Anti-debugging-techniques

Anti-Debugging detection and obufuscation techniques that involved the use of Win32 API functions.

This simple tool was written in Assembler x86 Win32 API and the Anti-Debugging method are:

• NtGlobalFlag - PEB!NtGlobalFlags
• IsDebuggerPresent - kernel32!IsDebuggerPresent
• IsDebuggerPresent - PEB!IsDebugged
• FindWindows for ollydbg
• Software breakpoint detection
• Hardware breakpoint detection
• Self-modifying code
• Obfuscation

For example see follow code (first case):

;NtGlobalFlag - PEB!NtGlobalFlags
xor eax, eax
assume fs:nothing
mov eax, fs:[eax+30h]
mov eax, [eax+68h]
and eax, 70h
db 0ebh, 01h
db 0ffh, 085h, 0C0h
jne @Detected

The NtGlobalFlag field exists at offset 0x68 in the Process Environment Block
We look at the individual instructions:

mov eax, fs:[eax+30h] ; Process Environment Block</br>
mov al, [eax+68h] ; NtGlobalFlag</br>
and eax, 70h ; if value of eax is 70h</br>
db 0ebh, 01h ; means jmp and skip 1 junk byte</br>
db 0ffh, 085h, 0C0h ; Follows opcode "085h, 0C0h" matches with istruction test eax, eax</br>

I have tested the executable on Win7 32 bit and 64 bit.