Postel's law is a good principle when your threat model is nature; it leads to robustness in the presence of random failures. But it is not a good design princi

Postel's law is a good principle when your threat model is nature; it leads to robustness in the presence of random failures. But it is not a good design principle in an environment of intelligently malicious failures, i.e., the internet. In other words, for reliability in uncertain but benign conditions, yes---for security, no!