Muhammad Salam and  Nasir Rashid and  Shah Khalid and  Muhammad Raees Khan,  A NXM Version of 5X5 Playfair Cipher for any Natural Language (Urdu as Special Case).   journal   = {International Journal of Computer and Information Engineering}, [online]. World Academy of Science, Engineering and Technology.
    January 2011, vol. 49(1). 66 - 68
    [viewed 19 January 2020]. Available from: https://publications.waset.org/pdf/9796.