#include #include #include // only works with uppercase letters because i'm lazy. bool check_alpha(std::string text) { for (char c : text) { if (!isalpha(c)) return false; } return true; } std::string cipher(std::string text, const std::string key) { unsigned int key_length = key.length(); for (unsigned int i = 0; i < text.length(); ++i) { text[i] += key[i % key_length] - 'A'; if (text[i] > 'Z') text[i] -= 'Z' - 'A' + 1; } return text; } std::string decipher(std::string text, std::string key) { unsigned int key_length = key.length(); for (unsigned int i = 0; i < text.length(); ++i) { text[i] -= key[i % key_length] - 'A'; if (text[i] < 'A') text[i] += 'Z' - 'A' + 1; } return text; } std::string find_key(std::string text, std::string cipher) { if (text.length() != cipher.length()) { text = "string lengths don't match, no key possible"; return text; } for (unsigned int i = 0; i < text.length(); ++i) { if (text[i] == cipher[i]) text[i] = 'A'; else if (text[i] < cipher[i]) text[i] = cipher[i] - text[i] + 'A'; else text[i] = cipher[i] - text[i] + 'Z' + 1; } return text; } int main() { std::string text = "secret"; std::string key = "akey"; if (!check_alpha(text) or !check_alpha(key)) { std::cout << "error: enter text only"; return 0; } std::transform(text.begin(), text.end(), text.begin(), toupper); std::transform(key.begin(), key.end(), key.begin(), toupper); std::cout << "text: " << text << std::endl; std::cout << "key: " << key << std::endl; std::string text_ciphered = cipher(text, key); std::cout << "\nciphered text: " << text_ciphered << std::endl; std::cout << "deciphered text: " << decipher(text_ciphered, key) << std::endl; std::cout << "used key: " << find_key(text, text_ciphered); return 0; }

Vigenère cipher (polyalphabetic substitution)