Pkware Data Compression Library (DCL)

[SW]

I'm attempting to reverse engineer a file format used by a program which uses
DCL to compress part of its data, i have the decompressor released by Mark
Adler, which works great. however, in order to be able to make files of this
type i need to be able to compress data with the DCL algorithm, is there open
source code available to do this? Or is it legal to reverse engineer the DCL
encoding algorithm and make an open source variant of it?

Thanks.
SW

[Mark Adler]

SW <do...@disturb.net> wrote in message news:<woP_a.103177$It4....@rwcrnsc51.ops.asp.att.net>...

> however, in order to be able to make files of this
> type i need to be able to compress data with the DCL algorithm, is there open
> source code available to do this?

It would be very easy to write a DCL compressor, but I'm not aware of
one (other than the one PKWare sells, of course). By the way, if you
have control over both the compression and decompression ends, then
you should use something else (e.g. zlib, libbzip2, lzo, etc.).

> Or is it legal to reverse engineer the DCL
> encoding algorithm and make an open source variant of it?

I think it's legal, but there is still quite a bit of debate over what
DMCA means for this sort of thing. Since my decompressor could only
improve the market for PKWare's crummy DCL compressor, I considered a
legal challenge unlikely. However if someone wrote an open source DCL
compressor, that might provide more incentive for a challenge.

Here are some interesting links on the status of reverse-engineering:

http://www.eff.org/IP/DRM/fair_use_and_drm.html
http://www.chillingeffects.org/reverse/faq.cgi

mark