[lug] compressed cpio archive problems

[rm at fabula.de]

On Sun, Nov 18, 2001 at 03:33:19PM -0700, Tom Tromey wrote:
> [...]
> I don't think it is possible.  But don't take my word for it.  Find a
> coding expert.  Or you can read the paper on which compress is based;
> it is referenced in the man page.

Doesn't work, AFAIK. That is one of the major disadvantages of 
compression algorythms like 'compress' or 'zip' ....

> There's probably some small chance that there are bugs or
> incompatibilities between the compress you used to create this file
> and the current uncompress.  What media did you store these files on?
> I.e., is there a reasonable chance that they are really corrupt?
> Anyway one thing that might be worth trying is to find a system
> similar to the creating system and uncompress and unarchive there.
> 
> Luke> cpio: warning: skipped 1247 bytes of junk
> 
> One route open to you, which you may not like, is to read up on the
> various cpio formats, and then examine the archive file using a hex
> editor.  As I recall (I hacked on GNU cpio for a short time back in
> 1994 or so), the cpio formats are pretty straightforward.  So this
> wouldn't be as hard a job as it sounds.

Hmm, cpio format _is_ rather trivial, but Luke has to deal with
_compressed_ data, and if he manages to read compressed data in a
hex editor he'll be my guru of the year :-)
Still, if he's really desparate he could find the "offending" place
in the archive and write a little perl program to produce variants of
the archive by altering the bits at the offending spot and tests the 
result by trying to uncompress it (kind of a brute force attack. Which
shows that compression and cryptography are closely related topics).

Ralf Mattes


> Tom
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