R4ndom

程序在__libc_csu_init里面分别偷偷调用了a和b函数。
a函数负责进行ptrace反调试

b函数则初始化了srand

写一个cpp（在linux下运行，因为win和linux下rand不一样）
收集randTable（count=42）

#include <iostream>
using namespace std;

int main(){
        cout << "count:";
        int c;
        cin >> c;
        cout << "[";
        for(int i = 0;i < c; i++)
        {
                if(i != 0) cout << ", ";
                cout << rand();
        }

        cout << "]";
        return 0;
}

然后从程序里面抄出来Table放z3里面，并使用z3的Array和Select实现对于表的取值

table = [...]
z3Table = Array('z3-table', BitVecSort(8), BitVecSort(8))
for i in range(len(table)): s.add(z3Table[i] == table[i])

然后使用Select(x, i)  # x[i]

from z3 import *
table = [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]
randTable = [1339546161, 401979842, 1084912717, 882247430, 1048050849, 1950252444, 1188894224, 1035316485, 1004145938, 292996994, 698777994, 1572612448, 187344395, 1998928827, 490869405, 1976471722, 861192779, 1683160727, 1968082326, 1836887756, 1806801098, 176220730, 2616407, 375557835, 1798606494, 1079742625, 657352025, 1384338308, 1249182411, 600742620, 1626386373, 441244924, 1002722462, 563815442, 1323492354, 2050773311, 366584239, 364902931, 938606148, 1370730177, 657899925, 1637384142] 
ans = [0x3513AB8AB2D7E6EE, 0x2EEDBA9CB9C97B02, 0x16E4F8C8EEFA4FBD, 0x383014F4983B6382, 0xEA32360C3D843607, 0xA655]

aa = b""
for i in ans:
    aa += i.to_bytes(8, 'little')
ans = list(aa)

s = Solver()
x = [BitVec(f"x{i}", 8) for i in range(42)]

table_z3 = Array('t1', BitVecSort(8), BitVecSort(8))
for i in range(len(table)): s.add(table_z3[i] == table[i])

for i in range(42):
    v3 = x[i]
    v4 = randTable[i]
    s.add(Select(table_z3, (16 * ((v3 + v4 % 255) >> 4) + 15) & (v3 + v4 % 255)) == ans[i])
    s.add(x[i] >= 0x20)
    s.add(x[i] <= 0x7f)

print(s.check())
m = s.model()
for i in range(42):
    print(chr(m[x[i]].as_long()), end='')

sat
flag{B8452786-DD8E-412C-E355-2B6F27DAB5F9}