BUUCTF Reverse/[GWCTF 2019]re3

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main函数代码，这里改写了内存空间的属性，还是自解密

void __fastcall __noreturn main(int a1, char **a2, char **a3)
{
  int i; // [rsp+8h] [rbp-48h]
  char s[40]; // [rsp+20h] [rbp-30h] BYREF
  unsigned __int64 v5; // [rsp+48h] [rbp-8h]

  v5 = __readfsqword(0x28u);
  __isoc99_scanf("%39s", s);
  if ( (unsigned int)strlen(s) != 32 )
  {
    puts("Wrong!");
    exit(0);
  }
  mprotect(&dword_400000, 0xF000uLL, 7);
  for ( i = 0; i <= 223; ++i )
    *((_BYTE *)sub_402219 + i) ^= 0x99u;
  sub_40207B(&unk_603170);
  sub_402219(s);
}

这里一坨数字，盲猜这里就是自解密的地方

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整个idc脚本，运行完后选中这段数字，按c强制转换为代码，再将所有标红的部分选中按p，就能正常f5了

#include <idc.idc>

static main()
{
    auto addr = 0x0040221A;   //这里填入要解密字节串的起始地址
    auto i = 0;
    for(i=0;i<=223;i++)   //循环结束的条件为字节串的结束地址
    {
        PatchByte(addr+i,Byte(addr+i)^0x99);   //异或的数字根据情况修改
    }
}

反汇编出的伪代码

__int64 __fastcall sub_40221A(__int64 a1)
{
  unsigned int v2; // [rsp+18h] [rbp-D8h]
  int i; // [rsp+1Ch] [rbp-D4h]
  char v4[200]; // [rsp+20h] [rbp-D0h] BYREF
  unsigned __int64 v5; // [rsp+E8h] [rbp-8h]

  v5 = __readfsqword(0x28u);
  sub_400A71(v4, &unk_603170);
  sub_40196E(v4, a1);
  sub_40196E(v4, a1 + 16);
  v2 = 1;
  for ( i = 0; i <= 31; ++i )
  {
    if ( *(_BYTE *)(i + a1) != byte_6030A0[i] )
      v2 = 0;
  }
  return v2;
}

明显byte_6030A0中就是最后变换的flag，可以shift+e提取出来

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看了下sub_40196E(v4, a1); 中的加密算法，有点复杂不太想看，还是直接动调吧

__int64 __fastcall sub_401828(__int64 a1, __int64 flag)
{
  unsigned __int8 i; // [rsp+1Fh] [rbp-1h]

  sub_400B0A(0LL, a1, flag);
  for ( i = 1; i <= 9u; ++i )
  {
    sub_400BAC(a1);
    sub_400C1F(a1);
    sub_400D27(a1);
    sub_400B0A(i, a1, flag);
  }
  sub_400BAC(a1);
  sub_400C1F(a1);
  return sub_400B0A(10LL, a1, flag);
}

方法参考：IDA动调ELF文件， IDA远程动态调试(linux & Windows)

添加权限

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看下当前路径

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填写对应信息

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开始dbg，下断点输入32位字符

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跟进 sub_401828,这里我把变量名改了下，方便看

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这里就对flag进行了一波变换

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看汇编代码，edi中存的就是输入flag的值，eax中存储的就是上面代码异或的值，打个断点，依次将eax的值记录下来

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查看v4的值

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直接跳转

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因为v4 的大小最大为200，就将7FFEA43B22E0到00007FFEA43B238A的数据提取出来

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还是得写脚本来逆。。。

试了下把 sub_40196E() 逆出来，，

from z3 import *
import numpy as np
v4 = [
  0xCB, 0x8D, 0x49, 0x35, 0x21, 0xB4, 0x7A, 0x4C, 0xC1, 0xAE, 
  0x7E, 0x62, 0x22, 0x92, 0x66, 0xCE, 0x85, 0xBE, 0xC2, 0xA6, 
  0xA4, 0x0A, 0xB8, 0xEA, 0x65, 0xA4, 0xC6, 0x88, 0x47, 0x36, 
  0xA0, 0x46, 0x82, 0x5E, 0x98, 0x06, 0x26, 0x54, 0x20, 0xEC, 
  0x43, 0xF0, 0xE6, 0x64, 0x04, 0xC6, 0x46, 0x22, 0x32, 0x04, 
  0x0B, 0xF4, 0x14, 0x50, 0x2B, 0x18, 0x57, 0xA0, 0xCD, 0x7C, 
  0x53, 0x66, 0x8B, 0x5E, 0x09, 0x39, 0x53, 0x19, 0x1D, 0x69, 
  0x78, 0x01, 0x4A, 0xC9, 0xB5, 0x7D, 0x19, 0xAF, 0x3E, 0x23, 
  0x60, 0x8B, 0x75, 0xCD, 0x7D, 0xE2, 0x0D, 0xCC, 0x37, 0x2B, 
  0xB8, 0xB1, 0x2E, 0x84, 0x86, 0x92, 0x1F, 0xCF, 0x3A, 0xFC, 
  0x62, 0x2D, 0x37, 0x30, 0x55, 0x06, 0x8F, 0x81, 0x7B, 0x82, 
  0x09, 0x13, 0x4C, 0xCE, 0x47, 0xDD, 0x2E, 0xE3, 0x70, 0xED, 
  0x7B, 0xE5, 0xFF, 0x6C, 0x00, 0x67, 0xF6, 0x7F, 0x49, 0x8C, 
  0x95, 0xBE, 0x67, 0x6F, 0xE5, 0x53, 0x1C, 0x8A, 0x1A, 0x3F, 
  0x1C, 0xED, 0xEC, 0x40, 0x07, 0x42, 0x9C, 0x22, 0x60, 0x2D, 
  0x79, 0x71, 0x7C, 0xA7, 0x63, 0x4E, 0x60, 0x4A, 0x8F, 0x0E, 
  0xE7, 0x31, 0x37, 0xF2, 0x87, 0x1C, 0x4E, 0x83, 0xFB, 0xBB, 
  0x2D, 0xCD, 0x9B, 0xF1, 0xA2, 0xC3, 0x7A, 0xC5, 0xFB, 0xAC, 
  0x91, 0x1F, 0x3B, 0x36, 0x78, 0x41, 0xF8, 0xDC, 0xEC, 0xC9, 
  0xDB, 0x46, 0x00, 0x23, 0x40
]
byte_4023A0 = [
  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
]
def sub_400B0A(a1,flag):
    for i in range(4):
        for j in range(4):
            #print(i + 4 * j,"  " , 4 * (4 * a1 + i) + j)
            flag[i * 4 + j] ^= v4[4 * (4 * a1 + i) + j] 
            flag[i * 4 + j] %= 256


def sub_400BAC(flag):
    for i in range(4):
        for j in range(4):
            #print(flag[i + 4 * j])
            flag[i + 4 * j] = byte_4023A0[flag[i + 4 * j]]
def sub_400BAC_reverse(flag):
     for i in range(4):
        for j in range(4):
            flag[i + 4 * j] = byte_4023A0.index(flag[i + 4 * j])

def sub_400C1F(flag):
    v2 = flag[1]
    flag[1] = flag[5]
    flag[5] = flag[9]
    flag[9] = flag[13]
    flag[13] = v2
    v3 = flag[2]
    flag[2] = flag[10]
    flag[10] = v3
    v4 = flag[6]
    flag[6] = flag[14]
    flag[14] = v4
    v5 = flag[3]
    flag[3] = flag[15]
    flag[15] = flag[11]
    flag[11] = flag[7]
    flag[7] = v5
#flag移位
def sub_400C1F_reverse(flag):
    v5 = flag[7]
    flag[7] = flag[11]
    flag[11] = flag[15]
    flag[15] = flag[3]
    flag[3] = v5
    v4 = flag[14]
    flag[14] = flag[6]
    flag[6] = v4
    v3 = flag[10]
    flag[10] = flag[2]
    flag[2] = v3
    v2 = flag[13]
    flag[13] = flag[9]
    flag[9] = flag[5]
    flag[5] = flag[1]
    flag[1] = v2

def sub_400CFA(temp):
    return (2 * temp) ^ (27 * (temp // (2**7)))

def sub_400D27(flag):
    for i in range(4):
        v2 = flag[4 * i]
        v3 = (flag[4 * i + 2] ^ flag[4 * i + 1] ^ v2 ^ flag[4 * i + 3]) % 256
        flag[4 * i] = (v3 ^ sub_400CFA(v2 ^ flag[4 * i + 1]) ^ v2) %256
        flag[4 * i + 1] ^= v3 ^ sub_400CFA(flag[4 * i + 1] ^ flag[4 * i + 2])
        flag[4 * i + 1] %= 256
        flag[4 * i + 2] ^= v3 ^ sub_400CFA(flag[4 * i + 2] ^ flag[4 * i + 3]) 
        flag[4 * i + 2] %= 256
        flag[4 * i + 3] ^= v3 ^ sub_400CFA(v2 ^ flag[4 * i + 3])
        flag[4 * i + 3] %= 256

# 之前试的爆破脚本。。。超级慢
def sub_400D27_reverse(flag):
    f = []
    for i in range(0,4):
        for j0 in range(33,128):
            for j1 in range(33,128):
                for j2 in range(33,128):
                    for j3 in range(33,128):
                        temp = [j0,j1,j2,j3]
                        print(temp)
                        v2 = temp[0]
                        v3 = (temp[ 2] ^ temp[ 1] ^ v2 ^ temp[ 3]) % 256
                        temp[0] = (v3 ^ sub_400CFA(v2 ^ temp[ 1]) ^ v2) %256
                        temp[ 1] ^= v3 ^ sub_400CFA(temp[ 1] ^ temp[ 2])
                        temp[ 1] %= 256
                        temp[ 2] ^= v3 ^ sub_400CFA(temp[  2] ^ temp[ 3]) 
                        temp[ 2] %= 256
                        temp[3] ^= v3 ^ sub_400CFA(v2 ^ temp[  3])
                        temp[ 3] %= 256
                        if temp == flag[i:i+4]:
                            f.append(j0)
                            f.append(j1)
                            f.append(j2)
                            f.append(j3)
                            break
                else:
                    continue
                break
            else:
                continue
            break
    flag = f[:]
    print(flag)

#这里用了z3去解，，，但是中间有些解不出来
def sub_400D27_reverse_2(flag):
    print(flag)
    f = []
    for i in range(4):
        print("flag",flag[4 * i:4*i + 4])
        s = Solver()
        t_0,t_1,t_2,t_3 = BitVecs('t_0 t_1 t_2 t_3',8)
        #t = [BitVecs(('t%d'% i),8) for i in range(4) ]
        '''
        for j in t:
            s.add(j>0)
            s.add(j<255)
        
        s.add(flag[4 * i] == t[0] ^ t[0] ^ t[1] ^ t[2] ^ t[3] ^ ( 2 * (t[0] ^ t[1]) ^ (27 * (t[0] ^ t[1]) >> 7)) )
        s.add(flag[4 * i + 1] == t[1] ^ t[0] ^ t[1] ^ t[2] ^ t[3] ^ ( ( 2 * (t[1] ^ t[2])) ^ (27 * (t[1] ^ t[2]) >> 7)) ) 
        s.add(flag[4 * i + 2] == t[2] ^ t[0] ^ t[1] ^ t[2] ^ t[3] ^ ( ( 2 * (t[2] ^ t[3])) ^ (27 * (t[2] ^ t[3]) >> 7)))
        s.add(flag[4 * i + 3] == t[3] ^ t[0] ^ t[1] ^ t[2] ^ t[3] ^  ( ( 2 * (t[0] ^ t[3])) ^ (27 * (t[0] ^ t[3]) >> 7)))
        '''
        s.add(flag[4 * i] == (t_0 ^ t_0 ^ t_1 ^ t_2 ^ t_3 ^ (( 2 * (t_0 ^ t_1) ^ (27 * (t_0 ^ t_1) >> 7)) % 256 )) % 256)
        s.add(flag[4 * i + 1] == (t_1 ^ t_0 ^ t_1 ^ t_2 ^ t_3 ^ ( (( 2 * (t_1 ^ t_2)) ^ (27 * (t_1 ^ t_2) >> 7)) % 256 )) % 256)
        s.add(flag[4 * i + 2] == (t_2 ^ t_0 ^ t_1 ^ t_2 ^ t_3 ^ ( (( 2 * (t_2 ^ t_3)) ^ (27 * (t_2 ^ t_3) >> 7)) % 256) ) % 256)
        s.add(flag[4 * i + 3] == (t_3 ^ t_0 ^ t_1 ^ t_2 ^ t_3 ^ ( ( ( 2 * (t_0 ^ t_3)) ^ (27 * (t_0 ^ t_3) >> 7)) % 256)) % 256)
        s.check()
        m = s.model()
        print(m)
        '''
        t_0,t_1,t_2,t_3 = BitVecs('t_0 t_1 t_2 t_3',8)
        v3 = t_0 ^ t_1 ^ t_2 ^ t_3
        s.add(flag[4 * i] == t_0 ^ t_1 ^ t_2 ^ t_3 ^ (2 * (t_0 ^ t_1)) ^ t_0) 
        '''
    flag = f[:]
    print(f)

def sub_401828(flag):
    print(flag)
    sub_400B0A(0,flag)
    for i in range(1,10):
        sub_400BAC(flag)
        sub_400C1F(flag)
        sub_400D27(flag)
        sub_400B0A(i,flag)
    sub_400BAC(flag)
    sub_400C1F(flag)
    sub_400B0A(0xA,flag)
    return flag

def sub_401828_reverse(flag):
    print("flag1",flag)
    sub_400B0A(0xA,flag)   #异或
    print("flag2",flag)
    sub_400C1F_reverse(flag)  #交换
    print("flag3",flag)
    sub_400BAC_reverse(flag)  #取值
    print("flag4",flag)
    for i in range(9,0,-1):
        sub_400B0A(i,flag)   #异或
        sub_400D27_reverse_2(flag)  #加密
        sub_400C1F_reverse(flag)
        sub_400BAC_reverse(flag)
    sub_400B0A(0,flag)
    return flag



if __name__ == "__main__":
    flag = [0xBC, 0x0A, 0xAD, 0xC0, 0x14, 0x7C, 0x5E, 0xCC, 0xE0, 0xB1, 
  0x40, 0xBC, 0x9C, 0x51, 0xD5, 0x2B, 0x46, 0xB2, 0xB9, 0x43, 
  0x4D, 0xE5, 0x32, 0x4B, 0xAD, 0x7F, 0xB4, 0xB3, 0x9C, 0xDB, 
  0x4B, 0x5B]
    f = []
    f += sub_401828_reverse(flag[0:16])
    f += sub_401828_reverse(flag[16:]) 
    
    
    print(f)

但是失败了，，，，估计中间步骤哪有问题。。。。翻了下别的大佬的wp，sub_40196E()是AES加密，，，白浪费时间写脚本了，寄

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下断点运行到这里可以获得unk_603170的值：CB8D493521B47A4CC1AE7E62229266CE ，这个是作为AES的初始秘钥

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byte_6030A0的值也可以提出来：BC0AADC0147C5ECCE0B140BC9C51D52B46B2B9434DE5324BAD7FB4B39CDB4B5B

直接AES解密就行

    flag = binascii.unhexlify('BC0AADC0147C5ECCE0B140BC9C51D52B46B2B9434DE5324BAD7FB4B39CDB4B5B')
    key = binascii.unhexlify('CB8D493521B47A4CC1AE7E62229266CE')
    mode = AES.MODE_ECB
    aes = AES.new(key,mode)
    text = aes.decrypt(flag)
    print(text)