“Don’t roll your own crypto” is great sense for production software. It is not good advice for people who are interested in learning to write good crypto, which

“Don’t roll your own crypto” is great sense for production software. It is not good advice for people who are interested in learning to write good crypto, which we will continue to need. For those people: roll as much as you can! Roll your own Feistel network. Roll your own AES implementation, and then roll your own side channel attack to break it. Roll your own timing attack. And then eventually, maybe you’ll be the one to roll the first draft of the built-in implementation of $WELL_KNOWN_PRIMITIVE in $NEW_MAJOR_LANGUAGE. :)