CHAPTER 79. “QR9”: RUBIK’S CUBE INSPIRED AMATEUR CRYPTO-ALGORITHM CHAPTER 79. “QR9”: RUBIK’S CUBE INSPIRED AMATEUR CRYPTO-ALGORITHM

Chapter 79

79 “QR9”: Rubik’s cube inspired amateur crypto-algorithm

crypto-algorithm

Sometimes amateur cryptosystems appear to be pretty bizarre.

The author of this book was once asked to reverse engineer an amateur cryptoalgorithm of some data encryption utility, the
source code for which was lost^1.

Here is the listing exported fromIDAfor the original encryption utility:

.text:00541000 set_bit proc near ; CODE XREF: rotate1+42
.text:00541000 ; rotate2+42 ...
.text:00541000
.text:00541000 arg_0 = dword ptr 4
.text:00541000 arg_4 = dword ptr 8
.text:00541000 arg_8 = dword ptr 0Ch
.text:00541000 arg_C = byte ptr 10h
.text:00541000
.text:00541000 mov al, [esp+arg_C]
.text:00541004 mov ecx, [esp+arg_8]
.text:00541008 push esi
.text:00541009 mov esi, [esp+4+arg_0]
.text:0054100D test al, al
.text:0054100F mov eax, [esp+4+arg_4]
.text:00541013 mov dl, 1
.text:00541015 jz short loc_54102B
.text:00541017 shl dl, cl
.text:00541019 mov cl, cube64[eax+esi8]
.text:00541020 or cl, dl
.text:00541022 mov cube64[eax+esi8], cl
.text:00541029 pop esi
.text:0054102A retn
.text:0054102B
.text:0054102B loc_54102B: ; CODE XREF: set_bit+15
.text:0054102B shl dl, cl
.text:0054102D mov cl, cube64[eax+esi8]
.text:00541034 not dl
.text:00541036 and cl, dl
.text:00541038 mov cube64[eax+esi8], cl
.text:0054103F pop esi
.text:00541040 retn
.text:00541040 set_bit endp
.text:00541040
.text:00541041 align 10h
.text:00541050
.text:00541050 ; =============== S U B R O U T I N E =======================================
.text:00541050
.text:00541050
.text:00541050 get_bit proc near ; CODE XREF: rotate1+16
.text:00541050 ; rotate2+16 ...
.text:00541050
.text:00541050 arg_0 = dword ptr 4

(^1) He also got permission from the customer to publish the algorithm’s details