SMS technology was not designed to transmit secure data; it does not provide built-in support for any security feature (e.g., authentication and confidentiality) between SMS communicators, in this book, a centralized secure messaging system (CSMS) is introduced. It allows the system clients to exchange highly secured messages exclusively via trusted third party (i.e. server). The main server contains a central database that holds clients' information. Depending on this information the server does the required message processing and forwards it to its final destination. The communication of the proposed CSMS is based on GPRS in case of internet availability. Also, beside GPRS the system is fully functional depending on Global System for Mobile communications (GSM). The transmitted encrypted SMS passes through some coding stages (i.e., convolution and shuffling) to meet the diffusion and confusion requirement, then it is further encrypted using Rivest Cipher (RC4) with dynamic peer to peer (P2P) encryption key. The users can send SMS using a dedicated Android based application, also, they can send it using an established HTTP server via a dedicated website.
