Capture The Flag is a popular format for computer hacking competitions, appearing at dozens of conferences around the world, and was the basis for last year's DARPA Cyber Grand Challenge. CTF games are built on challenges, but building fun, solvable, and educational challenges is difficult!
This talk covers lessons learned from the past four years of DEF CON CTF, minutiae of making challenges that aren't a huge mission to keep running, how challenges differ from normal production software, and how to match player skill to appropriate challenges.