Furthermore, I think that we the upper bound should be something that the average IPFire box is able to handle.
I agree with that. Maybe 3072 bits is a good deal between speed and security, what do you think?
That depends entirely on the hardware. We cannot know what people are using. That makes it rather complicated to decide.
Is there a way to present the users a message and let them decide which length they want to use?
There seems to be a problem with the word "recommended". In the patches submitted, I recommended always the most strongest cipher. However, as you said, some of them are simply one step too much. Should then both be recommended?
I am not sure. Can anyone come up with a more fitting expression? If we mark everything as "recommended" that is strong enough for now after our consideration, we will have most of them tagged with that word. In that case it would make more sense to mark the weak stuff as such to keep readability. Maybe that is the way to go. But does the average Joe know what is meant by "weak"?
Joe should know enough that "weak" is normally not what is wanted. Otherwise he should RTFM ;-)
You could recommend the strongest cipher that would take an attacker millions of years to break, but on the other hand force the hardware to burn its CPU, while another "not as strong as the recommended one" cipher would also take an attacker thousands of years, but not consume that much CPU. Would have to differentiate between "recommended for high performance CPU" and "recommended for your small box". So, that doesn't sound good.
Weak is weak for every kind of hardware. So +1 for "weak".
Lars