40 lines
2.3 KiB
HTML
40 lines
2.3 KiB
HTML
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So, I've heard you're kinda new to reverse-engineering ?<br>
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<br>
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Basically, in almost every challenge you'll be provided a binary hiding a secret.<br>
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Your goal is generally to break the secret checking function in order to recover the flag.<br>
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For this you'll need to understand the assembly code and write back the corresponding C code if you need to (or you can do it in real-time if you're not human).<br>
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<br>
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To make it easier, i'll give you the flag checking function only and your task will be to recover which input returns 1.<br>
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I advise you to do some research about x86 ISA and x86 linux calling convention first.<br>
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<br>
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Good luck !<br>
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<br>
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<pre style="color:#cecece; padding-left: 15px; background-color:#000; font-weight: bolder;">
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<code>
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0000000000001139 <check_secret>:
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1139: 55 push rbp
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113a: 48 89 e5 mov rbp,rsp
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113d: 48 89 7d e8 mov QWORD PTR [rbp-0x18],rdi
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1141: 48 8b 45 e8 mov rax,QWORD PTR [rbp-0x18]
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1145: 48 89 45 f8 mov QWORD PTR [rbp-0x8],rax
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1149: 48 8b 45 f8 mov rax,QWORD PTR [rbp-0x8]
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114d: 8b 00 mov eax,DWORD PTR [rax]
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114f: 35 40 20 5b 7f xor eax,0x7f5b2040
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1154: 89 45 f0 mov DWORD PTR [rbp-0x10],eax
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1157: 48 8b 45 f8 mov rax,QWORD PTR [rbp-0x8]
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115b: 48 83 c0 04 add rax,0x4
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115f: 8b 00 mov eax,DWORD PTR [rax]
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1161: 35 53 23 59 76 xor eax,0x76592353
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1166: 89 45 f4 mov DWORD PTR [rbp-0xc],eax
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1169: 81 7d f0 37 13 37 13 cmp DWORD PTR [rbp-0x10],0x13371337
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1170: 75 10 jne 1182 <check_secret+0x49>
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1172: 81 7d f4 37 13 37 13 cmp DWORD PTR [rbp-0xc],0x13371337
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1179: 75 07 jne 1182 <check_secret+0x49>
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117b: b8 01 00 00 00 mov eax,0x1
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1180: eb 05 jmp 1187 <check_secret+0x4e>
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1182: b8 00 00 00 00 mov eax,0x0
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1187: 5d pop rbp
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1188: c3 ret
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</code>
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</pre>
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<br>
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