Challenge 3: "Kung Pow: Enter the Code"

Challenge Description

Your task is to reverse engineer the provided C code and uncover the correct key to unlock the flag. (Capitalization counts here!)

Key Submission

C Code

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

void generate_key(char *key) {
    int i;
    
    int base_values[] = {96, 101, 118, 120, 127};  

    for (i = 0; i < 5; i++) {
        base_values[i] = base_values[i] + 3;
        base_values[i] = base_values[i] * 2;
        base_values[i] = base_values[i] / 2;
        base_values[i] = base_values[i] - (i * 2);
        base_values[i] = base_values[i] - 1;
    }

    for (i = 0; i < 5; i++) {
        key[i] = (char)base_values[i];
    }
    key[5] = '\0';
}

int validate_key(char *key) {
    CURL *curl;
    CURLcode res;
    int is_valid = 0;
    
    curl = curl_easy_init();
    if(curl) {
        char post_data[50];
        sprintf(post_data, "key=%s", key);

        curl_easy_setopt(curl, CURLOPT_URL, "https://fake-server.com/validate");

        curl_easy_setopt(curl, CURLOPT_POSTFIELDS, post_data);

        res = curl_easy_perform(curl);
        if(res == CURLE_OK) {
            printf("Server validation succeeded!\n");
            is_valid = 1;
        } else {
            printf("Server validation failed: %s\n", curl_easy_strerror(res));
        }

        curl_easy_cleanup(curl);
    }
    
    return is_valid;
}

int main() {
    char input[100];
    char correct_key[6];

    generate_key(correct_key);

    printf("Enter the secret key: ");
    scanf("%s", input);

    if (strcmp(input, correct_key) == 0) {
        if (validate_key(correct_key)) {
            printf("Correct! The flag will be sent by the server.\n");
        } else {
            printf("Server validation failed.\n");
        }
    } else {
        printf("Incorrect key. Try again.\n");
    }

    return 0;
}