There is an optional lesson on one way functions and computationally hard problems that you may be interested in using (https://curriculum.code.org/csp/unit4/6/optional/2/)
The original lesson was pencil and paper based but it felt like it would be much more engaging if it was an interactive web tool, so I built one.
I used it with my students this past week and most of the kids got really into it. It allows them to solve puzzles including the original puzzle in the lesson, as well as create and share their own puzzles. In fact, all the puzzles the students create become part of the site and can be randomly selected to be shown to another user who asks for a new puzzle to solve. In this way, it is a nice example of crowdsourcing since the students are (somewhat unknowingly) creating the content for the site.
Here is the link for the puzzle from the first activity: http://vertexcover.herokuapp.com/hotspot/CODE
Here is the link for the build your own puzzle activity: http://vertexcover.herokuapp.com/create
If you just load the main site, it chooses a small puzzle at random, but students can also choose what size puzzle they want to solve by clicking on "Try Another Graph"
Feel free to use this with your students and let me know if you have any feedback to share.