Changing preferences

[David Shaw]

On Sep 21, 2008, at 8:27 PM, Faramir wrote:

> David Shaw escribió:
> ...
>> This is not true.  GPG will never use a cipher that the recipient  
>> does
>> not prefer.  It may not use the recipient's #1 choice, but it will
>> always use something from the recipient's list.
>
>  By the way... if I use setpref to set my encryption algorithms to
> AES256 and AES128, does it mean people won't be able to use, let's  
> say,
> 3DES to send encrypted messages to, even if they are incapable of  
> using
> AES? I mean... if I forget to add some algo, would I be making my key
> less compatible with other OpenPGP software?

No.  Every preference list has 3DES in it.  If you don't include it  
yourself, GPG adds it automatically to the end.

If you set your preferred algorithms to AES256 and AES128, you're  
really setting it to AES256, AES128, and 3DES.

>  I ask this question because, while maybe I would rather receive
> messages with some algorithms, that doesn't mean I don't want to use
> other algorithms if the preferred ones are not available... I figure  
> the
> answer is "no, the sender still can use the algo's you forgot to add  
> to
> your preferences list", but I want to be sure before doing any  
> change...

No, that is not the case.  The sender cannot use any algorithm that  
you don't include in your preference list.  To do so would violate  
OpenPGP, and cause major interoperability problems as the sender  
doesn't know if you even have the algorithm in question.

The whole point of a preference list is that you list the algorithms  
in the order in which you prefer them.  If you prefer some algorithms  
more, put them earlier.  If you prefer some algorithms less, put them  
later.   If you never want to see that algorithm used ever, leave it  
off the list completely.

David