Quick introduction to reverse engineering for beginners

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.text:00541249 .text:00541249 next_character_in_password: ; CODE XREF: rotate_all_with_password+26 .text:00541249 ; rotate_all_with_password+2A ... .text:00541249 mov al, [ebp+1] .text:0054124C inc ebp .text:0054124D test al, al .text:0054124F jnz loop_begin .text:00541255 pop edi .text:00541256 pop esi .text:00541257 pop ebx .text:00541258 .text:00541258 exit: ; CODE XREF: rotate_all_with_password+A .text:00541258 pop ebp .text:00541259 retn .text:00541259 rotate_all_with_password endp .text:00541259 .text:00541259 ; --------------------------------------------------------------------------- .text:0054125A align 10h .text:00541260 .text:00541260 ; =============== S U B R O U T I N E ======================================= .text:00541260 .text:00541260 .text:00541260 crypt proc near ; CODE XREF: crypt_file+8A .text:00541260 .text:00541260 arg_0 = dword ptr 4 .text:00541260 arg_4 = dword ptr 8 .text:00541260 arg_8 = dword ptr 0Ch .text:00541260 .text:00541260 push ebx .text:00541261 mov ebx, [esp+4+arg_0] .text:00541265 push ebp .text:00541266 push esi .text:00541267 push edi .text:00541268 xor ebp, ebp .text:0054126A .text:0054126A loc_54126A: ; CODE XREF: crypt+41 .text:0054126A mov eax, [esp+10h+arg_8] .text:0054126E mov ecx, 10h .text:00541273 mov esi, ebx .text:00541275 mov edi, offset cube64 .text:0054127A push 1 .text:0054127C push eax .text:0054127D rep movsd .text:0054127F call rotate_all_with_password .text:00541284 mov eax, [esp+18h+arg_4] .text:00541288 mov edi, ebx .text:0054128A add ebp, 40h .text:0054128D add esp, 8 .text:00541290 mov ecx, 10h .text:00541295 mov esi, offset cube64 155
.text:0054129A add ebx, 40h .text:0054129D cmp ebp, eax .text:0054129F rep movsd .text:005412A1 jl short loc_54126A .text:005412A3 pop edi .text:005412A4 pop esi .text:005412A5 pop ebp .text:005412A6 pop ebx .text:005412A7 retn .text:005412A7 crypt endp .text:005412A7 .text:005412A7 ; --------------------------------------------------------------------------- .text:005412A8 align 10h .text:005412B0 .text:005412B0 ; =============== S U B R O U T I N E ======================================= .text:005412B0 .text:005412B0 .text:005412B0 ; int __cdecl decrypt(int, int, void *Src) .text:005412B0 decrypt proc near ; CODE XREF: decrypt_file+99 .text:005412B0 .text:005412B0 arg_0 = dword ptr 4 .text:005412B0 arg_4 = dword ptr 8 .text:005412B0 Src = dword ptr 0Ch .text:005412B0 .text:005412B0 mov eax, [esp+Src] .text:005412B4 push ebx .text:005412B5 push ebp .text:005412B6 push esi .text:005412B7 push edi .text:005412B8 push eax ; Src .text:005412B9 call __strdup .text:005412BE push eax ; Str .text:005412BF mov [esp+18h+Src], eax .text:005412C3 call __strrev .text:005412C8 mov ebx, [esp+18h+arg_0] .text:005412CC add esp, 8 .text:005412CF xor ebp, ebp .text:005412D1 .text:005412D1 loc_5412D1: ; CODE XREF: decrypt+58 .text:005412D1 mov ecx, 10h .text:005412D6 mov esi, ebx .text:005412D8 mov edi, offset cube64 .text:005412DD push 3 .text:005412DF rep movsd .text:005412E1 mov ecx, [esp+14h+Src] .text:005412E5 push ecx .text:005412E6 call rotate_all_with_password .text:005412EB mov eax, [esp+18h+arg_4] .text:005412EF mov edi, ebx .text:005412F1 add ebp, 40h .text:005412F4 add esp, 8 .text:005412F7 mov ecx, 10h 156
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Quick introduction to reverse engin
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1.16 C++ classes . . . . . . . . .
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Preface Here (will be) some of my n
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1.1 Hello, world! Let’s start wit
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1.2 Stack Stack — is one of the m
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(_snprintf() function works just li
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1.3 printf() with several arguments
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1.4 scanf() Now let’s use scanf()
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GCC replaced first printf() call to
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}; return 0; printf ("What you ente
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1.5 Passing arguments via stack Now
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1.6 One more word about results ret
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push OFFSET $SG741 ; ’a
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1.8 switch()/case/default 1.8.1 Few
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1.8.2 A lot of cases If switch() st
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loc_804840C: ; DATA XREF: .rodata:0
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et 0 _main ENDP Nothing very specia
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add esp, 1Ch xor eax, eax ; return
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C/C++ standard defines char type as
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eax=eax+ecx return eax ... and this
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mov eax, ecx imul edx sar edx, 1 mo
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; current stack state: ST(0) = resu
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; in local stack here 8 bytes still
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fld QWORD PTR _a$[esp-4] ; current
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In other words, fnstsw ax / sahf in
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1.13 Arrays Array is just a set of
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mov [esp+70h+var_70], eax call _pri
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jge SHORT $LN1@main mov ecx, DWORD
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ebp 0x15 0x15 esi 0x0 0 edi 0x0 0 e
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1.14 Bit fields A lot of functions
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So, let’s download Linux Kernel 2
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There are some redundant code prese
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y 10 just by dropping last digit (3
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_key$ = 8 ; size = 4 _len$ = 12 ; s
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1.15 Structures It can be defined t
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call DWORD PTR __imp__GetSystemTime
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1.15.4 Fields packing in structure
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}; int b; struct outer_struct { cha
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}; printf ("stepping=%d\n", tmp->st
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call ___printf_chk mov eax, esi shr
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mov edx, DWORD PTR _t$[ebp] or edx,
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1.16 C++ classes I placed a C++ cla
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push ecx mov DWORD PTR _this$[ebp],
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call _ZN1c4dumpEv lea eax, [esp+20h
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1.17 Unions 1.17.1 Pseudo-random nu
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xor eax, eax pop esi mov esp, ebp p
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Let’s compile it in MSVC 2010 (I
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comp() function: public comp comp p
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Some compilers can do vectorization
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mov ecx, [esp+10h+var_10] mov edx,
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GCC In all other cases, non-SSE2 co
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add ebx, edx lea esi, [esi+0] loc_8
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movdqa xmm1, XMMWORD PTR [ecx+16] a
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1.20 x86-64 It’s a 64-bit extensi
Page 110 and 111: } x40 = a3 | x31; x41 = x24 & ~x37;
Page 112 and 113: or ebx, DWORD PTR _x6$[esp+36] mov
Page 114 and 115: and r11, r8 and rsi, r8 and r10, r1
Page 116 and 117: pop rdi pop rsi ret 0 s1 ENDP Nothi
Page 118 and 119: 2.1 LEA instruction LEA (Load Effec
Page 120 and 121: 2.3 npad It’s an assembler macro
Page 122 and 123: 2.4 Signed number representations T
Page 124 and 125: call function function: .. do somet
Page 126 and 127: 3.2 String Debugging messages are o
Page 128 and 129: .text:3011E91B DD 1E fstp qword ptr
Page 130 and 131: loc_80483F2: pop ebp retn _f endp 4
Page 132 and 133: loc_8048444: loc_8048448: loc_80484
Page 134 and 135: public f2 f2 proc near push ebp mov
Page 136 and 137: loc_804840A: loc_804842E: loc_80484
Page 138 and 139: mov esi, DWORD PTR _k$[esp+16] push
Page 140 and 141: or eax, edx retn f endp 4.1.8 Task
Page 142 and 143: 4.2 Middle level 4.2.1 Task 2.1 Wel
Page 144 and 145: mov [edx+eax], bl mov ebx, edi mov
Page 146 and 147: loc_80485AB: ; CODE XREF: f+1E0 ; f
Page 148 and 149: mov [ecx+eax], dl inc eax cmp ebx,
Page 150 and 151: Chapter 5 Tools ∙ IDA as disassem
Page 152 and 153: Chapter 7 More examples 147
Page 154 and 155: .text:00541050 arg_0 = dword ptr 4
Page 156 and 157: .text:005410F3 .text:005410F3 loc_5
Page 158 and 159: .text:005411A9 pop ebx .text:005411
Page 162 and 163: .text:005412FC mov esi, offset cube
Page 164 and 165: .text:005413DC call _fwrite ; write
Page 166 and 167: .text:005414A7 push ecx ; Filename
Page 168 and 169: .text:005413A3 mov ecx, [esp+44h+pa
Page 170 and 171: .text:00541408 push offset aRb ; "r
Page 172 and 173: }; }; return; fseek (f, 0, SEEK_END
Page 174 and 175: .text:005411B5 mov ebp, eax Check f
Page 176 and 177: .text:0054124C inc ebp .text:005412
Page 178 and 179: This instruction clears bit, in oth
Page 180 and 181: .text:005410CD add esp, 40h .text:0
Page 182 and 183: }; for (i=0; i
Page 184 and 185: }; tmp[y][z]=get_bit (row, y, z); f
Page 186 and 187: }; fread (buf, flen, 1, f); fclose
Page 188 and 189: 7.2 SAP client network traffic comp
Page 190 and 191: .text:64413F68 .text:64413F68 loc_6
Page 192 and 193: .text:64405171 call dbg .text:64405
Page 194 and 195: .text:64404FF7 push offset aLogging
Page 196 and 197: .text:64405113 loc_64405113: .text:
Page 198 and 199: Now let’s dig deeper and find con
Page 200 and 201: .text:64411E0B .text:64411E0B loc_6
Page 202 and 203: Chapter 8 Other things 8.1 Compiler
Page 204 and 205: Chapter 9 Tasks solutions 9.1 Easy
Page 206 and 207: 9.1.5 Task 1.5 Hint #1: Keep in min
Page 208 and 209: } 9.1.8 Task 1.8 Solution: two 100*
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#define PUSH(low, high) ((void) ((t
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} } ignore one or both. Otherwise,
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