Re: Legitimate encryption
"Thought experiment. Gov't introduce backdoored encryption and mandate its use for personal communications (things like banks are allowed to use better stuff). Bad guys simply use good encryption which they then super-encrypt with the mandated backdoored encryption. How would the gov't ever know? Only when they get the warrant will they find out that the baddies have thwarted them."
The problem with that theory is VPNs. VPNs are legitimate use of encryption, especially for business. A previous Oz government has even said that VPNs are a legitimate tool for bypassing geoblocks for consumers to get around the "Aussie tax" overseas companies levy on us coz they can. So you use your VPN to make a HTTPS to some foreign companies ordering web site. The VPN connection starts in your Aussie lounge room, so uses the backdoored Aussie encryption, but the other end is the foreign VPN providers server in the foreign country. You use good HTTPS encryption that is tunneled through the VPN, coz the foreign web site thinks you are a local, and doesn't support backdoored Aussie encryption for it's locals. You are not being naughty, you are following the governments advice, but you get flagged as being naughty.
Tough luck for overseas visitors using the existing VPN software on their laptop / phone to do business with their office in country of origin.
"Oh, and anyone tempted to use codes should try to ensure that the messages they produce make some sort of sense. :)"
coded messages can make purfect sense if then cotes look like typeoz. If you get really clever, you don't even need code books. B-)