Gnupg compression

Thomas Martin toskp10 at
Thu Feb 9 19:55:18 CET 2012

Hello all,

I've been playing around with encrypted files, trying to decrypt them
independently. I've used Maple to decrypt the RSA, and openssl to
decrypt the AES, sha1sum to verify the hashes, but I'm having problems
with the compressed files. I (perhaps naively) thought that once I'd
undone the encryption, it would be possible to extract just the
compressed data and use a decompression command to retrieve the
original file. I know Gnupg uses zlib by default, but I used
"--personal-compress-preferences zip" to use zip instead, and tried 7z
to decompress. Not only did it not work, but trying to compress the
original file with 7z came up with a very different file (different
size as well as content). Even when I used no compression and
encrypted a 1k all-zero file, the decrypted file only had 990 zero
bytes. With the redundant 16 bits in the CFB mode, and the hash
digests, I know I'm doing most things right. Can anyone help with
these final steps? Do there exist commands (Windows or Linux) that
will compress/decompress a file in the exact same manner as Gnupg, for
any or all three compression algorithms?


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