Having implemented crypto algorithms for educational and enjoyment purposes, I've always looked at "don't roll your own crypto" as less having to do with the ac

Having implemented crypto algorithms for educational and enjoyment purposes, I've always looked at "don't roll your own crypto" as less having to do with the actual writing of code which, as you state, isn't really that hard. Instead, what that statement is saying is that when you write your own code, you'll almost never get enough attention from the white-hat community to have any confidence that the code can be used in production. You're right that the code written by professionals has lots of bugs. Bug is a term that describes a problem in code that has been found. With crypto software, the danger isn't the problems that get found (and then addressed), it's the problems that aren't found. "Roll your own" solutions have problems that never get found. That's the danger and it has nothing to do with the skill of the programmer.