The ubiquity of truly mobile appliances such as WiFi-enabled mobile phones, PDAs, and Internet web pads stands in stark contrast to the lack of mobility support in today's communication protocols. Many of these devices are multihomed and use standard protocols like IP and TCP, which have been designed for non-mobile computers with a single network device. Therefore, they are not able to cope with mobility and multihoming appropriately. Several protocols and protocol extensions have been proposed in order to add mobility support to TCP/IP. One of the most promising among them is the Host Identity Protocol (HIP) which adds an additional protocol layer between TCP and IP to hide host mobility from the transport layer. However, especially mobile devices with few CPU resources are slowed down by HIP. The poor performance of HIP on these mobile devices results from the extensive use of public-key cryptography for securing the main HIP protocol functions.

Lightweight HIP is a protocol extension which enables HIP to offer mobility and multihoming support without the use of public key cryptography. The goal of LHIP is to speed up HIP in order to make it usable for weak mobile devices. To achieve this goal, LHIP utilizes and refines several alternative authentication mechanisms like interactive hash chain authentication and incorporates them seamlessly into the HIP protocol design. First results prove that LHIP is able to provide decentralized mobility and multihoming support even to very resource-restricted devices. Thus, LHIP extends the scope of HIP to a wide range of truly mobile appliances.

The LHIP project is part of a long-term cooperation project between the Distributed Systems Group and the Helsinki Institute for Information Technology (HIIT). The collaboration is partly funded by the German Academic Exchange Service (DAAD).