mirror of https://github.com/dirtbags/moth.git
53 lines
2.6 KiB
Plaintext
53 lines
2.6 KiB
Plaintext
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You are doing a forensics evaluation of a linux box that you know has
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been compromised. You find a binary on the system and assume it was
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used by the attackers to hide data on box that they were going to
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exfiltrate. You dissamble the file and find the following lines of x86
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assembly - this function was used to encode a buffer in place to
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obfuscate a file. What is the 1 byte key used to obfuscate the data (in
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hex)?
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HINT: The function was orginally defined as void convert_buf(unsigned
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char * buf, int len). You can solve this puzzle by writing some code,
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or by using some of the advanced functions of some of the hex editors
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out there.
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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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