Just as my first product was about to go to market, the company president decided we needed copy protection. He wanted Prolok. I objected, and proposed that if I could break it in 24 hours, we wouldn't use it. I took 25 hours, and we did use it (fair is fair). I finally found my notes and the unlock tool. The very cryptic notes included inline. I haven't decided where to post the source yet. If anyone has prolok'ed disks and want to try it out, I'll be happy to send it to you. I don't run physical DOS machines any more, so my ability to test is limited. If you want to just run a random EXE from 1983, you can try UNPROLOK.EXE here. https://drive.google.com/corp/drive/folders/1amoYi_fY6f2UYdYeTA1o86rmAtYpsL… --- snip --- prolok.doc prolok information sheet How to Un-Prolok a file db xxx.exe A: g 20 start up g =27 3b skip int 1 and int 3 steal r si 1 ruin debugger test g 443 t t t should be at 54b g =47d 481 AL is set to correct disk B: g 4a8 make sure AH is 0x10, Carry set at 4c3 the is a write interrupt that must succeed g 4c5 r f NC clear Carry bit r AX 0 set AH to 0 g 4d2 Carry should be on, AX = 1000 g 4ea make sure BX has 47 (from table at 870) C: repeat area from B to C for second entry in table D: g 51c trick decryption part t 700 t c0 t until SI = 533 (about 20 times) g 53e BX should be 0, g 54e r ax = 0, bx = 0, cx = 0, dx = 1, sp = 866, bp = 0 si = 45a, di = 54d, cs, ss, ds, es = 283e flags: NV UP EI PL ZR NA PE NC g 57e r f ZR g 58b r f ZR g 5b0 t g =5b6 5b9 skip steal of int 21 t g =5bf 5d3 g =5e4 5e6 skip steal of int 27h F: convert user program r BX = number of 512 byte PAGES in file g 5f4 ax has base segment of user code g 627 at this point we have the converted user program in main memory. G: write it to disk d 0 examine the first few bytes if the first two are 5a 4d or 4d 5a then it is a .EXE file else a .COM file. N outfile.com if it was .EXE you will have to rename it after compute PAGES * 0x200 r cx, bx the above value w 970 q if you continue from this point bx, cx are set wrong H: if we continued rather than writing the file g 637 g =642 644 --- Data Areas (all in CS) Address (+100) What 78b 88b store initial int 21h vector IP (0:84) 78d 88d store initial int 21h vector CS (0:86) 78b 88b store initial int 21h vector IP (0:9c) 78b 88b store initial int 21h vector CS (0:9e) 78b 88b segment of base of user code (cs:970) ^L How to disassemble Un-Prolok.exe d 0 l 100 d cs:0 l 450 u 11 l 40 u 430 l 29 d 458 l 3 u 45b l 23 u 47d l 90 u 50d l f d cs:50d l f u 51c l 32 u 54e l 98 u 5e6 l 180 d cs:765 l b u 770 l 73 u 7e2 l 50 d cs:820 l 150 u 970 l 360 d cs:0800 l 800 d cs:1000 l 800 d cs:1800 l 800 d cs:2000 l 400 q