這題的 code 長這樣 ```c #include <stdio.h> int main(){ unsigned int random; random = rand(); // random value! unsigned int key=0; scanf("%d", &key); if( (key ^ random) == 0xdeadbeef ){ printf("Good!\n"); system("/bin/cat flag"); return 0; } printf("Wrong, maybe you should try 2^32 cases.\n"); return 0; } ``` 然後就開心的看到 `rand` 沒有給 seed 所以可以直接試出來沒有 seed 的話出來會是 1804289383 要讓 `(key ^ random) == 0xdeadbeef` 所以 `key` 就是 0xdeadbeef ^ 1804289383 = 3039230856 輸入就有 flag 了 `Mommy, I thought libc random is unpredictable...` sumbit，通過，開心