Simple Reverse - 0x26(2023 HW - Banana Donut Verifier)

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Simple Reverse - 0x26(2023 HW - Banana Donut Verifier)

Source Code

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__int64 __fastcall main(int a1, char **a2, char **a3)
{
  // [COLLAPSED LOCAL DECLARATIONS. PRESS KEYPAD CTRL-"+" TO EXPAND]

  v47 = 0.0;
  v46 = 0.0;
  v42 = 0LL;
  memset(user_input, 0, 1024);
  printf("Dount Verifier\nInput: ");
  __isoc99_scanf("%1023s", user_input);
  printf("\x1B[2J");                            // 這個意思是清除整個頁面
  for ( i = 0LL; i <= 499; ++i )
  {
    memset(s, 32, sizeof(s));
    memset(v20, 0, sizeof(v20));
    for ( j = 0.0; j < 6.28; j = v14 )
    {
      v40 = 0;
      for ( k = 0.0; k < 6.28; k = v13 )
      {
        v3 = _mm_cvtsi32_si128(LODWORD(k));
        *v3.m128i_i64 = (compute_sinf)(*v3.m128i_i64);// 計算浮點數的正弦值，參考自https://learn.microsoft.com/zh-tw/cpp/c-runtime-library/reference/sin-sinf-sinl?view=msvc-170
        v37 = COERCE_FLOAT(_mm_cvtsi128_si32(v3));
        v4 = _mm_cvtsi32_si128(LODWORD(j));
        *v4.m128i_i64 = (compute_conf)(*v4.m128i_i64);// 計算餘弦值，參考自https://learn.microsoft.com/zh-tw/cpp/c-runtime-library/reference/cos-cosf-cosl?view=msvc-170
        v36 = COERCE_FLOAT(_mm_cvtsi128_si32(v4));
        v5 = _mm_cvtsi32_si128(LODWORD(v47));
        *v5.m128i_i64 = (compute_sinf)(*v5.m128i_i64);
        v35 = COERCE_FLOAT(_mm_cvtsi128_si32(v5));
        v6 = _mm_cvtsi32_si128(LODWORD(j));
        *v6.m128i_i64 = (compute_sinf)(*v6.m128i_i64);
        v34 = COERCE_FLOAT(_mm_cvtsi128_si32(v6));
        v7 = _mm_cvtsi32_si128(LODWORD(v47));
        *v7.m128i_i64 = (compute_conf)(*v7.m128i_i64);
        v33 = COERCE_FLOAT(_mm_cvtsi128_si32(v7));
        v32 = v36 + 2.0;
        v31 = 1.0 / ((((v37 * (v36 + 2.0)) * v35) + (v34 * v33)) + 5.0);
        v8 = _mm_cvtsi32_si128(LODWORD(k));
        *v8.m128i_i64 = (compute_conf)(*v8.m128i_i64);
        v30 = COERCE_FLOAT(_mm_cvtsi128_si32(v8));
        v9 = _mm_cvtsi32_si128(LODWORD(v46));
        *v9.m128i_i64 = (compute_conf)(*v9.m128i_i64);
        v29 = COERCE_FLOAT(_mm_cvtsi128_si32(v9));
        v10 = _mm_cvtsi32_si128(LODWORD(v46));
        *v10.m128i_i64 = (compute_sinf)(*v10.m128i_i64);
        v28 = COERCE_FLOAT(_mm_cvtsi128_si32(v10));
        v27 = ((v37 * v32) * v33) - (v34 * v35);
        v26 = (((v31 * 30.0) * (((v30 * v32) * v29) - (v27 * v28))) + 40.0);
        v25 = (((v31 * 15.0) * ((v27 * v29) + ((v30 * v32) * v28))) + 12.0);
        v24 = 80 * v25 + v26;
        v23 = (8.0
             * ((((((v34 * v35) - ((v37 * v36) * v33)) * v29) - ((v37 * v36) * v35)) - (v34 * v33)) - ((v30 * v36) * v28)));
        if ( v25 <= 21 && v25 > 0 && v26 > 0 && v26 <= 79 && v31 > v20[v24] )
        {
          v20[v24] = v31;
          v11 = v23;
          if ( v23 < 0 )
            v11 = 0;
          s[v24] = special_char[v11];           // special_char就是印出甜甜圈的素材
        }
        if ( v40 == 30 && v42 <= 0x3FF )
        {
          v22 = v24 ^ v23 ^ (v26 + v25);
          v12 = v42++;
          *(user_input + v12) ^= v24 ^ v23 ^ (v26 + v25);
        }
        ++v40;
        v13 = k + 0.02;
      }
      v14 = j + 0.07000000000000001;
    }
    printf("\x1B[H");                           // 這個代表游標回到home position
    for ( idx = 0; idx <= 0x6E0; ++idx )        // 這一段for loop就是在印出甜甜圈
    {
      if ( idx % 80 )
        v15 = s[idx];
      else
        v15 = 10;
      putchar(v15);
      v16 = v47 + 0.00004;
      v47 = v16;
      v17 = v46 + 0.00002;
      v46 = v17;
    }
    usleep(30000u);                             // 睡眠0.03秒
  }
  cipher_1 = verification(user_input, 0x400uLL);
  cipher_2 = verification(key, 0x400uLL);
  if ( cipher_1 == cipher_2 )
    puts("Donut likes your input!! :D");
  else
    puts("Donut Reject You!! :(");
  puts("No matter donut accept you or not. Here's a bananacat for you");
  puts("                                       ░░ ░░                                                        ");
  puts(
    "                                     ░░░▒▓▒░░░                                                      ");
  puts(
    "                                     ░▒██████░                                                      ");
  puts(
    "                                     ░▓██████▒ ░                                                    ");
  puts(
    "                                      ░██████▓░                                                     ");
  puts(
    "                                      ░░██████▒ ░                                                   ");
  puts(
    "                                       ░▒█████▓░  ░  ░                                              ");
  puts(
    "                                     ░ ░░▓█████▓▓▓░░                                                ");
  puts(
    "                                     ░ ░▒███▓▓▒▒▒▒▒▒▒░░                                             ");
  puts(
    "                                      ░▓▒▓█▓▒▒░░░░░░▒▒▒░ ░                                          ");
  puts(
    "                                     ░▒▒▒▒▓▒▒░░░░░░░░▒▒▓▒░░  ░░                                     ");
  puts(
    "                                   ░ ░▓▒▒▒▒▒░░░░░░░░░░▒▒▒▓▒░░                                       ");
  puts(
    "                                 ░  ░▒▒▒▒▒▒▒░░░░░░░░░░░▒▒▒▓▓▒░                                      ");
  puts(
    "                                  ░ ░▒▓▒▒▒▒▒▒▒▒░░░░░░░░░▒▒▒▒▓░                                      ");
  puts(
    "                                   ░▒▒▓▒▒▒▒▒▒▒▒▒░░░░░░░░▒▒▒▒▓▓░                                     ");
  puts(
    "                                   ░▒▓▓▒▒▒▓▓▓▓▓▓▒▒▒▒▒▒░▒▒▒▒▒▒▓░ ░                                   ");
  puts(
    "                                   ░▒▓▓▓▒▓▒▒▒▒▒▒▓▓▓▓▓▒▒▒▒▒▒▒▓▓▓░  ░                                 ");
  puts(
    "                                  ░░▒▓▒▒▓▓▓▒▒▒▒▒▓▓▓▓▓▓▓▒▒▒▒▒▒▓▓░                                    ");
  puts(
    "                                 ░ ░▒▓▓▒▒▓▓▓▒▒▒▓▓▓▓▓▓▓▓▓▒▒▒▒▒▒▓▒░                                   ");
  puts(
    "                                 ░░▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▓▓▒▒▒▒▒▒▒▒  ░                                 ");
  puts(
    "                                  ░▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▓▓▒▒▒▒▒▒▒░                                   ");
  puts(
    "                                 ░░▒▓▓█▓▒▒▒▒▒▒▒▒▒▒▓▓▓▓▓▒▓▓▓▒▒▒▒▒░  ░                                ");
  puts(
    "                                 ░░▒▓███▓▓▒▒▒▒▒▒▒▓██▓█▓▒▒▓▒▒▒▒▒▒░                                   ");
  puts(
    "                                  ░░▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▓▒▒▒▒▒▒▒░                                   ");
  puts(
    "                                   ░░▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▓▓▒▒▒░▒▒▒▒▒░                                   ");
  puts(
    "                                   ░░▒▒▒▒▒▓▓▓▓▓▒▒▒▒▒▓▒▒▒▒▒▒▒▒▒▒▒░                                   ");
  puts(
    "                                      ▒▒▒▓▓▓▓▓▓▓▓▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒░                                   ");
  puts(
    "                                       ░▓▓▓▒▓▓▓▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒░                                   ");
  puts(
    "                                     ░ ░▓▓▒▒▒▒▒▒▒▒▒▒▒░▒▒▒▒▒▒▒▒▓▒░                                   ");
  puts(
    "                                       ░▓▓▒▒▒▒▒▒▒▒▒▒▒░░▒▒▒▒▒▒▒▓▒  ░                                 ");
  puts(
    "                                     ░░░▓▒▒▒▒▒▒▒▒▒▒░▒▒░▒▓▒▒▒▒▒▒▒ ░                                  ");
  puts(
    "                                   ░ ░░▒▓▒▒▒▒▒▒▒▒▒░░▒░▒▒▓▒▒▒▒▒▒▒▒░░ ░                               ");
  puts(
    "                                  ░░░▒▒▒▓▒▒▒▒▒▒▒▒▒▒▒░▒▒▒▒▒▒▒▒▒▒▒▒▒▓▒░                               ");
  puts(
    "                                 ░░▒▒▒▓▓█▓▒▓▒▒▒░░░░░▒▒▓▒▒▒▒▒▓▒▒▒▒▒▒▒▓░░░                            ");
  puts(
    "                                 ░▒▓▓▓░░█▓▒▓▓▓▒░░░░▒▒▒▒▒▒▒▓▓▓▒▓▓▒▒▒▒▓▒░                             ");
  puts(
    "                                 ░▓▓▒░░░▓▓▓█▓▓▒▒▒▒▒▒▒▒▒▒▒▓▓▓█▒░░▒▓▓▓▓▒░                             ");
  puts(
    "                                       ░▓██████▓▓▒▒▒▒▒▒▓▓▓▓▓░   ░░▒░░                               ");
  puts(
    "                                    ░  ░░▓█████▓▒▒▒▒▒▒▒▓▓▓▒░  ░     ░  ░                            ");
  puts(
    "                                       ░░▓██████▓▒▒▓▓▒▒▒▒▒░                                         ");
  puts(
    "                                     ░ ░▒▓▒▓▓▓▓██▓█▓▓▒▒▒▒▒░  ░                                      ");
  puts(
    "                                       ░▒▓▓▓▓▓▓░▒▒▒▒▓▒▒▒▒▒▒░                                        ");
  puts(
    "                                      ░░▓▓▓▓▓▓▓▒   ░▒▓▒▒▒▒▒▒░                                       ");
  puts(
    "                                     ░░░▒▒▒▒▒░░░   ░▒▓▒▒▒▒▓▓░ ░                                     ");
  puts(
    "                                                 ░  ░░░░░░░░                                        ");
  puts("                                          ░░         ");
  return 0LL;
}

Recon

初步的基礎操作逆完之後，主要流程是這樣:

  1. 先輸入1023個char
  2. 他會對這1023個char進行一些操作外，主要是運算甜甜圈怎麼畫(對float運算sin和cos)
  3. 把我們的input丟到verification function
  4. 把原本儲存在程式碼的key也丟到verification function
  5. 比對兩個return的結果
  6. 一樣就吐Donut likes your input!! :D

我這一題的想法是直接用上一次HW(crackme_vectorization)的思維嘗試找出他的邏輯，以下實驗結果都是在進入verification function之前的user_input

  1. 首先我如果全部輸入\x00 
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     3D 3A 8B 8A 8A 8A 89 89 88 88 88 88 59 56 54 54 54 56 59 59 27 56 56 57 4B 4B 48 48 49 49 4E 4E 4B F9 F9 F8 07 07 07 05 04 07 07 06 01 01 02 02 01 01 00 B1 B5 BA BA BA BA BA A7 A7 A8 A8 A8 AB
 ...
  2. 如果輸入全部都是\x10 
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     2D 2A 9B 9A 9A 9A 99 99 98 98 98 98 49 46 44 44 44 46 49 49 37 46 46 47 5B 5B 58 58 59 59 5E 5E 5B E9 E9 E8 17 17 17 15 14 17 17 16 11 11 12 12 11 11 10 A1 A5 AA AA AA AA AA B7 B7 B8 B8 B8 BB
 ...
  3. 要比對的key 
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     47 56 F8 BE FD FB A6 FB A7 FF F2 F2 0C 63 33 11 65 2F 18 21 69 63 35 25 2D 2E 2C 21 70 78 17 7A 0F 92 BE 99 54 48 43 35 75 52 48 36 57 34 32 3F 01 01 00 B1 B5 BA BA BA BA BA A7 A7 A8 A8 A8 AB
 ...

從以上的memory dump出來的結果就知道全部輸入\x00和要比對的key只有前面48 bytes不一樣，但後面都一樣，而和全部都是\x10的輸出結果比較發現都是差\x10(不管正負)，因此我有大膽的想法，這該不會是XOR的操作ㄅ，經過比對果然無誤，所以我只要把要比對的key和全部都是\x00的結果進行XOR就知道我應該輸入甚麼了

Exploit

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root = "./Reverse/HW2/Banana Donut Verifier/"
input_0x0 = open(root + 'user_input_all_0.mem', 'rb').read()

real_key = open(root + 'real_key.mem', 'rb').read()
# flag_file = open(root + 'flag.mem', 'wb')

flag = b''
for i in range(len(real_key)):
    flag += bytes([real_key[i] ^ input_0x0[i]])

# flag_file.write(flag)
# flag_file.close()
print("Exchange Flag is: " + flag.decode())
# Exchange Flag is: zls4wq/r/wzzU5gE1yAxN5crfedi91Y4DkGaSOD0qUO0V50=

圖片.png

Flag: FLAG{d0_Y0u_l1k3_b4n4Na_d0Nut?}