Secure Mobile Instant Messaging key exchanging protocol with One-Time-Pad substitution transposition cryptosystem

The Mobile Instant Messaging Service (MIMS) is a popular feature on mobile communication devices today. It is a powerful and cheap facility to send and to receive messages through a handheld portable tool. Currently, many MIMS applications are available to support humans' activities in their everyday life. However, the security of this service needs to be increased for further applications such as a more friendly and easily approach on secure mobile transactions and personal health assistance. In this paper, we propose a new simple cryptography scheme for MIMS that is based on the Diffie-Hellman Key Exchange and Pseudo One Time Pad encryption. This scheme is designed for mobile devices that have limitations because of small memory and a low-speed processor. Furthermore, it extends the security level of the previous schemes which are Crypt21 and RTC-MTT.