I love the Z80 too, and Turbo Pascal! In 1980 I was writing custom comm software for TRS-80 then Kaypro and Vector Graphic model 3. I wrote in assembly a CP/M TSR that loaded, hooked BDOS and allowed any existing program to transparently "encrypt" to and from disk by opening files matching a selectable mask (like !???????.???) so you could save "encrypted" docs from any app like WordStar. I use "encrypt" in scare quotes because it was only a snake oil XOR proof of concept... I had DES flowcharted out but saw right away that proper implementation would murder the TSR's size and throughput with 4MHz Z80 would be dismal.

Too bad, lost interest. Only a few years later with 16bit and MSDOS and faster CPU it became practical and I could have been the first such product to market but I was stupid.

I also had written a Turbo Pascal TSR program (using a 3rd party TSR toolkit) that was like strace on linux, writing system calls to disk in the background. I used it to troubleshoot many application program mysteries.