Pb decrypting with PGP 6.5.3 and GnuPG

[Werner Koch]

On Fri, 25 Aug 2000, Mr Griffon wrote:

> I'm having a problem with inter-operating PGP 6.5.3 and GNUPG on Windows. I 
> got to export my public and private keys from GNUPG to PGP without problems 
> - and I can use it to encrypt/decrypt with PGP, but everytime I try decrypt 
> with PGP a message encrypted with GNUPG I get a "bad packet" error. Did 
> anyone got this problem and found a solution ?

PGP does not understand the Blowfish cipher algorithm but die to the
fact that you created the key with GnuPG, this key indicates GnuPG that
your decryption software understands Blowfish.

Blowfish used to be in the first PGP 5 version which I used for
interoperabilty testing - later versions of PGP removed Blowfish.
However Blowfish is a legal OpenPGP algorithm.  Due to these problems 
I am going to change the preferences to use CAST5 in favor of Blowfish.

Neither GnuPG nor PGP has currently a simple way to chnage the
preferences.  With GnuPG is is possible but you need to know a little
bit aboput programming:  Edit the file g10/keygen.c, function
keygen_add_std_prefs() and change the sequence of algorithms given there
to have CAST5 come before Blowfish:

 Original:
    buf[0] = CIPHER_ALGO_TWOFISH;
    buf[1] = CIPHER_ALGO_BLOWFISH;
    buf[2] = CIPHER_ALGO_CAST5;
 After your modification:
    buf[0] = CIPHER_ALGO_CAST5;
    buf[1] = CIPHER_ALGO_TWOFISH;
    buf[2] = CIPHER_ALGO_BLOWFISH;
    
then use gpg's edit menu and for example use "expire" to recreate your 
self-signature.   In General it is not a good idea to chnage
implementaions after creating the key; the preferences mechanism
assumes that you use the same implementations. Negotiating parameters 
in am email system is not rwally possible and preferences are the only
thing we can do.
 
In future we are going to use Twofish and I have checked with the PGP
creators, that we can interoperate.

There is also a GnuPG version for Windows available.


  Werner




-- 
Werner Koch				GnuPG key:  621CC013
OpenIT GmbH                             http://www.OpenIT.de

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