choice of encryption algorithms

[Robert J. Hansen]

On 6/20/12 1:10 PM, John wrote:
> When someone uses my public key to encrypt a message to me, what
> prevents them from trying to use an encryption algorithm of his choice.

Nothing.  They can use --cipher-algo to force whatever symmetric 
algorithm they wish.  This may wind up with a message that you're unable 
to read -- for instance, if your recipient forces AES256 and you're 
using PGP 7.0, you'll be unable to read it.  (This is why most of us 
advise against using --cipher-algo.)

The certificate does list what algorithms you're capable of reading, and 
most well-behaved OpenPGP applications will interpret that as ranked 
preferences ("I most prefer this, then that, then the other").  However, 
this is purely advisory and the sender can easily ignore it.