Incompatibility between gnupg 0.9.7 and >0.9.10 in conv. 3des encryption

[Enzo Michelangeli]

I'm not sure whether it's a known problem, but if one encrypts with:

 ./gpg097 -a -c --cipher-algo 3des q

and then tries to decrypt with gpg version 0.9.10 or later:

 gpg q.asc

the result is an error message:

 gpg: decryption failed: bad key

The incompatibility is mutual: files encrypted with 0.9.10 can't be
decrypted by the 0.9.7 either. If the --cipher-algo is not specified,
everything works fine.

Listing the packets does indeed show a difference. A q.asc produced by the
version 0.9.7 lists as:

 $ gpg --list packets q.asc
 gpg: Option "--list" is ambiguous
 bash-2.03$ gpg --list-packets q.asc
 :symkey enc packet: version 4, cipher 2, s2k 1, hash 3
         salt b742d414bb37d32f

...whereas one produced with the version 0.9.10 or later shows:

 $ gpg --list-packets q.asc
 :symkey enc packet: version 4, cipher 2, s2k 3, hash 3
         salt 08cbb4030fd47883, count 96

However, I would expect that backward compatibility with older s2k values be
preserved in decryption.

Cheers --

Enzo