//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  ):   x    y     u    v   =   0    1     1    0   while   a   !=   0  :   q     r   =   b  //  a     b  %  a   m     n   =   x  -  u  *  q     y  -  v  *  q   b    a     x    y     u    v   =   a    r     u    v     m    n   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.