I'm aware. But Kerckhoff's principle is just saying that your mechanism of encryption shouldn't be obscured. It doesn't change that I can't define 'obscure' in a way that doesn't make it a mechanism (in itself inobscure) of obscuring data.
Also, there are plenty of historical ciphers that fall foul of Kerckhoff, I don't think we can say retrospectively that they weren't done for security, and in many cases were probably totally adequate for some time, if not their lifespan.
Also, there are plenty of historical ciphers that fall foul of Kerckhoff, I don't think we can say retrospectively that they weren't done for security, and in many cases were probably totally adequate for some time, if not their lifespan.