I understand Kerckhoff's principle, in a very practical sense, that the *best* attack that can be performed on a given cryptographic algorithm should be only as practical, if not less practical, than an exhaustive key search, that is, testing every possible key. My question is, if this is the case, then why go through the trouble of creating a cipher in the first place? Why not simply use a ridiculously long key, if you're gonna create a cipher that only takes as long as an exhaustive key search anyway?