gpg - PGP compatibility ?

Brian M. Carlson
Fri Oct 11 11:54:16 2002

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On Thu, Oct 10, 2002 at 02:48:04PM -0700, DuVall, Rick wrote:
> We are having intermittent problems with files encrypted using GPG 1.0.6 =
being sent to another party using PGP 6.5.  They get PGP errors every once =
and a while that say "problem expanding" data.

I haven't used PGP in years, ever since I started using Linux, but what
it sounds like is that you are using zlib (compression algorithm 2) and
PGP cannot handle any algorithm but zip (algo 1) with <=3D 13 bits of
compression. So you either need to use --compress-algo 1 on the command
line or "compress-algo 1" in your options file (in 1.2, gpg.conf).

gpg should not compress to an algorithm that the recipient does not
support. You can tell what compression algorithms a recipient supports
by looking at a dump of the key. Export the key and run it through, which dumps pgp packet data. Part of the output should
look like the below:

        Hashed Sub: preferred compression algorithms(sub 22)(3 bytes)
                Comp alg - ZLIB <RFC1950>(comp 2)
                Comp alg - ZIP <RFC1951>(comp 1)
                Comp alg - Uncompressed(comp 0)

The algorithms are listed in order. zlib should not be listed if the
recipient is using PGP, because it does not support it. If there is no
such section, then the default is [ZIP, Uncompressed], and there is
probably a bug in gpg.

Brian M. Carlson <> <> 0x560553=
It is better to kiss an avocado than to get in a fight with an aardvark.

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