Is 40 bits too little?

[wcs at anchor.ho.att.com]

h
Yes, 40 bits would be too little, especially since you can probably tell
if you've got the correct key by the form of the data, but they're actually
generating your 80-bit key as the XOR of two other 80-bit numbers,
and searching 2**80 still takes reasonably long.  Unfortunately,
the method of generating the two 80-bit numbers is disturbingly suspect;
see articles in sci.crypt and alt.privacy.clipper posted by Steve Bellovin
and somebody with email from Martin Hellman and Dorothy Denning.
			Bill Stewart