If you’ve spent any time on the “dark web” this is super-obvious. They all love encryption, and most software developers are completely incompetent when it comes to encryption so backdooring an app is trivial. Hell, even well-known crypto libraries have implementations that rely on clearly false assumptions.
Wrote a basic primality checker library, it’s not by far my most interesting or complex project but I like that I accomplished all my initial goals in a timely fashion.