Determine WEP key type from scan?

[Shawn Rutledge]

Is there any way to determine the WEP key length from scan results?
(40 bit or 104 bit)  I see that wpa_gui does not enforce any
particular number of characters, but a 64-bit key should require 5
characters if entered in ASCII form, and a 104-bit key requires 13.
Is there a reason why the supplicant can't detect which length it is,
or is that one of the security features of WEP that you aren't
supposed to know which length is required?