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攻防世界Reverse解题（一）

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导读：本篇文章讲解 攻防世界Reverse解题（一），希望对大家有帮助，欢迎收藏，转发！站点地址：www.bmabk.com

攻防世界Reverse解题（一）


介绍:记录解题过程

1.insanity(winhex打开,搜索字符串flag)

题目描述：菜鸡觉得前面的题目太难了，来个简单的缓一下
题目场景： 暂无
题目附件： 附件1

  • 下载附件1 得到一个无后缀文件
  • 用winhex打开,搜索字符串flag
    在这里插入图片描述
  • 得到flag
9447{This_is_a_flag}

2.python-trade(反编译pyc文件,逆向加密算法)

题目描述：菜鸡和菜猫进行了一场Py交易
题目场景： 暂无
题目附件： 附件1

  • 下载附件1 得到一个pyc文件
    pyc文件反编译
    Easy Python Decompiler反编译工具,pyc文件反编译得到:
# Embedded file name: 1.py
import base64


def encode(message):
    s = ''
    for i in message:
        x = ord(i) ^ 32
        x = x + 16
        s += chr(x)

    return base64.b64encode(s)


correct = 'XlNkVmtUI1MgXWBZXCFeKY+AaXNt'
flag = ''
print('Input flag:')
flag = input()
if encode(flag) == correct:
    print('correct')
else:
    print('wrong')
  • 逆向算法得到flag:
import base64

def uncode(message):
    s = base64.b64decode(message)
    b = ''
    for x in s:
        x = x - 16
        x = x ^ 32
        b += chr(x)
    return b

correct = 'XlNkVmtUI1MgXWBZXCFeKY+AaXNt'
print('flag:', uncode(correct))

flag: nctf{d3c0mpil1n9_PyC}

3.re1(开始学习逆向工程)

题目描述：菜鸡开始学习逆向工程，首先是最简单的题目
题目场景： 暂无
题目附件： 附件1

下载附件1 得到一个exe文件

方法一:直接搜flag

  • Notepad打开直接搜flag

在这里插入图片描述

DUTCTF{We1c0met0DUTCTF}

方法二:

F5反编译

int __cdecl main(int argc, const char **argv, const char **envp)
{
  int v3; // eax
  __m128i v5; // [esp+0h] [ebp-44h] BYREF
  __int64 v6; // [esp+10h] [ebp-34h]
  int v7; // [esp+18h] [ebp-2Ch]
  __int16 v8; // [esp+1Ch] [ebp-28h]
  char v9[32]; // [esp+20h] [ebp-24h] BYREF

  v5 = _mm_loadu_si128((const __m128i *)&xmmword_413E34);
  v7 = 0;
  v6 = 0x7D465443545544i64;
  v8 = 0;
  printf("欢迎来到DUTCTF呦\n");
  printf("这是一道很可爱很简单的逆向题呦\n");
  printf("输入flag吧:");
  scanf("%s", v9);
  v3 = strcmp(v5.m128i_i8, v9);
  if ( v3 )
    v3 = v3 < 0 ? -1 : 1;
  if ( v3 )
    printf(aFlag_0);
  else
    printf(aFlagGet);
  system("pause");
  return 0;
}

由逻辑可知:
用户输入v9与v5比较,同则输出flag,所以flag在v5,跟踪v5

在这里插入图片描述

  • 发现一串十六进制字符串,按R将其转化成字符串:
0tem0c1eW{FTCTUD
}FTCTUD
  • flag出现，但要注意在x86处理器中字符是按照小端序储存的，即低位字节存入低地址，高位字节存入高地址
  • 所以正确的flag应为
DUTCTF{We1c0met0DUTCTF}

4.game

题目描述：菜鸡最近迷上了玩游戏，但它总是赢不了，你可以帮他获胜吗
题目场景： 暂无
题目附件： 附件1

  • 下载附件1 得到一个exe文件,是一个小游戏
                     |------------／ --------△--------|
                     |------------／ --------○--------|
                     |------------／ --------◇--------|
                     |------------／ --------□--------|
|--------------------|------------／ --------☆--------|
|                    |------------／ --------▽--------|
|                    |------------／ -----(￣▽￣)／---|
|                    |------------／ -----(;°Д°)----|
二                                                     |
|              by 0x61                                 |
|                                                      |
|------------------------------------------------------|
Play a game
The n is the serial number of the lamp,and m is the state of the lamp
If m of the Nth lamp is 1,it's on ,if not it's off
At first all the lights were closed
Now you can input n to change its state
But you should pay attention to one thing,if you change the state of the Nth lamp,the state of (N-1)th and (N+1)th will be changed too
When all lamps are on,flag will appear
Now,input n
input n,n(1-8)
1.△ 2.○ 3.◇ 4.□ 5.☆ 6.▽ 7.(￣▽￣)／ 8.(;°Д°) 0.restart
n=

方法一:直接通关

  • 12345678
done!!! the flag is zsctf{T9is_tOpic_1s_v5ry_int7resting_b6t_others_are_n0t}
input n,n(1-8)
1.△ 2.○ 3.◇ 4.□ 5.☆ 6.▽ 7.(￣▽￣)／ 8.(;°Д°) 0.restart
n=

方法二:逆向算法

<1>.PEiD查壳:
在这里插入图片描述

<2>.放入IDA

  • main_0:
int __cdecl main_0(int argc, const char **argv, const char **envp)
{
  char v4; // [esp+0h] [ebp-FCh]
  char v5; // [esp+0h] [ebp-FCh]
  char v6; // [esp+0h] [ebp-FCh]
  char v7; // [esp+0h] [ebp-FCh]
  char v8; // [esp+0h] [ebp-FCh]
  char v9; // [esp+0h] [ebp-FCh]
  char v10; // [esp+0h] [ebp-FCh]
  char v11; // [esp+0h] [ebp-FCh]
  char v12; // [esp+0h] [ebp-FCh]
  char v13; // [esp+0h] [ebp-FCh]
  char v14; // [esp+0h] [ebp-FCh]
  char v15; // [esp+0h] [ebp-FCh]
  char v16; // [esp+0h] [ebp-FCh]
  char v17; // [esp+0h] [ebp-FCh]
  char v18; // [esp+0h] [ebp-FCh]
  char v19; // [esp+0h] [ebp-FCh]
  char v20; // [esp+0h] [ebp-FCh]
  char v21; // [esp+0h] [ebp-FCh]
  char v22; // [esp+0h] [ebp-FCh]
  char v23; // [esp+0h] [ebp-FCh]
  int i; // [esp+DCh] [ebp-20h]
  int v25; // [esp+F4h] [ebp-8h] BYREF

  sub_45A7BE((int)&unk_50B110, v4);
  sub_45A7BE((int)&unk_50B158, v5);
  sub_45A7BE((int)&unk_50B1A0, v6);
  sub_45A7BE((int)&unk_50B1E8, v7);
  sub_45A7BE((int)&unk_50B230, v8);
  sub_45A7BE((int)&unk_50B278, v9);
  sub_45A7BE((int)&unk_50B2C0, v10);
  sub_45A7BE((int)&unk_50B308, v11);
  sub_45A7BE((int)"二                                                     |\n", v12);
  sub_45A7BE((int)"|              by 0x61                                 |\n", v13);
  sub_45A7BE((int)"|                                                      |\n", v14);
  sub_45A7BE((int)"|------------------------------------------------------|\n", v15);
  sub_45A7BE(
    (int)"Play a game\n"
         "The n is the serial number of the lamp,and m is the state of the lamp\n"
         "If m of the Nth lamp is 1,it's on ,if not it's off\n"
         "At first all the lights were closed\n",
    v16);
  sub_45A7BE((int)"Now you can input n to change its state\n", v17);
  sub_45A7BE(
    (int)"But you should pay attention to one thing,if you change the state of the Nth lamp,the state of (N-1)th and (N+1"
         ")th will be changed too\n",
    v18);
  sub_45A7BE((int)"When all lamps are on,flag will appear\n", v19);
  sub_45A7BE((int)"Now,input n \n", v20);
  while ( 1 )
  {
    while ( 1 )
    {
      sub_45A7BE((int)"input n,n(1-8)\n", v21);
      sub_459418();
      sub_45A7BE((int)"n=", v22);
      sub_4596D4("%d", &v25);
      sub_45A7BE((int)"\n", v23);
      if ( v25 >= 0 && v25 <= 8 )
        break;
      sub_45A7BE((int)"sorry,n error,try again\n", v21);
    }
    if ( v25 )
    {
      sub_4576D6(v25 - 1);
    }
    else
    {
      for ( i = 0; i < 8; ++i )
      {
        if ( (unsigned int)i >= 9 )
          j____report_rangecheckfailure();
        byte_532E28[i] = 0;
      }
    }
    j__system("CLS");
    sub_458054();
    if ( byte_532E28[0] == 1
      && byte_532E28[1] == 1
      && byte_532E28[2] == 1
      && byte_532E28[3] == 1
      && byte_532E28[4] == 1
      && byte_532E28[5] == 1
      && byte_532E28[6] == 1
      && byte_532E28[7] == 1 )
    {
      sub_457AB4();
    }
  }
}
  • 成功后会执行
sub_457AB4();
  • 跟踪:
int sub_45E940()
{
  int i; // [esp+D0h] [ebp-94h]
  char v2[22]; // [esp+DCh] [ebp-88h]
  char v3[32]; // [esp+F2h] [ebp-72h] BYREF
  char v4[4]; // [esp+112h] [ebp-52h] BYREF
  char v5[64]; // [esp+120h] [ebp-44h]

  sub_45A7BE("done!!! the flag is ");
  v5[0] = 18;
  v5[1] = 64;
  v5[2] = 98;
  v5[3] = 5;
  v5[4] = 2;
  v5[5] = 4;
  v5[6] = 6;
  v5[7] = 3;
  v5[8] = 6;
  v5[9] = 48;
  v5[10] = 49;
  v5[11] = 65;
  v5[12] = 32;
  v5[13] = 12;
  v5[14] = 48;
  v5[15] = 65;
  v5[16] = 31;
  v5[17] = 78;
  v5[18] = 62;
  v5[19] = 32;
  v5[20] = 49;
  v5[21] = 32;
  v5[22] = 1;
  v5[23] = 57;
  v5[24] = 96;
  v5[25] = 3;
  v5[26] = 21;
  v5[27] = 9;
  v5[28] = 4;
  v5[29] = 62;
  v5[30] = 3;
  v5[31] = 5;
  v5[32] = 4;
  v5[33] = 1;
  v5[34] = 2;
  v5[35] = 3;
  v5[36] = 44;
  v5[37] = 65;
  v5[38] = 78;
  v5[39] = 32;
  v5[40] = 16;
  v5[41] = 97;
  v5[42] = 54;
  v5[43] = 16;
  v5[44] = 44;
  v5[45] = 52;
  v5[46] = 32;
  v5[47] = 64;
  v5[48] = 89;
  v5[49] = 45;
  v5[50] = 32;
  v5[51] = 65;
  v5[52] = 15;
  v5[53] = 34;
  v5[54] = 18;
  v5[55] = 16;
  v5[56] = 0;
  v2[0] = 123;
  v2[1] = 32;
  v2[2] = 18;
  v2[3] = 98;
  v2[4] = 119;
  v2[5] = 108;
  v2[6] = 65;
  v2[7] = 41;
  v2[8] = 124;
  v2[9] = 80;
  v2[10] = 125;
  v2[11] = 38;
  v2[12] = 124;
  v2[13] = 111;
  v2[14] = 74;
  v2[15] = 49;
  v2[16] = 83;
  v2[17] = 108;
  v2[18] = 94;
  v2[19] = 108;
  v2[20] = 84;
  v2[21] = 6;
  qmemcpy(v3, "`S,yhn _uec{", 12);
  v3[12] = 127;
  v3[13] = 119;
  v3[14] = 96;
  v3[15] = 48;
  v3[16] = 107;
  v3[17] = 71;
  v3[18] = 92;
  v3[19] = 29;
  v3[20] = 81;
  v3[21] = 107;
  v3[22] = 90;
  v3[23] = 85;
  v3[24] = 64;
  v3[25] = 12;
  v3[26] = 43;
  v3[27] = 76;
  v3[28] = 86;
  v3[29] = 13;
  v3[30] = 114;
  v3[31] = 1;
  strcpy(v4, "u~");
  for ( i = 0; i < 56; ++i )
  {
    v2[i] ^= v5[i];
    v2[i] ^= 0x13u;
  }
  return sub_45A7BE("%s\n");
}
  • 修改代码输出flag:
zsctf{T9is_tOpic_1s_v5ry_int7resting_b6t_others_are_n0t}

方法三:修改程序逻辑:

  • 修改前:
if ( byte_532E28[0] == 1
      && byte_532E28[1] == 1
      && byte_532E28[2] == 1
      && byte_532E28[3] == 1
      && byte_532E28[4] == 1
      && byte_532E28[5] == 1
      && byte_532E28[6] == 1
      && byte_532E28[7] == 1 )

在这里插入图片描述

  • jnz的机器码为75，只需将其改为jz的机器码74。修改方法：Edit/Patch program/Change byte(jnz->jz)
    在这里插入图片描述

  • 修改后:

if ( byte_532E28[0] == 1
      && byte_532E28[1] == 1
      && byte_532E28[2] == 1
      && byte_532E28[3] != 1
      && byte_532E28[4] != 1
      && byte_532E28[5] != 1
      && byte_532E28[6] != 1
      && byte_532E28[7] != 1 )
  • 修改完后Edit/Patch program/Apply patches to input file保存修改后的文件，运行输个2得到flag:
done!!! the flag is zsctf{T9is_tOpic_1s_v5ry_int7resting_b6t_others_are_n0t}

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