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[原创]逆向魔改tea+简单异或+z3运算
发表于: 2023-12-14 08:56 3862

[原创]逆向魔改tea+简单异或+z3运算

2023-12-14 08:56
3862

首先是一个ELF64程序
图片描述
进入程序函数名隐写,咱们可以动调得到输入函数和加密函数
图片描述
箭头指向函数均会改变输入变量的值
咱们从最下面的开始逆
图片描述进入函数看到一大堆的比较,一看就是Z3,可以copy给python用来Z3

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from z3 import *
a1=[0]*16
for i in range(16):
   a1[i]=z3.Int('a['+str(i)+']')
s=Solver()
s.add(-202850 * a1[0] == -34078800)
s.add(182136 *a1[0] - 75396 * a1[1] == 18610884)
s.add(-360745 * a1[1] - 465588 * a1[2] - 300043 * a1[0] == -145478307)
s.add(-97624 * a1[0] + 386642 * a1[3] - 515451 * a1[2] + 42526 * a1[1] == -8086825)
s.add(31288 * a1[0] + -324524 * a1[3] + -89265 * a1[1] - 239750 * a1[4] - 241348 * a1[2] == -91924377)
s.add(-266640 * a1[2] + 216272 * a1[5] + 411737 * a1[0] + 210304 * a1[3] - 8658 * a1[4] + 454111 * a1[1] == 144299767)
s.add(-402351 * a1[4]
     + -496724 * a1[0]
     + 367831 * a1[2]
     + 371046 * a1[5]
     + -123257 * a1[3]
     + 188174 * a1[1]
     + 178541 * a1[6] == -37352471)
s.add(-415443 * a1[1]
     + 237549 * a1[5]
     + -323336 * a1[7]
     + -207212 * a1[3]
     + -23780 * a1[0]
     + 94300 * a1[4]
     + 364867 * a1[6]
     + 273839 * a1[2] == -8993582)
s.add( 511561 * a1[5]
     + -215494 * a1[0]
     + 44567 * a1[6]
     + 179735 * a1[2]
     + 55541 * a1[8]
     + -204854 * a1[7]
     + -160275 * a1[1]
     + 441741 * a1[4]
     + 443248 * a1[3] == 57425926)
s.add(407430 * a1[0]
     + 407030 * a1[3]
     + 503571 * a1[6]
     + -434809 * a1[5]
     + 385646 * a1[4]
     + 437781 * a1[7]
     + 20147 * a1[9]
     + -10713 * a1[2]
     - 247694 * a1[8]
     + 4963 * a1[1] == 267063706)
s.add( 128236 * a1[7]
     + -189787 * a1[4]
     + 298269 * a1[2]
     + 117737 * a1[8]
     + -59638 * a1[1]
     + 503873 * a1[5]
     + -288072 * a1[9]
     + -449297 * a1[3]
     + -307883 * a1[6]
     - 60891 * a1[0]
     + 313065 * a1[10] == -99001600)
s.add(127585 * a1[3]
     + 447223 * a1[10]
     + -511720 * a1[0]
     + -64919 * a1[1]
     + -115935 * a1[11]
     + -328029 * a1[6]
     + 2659 * a1[4]
     + -246110 * a1[2]
     + -491943 * a1[8]
     + -392232 * a1[9]
     - 178041 * a1[5]
     + 49684 * a1[7] == -319105050 )
s.add(431281 * a1[7]
     + 303436 * a1[10]
     + 322142 * a1[8]
     + 190343 * a1[2]
     + 522606 * a1[5]
     + -368910 * a1[9]
     + 427328 * a1[12]
     + -403570 * a1[11]
     + -430137 * a1[0]
     + 436111 * a1[4]
     + -435520 * a1[6]
     - 267519 * a1[3]
     - 525665 * a1[1] == -150506496)
s.add(-423522 * a1[4]
     + -393086 * a1[6]
     + -323745 * a1[12]
     + 463495 * a1[1]
     + 345256 * a1[8]
     + 138356 * a1[7]
     + -225302 * a1[0]
     + 251299 * a1[11]
     + -82368 * a1[9]
     + -428085 * a1[10]
     + 71943 * a1[13]
     + 425456 * a1[2]
     + 56298 * a1[3]
     - 365233 * a1[5] == -14594715)
s.add(-26106 * a1[14]
     + -143761 * a1[3]
     + 15549 * a1[13]
     + -503539 * a1[10]
     + -398270 * a1[9]
     + 36874 * a1[2]
     + -84278 * a1[7]
     + 434801 * a1[12]
     + -472636 * a1[0]
     + 448925 * a1[8]
     + -46393 * a1[5]
     + -129268 * a1[4]
     + -43783 * a1[11]
     + 60534 * a1[6]
     + 441341 * a1[1] == -38159340)
s.add(-408983 * a1[3]
     + -453493 * a1[9]
     + 246957 * a1[5]
     + 197292 * a1[15]
     + -62054 * a1[8]
     + -21100 * a1[6]
     + -500028 * a1[14]
     + -386306 * a1[2]
     + 415182 * a1[13]
     + 24237 * a1[0]
     + -414063 * a1[4]
     + 524530 * a1[1]
     + 93336 * a1[10]
     + 7350 * a1[12]
     + 129819 * a1[11]
     - 293569 * a1[7] == -124057838)
s.check()
print(s.model())
结果
[a[5] = 9,
 a[15] = 55,
 a[0] = 168,
 a[8] = 241,
 a[11] = 168,
 a[7] = 115,
 a[13] = 113,
 a[4] = 113,
 a[1] = 159,
 a[9] = 171,
 a[14] = 103,
 a[10] = 137,
 a[12] = 73,
 a[3] = 112,
 a[6] = 237,

一般来说只要处理正确是会有解的。
拿到数据后接着往上看
图片描述
简单异或就不再说明
图片描述再看这个
图片描述
有一个表,相当于寻表找偏移了。表中对应的偏移即为密文。
图片描述
最后一个加密则为tea魔改了sum正常解就行

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int enc2[] = { 168,159,81,112,113,9,237,115,89,52,216,216,56,120,138,68 };
int enc3[] = { 6,176,58,186,200,204,138,50,112,52,53,53,99,48,100,51 };
unsigned int enc4[] = { 0xBA3AB006,0x328ACCC8 };
//int key[] = { 0x35353470, 0x33643063,0x6563696E, 0x33643063, };
int key[] = { 0x35353470, 0x33643063,0x6563696E,0x756f7932 };
unsigned int sum = 0x468ACF00;
 unsigned int v1 = enc4[0], v2 = enc4[1];
for (int i = 0; i <32; i++)
{
    v2 -= (v1 + sum) ^ ( (v1<<4) + key[2]) ^ ((v1 >> 5) + key[3]);
    v1 -= (v2 + sum) ^ ((v2<<4) + key[0]) ^ ((v2 >> 5) + key[1]);
    sum -= 0x12345678;
}
enc4[0] = v1;
enc4[1] = v2;
return 0;

强调一下变量的类型一定要是无符号的,如果是有符号的话数字的大小是不正确的会考虑符号位,所以一定要无符号才能跑的出结果

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flag{y0u_g0t_p455c0d3}

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目标实例以论坛附件形式提供一下?
2023-12-18 15:20
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