WASET
Salam, M. , Rashid, N. , Khalid, S. , Khan, M.. "A NXM Version of 5X5 Playfair Cipher for any Natural Language (Urdu as Special Case)". World Academy of Science, Engineering and Technology, Open Science Index 49, International Journal of Computer and Information Engineering, (2011), 5(1), 66 - 68.