/****************************************** Author: Nautash Ahmad Created: 4th September, 2018 ------------------------------------------- Description: The Gronsfeld cipher is essentially a Vigenère cipher, but uses numbers instead of letters in a key. Cracking Methods And Weaknesses: Frequency analysis is best attack method. ------------------------------------------- How to use in CPG: First enter the text you want to encrypt then enter the numeric key. Referal Links: https://en.m.wikipedia.org/wiki/Vigenère_cipher https://www.dcode.fr/gronsfeld-cipher ******************************************/ #include #include #include using namespace std; string GenerateKey(string str, string keyword); string CipheredText(string str, string key); int main() { string str, keyword; cin >> str; cout << "Entered text: " << str << endl; cin >> keyword; cout << "Entered key: " << keyword << endl << endl; //Checking if the key is entered while(keyword.empty()) { cout << "\nNo key entered, enter the for encryption: "; cin >> keyword; cout << "\nEntered key: " << keyword << endl << endl; } //Checking if key's length is greater than text length if(keyword.size() > str.size()) { cout << "Length of key cannot be greater than the length of text\n"; return 0; } //Checking if the text contain numbers or special characters for(int i = 0; i < str.size(); i++) { if(isdigit(str[i]) || ispunct(str[i])) { cout << "Cannot encrypt text because the text contains special character or number \n"; return 0; } } //Checking if the key contain alphabets or special characters for(int i = 0; i < keyword.size(); i++) { if(isalpha(keyword[i]) || ispunct(keyword[i])) { cout << "Cannot encrypt text because the key contains special character or an alphabet\n"; return 0; } } //Converting the text to uppercase for(int i = 0; i < str.size(); i++) { if(islower(str[i])) str[i] = toupper(str[i]); } string key = GenerateKey(str, keyword); string cipherStr = CipheredText(str, key); cout << "Encrypted text: " << cipherStr << endl; return 0; } //This function generates the key in a cyclic manner until it's length isn't equal to the length of the plain text string GenerateKey(string str, string keyword) { int sizeOfText = str.size(); string key = "\0"; if(str.size() == keyword.size()) key = keyword; else { int index = 0, count = 0; while(count < sizeOfText) { key += keyword[index]; if(index == (keyword.size() -1)) index = -1; index++; count++; } } return key; } //This function will generate the Encrypted text with the help of a key string CipheredText(string str, string key) { string cipherStr = "\0"; for(int i = 0; i < str.size(); i++) { int num = key[i] - '0'; int x = str[i] + num; if(x > 90) x -= 26; cipherStr += (char)x; } return cipherStr; }

Gronsfeld Cipher