;=============================================================================================================================================
;                                                              step_23.asm
;Let's check if the file has the MZ signature
;                                                               Algorithm
;A1: Get the name of the file to check!
;A2: Open the file for reading
;A3: Read first 2 bytes
;A4: Check if "MZ"
;(C)I don't take any responsibility for the use of this program
;										                 Zedr0n -- connection closed
;=============================================================================================================================================
;=============================================================================================================================================
; Options/Declarations
;=============================================================================================================================================
.386
.model flat, stdcall
option casemap:none
include windows.inc
include kernel32.inc
include comdlg32.inc
include user32.inc

includelib \masm32\lib\kernel32.lib
includelib \masm32\lib\comdlg32.lib
includelib \masm32\lib\user32.lib

;=============================================================================================================================================
; Data segment
;=============================================================================================================================================
.data
Caption     db  "Zedr0n's step #23",0
Filter      db  "Exe files",0
            db  "*.exe",0,0
Err_1       db  "Error creating a dialog!",0
Err_2       db  "Error finding correct instance of the module!",0
Err_3       db  "Error setting the structure size!",0
Err_4       db  "Error opening file!",0
Err_5       db  "Error reading file!",0
ToRead      equ  2
Exe         db  "This is a real EXE file!",0
Not_Exe     db  "This file just has .exe extension!",0
;============================================================================================================================================
; Variables segment
;============================================================================================================================================
.data?
buffer      db  256 dup(?)
buffer_2    db  10  dup(?)
op          OPENFILENAME <>
op_size equ $-op
hModule     HANDLE  ?
hFile       HANDLE  ?
Read        dd  ?
;=============================================================================================================================================
; Code segment
;=============================================================================================================================================
.code
start:
A1:
    invoke GetModuleHandle,NULL
    mov hModule,eax
    mov op.lpstrFilter,offset Filter
    mov op.lpstrTitle,offset Caption
    mov op.lpstrFileTitle,offset buffer
    mov op.hwndOwner,NULL
    mov op.nMaxFileTitle,256
    mov op.hInstance,eax
    mov op.lStructSize,op_size
    invoke GetOpenFileName,offset op
    .if eax==0
        invoke CommDlgExtendedError
        .if eax==CDERR_DIALOGFAILURE
            invoke MessageBox,NULL,offset Err_1,offset Caption,MB_OK
         .elseif eax==CDERR_NOHINSTANCE
            invoke MessageBox,NULL,offset Err_2,offset Caption,MB_OK
        .elseif eax==CDERR_STRUCTSIZE
            invoke MessageBox,NULL,offset Err_3,offset Caption,MB_OK
        .endif
        invoke CloseHandle,hModule
        invoke ExitProcess,NULL
    .endif
A2:
    invoke CreateFile,offset buffer,GENERIC_READ,NULL,NULL,OPEN_EXISTING,FILE_ATTRIBUTE_ARCHIVE,NULL
    mov hFile,eax
    .if eax==INVALID_HANDLE_VALUE
        invoke MessageBox,NULL,offset Err_4,offset Caption,MB_OK
        invoke CloseHandle,hModule
        invoke ExitProcess,NULL
    .endif
A3:
    invoke ReadFile,hFile,offset buffer_2,ToRead,offset Read,NULL
    .if eax==0
        invoke MessageBox,NULL,offset Err_5,offset Caption,MB_OK
        invoke CloseHandle,hModule
        invoke CloseHandle,hFile
        invoke ExitProcess,NULL
    .endif
    .if buffer_2[0]=='M'
        .if buffer_2[1]=='Z'
            invoke MessageBox,NULL,offset Exe,offset Caption,MB_OK
        .endif
    .else
        invoke MessageBox,NULL,offset Not_Exe,offset Caption,MB_OK
    .endif
    invoke CloseHandle,hModule
    invoke CloseHandle,hFile
    invoke ExitProcess,NULL
end start