攻防世界-进阶-parallel-comparator-200
C文件
#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
#define FLAG_LEN 20
void * checking(void *arg) {
char *result = malloc(sizeof(char));
char *argument = (char *)arg;
*result = (argument[0]+argument[1]) ^ argument[2];//argument[0]>97
return result;
}
int highly_optimized_parallel_comparsion(char *user_string)
{
int initialization_number;
int i;
char generated_string[FLAG_LEN + 1];
generated_string[FLAG_LEN] = '\0';
while ((initialization_number = random()) >= 64);//开始认为随机数且大于64,事实上为一固定数37
int first_letter;
first_letter = (initialization_number % 26) + 97;//97-123
pthread_t thread[FLAG_LEN];
char differences[FLAG_LEN] = {0, 9, -9, -1, 13, -13, -4, -11, -9, -1, -7, 6, -13, 13, 3, 9, -13, -11, 6, -7};
char *arguments[20];
//没有全部执行,
for (i = 0; i < FLAG_LEN; i++) {
arguments[i] = (char *)malloc(3*sizeof(char));
arguments[i][0] = first_letter;//三个数拼接到一起 随机的
arguments[i][1] = differences[i];//固定的
arguments[i][2] = user_string[i];//输入的
pthread_create((pthread_t*)(thread+i), NULL, checking, arguments[i]);
}
void *result;
int just_a_string[FLAG_LEN] = {115, 116, 114, 97, 110, 103, 101, 95, 115, 116, 114, 105, 110, 103, 95, 105, 116, 95, 105, 115};
for (i = 0; i < FLAG_LEN; i++) {
pthread_join(*(thread+i), &result);
generated_string[i] = *(char *)result + just_a_string[i];
free(result);
free(arguments[i]);
}
int is_ok = 1;
for (i = 0; i < FLAG_LEN; i++) {
if (generated_string[i] != just_a_string[i])
return 0;
}
return 1;
}
int main()
{
char *user_string = (char *)calloc(FLAG_LEN+1, sizeof(char));
fgets(user_string, FLAG_LEN+1, stdin);
int is_ok = highly_optimized_parallel_comparsion(user_string);
if (is_ok)
printf("You win!\n");
else
printf("Wrong!\n");
return 0;
}
代码分析
generated_string[i] = *(char *)result + just_a_string[i];
if (generated_string[i] != just_a_string[i])
return 0;
说明result为固定值零。
解题脚本
#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#define FLAG_LEN 20
char differences[FLAG_LEN] = {0, 9, -9, -1, 13, -13, -4, -11, -9, -1, -7, 6, -13, 13, 3, 9, -13, -11, 6, -7};
int main()
{
int initialization_number,first_letter;
while ((initialization_number = random()) >= 64);
first_letter = (initialization_number % 26) + 97;
printf("%d",initialization_number);
for(int i=0;i<FLAG_LEN;i++)
{
printf("%c",first_letter+differences[i]);
}
printf("\n");
}