The US government considers encryption a weapon, in the context of export laws: no exporting weapons to enemy nations. As you know the Second Amendment protects our right to have weapons. So some people think that it extends to encryption. Problem is despite the Second, weapons can be confiscated in the name of preventing crime, which is what's going on in this case with FB, so the argument doesn't really work.
Not anymore. Back in 1994, Clinton signed EO10326 that transferred all commercial encryption technology off the Munitions list (meaning, no longer a weapon) to the Department of Commerce, making it a commodity. That basically means that it will not be treated as a weapon as far as export regulations are concerned. That EO was part of the reasoning why the US dropped its case against Zimmerman.
Strong commercial cryptography is no longer considered munitions, let alone a weapon.
Also, I don't think encryption is a weapon. But I wonder if the First protects it since it's a form of speech, heh.
The 1A protects it. The 4A protects it also, as well as various decisions handed down by SCOTUS.
BL.