Reverse Engineering 7

분석

Main 내부 함수

; int __fastcall main(int argc, const char **argv, const char **envp)
main proc near

var_118= byte ptr -118h
var_18= qword ptr -18h

; __unwind { // __GSHandlerCheck
push    rdi
sub     rsp, 130h
mov     rax, cs:__security_cookie
xor     rax, rsp
mov     [rsp+138h+var_18], rax
lea     rax, [rsp+138h+var_118]
mov     rdi, rax
xor     eax, eax
mov     ecx, 100h
rep stosb
lea     rcx, aInput     ; "Input : "
call    sub_1400011B0
lea     rdx, [rsp+138h+var_118]
lea     rcx, a256s      ; "%256s"
call    sub_140001210
lea     rcx, [rsp+138h+var_118]
call    sub_140001000
test    eax, eax
jz      short loc_140001186

 대충 훑어보면 입력값을 받고 비교를 한다는 것을 알 수 있습니다.

좀 더 쉽게 보기 위해서 디컴파일링 해보겠습니다.

int __fastcall main(int argc, const char **argv, const char **envp)
{
  char v4[256]; // [rsp+20h] [rbp-118h] BYREF

  memset(v4, 0, sizeof(v4));
  sub_1400011B0("Input : ", argv, envp);
  sub_140001210("%256s", v4);
  if ( (unsigned int)sub_140001000(v4) )
    puts("Correct");
  else
    puts("Wrong");
  return 0;
}

if문을 보면 sub_140001000일 경우 Correct, 아닐경우 Wrong을 출력한다고 나와있네요

그럼 sub_140001000의 값을 봐야겠습니다. sub_140001000내부로 이동하겠습니다.

 

__int64 __fastcall sub_140001000(__int64 a1)
{
  int i; // [rsp+0h] [rbp-18h]

  for ( i = 0; (unsigned __int64)i < 0x12; ++i )
  {
    if ( byte_140003020[*(unsigned __int8 *)(a1 + i)] != byte_140003000[i] )
      return 0i64;
  }
  return 1i64;
}

if문의 ( byte_140003020[*(unsigned __int8 *)(a1 + i)] != byte_140003000[i] ) 이 부분을 간단하게 정리하면

            byte_140003020[a1 [i] ] != byte_140003000[i]로 바꿀 수 있습니다.

주소를 따라가서 어떤 값이 저장되어 있는지 확인후, C언어로 바꿔보겠습니다.

 

C언어 구현

#include <stdio.h>

int main() {
   
    unsigned char nums[] = {
        0x63, 0x7C, 0x77, 0x7B, 0xF2, 0x6B, 0x6F, 0xC5, 0x30, 0x01, 0x67, 0x2B, 0xFE, 0xD7, 0xAB, 0x76, 
        0xCA, 0x82, 0xC9, 0x7D, 0xFA, 0x59, 0x47, 0xF0, 0xAD, 0xD4, 0xA2, 0xAF, 0x9C, 0xA4, 0x72, 0xC0, 
        0xB7, 0xFD, 0x93, 0x26, 0x36, 0x3F, 0xF7, 0xCC, 0x34, 0xA5, 0xE5, 0xF1, 0x71, 0xD8, 0x31, 0x15, 
        0x04, 0xC7, 0x23, 0xC3, 0x18, 0x96, 0x05, 0x9A, 0x07, 0x12, 0x80, 0xE2, 0xEB, 0x27, 0xB2, 0x75, 
        0x09, 0x83, 0x2C, 0x1A, 0x1B, 0x6E, 0x5A, 0xA0, 0x52, 0x3B, 0xD6, 0xB3, 0x29, 0xE3, 0x2F, 0x84, 
        0x53, 0xD1, 0x00, 0xED, 0x20, 0xFC, 0xB1, 0x5B, 0x6A, 0xCB, 0xBE, 0x39, 0x4A, 0x4C, 0x58, 0xCF, 
        0xD0, 0xEF, 0xAA, 0xFB, 0x43, 0x4D, 0x33, 0x85, 0x45, 0xF9, 0x02, 0x7F, 0x50, 0x3C, 0x9F, 0xA8, 
        0x51, 0xA3, 0x40, 0x8F, 0x92, 0x9D, 0x38, 0xF5, 0xBC, 0xB6, 0xDA, 0x21, 0x10, 0xFF, 0xF3, 0xD2, 
        0xCD, 0x0C, 0x13, 0xEC, 0x5F, 0x97, 0x44, 0x17, 0xC4, 0xA7, 0x7E, 0x3D, 0x64, 0x5D, 0x19, 0x73, 
        0x60, 0x81, 0x4F, 0xDC, 0x22, 0x2A, 0x90, 0x88, 0x46, 0xEE, 0xB8, 0x14, 0xDE, 0x5E, 0x0B, 0xDB, 
        0xE0, 0x32, 0x3A, 0x0A, 0x49, 0x06, 0x24, 0x5C, 0xC2, 0xD3, 0xAC, 0x62, 0x91, 0x95, 0xE4, 0x79, 
        0xE7, 0xC8, 0x37, 0x6D, 0x8D, 0xD5, 0x4E, 0xA9, 0x6C, 0x56, 0xF4, 0xEA, 0x65, 0x7A, 0xAE, 0x08, 
        0xBA, 0x78, 0x25, 0x2E, 0x1C, 0xA6, 0xB4, 0xC6, 0xE8, 0xDD, 0x74, 0x1F, 0x4B, 0xBD, 0x8B, 0x8A, 
        0x70, 0x3E, 0xB5, 0x66, 0x48, 0x03, 0xF6, 0x0E, 0x61, 0x35, 0x57, 0xB9, 0x86, 0xC1, 0x1D, 0x9E, 
        0xE1, 0xF8, 0x98, 0x11, 0x69, 0xD9, 0x8E, 0x94, 0x9B, 0x1E, 0x87, 0xE9, 0xCE, 0x55, 0x28, 0xDF, 
        0x8C, 0xA1, 0x89, 0x0D, 0xBF, 0xE6, 0x42, 0x68, 0x41, 0x99, 0x2D, 0x0F, 0xB0, 0x54, 0xBB, 0x16
    };
    unsigned char nums2[] = {
        0x00, 0x4D, 0x51, 0x50, 0xEF, 0xFB, 0xC3, 0xCF, 0x92, 0x45, 0x4D, 0xCF, 0xF5, 0x04, 0x40, 0x50, 0x43, 0x63
    };

    int res[0x12] = {0};

    for (int i = 0; i < sizeof(nums2); i++) {
        for (int j = 0; j < sizeof(nums); j++) {
            if (nums2[i] == nums[j]) {
                res[i] = j;
                printf("%c", j);
                break;
            }
        }
    }
    return 0;
}

 배열을 초기화하고,  이중 for 문을 통해 값 비교 및 결과 저장합니다.(for for if 부분)

 

비주얼 스튜디오에서 실행하면 값이 나오게됩니다.