BUUCTF reverse wp 65

[SWPU2019]ReverseMe

在这里插入图片描述

反编译的伪码看不明白, 直接动调
在这里插入图片描述

这里显示"Please input your flag", 然后接受输入, 再和32进行比较, 应该是flag长度要求32位, 符合要求则跳转到loc_E528EE分支继续执行

动调之后伪码可以读了

int __cdecl main(int argc, const char **argv, const char **envp)
{
  int v3; // ecx
  int *v4; // eax
  int v5; // ecx
  int *v6; // eax
  char *v7; // esi
  int i; // edi
  unsigned int xor_len; // kr00_4
  void **v10; // ecx
  __int128 *v11; // ecx
  char *checkval; // ecx
  __int128 *buf; // edx
  unsigned int v14; // edi
  int checkarr; // eax
  int v16; // eax
  bool v17; // cf
  unsigned __int8 v18; // al
  unsigned __int8 v19; // al
  unsigned __int8 v20; // al
  const char *output; // edx
  int *v22; // eax
  char *v23; // eax
  int v25; // [esp-14h] [ebp-D8h]
  int v26; // [esp-10h] [ebp-D4h]
  void *input[4]; // [esp+24h] [ebp-A0h] BYREF
  int length; // [esp+34h] [ebp-90h]
  unsigned int v29; // [esp+38h] [ebp-8Ch]
  __int128 processed[2]; // [esp+3Ch] [ebp-88h] BYREF
  int v31; // [esp+5Ch] [ebp-68h]
  __int128 v32; // [esp+60h] [ebp-64h] BYREF
  __int128 v33; // [esp+70h] [ebp-54h]
  int v34; // [esp+80h] [ebp-44h]
  char xorval[16]; // [esp+84h] [ebp-40h] BYREF
  char v36[32]; // [esp+94h] [ebp-30h] BYREF
  int v37; // [esp+C0h] [ebp-4h]

  length = 0;
  v29 = 15;
  LOBYTE(input[0]) = 0;
  v37 = 1;
  v4 = sub_E52DA0(v3, "Please input your flag: ");
  sub_E53050(v4);
  sub_E537B0((int)&dword_E80068, input);
  strcpy(xorval, "SWPU_2019_CTF");
  if ( length == 32 )
  {
    *(_DWORD *)&v36[16] = -1173078761;
    *(_DWORD *)&v36[20] = 494076752;
    *(_DWORD *)&v36[24] = -1811652486;
    *(_DWORD *)&v36[28] = 688582768;
    i = 0;
    v32 = 0i64;
    v34 = 0;
    v33 = 0i64;
    xor_len = strlen(xorval);
    do                                          // xor
    {
      v10 = input;
      if ( v29 >= 0x10 )
        v10 = (void **)input[0];
      *((_BYTE *)v10 + i) ^= xorval[i % xor_len];
      ++i;
    }
    while ( i < 32 );
    v11 = (__int128 *)input;
    v7 = (char *)input[0];
    if ( v29 >= 0x10 )
      v11 = (__int128 *)input[0];
    v31 = 0;
    memset(processed, 0, sizeof(processed));
    v32 = *v11;
    v33 = v11[1];
    sub_E525C0(v25, v26, 256, (unsigned int)&v32, (unsigned int)processed);// ?
    *(_DWORD *)v36 = 4161746867;
    *(_DWORD *)&v36[4] = 1571732668;
    checkval = v36;
    *(_DWORD *)&v36[8] = -2041750854;
    buf = processed;
    *(_DWORD *)&v36[12] = -748513468;
    v14 = 28;
    *(_DWORD *)&v36[16] = 371505743;
    *(_DWORD *)&v36[20] = 443719435;
    *(_DWORD *)&v36[24] = 644704357;
    *(_DWORD *)&v36[28] = 1741188026;
    while ( 1 )
    {
      checkarr = *(_DWORD *)checkval;
      if ( *(_DWORD *)checkval != *(_DWORD *)buf )
        break;
      checkval += 4;
      buf = (__int128 *)((char *)buf + 4);
      v17 = v14 < 4;
      v14 -= 4;
      if ( v17 )
      {
        v16 = 0;
        goto LABEL_19;
      }
    }
    v17 = (unsigned __int8)checkarr < *(_BYTE *)buf;// v15 < v13
    if ( (_BYTE)checkarr == *(_BYTE *)buf
      && (v18 = checkval[1], v17 = v18 < *((_BYTE *)buf + 1), v18 == *((_BYTE *)buf + 1))
      && (v19 = checkval[2], v17 = v19 < *((_BYTE *)buf + 2), v19 == *((_BYTE *)buf + 2))
      && (v20 = checkval[3], v17 = v20 < *((_BYTE *)buf + 3), v20 == *((_BYTE *)buf + 3)) )
    {
      v16 = 0;
    }
    else
    {
      v16 = v17 ? -1 : 1;                       // v17 should be True
    }
LABEL_19:
    if ( v16 )                                  // v16 should be 0
      output = "Try again!\r\n";
    else
      output = "Congratulations! I always knew you could do it.";
    v22 = sub_E52DA0((int)checkval, output);
    sub_E53050(v22);
    sub_E5ADBE("pause");
  }
  else
  {
    v6 = sub_E52DA0(v5, "Try again!\r\n");
    sub_E53050(v6);
    sub_E5ADBE("pause");
    v7 = (char *)input[0];
  }
  if ( v29 >= 0x10 )
  {
    v23 = v7;
    if ( v29 + 1 >= 0x1000 )
    {
      v7 = (char *)*((_DWORD *)v7 - 1);
      if ( (unsigned int)(v23 - v7 - 4) > 0x1F )
        _invalid_parameter_noinfo_noreturn();
    }
    sub_E564DE(v7);
  }
  return 0;
}

checkval可以直接动调出来, 和input处理过后的值进行比较, 全部通过就是congratulation, 需要逆sub_E525C0这个函数, 动调一下猜测是某种加密函数, Findcrypt一下没有明确结果, 继续读一下伪码

void __cdecl sub_E525C0(int a1, int a2, int a3, unsigned int input, unsigned int processed)
{
  unsigned __int8 *v5; // ecx
  unsigned int process_tmp; // ebx
  unsigned __int8 *v7; // esi
  unsigned int v8; // edi
  unsigned int v9; // esi
  unsigned int v10; // edx
  unsigned int v11; // esi
  _DWORD *v12; // ecx
  int v13; // eax
  unsigned int v14; // ebx
  char *v15; // esi
  __m128i v16; // xmm0
  __m128i v17; // xmm1
  __m128i v18; // xmm0
  __m128i v19; // xmm1
  __m128i v20; // xmm0
  __m128i v21; // xmm1
  __m128i v22; // xmm0
  __m128i v23; // xmm1
  int v24; // ebx
  unsigned int v25; // eax
  char *v26; // esi
  unsigned int v27; // edi
  int v28; // ecx
  signed int v29; // [esp+20h] [ebp-20h]
  int v30; // [esp+24h] [ebp-1Ch]
  _DWORD *Block; // [esp+28h] [ebp-18h]
  int v32[4]; // [esp+2Ch] [ebp-14h] BYREF

  process_tmp = processed;
  v7 = v5;
  v8 = (unsigned int)(a3 + 31) >> 5;
  v30 = 4 * v8;
  Block = malloc(4 * v8);
  v32[0] = -1839987866;
  v32[1] = 120;
  v32[2] = -1839987866;
  v32[3] = 120;
  sub_E52270(v7, (unsigned __int8 *)v32);
  sub_E520E0();
  sub_E52150();
  sub_E51F80();
  v29 = 0;
  if ( v8 )
  {
    do
    {
      dword_E80D94 = (2 * dword_E80DA4) ^ (unsigned __int16)(dword_E80DBC ^ (2 * dword_E80DA4));
      dword_E80D78 = (dword_E80DB8 << 16) | ((unsigned int)dword_E80DAC >> 15);
      v9 = (dword_E80D70 << 16) | ((unsigned int)dword_E80D90 >> 15);
      dword_E80D8C = (dword_E80D68 << 16) | ((unsigned int)dword_E80D84 >> 15);
      dword_E80D7C = v9;
      Block[v29] = v9 ^ sub_E52150();
      sub_E51F80();
      ++v29;
    }
    while ( v29 < (int)v8 );
    process_tmp = processed;
  }
  v10 = 0;
  if ( v8 )
  {
    v11 = input;
    if ( v8 < 0x10 || process_tmp <= input + v30 - 4 && process_tmp + v30 - 4 >= input )
    {
      v12 = Block;
    }
    else
    {
      v12 = Block;
      if ( process_tmp > (unsigned int)&Block[v8 - 1] || process_tmp + v30 - 4 < (unsigned int)Block )
      {
        v13 = input + 16;
        v12 = Block;
        v14 = process_tmp + 32;
        v15 = (char *)Block - input;
        do
        {
          v16 = *(__m128i *)(v13 - 16);
          v13 += 64;
          v14 += 64;
          v17 = _mm_xor_si128(*(__m128i *)&Block[v10], v16);
          v18 = *(__m128i *)(v13 - 64);
          *(__m128i *)(v14 - 96) = v17;
          v19 = _mm_xor_si128(*(__m128i *)&v15[v13 - 64], v18);
          v20 = *(__m128i *)(v13 - 48);
          *(__m128i *)(processed - input + v13 - 64) = v19;
          v15 = (char *)Block - input;
          v21 = _mm_xor_si128(*(__m128i *)((char *)Block + v14 - processed - 64), v20);
          v22 = *(__m128i *)(v13 - 32);
          *(__m128i *)(v14 - 64) = v21;
          v23 = *(__m128i *)&Block[v10 + 12];
          v10 += 16;
          *(__m128i *)(v14 - 48) = _mm_xor_si128(v23, v22);
        }
        while ( v10 < (v8 & 0xFFFFFFF0) );
        process_tmp = processed;
        v11 = input;
      }
    }
    if ( v10 < v8 )
    {
      v24 = process_tmp - input;
      v25 = v11 + 4 * v10;
      v26 = (char *)v12 - input;
      v27 = v8 - v10;
      do
      {
        v28 = *(_DWORD *)&v26[v25];
        v25 += 4;
        *(_DWORD *)(v24 + v25 - 4) = *(_DWORD *)(v25 - 4) ^ v28;
        --v27;
      }
      while ( v27 );
    }
  }
  free(Block);
}

发现processed在前面一大段操作里并没有作为左值进行, 只有最后一段进行了相关的赋值操作, 所以processed的值只在这一段指令之后确定

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伪码不清不楚, 直接读汇编, 结合动调的数值进行对比, 得知[esi + eax]存的就是与input处理之后数值xor的数组
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shift+E导出, 两次xor处理, 逆回去就是flag

xorval = 'SWPU_2019_CTF'

checkval = [
    0xB3, 0x37, 0x0F, 0xF8, 0xBC, 0xBC, 0xAE, 0x5D, 0xBA, 0x5A, 
    0x4D, 0x86, 0x44, 0x97, 0x62, 0xD3, 0x4F, 0xBA, 0x24, 0x16, 
    0x0B, 0x9F, 0x72, 0x1A, 0x65, 0x68, 0x6D, 0x26, 0xBA, 0x6B, 
    0xC8, 0x67
]
# print(len(xorval))

process = [
    0x86, 0x0C, 0x3E, 0xCA, 0x98, 0xD7, 0xAE, 0x19, 0xE2, 0x77, 
    0x6B, 0xA6, 0x6A, 0xA1, 0x77, 0xB0, 0x69, 0x91, 0x37, 0x05, 
    0x7A, 0xF9, 0x7B, 0x30, 0x43, 0x5A, 0x4B, 0x10, 0x86, 0x7D, 
    0xD4, 0x28
]

tmp = [0 for _ in range(32)]
for i in range(32):
    tmp[i] = process[i] ^ checkval[i]

for i in range(32):
    tmp[i] ^= ord(xorval[i % len(xorval)])
    tmp[i] = chr(tmp[i])

flag = ''.join(tmp)
print(flag)

[羊城杯 2020]login

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pyinstaller, 解包工具 https://github.com/extremecoders-re/pyinstxtractor

>python pyinstxtractor.py attachment.exe
[+] Processing attachment.exe
[+] Pyinstaller version: 2.1+
[+] Python version: 3.6
[+] Length of package: 6021662 bytes
[+] Found 59 files in CArchive
[+] Beginning extraction...please standby
[+] Possible entry point: pyiboot01_bootstrap.pyc
[+] Possible entry point: login.pyc
[!] Warning: This script is running in a different Python version than the one used to build the executable.
[!] Please run this script in Python 3.6 to prevent extraction errors during unmarshalling
[!] Skipping pyz extraction
[+] Successfully extracted pyinstaller archive: attachment.exe

You can now use a python decompiler on the pyc files within the extracted directory

用uncompyle6进行反编译, 拿到源码

# uncompyle6 version 3.9.0
# Python bytecode version base 3.6 (3379)
# Decompiled from: Python 3.6.13 |Anaconda, Inc.| (default, Mar 16 2021, 11:37:27) [MSC v.1916 64 bit (AMD64)]
# Embedded file name: login.py
import sys
input1 = input('input something:')
if len(input1) != 14:
    print('Wrong length!')
    sys.exit()
else:
    code = []
    for i in range(13):
        code.append(ord(input1[i]) ^ ord(input1[i + 1]))

    code.append(ord(input1[13]))
    a1 = code[2]
    a2 = code[1]
    a3 = code[0]
    a4 = code[3]
    a5 = code[4]
    a6 = code[5]
    a7 = code[6]
    a8 = code[7]
    a9 = code[9]
    a10 = code[8]
    a11 = code[10]
    a12 = code[11]
    a13 = code[12]
    a14 = code[13]
    if (a1 * 88 + a2 * 67 + a3 * 65 - a4 * 5 + a5 * 43 + a6 * 89 + a7 * 25 + a8 * 13 - a9 * 36 + a10 * 15 + a11 * 11 + a12 * 47 - a13 * 60 + a14 * 29 == 22748) & \
    (a1 * 89 + a2 * 7 + a3 * 12 - a4 * 25 + a5 * 41 + a6 * 23 + a7 * 20 - a8 * 66 + a9 * 31 + a10 * 8 + a11 * 2 - a12 * 41 - a13 * 39 + a14 * 17 == 7258) & \
    (a1 * 28 + a2 * 35 + a3 * 16 - a4 * 65 + a5 * 53 + a6 * 39 + a7 * 27 + a8 * 15 - a9 * 33 + a10 * 13 + a11 * 101 + a12 * 90 - a13 * 34 + a14 * 23 == 26190) & \
    (a1 * 23 + a2 * 34 + a3 * 35 - a4 * 59 + a5 * 49 + a6 * 81 + a7 * 25 + (a8 << 7) - a9 * 32 + a10 * 75 + a11 * 81 + a12 * 47 - a13 * 60 + a14 * 29 == 37136) & \
    (a1 * 38 + a2 * 97 + a3 * 35 - a4 * 52 + a5 * 42 + a6 * 79 + a7 * 90 + a8 * 23 - a9 * 36 + a10 * 57 + a11 * 81 + a12 * 42 - a13 * 62 - a14 * 11 == 27915) & \
    (a1 * 22 + a2 * 27 + a3 * 35 - a4 * 45 + a5 * 47 + a6 * 49 + a7 * 29 + a8 * 18 - a9 * 26 + a10 * 35 + a11 * 41 + a12 * 40 - a13 * 61 + a14 * 28 == 17298) & \
    (a1 * 12 + a2 * 45 + a3 * 35 - a4 * 9 - a5 * 42 + a6 * 86 + a7 * 23 + a8 * 85 - a9 * 47 + a10 * 34 + a11 * 76 + a12 * 43 - a13 * 44 + a14 * 65 == 19875) & \
    (a1 * 79 + a2 * 62 + a3 * 35 - a4 * 85 + a5 * 33 + a6 * 79 + a7 * 86 + a8 * 14 - a9 * 30 + a10 * 25 + a11 * 11 + a12 * 57 - a13 * 50 - a14 * 9 == 22784) & \
    (a1 * 8 + a2 * 6 + a3 * 64 - a4 * 85 + a5 * 73 + a6 * 29 + a7 * 2 + a8 * 23 - a9 * 36 + a10 * 5 + a11 * 2 + a12 * 47 - a13 * 64 + a14 * 27 == 9710) & \
    (a1 * 67 - a2 * 68 + a3 * 68 - a4 * 51 - a5 * 43 + a6 * 81 + a7 * 22 - a8 * 12 - a9 * 38 + a10 * 75 + a11 * 41 + a12 * 27 - a13 * 52 + a14 * 31 == 13376) & \
    (a1 * 85 + a2 * 63 + a3 * 5 - a4 * 51 + a5 * 44 + a6 * 36 + a7 * 28 + a8 * 15 - a9 * 6 + a10 * 45 + a11 * 31 + a12 * 7 - a13 * 67 + a14 * 78 == 24065) & \
    (a1 * 47 + a2 * 64 + a3 * 66 - a4 * 5 + a5 * 43 + a6 * 112 + a7 * 25 + a8 * 13 - a9 * 35 + a10 * 95 + a11 * 21 + a12 * 43 - a13 * 61 + a14 * 20 == 27687) & \
    (a1 * 89 + a2 * 67 + a3 * 85 - a4 * 25 + a5 * 49 + a6 * 89 + a7 * 23 + a8 * 56 - a9 * 92 + a10 * 14 + a11 * 89 + a12 * 47 - a13 * 61 - a14 * 29 == 29250) & \
    (a1 * 95 + a2 * 34 + a3 * 62 - a4 * 9 - a5 * 43 + a6 * 83 + a7 * 25 + a8 * 12 - a9 * 36 + a10 * 16 + a11 * 51 + a12 * 47 - a13 * 60 - a14 * 24 == 15317):
        print('flag is GWHT{md5(your_input)}')
        print('Congratulations and have fun!')
    else:
        print('Sorry,plz try again...')
# okay decompiling login.pyc

z3解方程组

from z3 import *


a1 = Int('a1')
a2 = Int('a2')
a3 = Int('a3')
a4 = Int('a4')
a5 = Int('a5')
a6 = Int('a6')
a7 = Int('a7')
a8 = Int('a8')
a9 = Int('a9')
a10 = Int('a10')
a11 = Int('a11')
a12 = Int('a12')
a13 = Int('a13')
a14 = Int('a14')

solver = Solver()
solver.add(a1 * 88 + a2 * 67 + a3 * 65 - a4 * 5 + a5 * 43 + a6 * 89 + a7 * 25 + a8 * 13 - a9 * 36 + a10 * 15 + a11 * 11 + a12 * 47 - a13 * 60 + a14 * 29 == 22748)
solver.add(a1 * 89 + a2 * 7 + a3 * 12 - a4 * 25 + a5 * 41 + a6 * 23 + a7 * 20 - a8 * 66 + a9 * 31 + a10 * 8 + a11 * 2 - a12 * 41 - a13 * 39 + a14 * 17 == 7258)
solver.add(a1 * 28 + a2 * 35 + a3 * 16 - a4 * 65 + a5 * 53 + a6 * 39 + a7 * 27 + a8 * 15 - a9 * 33 + a10 * 13 + a11 * 101 + a12 * 90 - a13 * 34 + a14 * 23 == 26190)
solver.add(a1 * 23 + a2 * 34 + a3 * 35 - a4 * 59 + a5 * 49 + a6 * 81 + a7 * 25 + a8 * 128 - a9 * 32 + a10 * 75 + a11 * 81 + a12 * 47 - a13 * 60 + a14 * 29 == 37136)
solver.add(a1 * 38 + a2 * 97 + a3 * 35 - a4 * 52 + a5 * 42 + a6 * 79 + a7 * 90 + a8 * 23 - a9 * 36 + a10 * 57 + a11 * 81 + a12 * 42 - a13 * 62 - a14 * 11 == 27915)
solver.add(a1 * 22 + a2 * 27 + a3 * 35 - a4 * 45 + a5 * 47 + a6 * 49 + a7 * 29 + a8 * 18 - a9 * 26 + a10 * 35 + a11 * 41 + a12 * 40 - a13 * 61 + a14 * 28 == 17298)
solver.add(a1 * 12 + a2 * 45 + a3 * 35 - a4 * 9 - a5 * 42 + a6 * 86 + a7 * 23 + a8 * 85 - a9 * 47 + a10 * 34 + a11 * 76 + a12 * 43 - a13 * 44 + a14 * 65 == 19875)
solver.add(a1 * 79 + a2 * 62 + a3 * 35 - a4 * 85 + a5 * 33 + a6 * 79 + a7 * 86 + a8 * 14 - a9 * 30 + a10 * 25 + a11 * 11 + a12 * 57 - a13 * 50 - a14 * 9 == 22784)
solver.add(a1 * 8 + a2 * 6 + a3 * 64 - a4 * 85 + a5 * 73 + a6 * 29 + a7 * 2 + a8 * 23 - a9 * 36 + a10 * 5 + a11 * 2 + a12 * 47 - a13 * 64 + a14 * 27 == 9710)
solver.add(a1 * 67 - a2 * 68 + a3 * 68 - a4 * 51 - a5 * 43 + a6 * 81 + a7 * 22 - a8 * 12 - a9 * 38 + a10 * 75 + a11 * 41 + a12 * 27 - a13 * 52 + a14 * 31 == 13376)
solver.add(a1 * 85 + a2 * 63 + a3 * 5 - a4 * 51 + a5 * 44 + a6 * 36 + a7 * 28 + a8 * 15 - a9 * 6 + a10 * 45 + a11 * 31 + a12 * 7 - a13 * 67 + a14 * 78 == 24065)
solver.add(a1 * 47 + a2 * 64 + a3 * 66 - a4 * 5 + a5 * 43 + a6 * 112 + a7 * 25 + a8 * 13 - a9 * 35 + a10 * 95 + a11 * 21 + a12 * 43 - a13 * 61 + a14 * 20 == 27687)
solver.add(a1 * 89 + a2 * 67 + a3 * 85 - a4 * 25 + a5 * 49 + a6 * 89 + a7 * 23 + a8 * 56 - a9 * 92 + a10 * 14 + a11 * 89 + a12 * 47 - a13 * 61 - a14 * 29 == 29250)
solver.add(a1 * 95 + a2 * 34 + a3 * 62 - a4 * 9 - a5 * 43 + a6 * 83 + a7 * 25 + a8 * 12 - a9 * 36 + a10 * 16 + a11 * 51 + a12 * 47 - a13 * 60 - a14 * 24 == 15317)

if solver.check():
    model = solver.model()
    print(model)

'''
[a13 = 88,
 a3 = 10,
 a4 = 7,
 a10 = 108,
 a12 = 74,
 a1 = 119,
 a7 = 28,
 a6 = 43,
 a9 = 52,
 a14 = 33,
 a5 = 104,
 a8 = 91,
 a2 = 24,
 a11 = 88]
'''

提取置换表, 然后xor逆回去

'''
[a13 = 88,
 a3 = 10,
 a4 = 7,
 a10 = 108,
 a12 = 74,
 a1 = 119,
 a7 = 28,
 a6 = 43,
 a9 = 52,
 a14 = 33,
 a5 = 104,
 a8 = 91,
 a2 = 24,
 a11 = 88]

a1 = code[2]
a2 = code[1]
a3 = code[0]
a4 = code[3]
a5 = code[4]
a6 = code[5]
a7 = code[6]
a8 = code[7]
a9 = code[9]
a10 = code[8]
a11 = code[10]
a12 = code[11]
a13 = code[12]
a14 = code[13]
'''

flag = [0 for _ in range(14)]

table = [2, 1, 0, 3, 4, 5, 6, 7, 9, 8, 10, 11, 12, 13]
sols = [119, 24, 10, 7, 104, 43, 28, 91, 52, 108, 88, 74, 88, 33]
table_sols = [0 for _ in range(14)]

for i in range(14):
    table_sols[i] = sols[table[i]]

flag[13] =  table_sols[13]
for i in range(12, -1, -1):
    flag[i] = table_sols[i] ^ flag[i + 1]

for i in range(14):
    flag[i] = chr(flag[i])

flag = ''.join(flag)
print(flag)

[QCTF2018]Xman-babymips

在这里插入图片描述

注意python进行移位操作, 需要& 0xff确保不溢出

checklist = [
   82, 253,  22, 164, 137, 189, 146, 128,  19,  65, 
   84, 160, 141,  69,  24, 129, 222, 252, 149, 240, 
   22, 121,  26,  21,  91, 117,  31,   0
]

checkfirst = [81, 124, 106, 123, 103]

flag = ''

# first 5 bytes
for i in range(len(checkfirst)):
    flag += chr(checkfirst[i] ^ (32 - i))

# last bytes
for i in range(5, 32):
    checkval = checklist[i - 5]
    for j in range(128):
        tmp = j
        if i % 2 == 1: # odd
            v1 = ((tmp >> 2) & 0xff) | ((tmp << 6) & 0xff)
        else: # even
            v1 = ((tmp << 2) & 0xff) | ((tmp >> 6) & 0xff)
        
        if v1 == checkval:
            tmp ^= 32 - i
            flag += chr(tmp)
            print(i, chr(j))
            break

print(flag)

[UTCTF2020]babymips

在这里插入图片描述

int __cdecl main(int argc, const char **argv, const char **envp)
{
  int v3; // $v0
  char input[24]; // [sp+18h] [+18h] BYREF
  char flag[24]; // [sp+30h] [+30h] BYREF
  char checklist[84]; // [sp+48h] [+48h] BYREF

  std::string::basic_string(input, argv, envp);
  v3 = std::operator<<<std::char_traits<char>>(&std::cout, "enter the flag");
  std::ostream::operator<<(v3, &std::endl<char,std::char_traits<char>>);
  std::operator>><char>(&std::cin, input);
  memcpy(checklist, &checkval, sizeof(checklist));
  std::string::basic_string(flag, input);
  check((int)checklist, (int)flag);
  std::string::~string(flag);
  std::string::~string(input);
  return 0;
}

int __fastcall check(int checklist, int flag)
{
  int v2; // $v0
  int v4; // $v0
  unsigned int i; // [sp+1Ch] [+1Ch]

  if ( std::string::size(flag) != 78 )
  {
LABEL_2:                                        // wrong
    v2 = std::operator<<<std::char_traits<char>>(&std::cout, "incorrect");
    return std::ostream::operator<<(v2, &std::endl<char,std::char_traits<char>>);
  }
  else
  {
    for ( i = 0; i < std::string::size(flag); ++i )
    {
      if ( (*(char *)std::string::operator[](flag, i) ^ (i + 23)) != *(char *)(checklist + i) )
        goto LABEL_2;
    }                                           // correct
    v4 = std::operator<<<std::char_traits<char>>(&std::cout, "correct!");
    return std::ostream::operator<<(v4, &std::endl<char,std::char_traits<char>>);
  }
}

checklist = [
   98, 108, 127, 118, 122, 123, 102, 115, 118,  80, 
   82, 125,  64,  84,  85, 121,  64,  73,  71,  77, 
  116,  25, 123, 106,  66,  10,  79,  82, 125, 105, 
   79,  83,  12, 100,  16,  15,  30,  74, 103,   3, 
  124, 103,   2, 106,  49, 103,  97,  55, 122,  98, 
   44,  44,  15, 110,  23,   0,  22,  15,  22,  10, 
  109,  98, 115,  37,  57, 118,  46,  28,  99, 120, 
   43, 116,  50,  22,  32,  34,  68,  25,   0,  
]

flag = ''

for i in range(len(checklist) - 1):
    flag += chr(checklist[i] ^ (23 + i))

print(flag)

[GKCTF 2021]QQQQT

在这里插入图片描述

搜一下Enigma VB, 找到一个现有的解包工具 https://www.52pojie.cn/thread-1575691-1-1.html

shift+F12 没有明显的字符串, 那就一个个函数看(只需要考虑用户代码, 忽略框架代码), 找到可能的关键逻辑, 注释在伪码中

void __thiscall sub_4012F0(_DWORD *this)
{
  int v1; // edi
  _BYTE *v2; // esi
  const char *v3; // edx
  _BYTE *v4; // esi
  int v5; // ecx
  int v6; // eax
  int v7; // ecx
  int v8; // edx
  int v9; // edi
  int v10; // esi
  _BYTE *v11; // ecx
  unsigned int len_input; // ecx
  size_t v13; // [esp-8h] [ebp-A8h]
  char v15[4]; // [esp+10h] [ebp-90h] BYREF
  char v16[4]; // [esp+14h] [ebp-8Ch] BYREF
  _BYTE *v17; // [esp+18h] [ebp-88h]
  const char *input; // [esp+1Ch] [ebp-84h]
  int v19; // [esp+20h] [ebp-80h]
  int v20; // [esp+24h] [ebp-7Ch] BYREF
  _BYTE *v21; // [esp+28h] [ebp-78h] BYREF
  char v22[60]; // [esp+2Ch] [ebp-74h] BYREF
  __int128 v23[2]; // [esp+68h] [ebp-38h] BYREF
  __int64 v24; // [esp+88h] [ebp-18h]
  int v25; // [esp+9Ch] [ebp-4h]

  QLineEdit::text(*(_DWORD *)(this[6] + 4), v15);// input
  v25 = 0;
  QString::toLatin1(v15, v16);
  LOBYTE(v25) = 1;
  input = QByteArray::data((QByteArray *)v16);  // input processed
  memset(v23, 0, sizeof(v23));
  v24 = 0i64;
  strcpy(v22, "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz");// 58 chars guess it as base58
  v20 = 138 * strlen(input) / 0x64;
  v13 = v20 + 1;
  v1 = 0;
  v21 = malloc(v20 + 1);
  v2 = v21;
  memset(v21, 0, v13);
  v3 = input;
  v19 = (int)(input + 1);
  if ( strlen(input) )
  {
    v4 = &v2[v20];
    v17 = v4;
    while ( 1 )
    {
      v19 = ((char)*v4 << 8) + v3[v1];
      v5 = v19 / 58;
      *v4 = v19 % 58;
      if ( v5 )
      {
        do
        {
          v6 = (char)*--v4;
          v7 = (v6 << 8) + v5;
          v19 = v7 / 58;
          *v4 = v7 % 58;                        // / and % 58 
          v5 = v19;
        }
        while ( v19 );
        v4 = v17;
      }
      if ( ++v1 >= strlen(input) )
        break;
      v3 = input;
    }
    v2 = v21;
  }
  v8 = 0;
  if ( !*v2 )
  {
    do
      ++v8;
    while ( !v2[v8] );
  }
  v9 = v20;
  if ( v8 <= v20 )
  {
    v10 = v2 - (_BYTE *)v23;
    do
    {
      v11 = (char *)v23 + v8++;
      *v11 = v22[(char)v11[v10]];
    }
    while ( v8 <= v9 );
  }
  if ( !qstrcmp((const char *)v23, "56fkoP8KhwCf3v7CEz") )// check
  {
    if ( input )
      len_input = strlen(input);
    else
      len_input = -1;
    v21 = (_BYTE *)QString::fromAscii_helper(input, len_input);
    LOBYTE(v25) = 2;
    v20 = QString::fromAscii_helper("flag", 4);
    LOBYTE(v25) = 3;
    QMessageBox::warning(this, &v20, &v21, 1024, 0);// print flag
    QString::~QString((QString *)&v20);
    QString::~QString((QString *)&v21);
  }
  QByteArray::~QByteArray((QByteArray *)v16);
  QString::~QString((QString *)v15);
}