And 35 years ago I banged out a concept piece on MSDOS/Turbo Pascal that was terminate-stay-resident (with a purchased development kit) I had originally coded i

And 35 years ago I banged out a concept piece on MSDOS/Turbo Pascal that was terminate-stay-resident (with a purchased development kit) I had originally coded in native 8086 under CP/M. Config a list of wildcards and enter a key at runtime, and matching files are transparently encrypted when written and decrypted when read, using hooks into DOS calls. It worked well even with word processors of the time because even their temp files could be matched for encryption too. But I was too serious about security and the concept used fast snake oil to test the idea, and my attempt to implement even single DES gobbled so much CPU and real time it would have been a disaster product for a 'transparent' solution. And key/passphrase checking and features to prevent corruption of encrypted data (like an encrypted state flag!) would have required ghosting and protecting files and lots of out of band data store. The original concept was "everything in-place just encrypted" and it was fun and it worked for me. But I decided to save my sanity and stop at fun. I eventually lost my sanity but for other reasons.