; XOR crypting macro
macro crypt start,length,key {
  local x,y,key_size,key_pos
  virtual at 0
    db key
    key_size = $
  end virtual
  key_pos = 0
  repeat length
    load x from start+%-1
    virtual at 0
      db key
      load y from key_pos
    end virtual
    x = x xor y
    store x at start+%-1
    key_pos = key_pos + 1
    if key_pos >= key_size
      key_pos = 0
    end if
  end repeat
}

; data goes here... (tip: use file directive)
db 'Hello world!',13,10,'How are you?'
; encrypt
crypt 0,$,'testkey'
; decrypt
;crypt 0,$,'testkey'    

format PE CONSOLE
entry start

include '%fasminc%\win32a.inc'

macro begincrypt name
{
  name#.begin:
}

macro endcrypt name, key
{
   name#.end: 
   count = (rva name#.end - rva name#.begin)  
   repeat count - 1    
     load b byte from name#.begin+%-1  
     b = (b xor key) 
     store byte b at name#.begin+%-1
   end repeat
}

section '.text' code readable executable writeable
start:
   mov edi, layer.begin
   mov ecx, layer.end - layer.begin -1
 @@:
    mov al, byte [edi]
    xor al, 0x11
    stosb
    sub ecx, 1
    jne @b

   begincrypt layer
    invoke FindWindow, 0, szTitle
    push eax
    push edi
    mov edi, layer2.begin
    mov ecx, layer2.end - layer2.begin - 1
   @@:
      mov al, byte [edi]
      xor al, 0x05
      stosb
      sub ecx, 1
      jne @b
    pop edi

    begincrypt layer2
      pop eax
      invoke SetWindowText, eax, szMessage
    endcrypt layer2, 0x05 
    invoke ExitProcess, 0
   endcrypt layer, 0x11

   nop ; for visual purpose
   nop

section '.data' data readable writeable
  szMessage db 'Hello world!',0
  szTitle db 'flat assembler 1.56',0

section '.idata' import data readable writeable
  library kernel32,'kernel32.dll',\
          user32,'user32.dll'
  import kernel32,\
         ExitProcess,'ExitProcess'
  import user32,\
         FindWindow,'FindWindowA',\
         SetWindowText,'SetWindowTextA'
    

load b byte from %+ name#.begin -1
t = byte (((b xor key) + 220)  and 0xFF)
store byte t at %+ name#.begin -1    

db not ('F' xor 8), not ('A' xor 8), not ('S' xor 8), not ('M' xor 8)
    

include 'win32ax.inc'
; XOR crypting macro
macro crypt start,length,key { 
  local x,y,key_size,key_pos 
  virtual at 0 
    db key 
    key_size = $ 
  end virtual 
  key_pos = 0 
  repeat length 
    load x from start+%-1 
    virtual at 0 
      db key 
      load y from key_pos 
    end virtual 
    x = x xor y 
    store x at start+%-1 
    key_pos = key_pos + 1 
    if key_pos >= key_size 
      key_pos = 0 
    end if 
  end repeat 
}

main:
     call decrypt_code
     call start_code
     invoke ExitProcess,0

start_code:
     invoke MessageBox,0,'Hello world!','FASM rulez!',0
     ret
     db 'This data is also crypted! ',0
end_code:

decrypt_code:
     mov edi,start_code
     mov ecx,end_code-start_code
     @@:
     xor byte[edi],8
     inc edi
     dec ecx
     test ecx,ecx
     jnz @b
     ret

crypt start_code,end_code-start_code,8
.end main    

;DisASsembled file, Original file: test.exe  TatraDAS disassembler 2.9.8, Ivan Kohut (c) 2007

; ********************************************
; Code Section Number: 0
; ********************************************
BITS 32



;Program Entry point

  CALL _0x0040105E
  CALL _0x00401012
  PUSH byte 0x00

;Imported function 'ExitProcess' from 'KERNEL32.DLL' used
  CALL dword [0x0040205E]
;Call from 0x00401005
_0x00401012:
  BOUND ECX,[EAX]
  LOOPNE _0x0040101A
  OR byte [EAX],CL
  OR byte [ESI+0x49],CL
  POP EBX
  INC EBP
  SUB byte [EDX+0x7D],BH
  INSD 
  JB _0x0040104D
  OR AL,AH
  ADD EAX,dword 0x40080808
  INSD 
   UNDEFINED OPCODE!
  db 0x64
  db 0x64
  db 0x67
  db 0x28
  db 0x7F
  db 0x67
  db 0x7A
  db 0x64
  db 0x6C
  db 0x29
  db 0x08
  db 0x62
  db 0x08
  db 0xF7
  db 0x1D
  db 0x74
  db 0x28
  db 0x48
  db 0x08
  db 0xCB
  db 0x5C
  db 0x60
  db 0x61
  db 0x7B
  db 0x28
  db 0x6C
  db 0x69
  db 0x7C
  db 0x69
  db 0x28
  db 0x61
  db 0x7B
  db 0x28
;Jump from 0x00401022
_0x0040104D:
  IMUL ESP,[EBX+EDI*2+0x67],dword 0x717A6B28
  JS _0x004010D3
  INSD 
  INSB 
  SUB dword [EAX],EBP
  XOR AH,[ECX]
  db 0x08
;Call from 0x00401000
_0x0040105E:
  MOV EDI,dword 0x00401012
  MOV ECX,dword 0x0000004C
;Jump from 0x0040106F
_0x00401068:
  XOR byte [EDI],byte 0x08
  INC EDI
  DEC ECX
  TEST ECX,ECX
  JNE _0x00401068
  RETN    

f(x,y,z) = x^y (mod z)
    

Yes, I did, but there's your SHA512 code! (thought it was copyrighted, shouldn't u take it off???)

Still, your macro's simply do the powmod function, and apparently quite well. Would be a simple crypt by itself, am i right? I mean, as long as they can figure out how to decrypt .

AlexP: I can' t post my existing SHA code. Although written by me it is not owned by me, my company retains copyright. The macros I posted above are as far as I can go with posting code.

But looking at your code it is not all that clear. In my code I used macros named things like: sigma0, sigma1, alpha0, alpha1, cho, maj. Then a round macro and finally combined then into a short piece of code that is mostly macros that does the hashing. I find the macro names provide a clear overview of the process that is taking place in the main loop.