2024 NYCU 電腦安全 Project 4 CTF

#include <stdio.h>
#include <stdlib.h>
void purchase(int price, int your_money) {
    int amount;
    puts("Input the amount:");
    scanf("%d", &amount);
    if(amount > 0){
        int total_price = price*amount;
        if(your_money >= total_price){
            your_money -= total_price;
            printf("You have purchased the flag\n");
            getFlag();
        }
        else {
            puts("You don't have enough money!");
        }
    }
    else{
        puts("Invalid amount!");    
    }
}


void getFlag() {
    puts(getenv("FLAG"));
}

int main(int argc, char **argv){
    setvbuf(stdin, NULL, _IONBF, 0);
    setvbuf(stdout, NULL, _IONBF, 0);
    int flag_price = 999999, your_money = 10, choice;
    puts("Welcome to the server:");
    while(1) {
        printf("Current money: %d\n", your_money);
        puts("1. Purchase Flag");
        puts("2. Exit");
        puts("Input your choice:");
        scanf("%d", &choice);
        switch(choice) {
            case 1:
                purchase(flag_price, your_money);
                break;
            case 2:
                exit(0);
            default:
                puts("Invalid choice!");
                break;
        }
    }
}

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

char secret[0x10];

void init()
{
    setvbuf(stdin, NULL, _IONBF, 0);
    setvbuf(stdout, NULL, _IONBF, 0);
    setvbuf(stderr, NULL, _IONBF, 0);
    srand(time(0));
    for (int i = 0; i < 0x10; i++)
    {
        secret[i] = 48 + (rand() % (126 - 47) + 1);
    }
}

int main(){
    init();
    puts("Please enter the secret: ");
    char input[0x10];
    read(0, input, 0x10);
    if (strcmp(input, secret) == 0)
    {
        puts("You got it! Here is your flag!");
        puts(getenv("FLAG"));
    }
    else
    {
        puts("Guess wrong!");
    }
    return 0;
}

#include <stdio.h>
#include <stdlib.h>

void hackMe() {
	char buf[128];
	read(0, buf, 256);
}

int main(int argc, char **argv){
    setvbuf(stdin, NULL, _IONBF, 0);
    setvbuf(stdout, NULL, _IONBF, 0);
    puts("Welcome to the server!"); 
    hackMe();
    puts("Goodbye!");
}

#include <stdint.h>
#include <stdio.h>

int main(){
  setvbuf(stdout, 0, 2, 0);
  setvbuf(stdin, 0, 2, 0);
  
  char flag[40] = "FLAG{??????????????????????????????????}";
  char input[24];
  
  scanf("%s", input);
  printf(input);

  return 0;
}

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

char name[0x20] = "user";

void init(){
    setvbuf(stdin, NULL, _IONBF, 0);
    setvbuf(stdout, NULL, _IONBF, 0);
    setvbuf(stderr, NULL, _IONBF, 0);
}

int read_int(){
    char buf[0x10];
    read(0, buf, 0x10);
    return atoi(buf);
}

void hello() {
    puts("Hello, Hello, Hello~~~");
}

void editName(){
    char input[0x20];
    char y = '\0';
    while (1){
        puts("Enter your new name");
        write(1, "> ", 2);
        read(0, input, 0x80);
        printf("Set fans name to %s (Y/N)\n", input);
        y = getchar();
        if (y == 'Y' || y == 'y'){
            break;
        }
    }
    strcpy(name, input);
    puts("Name changed!");
}

int main(){
    init();
    puts("Welcome to the hello server, try to get the flag!\n");

    int choice = 0;
    while (1){
        puts("1. Edit Name");
        puts("2. Say Hello");
        puts("3. Exit");
        puts("Input your choice:");
        choice = read_int();
        switch (choice){
        case 1:
            editName();
            break;
        case 2:
            hello();
            break;
        case 3:
            exit(0);
            break;
        default:
            puts("Invalid argument!!");
            break;
        }
    }
    return 0;
}