Determining algorithm to be used?

[David Shaw]

On Mon, Nov 22, 2004 at 12:31:33AM +0100, Johan Wevers wrote:
> David Shaw wrote:
> 
> >You never want to use --cipher-algo with public key encryption.  It's
> >only safe to use with --symmetric.  The reason why is simple: the
> >above system to choose algorithms to use is safe - it will never pick
> >an algorithm that will result in an unusable message by one of the
> >recipients.
> 
> Yeah, well, that's the theory. Recently I sent encrypted messages to a
> friend but got replies that she could not decrypt them. It turned out
> that het key - generated with pgp 6.something - had preferences set
> that were incompatible with he new setup (gpg 1.2.4 without IDEA).
> After I understood this and overrode the cipher algo manually
> decrypting my messages was no problem any more.

Yes, this is a problem.  Your friend just needs to do "gpg --edit-key
xxxx updpref", and the preferences will be updated properly for his
new environment.  Without that, he's advertising the wrong preferences
and will have all sorts of problems.  GnuPG 1.4 actually does this on
key import automatically, so hopefully this will become less of a
problem in the future.

David