Function at 0x615870
Capabilities:
Encode data using xor
Get file size
Read file on windows
Write file on windows

Disassembly:
mov eax, dword fs:[0]
push 0xffffffffffffffff
push 0x756e80
push eax
mov dword fs:[0], esp
sub esp, 0x80
push ebx
mov ebx, dword [esp + 0x94]
push ebp
push esi
mov eax, dword [ebx + 8]
push edi
xor edi, edi
mov ebp, ecx
cmp eax, edi
jne 0x6158a8
xor eax, eax
jmp 0x615c10
mov eax, dword [ebx + 4]
cmp eax, edi
jne 0x6158b4
mov eax, 0x765608
push edi
push 0x80
push 3
push edi
push edi
push closesocket
push eax
call dword [sym.imp.kernel32.dll_CreateFileA]
mov esi, eax
cmp esi, 0xffffffff
jne 0x6158f2
mov ebx, dword [ebx + 4]
cmp ebx, edi
jne 0x6158dd
mov ebx, 0x765608
push ebx
push 0x7a45b8
call fcn.00455190
add esp, 8
xor eax, eax
jmp 0x615c10
push 0x7a45b0
lea eax, [esp + 0x48]
push ebx
push eax
call fcn.0040aca0
add esp, 0xc
lea ecx, [esp + 0x28]
mov dword [esp + 0x98], edi
push ecx
push esi
mov dword [esp + 0x30], edi
call dword [sym.imp.kernel32.dll_GetFileSize]
mov ebx, eax
cmp ebx, edi
ja 0x61595c
push esi
call dword [sym.imp.kernel32.dll_CloseHandle]
mov eax, dword [esp + 0x48]
cmp eax, edi
jne 0x615936
mov eax, 0x765608
push eax
call fcn.00727c17
add esp, 4
lea ecx, [esp + 0x44]
mov dword [esp + 0x98], 0xffffffff
push 1
call fcn.00404760
xor eax, eax
jmp 0x615c10
push ebx
call fcn.00726f70
add esp, 4
lea edx, [esp + 0x18]
mov edi, eax
mov dword [esp + 0x18], 0
push 0
push edx
push ebx
push edi
push esi
call dword [sym.imp.kernel32.dll_ReadFile]
push esi
call dword [sym.imp.kernel32.dll_CloseHandle]
xor esi, esi
mov edx, 0x816
test ebx, ebx
jle 0x6159ba
mov al, byte [esi + edi]
xor ecx, ecx
mov cl, dh
xor cl, al
movzx ax, al
add eax, edx
mov byte [esi + edi], cl
lea edx, [eax + eax*2]
shl edx, 6
add edx, eax
shl edx, 7
inc esi
cmp esi, ebx
lea edx, [edx + eax + 0x1608]
jl 0x615991
mov eax, dword [esp + 0x48]
test eax, eax
jne 0x6159c7
mov eax, 0x765608
push 0
push 0x80
push 2
push 0
push 0
push 0x40000000
push eax
call dword [sym.imp.kernel32.dll_CreateFileA]
mov esi, eax
lea eax, [esp + 0x18]
push 0
push eax
push ebx
push edi
push esi
call dword [sym.imp.kernel32.dll_WriteFile]
push esi
call dword [sym.imp.kernel32.dll_CloseHandle]
push edi
call fcn.00726ea6
mov eax, dword [esp + 0x4c]
add esp, 4
test eax, eax
jne 0x615a0f
mov eax, 0x765608
push 0
push 0x80
push 3
push 0
push 0
push closesocket
push eax
call dword [sym.imp.kernel32.dll_CreateFileA]
lea edi, [ebp + 4]
mov ebx, eax
mov ecx, edi
call fcn.0061c860
lea ecx, [ebp + 0x14]
call fcn.0061d110
mov esi, dword [sym.imp.kernel32.dll_ReadFile]
lea ecx, [esp + 0x1c]
push 0
push ecx
lea edx, [esp + 0x1c]
push 4
push edx
push ebx
mov dword [esp + 0x28], 0
call esi
mov al, byte [esp + 0x13]
xor ecx, ecx
mov byte [esp + 0x34], al
mov dword [esp + 0x38], ecx
mov dword [esp + 0x3c], ecx
mov dword [esp + 0x40], ecx
mov eax, dword [esp + 0x14]
mov byte [esp + 0x98], 1
cmp eax, ecx
jle 0x615aff
lea edx, [esp + 0x20]
mov dword [esp + 0x20], ecx
mov ecx, dword [ebp + 8]
push edx
push eax
push ecx
mov ecx, edi
call fcn.004ad7b0
mov edx, dword [esp + 0x14]
mov eax, dword [ebp + 8]
lea ecx, [esp + 0x1c]
push 0
push ecx
lea ecx, [edx*4]
push ecx
push eax
push ebx
call esi
lea edx, [esp + 0x34]
mov ecx, ebp
push edx
call fcn.0061f340
test eax, eax
je 0x615ae5
mov eax, dword [esp + 0x14]
mov ecx, dword [esp + 0x38]
cmp dword [ecx + eax*4], 0x1c
jne 0x615ad6
mov eax, dword [ebp + 8]
cmp dword [eax], 6
je 0x615afd
mov eax, dword [edi + 8]
mov ecx, dword [edi + 4]
push eax
push ecx
mov ecx, edi
call fcn.006d8d80
lea ecx, [esp + 0x34]
mov byte [esp + 0x98], 0
call fcn.005ba330
xor esi, esi
jmp 0x615b9d
xor ecx, ecx
lea edx, [esp + 0x1c]
push ecx
push edx
lea eax, [esp + 0x2c]
push 4
push eax
push ebx
call esi
mov eax, dword [esp + 0x24]
mov dword [esp + 0x20], 0
test eax, eax
jle 0x615b87
mov eax, dword [esp + 0x14]
xor esi, esi
test eax, eax
jle 0x615b4d
mov ecx, dword [esp + 0x38]
mov eax, dword [ebp + 8]
mov edx, dword [ecx + esi*4]
lea ecx, [esp + edx + 0x54]
mov edx, dword [eax + esi*4]
push ecx
push edx
push ebx
mov ecx, ebp
call fcn.0061f110
mov eax, dword [esp + 0x14]
inc esi
cmp esi, eax
jl 0x615b29
mov eax, dword [esp + 0x54]
mov ecx, 7
lea esi, [esp + 0x54]
lea edi, [esp + 0x74]
mov dword [esp + 0x70], eax
lea edx, [esp + 0x2c]
rep movsd dword es:[edi], dword [esi]
lea ecx, [esp + 0x70]
push ecx
push edx
lea ecx, [ebp + 0x14]
call fcn.0061c1b0
mov eax, dword [esp + 0x20]
mov ecx, dword [esp + 0x24]
inc eax
cmp eax, ecx
mov dword [esp + 0x20], eax
jl 0x615b1f
lea ecx, [esp + 0x34]
mov byte [esp + 0x98], 0
call fcn.005ba330
mov esi, 1
push ebx
call dword [sym.imp.kernel32.dll_CloseHandle]
test esi, esi
jne 0x615bc9
mov eax, dword [esp + 0xa0]
mov eax, dword [eax + 4]
test eax, eax
jne 0x615bbb
mov eax, 0x765608
push eax
push 0x7a458c
call fcn.00455190
add esp, 8
mov eax, dword [esp + 0x48]
test eax, eax
jne 0x615bd6
mov eax, 0x765608
push eax
call fcn.00727c17
mov ecx, dword [esp + 0x4c]
add esp, 4
test ecx, ecx
mov dword [esp + 0x98], 0xffffffff
je 0x615c0e
mov al, byte [ecx - 1]
test al, al
je 0x615c04
cmp al, 0xff
je 0x615c04
dec al
mov byte [ecx - 1], al
jmp 0x615c0e
dec ecx
push ecx
call fcn.00726ea6
add esp, 4
mov eax, esi
mov ecx, dword [esp + 0x90]
pop edi
pop esi
pop ebp
pop ebx
mov dword fs:[0], ecx
add esp, 0x8c
ret 4