Changing preferences

[Kevin Hilton]

> GnuPG in particular works like this:
>
> 1) Take the intersection of all recipients preference lists.  This
> rules out any algorithms that would be unusable by someone.
> 2) Elect a "decider".  The decider is the one person whose ordered
> list we will honor the rankings for.  If the user has specified a
> personal-*-prefs list, then the user is the decider.  If the user has
> not specified a list, then the last recipient key is used.
> 3) Walk the decider preference list from highest ranked to lowest
> ranked - as soon as we hit an algorithm that is part of the
> intersection from step #1, stop.
>
> For example:
>   Alice has AES CAST5 TWOFISH
>   Baker has CAST5 AES BLOWFISH
>   Charlie has BLOWFISH AES CAST5
>   Donald has CAMELLIA TWOFISH BLOWFISH
>
> Assuming that there is no personal-*-prefs list set), here's how it
> falls out:
>
>    Alice Baker Charlie == AES
>    Baker Alice Charlie == AES
>    Charlie Alice Baker == CAST5
>    Charlie Alice Baker Donald = 3DES


Thats a great explanation.  Perhaps this should be included in the
documentation.

Lastly however this is assuming the sender is not using the

cipher-algo
digest-algo

options.  From my reading of the documentation, this will force the
use of a particular cipher as dictated by the sender, even if the
algorithm is not contained in the list of the public keys.  I know
these two options are not recommended for use, however since they are
included as possible options, I think that they should at least be
covered by a "what if" scenario.

-- 
Kevin Hilton