Back in 1998, I wrote: Anyone, from the most clueless amateur to the best cryptographer, can create an algorithm that he himself can't break. In 2004, Cory Doctorow called this Schneier's law: ...what I think of as Schneier's Law: "any person can invent a security system so clever that she or he can't think of how to break it." The general idea is older than my writing. Wikipedia points out that in The Codebreakers, David Kahn writes: Few false ideas have more firmly gripped the minds of so many[...]
via "Schneier's Law"