菜鸡学逆向学得头皮发麻，终于它拿到了一段源代码

#include <stdio.h>
#include <string.h>

int main(int argc, char *argv[]) {
    if (argc != 4) {       //说明必须得是4个参数（其中注意文件名是一个）
        printf("what?\n");
        exit(1);
    }

    unsigned int first = atoi(argv[1]);
    if (first != 0xcafe) {　　　　//说明first=0xcafe的时候才能继续向下执行
        printf("you are wrong, sorry.\n");
        exit(2);
    }

    unsigned int second = atoi(argv[2]);
    if (second % 5 == 3 || second % 17 != 8) {　　　　　　//说明要么%5!=3,要么%17=8才能继续向下执行
        printf("ha, you won't get it!\n");
        exit(3);
    }

    if (strcmp("h4cky0u", argv[3])) {　　　　//说明argv[3]="h4cky0u"才能继续向下执行
        printf("so close, dude!\n");
        exit(4);
    }

    printf("Brr wrrr grr\n");

    unsigned int hash = first * 31337 + (second % 17) * 11 + strlen(argv[3]) - 1615810207;

    printf("Get your key: ");
    printf("%x\n", hash);
    return 0;
}

上面的分析可以知道

first=0xcafe

second % 17 == 8

strlen(argv[3]) == strlen("h4ck0u")
所以只要将上面的进行替换后运行就可以得出flag

#include <stdio.h>
#include <string.h>
 
int main() {
    
    unsigned int hash = 0xcafe * 31337 + 8 * 11 + strlen("h4cky0u") - 1615810207;
    
    printf("Get your key: ");
    
    printf("%x\n", hash);
    
    return 0;
}