Shrug, none of the things we are talking about are classified. I've read a lot about the nuclear fail-safes on wiki. Granted I'm not sure how they work on missiles since there isn't exactly a keypad on the missile itself but I assume it works in much the same way but requires very special hardware/interface devices making it that much more difficult. If you try to activate it wrongly X number of times (probably 3 like other nukes) the weapon renders itself unusable. The name of the system on US nukes is Permissive Action Link. Funny story, according to a nuclear security expert back in the 70's all of the Minuteman ICBM launch codes were 00000000 because the top guys were concerned they wouldn't be able to get the codes to all of them fast enough if the shit hit the fan.
Like I said, stealing a US nuke would be useful in studying its design and for the nuclear material to build your own bomb but I doubt you could bypass the safety features to make the bomb go boom. Maybe some people in the US who work on them but even that doesn't seem likely.
