//CPP program to illustrate Affine Cipher #include   using namespace std; //Key values of a and b const int a = 17; const int b = 20; string encryptMessage(string msg) {  ///Cipher Text initially empty  string cipher = '';   for (int i = 0; i < msg.length(); i++)  {  // Avoid space to be encrypted   if(msg[i]!=' ')   /* applying encryption formula ( a x + b ) mod m  {here x is msg[i] and m is 26} and added 'A' to   bring it in range of ascii alphabet[ 65-90 | A-Z ] */  cipher = cipher +   (char) ((((a * (msg[i]-'A') ) + b) % 26) + 'A');  else  //else simply append space character  cipher += msg[i];   }  return cipher; } string decryptCipher(string cipher) {  string msg = '';  int a_inv = 0;  int flag = 0;    //Find a^-1 (the multiplicative inverse of a   //in the group of integers modulo m.)   for (int i = 0; i < 26; i++)  {  flag = (a * i) % 26;    //Check if (a*i)%26 == 1  //then i will be the multiplicative inverse of a  if (flag == 1)  {   a_inv = i;  }  }  for (int i = 0; i < cipher.length(); i++)  {  if(cipher[i]!=' ')  /*Applying decryption formula a^-1 ( x - b ) mod m   {here x is cipher[i] and m is 26} and added 'A'   to bring it in range of ASCII alphabet[ 65-90 | A-Z ] */  msg = msg +   (char) (((a_inv * ((cipher[i]+'A' - b)) % 26)) + 'A');  else  //else simply append space character  msg += cipher[i];   }  return msg; } //Driver Program int main(void) {  string msg = 'AFFINE CIPHER';    //Calling encryption function  string cipherText = encryptMessage(msg);  cout << 'Encrypted Message is : ' << cipherText<<endl;    //Calling Decryption function  cout << 'Decrypted Message is: ' << decryptCipher(cipherText);  return 0; } 

// Java program to illustrate Affine Cipher class GFG  {  // Key values of a and b  static int a = 17;  static int b = 20;  static String encryptMessage(char[] msg)   {  /// Cipher Text initially empty  String cipher = '';  for (int i = 0; i < msg.length; i++)  {  // Avoid space to be encrypted   /* applying encryption formula ( a x + b ) mod m  {here x is msg[i] and m is 26} and added 'A' to   bring it in range of ascii alphabet[ 65-90 | A-Z ] */   if (msg[i] != ' ')   {  cipher = cipher  + (char) ((((a * (msg[i] - 'A')) + b) % 26) + 'A');  } else // else simply append space character  {  cipher += msg[i];  }  }  return cipher;  }  static String decryptCipher(String cipher)   {  String msg = '';  int a_inv = 0;  int flag = 0;  //Find a^-1 (the multiplicative inverse of a   //in the group of integers modulo m.)   for (int i = 0; i < 26; i++)   {  flag = (a * i) % 26;  // Check if (a*i)%26 == 1  // then i will be the multiplicative inverse of a  if (flag == 1)   {  a_inv = i;  }  }  for (int i = 0; i < cipher.length(); i++)   {  /*Applying decryption formula a^-1 ( x - b ) mod m   {here x is cipher[i] and m is 26} and added 'A'   to bring it in range of ASCII alphabet[ 65-90 | A-Z ] */   if (cipher.charAt(i) != ' ')   {  msg = msg + (char) (((a_inv *   ((cipher.charAt(i) + 'A' - b)) % 26)) + 'A');  }   else //else simply append space character  {  msg += cipher.charAt(i);  }  }  return msg;  }  // Driver code  public static void main(String[] args)   {  String msg = 'AFFINE CIPHER';  // Calling encryption function  String cipherText = encryptMessage(msg.toCharArray());  System.out.println('Encrypted Message is : ' + cipherText);  // Calling Decryption function  System.out.println('Decrypted Message is: ' + decryptCipher(cipherText));  } } // This code contributed by Rajput-Ji 

# Implementation of Affine Cipher in Python # Extended Euclidean Algorithm for finding modular inverse # eg: modinv(7 26) = 15 def egcd(a b): xy uv = 01 10 while a != 0: q r = b//a b%a m n = x-u*q y-v*q ba xy uv = ar uv mn gcd = b return gcd x y def modinv(a m): gcd x y = egcd(a m) if gcd != 1: return None # modular inverse does not exist else: return x % m # affine cipher encryption function  # returns the cipher text def affine_encrypt(text key):  '''  C = (a*P + b) % 26  ''' return ''.join([ chr((( key[0]*(ord(t) - ord('A')) + key[1] ) % 26) + ord('A')) for t in text.upper().replace(' ' '') ]) # affine cipher decryption function  # returns original text def affine_decrypt(cipher key):  '''  P = (a^-1 * (C - b)) % 26  ''' return ''.join([ chr((( modinv(key[0] 26)*(ord(c) - ord('A') - key[1])) % 26) + ord('A')) for c in cipher ]) # Driver Code to test the above functions def main(): # declaring text and key text = 'AFFINE CIPHER' key = [17 20] # calling encryption function affine_encrypted_text = affine_encrypt(text key) print('Encrypted Text: {}'.format( affine_encrypted_text )) # calling decryption function print('Decrypted Text: {}'.format ( affine_decrypt(affine_encrypted_text key) )) if __name__ == '__main__': main() # This code is contributed by # Bhushan Borole 

// C# program to illustrate Affine Cipher using System;   class GFG  {  // Key values of a and b  static int a = 17;  static int b = 20;  static String encryptMessage(char[] msg)   {  /// Cipher Text initially empty  String cipher = '';  for (int i = 0; i < msg.Length; i++)  {  // Avoid space to be encrypted   /* applying encryption formula ( a x + b ) mod m  {here x is msg[i] and m is 26} and added 'A' to   bring it in range of ascii alphabet[ 65-90 | A-Z ] */  if (msg[i] != ' ')   {  cipher = cipher  + (char) ((((a * (msg[i] - 'A')) + b) % 26) + 'A');  } else // else simply append space character  {  cipher += msg[i];  }  }  return cipher;  }  static String decryptCipher(String cipher)   {  String msg = '';  int a_inv = 0;  int flag = 0;  //Find a^-1 (the multiplicative inverse of a   //in the group of integers modulo m.)   for (int i = 0; i < 26; i++)   {  flag = (a * i) % 26;  // Check if (a*i)%26 == 1  // then i will be the multiplicative inverse of a  if (flag == 1)   {  a_inv = i;  }  }  for (int i = 0; i < cipher.Length; i++)   {  /*Applying decryption formula a^-1 ( x - b ) mod m   {here x is cipher[i] and m is 26} and added 'A'   to bring it in range of ASCII alphabet[ 65-90 | A-Z ] */  if (cipher[i] != ' ')   {  msg = msg + (char) (((a_inv *   ((cipher[i] + 'A' - b)) % 26)) + 'A');  }   else //else simply append space character  {  msg += cipher[i];  }  }  return msg;  }  // Driver code  public static void Main(String[] args)   {  String msg = 'AFFINE CIPHER';  // Calling encryption function  String cipherText = encryptMessage(msg.ToCharArray());  Console.WriteLine('Encrypted Message is : ' + cipherText);  // Calling Decryption function  Console.WriteLine('Decrypted Message is: ' + decryptCipher(cipherText));  } } /* This code contributed by PrinciRaj1992 */ 

//Javascript program to illustrate Affine Cipher //Key values of a and b let a = 17; let b = 20; function encryptMessage(msg) {  ///Cipher Text initially empty  let cipher = '';   for (let i = 0; i < msg.length; i++)  {  // Avoid space to be encrypted   if(msg[i] !=' ')   /* applying encryption formula ( a x + b ) mod m  {here x is msg[i] and m is 26} and added 'A' to   bring it in range of ascii alphabet[ 65-90 | A-Z ] */  cipher = cipher + String.fromCharCode((((a * (msg[i].charCodeAt(0)-65) ) + b) % 26) + 65);  else  //else simply append space character  cipher += msg[i];   }  return cipher; } function decryptCipher(cipher) {  let msg = '';  let a_inv = 0;  let flag = 0;    //Find a^-1 (the multiplicative inverse of a   //in the group of integers modulo m.)   for (let i = 0; i < 26; i++)  {  flag = (a * i) % 26;    //Check if (a*i)%26 == 1  //then i will be the multiplicative inverse of a  if (flag == 1)  {   a_inv = i;  }  }  for (let i = 0; i < cipher.length; i++)  {  if(cipher[i]!=' ')  /*Applying decryption formula a^-1 ( x - b ) mod m   {here x is cipher[i] and m is 26} and added 'A'   to bring it in range of ASCII alphabet[ 65-90 | A-Z ] */  msg = msg + String.fromCharCode(((a_inv * ((cipher[i].charCodeAt(0)+65 - b)) % 26)) + 65);  else  //else simply append space character  msg += cipher[i];   }  return msg; } //Driver Program let msg = 'AFFINE CIPHER'; //Calling encryption function let cipherText = encryptMessage(msg); console.log('Encrypted Message is : ' + cipherText); //Calling Decryption function console.log('Decrypted Message is: ' + decryptCipher(cipherText)); // The code is contributed by Arushi Jindal.