mirror of https://github.com/dirtbags/moth.git
49 lines
2.5 KiB
HTML
Executable File
49 lines
2.5 KiB
HTML
Executable File
<HTML>
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<BODY>
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<B>You are doing a forensics evaluation of a linux box that you know has been compromised. You find a binary on the system and assume it was used by the attackers to hide data on box that they were going to exfiltrate. You dissamble the file and find the following lines of x86 assembly - this function was used to encode a buffer in place to obfuscate a file. What is the 1 byte key used to obfuscate the data (in hex)?</B>
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<BR> HINT: The function was orginally defined as void convert_buf(unsigned char * buf, int len). You can solve this puzzle by writing some code, or by using some of the advanced functions of some of the hex editors out there.
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<BR>
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<PRE>
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.text:08048474 ; =============== S U B R O U T I N E =======================================
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.text:08048474
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.text:08048474 ; Attributes: bp-based frame
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.text:08048474
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.text:08048474 public convert_buf
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.text:08048474 convert_buf proc near ; CODE XREF: main+B2p
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.text:08048474
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.text:08048474 cnt = dword ptr -4
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.text:08048474 buf = dword ptr 8
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.text:08048474 len = dword ptr 0Ch
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.text:08048474
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.text:08048474 push ebp
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.text:08048475 mov ebp, esp
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.text:08048477 sub esp, 10h
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.text:0804847A mov [ebp+cnt], 0
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.text:08048481 mov [ebp+cnt], 0
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.text:08048488 jmp short loc_80484A4
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.text:0804848A ; ---------------------------------------------------------------------------
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.text:0804848A
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.text:0804848A loc_804848A: ; CODE XREF: convert_buf+36j
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.text:0804848A mov eax, [ebp+cnt]
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.text:0804848D mov edx, eax
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.text:0804848F add edx, [ebp+buf]
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.text:08048492 mov eax, [ebp+cnt]
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.text:08048495 add eax, [ebp+buf]
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.text:08048498 movzx eax, byte ptr [eax]
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.text:0804849B xor eax, 4Ch
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.text:0804849E mov [edx], al
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.text:080484A0 add [ebp+cnt], 1
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.text:080484A4
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.text:080484A4 loc_80484A4: ; CODE XREF: convert_buf+14j
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.text:080484A4 mov eax, [ebp+cnt]
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.text:080484A7 cmp eax, [ebp+len]
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.text:080484AA jl short loc_804848A
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.text:080484AC leave
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.text:080484AD retn
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.text:080484AD convert_buf endp
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.text:080484AD
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.text:080484AE
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</PRE>
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</BODY>
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</HTML>
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