> That there are now two secret keys doesn't alter the analysis substantially. It doesn't, and that's the point. There are no "separate levels" of security. Th

> That there are now two secret keys doesn't alter the analysis substantially. It doesn't, and that's the point. There are no "separate levels" of security. The attacker only has to break one of the keys, whichever is the weakest one. The "security level" of the whole system is the "security level" of its least secure part.