Chattering Laptops

Mobile computer users often have a false sense of anonymity when they connect to the Internet at cafes, hotels, airports or other public places. In this paper, we analyze information leaked by mobile computers to the local access link when they are outside their home domain. While most application data can be encrypted, there is no similar protection for signaling messages in the lower layers of the protocol stack. We found that all layers of the protocol stack leak various plaintext identifiers of the user, the computer and their affiliations to the local link, which a casual attacker can observe. This violates the user’s sense of privacy and may make the user or computer vulnerable to further attacks. It is, however, not possible to disable the offending protocols because many of them are critical to the mobile user experience. We argue that the most promising solutions to the information leaks are to filter outbound data, in particular name resolution requests, and to disable unnecessary service discovery depending on the network location. This is because most information leaks result from failed attempts by roaming computers to connect to services that are not available in the current access network.