An In-depth Look at Wireless WAN Security: Cellular Digital Packet Data Networks and their Security Issues

A Cellular Digital Packet Data (CDPD) network is one of the most common wireless infrastructures. A CDPD network is an overlay service on top of the existing AMPS (Advanced Mobile Phone Systems) cellular voice networks. A mobile unit in a CDPD network, also known, as Mobile End System (MES) is a computer with a CDPD modem. The CDPD network guaranties the packet delivery to the MES, while MES constantly changes its physical location. For an MES to have access to a CDPD network it must be authenticated either directly by Mobile Data Intermediate System's (MDIS) Mobile Home Function (MHF), while an MES' is in its home area or through MDIS's Mobile Serving Function (MSF) while roaming. Once authenticated, MES can access public networks such as internet. Although CDPD networks provide some level of encryption and authentication, the authentication scheme is unilateral, i.e. only MES are being authenticated by MHF. Neither MHF nor MSF will be authenticated by MES. In the meantime the traffic encryption is only available over the radio frequency. The lack of a bilateral authentication and partial route encryption are two of the major security concerns in CDPD networks. In this paper the security architecture of a CDPD network will be scrutinized and some possible solutions will be investigated.