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open-source Write Up

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open-source Write Up

难度：☆☆☆

这道题提供了一个c语言源代码：

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

int main(int argc, char *argv[]) {
    if (argc != 4) {
    	printf("what?\n");
    	exit(1);
    }

    unsigned int first = atoi(argv[1]);
    if (first != 0xcafe) {
    	printf("you are wrong, sorry.\n");
    	exit(2);
    }

    unsigned int second = atoi(argv[2]);
    if (second % 5 == 3 || second % 17 != 8) {
    	printf("ha, you won't get it!\n");
    	exit(3);
    }

    if (strcmp("h4cky0u", argv[3])) {
    	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;
}

很显然我们需要让这段代码跑起来并且跑到最后让程序自己算出来flag，

所以我们我们需要把main函数需要的参数值删掉并且放到main函数内去定义,修改如下：

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int main() {
	int argc = 4;
	char * argv[] = {"1","51966","25","h4cky0u"};

这里的atoi()函数的功能是从前往后取字符串整数部分，所以我们把argv[1]所需要的整数的十六进制转换成十进制0xcafe，即51996，即可

然后点击调试，程序即可顺利运行到最后