羊城杯逆向Writeup
羊城杯逆向Writeup
BabySmc
自解码，解密后代码虽然很多但从移位、密文及下面这个结构可以看出是base64编码：
细看一下他的加密过程，正常bases64的移位，但码表换了和最后多了一个异或。
所以解密的话就是先异或再提取出index，最后按照移位还原一下：
a = [0xE4, 0xC4, 0xE7, 0xC7, 0xE6, 0xC6, 0xE1, 0xC1, 0xE0, 0xC0, 0xE3, 0xC3, 0xE2, 0xC2, 0xED, 0xCD, 0xEC, 0xCC, 0xEF, 0xCF, 0xEE, 0xCE, 0xE9, 0xC9, 0xE8, 0xC8, 0xEB, 0xCB, 0xEA, 0xCA, 0xF5, 0xD5, 0xF4, 0xD4, 0xF7, 0xD7, 0xF6, 0xD6, 0xF1, 0xD1, 0xF0, 0xD0, 0xF3, 0xD3, 0xF2, 0xD2, 0xFD, 0xDD, 0xFC, 0xDC, 0xFF, 0xDF, 0x95, 0x9C, 0x9D, 0x92, 0x93, 0x90, 0x91, 0x96, 0x97, 0x94, 0x8A, 0x8E]
enc = "H>oQn6aqLr{DH6odhdm0dMe`MBo?lRglHtGPOdobDlknejmGI|ghDb<Q"
ans = []
enc = list(enc.encode())
for i in range(0, len(enc), 4):
ans += [a.index(enc[i]^0xa6)]
ans += [a.index(enc[i+1]^0xa3)]
ans += [a.index(enc[i+2]^0xa9)]
ans += [a.index(enc[i+3]^0xac)]
ans = ''.join(['{:0>6}'.format(bin(i)[2:]) for i in ans])
flag = ''
for i in range(len(ans)//8):
flag += chr(int(ans[8*i:8*(i+1)], 2))
print(flag)
Babyvm
开始简单调试了跟了一下，发现前面都是异或加密但后面有一部分加密有点复杂，跟起来会麻烦。
所以提取出vm部分代码，然后在编译器中修改编译一下这部分代码。
一是让程序直接打印出前面单字节异或加密对应的明文，二是打印出后面一部分的加密逻辑：
#include <stdio.h>
int dword_804B080[] = {0x7B, 0x2F, 0x37, 0x0E8};
char s[] = "********************************************";
int dword_804B060 = 0x0CF1304DC;
int dword_804B064 = 0x283B8E84;
char flag[100];
int cnt, count;
unsigned int sub_80487A8(unsigned int *a1)
{
unsigned char *v2; // [esp+18h] [ebp-20h]
//printf("%x\n", *(unsigned char *)a1[8] == 0xa1);
//return 0;
while ( 1 )
{
if ( *(unsigned char *)a1[8] == 113 )
{
printf("*******************\n");
a1[6] -= 4;
*(unsigned int *)a1[6] = *(unsigned int *)(a1[8] + 1);
a1[8] += 5;
}
if ( *(unsigned char *)a1[8] == 65 )
{
printf("%x += %x\n", a1[1], a1[2]);
a1[1] += a1[2];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 66 )
{
printf("%x -= %x\n", a1[1], a1[4]);
a1[1] -= a1[4];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 67 )
{
printf("%x *= %x\n", a1[1], a1[3]);
a1[1] *= a1[3];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 55 )
{
printf("a1[1] = %x\n", a1[5]);
a1[1] = a1[5];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 56 )
{
printf("a1[1]_%x ^= %x\n", a1[1], a1[4]);
a1[1] ^= a1[4];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 57 )
{
printf("a1[1]_%x ^= %x\n", a1[1], a1[5]);
a1[1] ^= a1[5];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 53 )
{
printf("a1[5] = %x\n", a1[1]);
a1[5] = a1[1];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 0xF7 )
{
printf("a1[9]_%x += %x\n", a1[9], a1[1]);
a1[9] += a1[1];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 68 )
{
printf("a1[1]_%x /= %x\n", a1[1], a1[5]);
a1[1] /= a1[5];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 0x80 )
{
a1[*(unsigned char *)(a1[8]+1)] = *(unsigned int *)(a1[8] + 2);
a1[8] += 6;
printf("%x\n", *(unsigned char *)(a1[8]));
}
if ( *(unsigned char *)a1[8] == 119 )
{
printf("a1[1]_%x ^= %x\n", a1[1], a1[9]);
a1[1] ^= a1[9];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 83 )
{
putchar(*(unsigned char *)a1[3]);
a1[8] += 2;
}
if ( *(unsigned char *)a1[8] == 34 )
{
printf("a1[1]_%x >>= %x\n", a1[1], a1[2]);
a1[1] >>= a1[2];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 35 )
{
printf("a1[1]_%x <= %x\n", a1[1], a1[2]);
a1[1] <<= a1[2];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 0x99 )
break;
if ( *(unsigned char *)a1[8] == 118 )
{
printf("??????????????????\n");
a1[3] = *(unsigned int *)a1[6];
*(unsigned int *)a1[6] = 0;
a1[6] += 4;
a1[8] += 5;
}
if ( *(unsigned char *)a1[8] == 84 )
{
printf("getchar()\n ------------------");
v2 = (unsigned char *)a1[3];
*v2 = getchar();
a1[8] += 2;
}
if ( *(unsigned char *)a1[8] == 48 )
{
printf("?????????????????????????????????????????????????\n");
a1[1] |= a1[2];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 49 )
{
printf("a1[1]_%x &= %x\n", a1[1], a1[2]);
a1[1] &= a1[2];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 50 )
{
a1[3] = *(unsigned __int8 *)(a1[8] + 1);
printf("a1[3] = %x\n", a1[3]);
a1[8] += 2;
}
if ( *(unsigned char *)a1[8] == 9 )
{
printf("a1[1]_%x = 1877735783\n", a1[1]);
a1[1] = 1877735783;
++a1[8];
}
if ( *(unsigned char *)a1[8] == 16 )
{
printf("a1[9]_%x = %x\n", a1[9], a1[1]);
a1[9] = a1[1];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 51 )
{
printf("a1[4]_%x = %x\n", a1[4], a1[1]);
a1[4] = a1[1];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 52 )
{
a1[2] = *(unsigned char *)(a1[8] + 1);
printf("a1[2] = %x\n", a1[2]);
a1[8] += 2;
}
if ( *(unsigned char *)a1[8] == 0xFE )
{
printf("a1[1]_%x = %x\n", a1[1], a1[9]);
a1[1] = a1[9];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 17 )
{
//printf("============================\n");
printf("%x\n", a1[1]);
++a1[8];
//printf("%x\n", *(unsigned char *)(a1[8]));
}
if ( *(unsigned char *)a1[8] == 0xA0 )
{
if ( a1[1] != 1877735783 )
printf("a1[1] != 1877735783 %x\n\n\n\n\n", a1[1]);
++a1[8];
}
if ( *(unsigned char *)a1[8] == 0xA1 )
{
//read(0, s, 0x2Cu);
//if ( strlen(s) != 44 )
//exit(0);
++a1[8];
}
if ( *(unsigned char *)a1[8] == 0xB1 )
{
//printf("?????????????????????????????????????????????????\n");
a1[9] = dword_804B080[0];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 0xB2 )
{
a1[9] = dword_804B080[1];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 0xA4 )
{
dword_804B080[*(unsigned __int8 *)(a1[8] + 1)] = a1[1];
a1[8] += 4;
}
if ( *(unsigned char *)a1[8] == 0xB3 )
{
a1[9] = dword_804B080[2];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 0xB4 )
{
a1[9] = dword_804B080[3];
++a1[8];
}
if ( *(unsigned char *)a1[8] == 0xC1 )
{
a1[1] = (unsigned char)s[*(unsigned char *)(a1[8] + 1)];
printf("a1[1] = %x\n", a1[1]);
a1[8] += 2;
if(count == 32)
{
printf("%x\n", *(unsigned char *)(a1[8]));
}
count++;
}
if ( *(unsigned char *)a1[8] == 0xC7 )
{
if ( dword_804B060 != a1[1] )
printf("%x != a1[1] %x\n\n\n", dword_804B060, a1[1]);
++a1[8];
}
if ( *(unsigned char *)a1[8] == 0xC8 )
{
if ( dword_804B064 != a1[1] )
printf("%x != a1[1] %x\n\n\n\n", dword_804B064, a1[1]);
++a1[8];
}
if ( *(unsigned char *)a1[8] == 0xC2 )
{
if ( (unsigned __int8)*(unsigned int *)(a1[8] + 1) != a1[1] )
{
printf("(unsigned __int8)*(unsigned int *)(a1[8] + 1) != a1[1]\n");
flag[cnt++] = (unsigned __int8)*(unsigned int *)(a1[8] + 1)^'*'^a1[1];
}
a1[8] += 5;
}
}
return 1;
}
int main(void)
{
unsigned char op[] = {0xA1, 0xC1, 0x00, 0xB1, 0x77, 0xC2, 0x4A, 0x01, 0x00, 0x00, 0xC1, 0x01, 0xB2, 0x77, 0xC2, 0x19, 0x01, 0x00, 0x00, 0xC1, 0x02, 0xB4, 0x77, 0xC2, 0xDD, 0x01, 0x00, 0x00, 0xC1, 0x03, 0xB3, 0x77, 0xC2, 0x0F, 0x01, 0x00, 0x00, 0xC1, 0x04, 0xB2, 0x77, 0xC2, 0x1B, 0x01, 0x00, 0x00, 0xC1, 0x05, 0xB4, 0x77, 0xC2, 0x89, 0x01, 0x00, 0x00, 0xC1, 0x06, 0xB1, 0x77, 0xC2, 0x19, 0x01, 0x00, 0x00, 0xC1, 0x07, 0xB3, 0x77, 0xC2, 0x54, 0x01, 0x00, 0x00, 0xC1, 0x08, 0xB1, 0x77, 0xC2, 0x4F, 0x01, 0x00, 0x00, 0xC1, 0x09, 0xB1, 0x77, 0xC2, 0x4E, 0x01, 0x00, 0x00, 0xC1, 0x0A, 0xB3, 0x77, 0xC2, 0x55, 0x01, 0x00, 0x00, 0xC1, 0x0B, 0xB3, 0x77, 0xC2, 0x56, 0x01, 0x00, 0x00, 0xC1, 0x0C, 0xB4, 0x77, 0xC2, 0x8E, 0x00, 0x00, 0x00, 0xC1, 0x0D, 0xB2, 0x77, 0xC2, 0x49, 0x00, 0x00, 0x00, 0xC1, 0x0E, 0xB3, 0x77, 0xC2, 0x0E, 0x01, 0x00, 0x00, 0xC1, 0x0F, 0xB1, 0x77, 0xC2, 0x4B, 0x01, 0x00, 0x00, 0xC1, 0x10, 0xB3, 0x77, 0xC2, 0x06, 0x01, 0x00, 0x00, 0xC1, 0x11, 0xB3, 0x77, 0xC2, 0x54, 0x01, 0x00, 0x00, 0xC1, 0x12, 0xB2, 0x77, 0xC2, 0x1A, 0x00, 0x00, 0x00, 0xC1, 0x13, 0xB1, 0x77, 0xC2, 0x42, 0x01, 0x00, 0x00, 0xC1, 0x14, 0xB3, 0x77, 0xC2, 0x53, 0x01, 0x00, 0x00, 0xC1, 0x15, 0xB1, 0x77, 0xC2, 0x1F, 0x01, 0x00, 0x00, 0xC1, 0x16, 0xB3, 0x77, 0xC2, 0x52, 0x01, 0x00, 0x00, 0xC1, 0x17, 0xB4, 0x77, 0xC2, 0xDB, 0x00, 0x00, 0x00, 0xC1, 0x18, 0xB1, 0x77, 0xC2, 0x19, 0x01, 0x00, 0x00, 0xC1, 0x19, 0xB4, 0x77, 0xC2, 0xD9, 0x00, 0x00, 0x00, 0xC1, 0x1A, 0xB1, 0x77, 0xC2, 0x19, 0x01, 0x00, 0x00, 0xC1, 0x1B, 0xB3, 0x77, 0xC2, 0x55, 0x01, 0x00, 0x00, 0xC1, 0x1C, 0xB2, 0x77, 0xC2, 0x19, 0x00, 0x00, 0x00, 0xC1, 0x1D, 0xB3, 0x77, 0xC2, 0x00, 0x01, 0x00, 0x00, 0xC1, 0x1E, 0xB1, 0x77, 0xC2, 0x4B, 0x01, 0x00, 0x00, 0xC1, 0x1F, 0xB2, 0x77, 0xC2, 0x1E, 0x00, 0x00, 0x00, 0xC1, 0x20, 0x80, 0x02, 0x18, 0x00, 0x00, 0x00, 0x23, 0x10, 0xC1, 0x21, 0x80, 0x02, 0x10, 0x00, 0x00, 0x00, 0x23, 0xF7, 0xC1, 0x22, 0x80, 0x02, 0x08, 0x00, 0x00, 0x00, 0x23, 0xF7, 0xC1, 0x23, 0xF7, 0xFE, 0x80, 0x02, 0x05, 0x00, 0x00, 0x00, 0x22, 0x77, 0x10, 0x80, 0x02, 0x07, 0x00, 0x00, 0x00, 0x23, 0x80, 0x02, 0x23, 0x77, 0xF1, 0x98, 0x31, 0x77, 0x10, 0x80, 0x02, 0x18, 0x00, 0x00, 0x00, 0x23, 0x80, 0x02, 0x20, 0xB9, 0xE4, 0x35, 0x31, 0x77, 0x10, 0x80, 0x02, 0x12, 0x00, 0x00, 0x00, 0x22, 0x77, 0xA0, 0xC1, 0x24, 0x80, 0x02, 0x18, 0x00, 0x00, 0x00, 0x23, 0x10, 0xC1, 0x25, 0x80, 0x02, 0x10, 0x00, 0x00, 0x00, 0x23, 0xF7, 0xC1, 0x26, 0x80, 0x02, 0x08, 0x00, 0x00, 0x00, 0x23, 0xF7, 0xC1, 0x27, 0xF7, 0xFE, 0x32, 0x20, 0x43, 0x33, 0x77, 0x80, 0x02, 0x11, 0x00, 0x00, 0x00, 0x22, 0x35, 0x37, 0x38, 0x77, 0x80, 0x02, 0x0D, 0x00, 0x00, 0x00, 0x23, 0x77, 0x38, 0x39, 0x10, 0x32, 0x20, 0x43, 0x33, 0x77, 0x80, 0x02, 0x11, 0x00, 0x00, 0x00, 0x22, 0x35, 0x37, 0x38, 0x77, 0x80, 0x02, 0x0D, 0x00, 0x00, 0x00, 0x23, 0x77, 0x38, 0x39, 0xC7, 0xC1, 0x28, 0x80, 0x02, 0x18, 0x00, 0x00, 0x00, 0x23, 0x10, 0xC1, 0x29, 0x80, 0x02, 0x10, 0x00, 0x00, 0x00, 0x23, 0xF7, 0xC1, 0x2A, 0x80, 0x02, 0x08, 0x00, 0x00, 0x00, 0x23, 0xF7, 0xC1, 0x2B, 0xF7, 0xFE, 0x32, 0x20, 0x43, 0x33, 0x77, 0x80, 0x02, 0x11, 0x00, 0x00, 0x00, 0x22, 0x35, 0x37, 0x38, 0x77, 0x80, 0x02, 0x0D, 0x00, 0x00, 0x00, 0x23, 0x77, 0x38, 0x39, 0x10, 0x32, 0x20, 0x43, 0x33, 0x77, 0x80, 0x02, 0x11, 0x00, 0x00, 0x00, 0x22, 0x35, 0x37, 0x38, 0x77, 0x80, 0x02, 0x0D, 0x00, 0x00, 0x00, 0x23, 0x77, 0x38, 0x39, 0xC8, 0x99};
unsigned int a1[10] = {0};
a1[8] = (unsigned int)op;
sub_80487A8(a1);
puts(flag);
//printf("%x\n", count);
}
运行得到前面32字节明文：16584abc45baff901c59dde3b1bb6701
后面12字节加密逻辑。
前4字节：
a1[1] = 2a
80
23
a1[1]_2a <= 18
a1[9]_2f = 2a000000
a1[1] = 2a
23
a1[1]_2a <= 10
a1[9]_2a000000 += 2a0000
a1[1] = 2a
23
a1[1]_2a <= 8
a1[9]_2a2a0000 += 2a00
a1[1] = 2a
a1[9]_2a2a2a00 += 2a
a1[1]_2a = 2a2a2a2a
22
a1[1]_2a2a2a2a >>= 5
a1[1]_1515151 ^= 2a2a2a2a
a1[9]_2a2a2a2a = 2b7b7b7b
23
a1[1]_2b7b7b7b <= 7
31
a1[1]_bdbdbd80 &= 98f17723
a1[1]_98b13500 ^= 2b7b7b7b
a1[9]_2b7b7b7b = b3ca4e7b
23
a1[1]_b3ca4e7b <= 18
31
a1[1]_7b000000 &= 35e4b920
a1[1]_31000000 ^= b3ca4e7b
a1[9]_b3ca4e7b = 82ca4e7b
22
a1[1]_82ca4e7b >>= 12
a1[1]_20b2 ^= 82ca4e7b
a1[1] != 1877735783 82ca6ec9
后面4字节加密逻辑：
a1[1] = 2a
23
a1[1]_2a <= 18
a1[9]_82ca4e7b = 2a000000
a1[1] = 2a
23
a1[1]_2a <= 10
a1[9]_2a000000 += 2a0000
a1[1] = 2a
23
a1[1]_2a <= 8
a1[9]_2a2a0000 += 2a00
a1[1] = 2a
a1[9]_2a2a2a00 += 2a
a1[1]_2a = 2a2a2a2a
a1[3] = 20
2a2a2a2a *= 20
a1[4]_0 = 45454540
a1[1]_45454540 ^= 2a2a2a2a
22
a1[1]_6f6f6f6a >>= 11
a1[5] = 37b7
a1[1] = 37b7
a1[1]_37b7 ^= 45454540
a1[1]_454572f7 ^= 2a2a2a2a
23
a1[1]_6f6f58dd <= d
a1[1]_eb1ba000 ^= 2a2a2a2a
a1[1]_c1318a2a ^= 45454540
a1[1]_8474cf6a ^= 37b7
a1[9]_2a2a2a2a = 8474f8dd
a1[3] = 20
8474f8dd *= 20
a1[4]_45454540 = 8e9f1ba0
a1[1]_8e9f1ba0 ^= 8474f8dd
22
a1[1]_aebe37d >>= 11
a1[5] = 575
a1[1] = 575
a1[1]_575 ^= 8e9f1ba0
a1[1]_8e9f1ed5 ^= 8474f8dd
23
a1[1]_aebe608 <= d
a1[1]_7cc10000 ^= 8474f8dd
a1[1]_f8b5f8dd ^= 8e9f1ba0
a1[1]_762ae37d ^= 575
cf1304dc != a1[1] 762ae608
最后4字节加密逻辑与上一组加密逻辑相同（从相同测试输入得到相同的加密结果推出）
按照打印出的加密逻辑，自己重写一下加密代码，再z3分组求解出对应的明文：
from z3 import *
s = Solver()904182048
'''
#第一组加密
tmp = BitVec('tmp', 32)
tmp = (tmp >> 5)^tmp
tmp = ((tmp << 7)&0x98f17723)^tmp
tmp = ((tmp << 0x18)&0x35e4b920)^tmp
tmp = (tmp >> 0x12)^tmp
s.add(tmp == 1877735783)
s.add((tmp&0xff) > 32, (tmp&0xff) < 127)
'''
#第二组加密
flag = BitVec('flag', 64)
a = (flag*0x20)&0xffffffff
tmp = (a^flag)&0xffffffff
b = (tmp >> 0x11)&0xffffffff
tmp = ((b^a)^flag)&0xffffffff
tmp = ((tmp << 0xd)^flag^a^b)&0xffffffff
t = tmp
a = (t*0x20)&0xffffffff
tmp = (t^a)&0xffffffff
b = (tmp >> 0x11)&0xffffffff
tmp = (a^b^t)&0xffffffff
tmp = ((tmp << 0xd)^t^a^b)&0xffffffff
#print(hex(tmp))
s.add(tmp == 0x283b8e84)
#s.add((tmp&0xff) > 32, (tmp&0xff) < 127)
if s.check() == sat:
print(s.model())
else:
print('Not Found!')
得到：a254b06cdc23
所以最后的flag就是：16584abc45baff901c59dde3b1bb6701a254b06cdc23
DeltX
先看到输入格式的要求，格式为SangFor{{}，然后输入范围[0, 9]与[A-F]
但最后交flag一直不对才注意到输入的第四组限定了输入的英文字符要为小写：
然后加密的话就是乘法和加法（看结构，调试看输入与输出的关系
最后z3约束求解：
from z3 import *
data = [0x249E15C5, 0xFFFF59BC, 0x34C7EAE2, 0x216B, 0x637973BA, 0x819D, 0xE5FD104, 0x9393]
flag = ''
for i in range(4):
s = Solver()
a, b = BitVecs("x1 x2", 32)
s.add(a*b == data[2*i+0])
s.add(a-b == data[2*i+1])
s.add(a > 0, a < 0xffff)
s.add(b > 0, b < 0xffff)
if s.check() == sat:
m = s.model()
flag += hex(m[a].as_long())[2:] + hex(m[b].as_long())[2:]
else:
print('Not Found!')
flag = flag[:12].upper()+flag[12:16].lower()+flag[16:].upper()
print('SangFor{'+flag+'}')
#SangFor{2C7BD2BF862564baED0B6B6EA94F15BC}
Ez_android
jeb打开apk，逻辑就是输入用户名和密码，然后用密码到：139.224.191.201 20080 去取密钥作为base64编码的码表。
用户名和密码jeb中直接就可以看到，但这里的密码的md5值是经过变换过的。
简答处理一下得到密码的正确md5值：
>>> s = "c232666f1410b3f5010dc51cec341f58"
>>> s = bytes.fromhex(s)
>>> s
b'\xc22fo\x14\x10\xb3\xf5\x01\r\xc5\x1c\xec4\x1fX'
>>> s = [s[i]+1 for i in range(len(s))]
>>> s
[195, 51, 103, 112, 21, 17, 180, 246, 2, 14, 198, 29, 237, 53, 32, 89]
>>> bytes(s).hex()
'c33367701511b4f6020ec61ded352059'
>>>
查一下这个md5，得到：654321
nc连接给的ip和端口后输入密码得到密钥。
最后解密：
import base64
s = "TGtUnkaJD0frq61uCQYw3-FxMiRvNOB/EWjgVcpKSzbs8yHZ257X9LldIeh4APom"
table = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
enc = "3lkHi9iZNK87qw0p6U391t92qlC5rwn5iFqyMFDl1t92qUnL6FQjqln76l-P"
ans = enc.translate(str.maketrans(s, table))
print(bytes(list(base64.b64decode(ans))))
#SangFor{212f4548-03d1-11ec-ab68-00155db3a27e}
Safe Box
程序用到父子进程反调试，Debug Blocker技术，其它来说流程都很清晰。
利用int3（0x80000003）断点把异常传递给父进程，然后父进程根据断点位置的不同进行不同的操作。
其中断点位置下个机器码是0x8b的地方将ecx改写了。
看到触发这个异常地方的代码：其实就是把随机数种子改成了0x534EB68
另外一个触发断点异常位置的下一个机器码是0x48的地方是进行对程序中的一个函数进行了解密。
再来看到程序的主逻辑：
第一输入：
这里z3约束求解即可。
from z3 import *
s = Solver()
Seed = BitVec('passwd', 64)
v2 = (Seed % 0x2540BE3FF)&0xff
v3 = ((Seed % 0x2540BE3FF) >> 8) & 0xF
v4 = ((Seed % 0x2540BE3FF) >> 20) & 0xFFF
v5 = v2 + 1;
v6 = ((Seed % 0x2540BE3FF) >> 12)&0xff
v7 = v3 + 1;
v8 = v4 + ~v2
v9 = v4
v10 = 21 * v6
for i in range(16):
v3 += v3 ^ v8
v2 += v4 | v2 & v7
v9 += (v10 + v9) % v5
v6 += v6 / v7
s.add(v3 == 0x38006F1)
s.add(v2 == 0x7291)
s.add(v9 == 0x8B3)
s.add(v6 == 0x80)
s.add(Seed > 0, Seed <= 0xffffffff)
if s.check() == sat:
print(s.model())
else:
print('Not Found!')
#1915969329
第二个输入：
上面对输入加密的函数sub_140001880就是父进程收到子进程断点异常后进行解密后的。
这里程序运行后，dump出内存就能看到这个完整的解密函数了。魔改的xtea加密。
解密：
#include <stdio.h>
unsigned int get_delat()
{
int i = 0;
unsigned int ans = 0, delat = 0x12345678;
for(i = 0; i < 32; i++)
ans += delat;
return ans;
}
void decipher(unsigned int num_rounds, unsigned int v[2], unsigned int const key[4]) {
unsigned int i;
unsigned int v0=v[0], v1=v[1], delta=0x12345678, sum=get_delat();
for (i=0; i < num_rounds; i++) {
v1 -= (((v0 >> 6) ^ (v0 << 5)) + v0) ^ (sum + key[(sum>>11) & 3]);
sum -= delta;
v0 -= (((v1 >> 6) ^ (v1 << 5)) + v1) ^ (sum + key[sum & 3]);
}
v[0]=v0; v[1]=v1;
}
int main()
{
/*
unsigned int v[2]={0x36C128C5, 0x0C4799A63};
unsigned int const k[4]={0x47, 0x57, 0x48, 0x54};
unsigned int r=32;
decipher(r, v, k);
printf("解密后的数据：%x %x\n",v[0],v[1]); */
unsigned int v[] = {0x36C128C5, 0xC4799A63, 0xE8013E6C, 0xA9F49003, 0x607EF54A, 0x542C2DDF, 0x558BD01C, 0x65512CA2, 0xBE1E3D05, 0x3C467DAD};
unsigned int const k[4]={0x47, 0x57, 0x48, 0x54};
unsigned int r=32;
for(int i = 0; i < 5; i++)
{
decipher(r, v+2*i, k);
}
for(int i = 0; i < 10; i++)
{
printf("%c", v[i]);
}
return 0;
}
//S_s0_fuNny
第三个输入：利用修改后的随机数种子生成32个随机数然后用前16个和输入进行异或。
生成随机数：
#include <stdio.h>
#include <stdlib.h>
unsigned int seed = 0x534EB68;
unsigned int a[16], b[16];
int main(void)
{
srand(seed);
for(int i = 0; i < 16; i++)
{
a[i] = rand();
printf("%#x, ", a[i]);
}
putchar(10);
srand(seed + 1);
for(int i = 0; i < 16; i++)
{
b[i] = rand();
printf("%#x, ", b[i]);
}
}
最后的比较函数中还进行了一些运算和打乱顺序，但我们可以不关心。因为分析生成的随机数看到都是16位的而输入是8位，他们在异或后只会改变低字节位置的值。
所以说我们只用把生成的前16字节随机数和密文中高字节和前16字节随机数高字节相同的数据找出来异或就是输入了。（虽然有相同的，但很少，简单多试就是
异或一下得到明文：
>>> a = [0x4147, 0x2f06, 0x5017, 0x7d6c, 0x1583, 0x37ea, 0x6fdc, 0xd03, 0x3f43, 0x4156, 0xed7, 0x1094, 0x5c4f, 0x173f, 0x193a, 0x1357]
>>>
>>> b = [0x4118, 0x2F62, 0x00005027, 0x00007D33, 0x000015DA, 0x00003785, 0x00006F89, 0x00000D5C, 0x00003F72, 0x0000413F, 0x00000EBC, 0x000010A7, 0x00005C10, 0x0000174B, 0x0000190A, 0x00001338]
>>> ans = [a[i]^b[i] for i in range(16)]
>>> ans
[95, 100, 48, 95, 89, 111, 85, 95, 49, 105, 107, 51, 95, 116, 48, 111]
>>> bytes(ans)
b'_d0_YoU_1ik3_t0o'
最后所有拼接起来就是flag：GWHT{r3_1S_s0_fuNny_d0_YoU_1ik3_t0o}