but I don't use it because
I talk more to/thru Unix boxes than Macs. Besides, for real compression,
COMIC beats most with one hand tied behind its back (though you'll have to
wait a long time).

Johnny Lee
jlee@watnow.waterloo.edu


