## 2 Mobile Social Networking
### Attacks and Defenses in CAMSN services
Such attacks attempt to violate the privacy of an end-user's location history by associating that history with a unique, application layer identifier. In peer-to-peer systems, such attacks are made possible by the exchange of unique identifiers (e.g. social networking service user names) and profile data between nodes. Malicious nodes can log these unique identifiers, allowing reconstruction of a target device's (or user's) location history. In client-server systems, where unique identifiers are not swapped between nodes but rather from clients to application servers, direct anonymity attacks are possible by inserting malicious devices into the network. These malicious devices can continuously query an application server for the unique identifiers (or user names) of nearby devices and record the times at which such unique identifiers were seen. In both cases, attackers can use the observed identifiers to find corresponding social networking profiles. Importantly, anonymity attacks do not require a malicious node to receive information beyond what it would normally receive. That is, malicious entities can carry out such a direct anonymity attack by recording _only_ a victim's unique identifier, that victim's physical locations, and the times at which the victim was seen (and correlating that information with the victim's profile). Services can prevent or mitigate anonymity attacks via the use of encryption, though encryption is hard in the peer-to-peer case due the challenge of establishing shared keys (see section 4). A system using anonymous identifiers at the application level has been proposed [26]. This system is applicable to hybrid mobile social networking service architectures. It presumes that devices 1) utilize a short range communication technology for discovering proximity information (e.g. Bluetooth) and 2) have communication with a trusted _identity server_ (e.g. via the Internet). In this system, no communications use unique identifiers. Rather, all communications use anonymous identifiers, which are assigned on a per-message basis by the trusted identity server. Only the identity server can map anonymous identifiers to specific devices, and the server will perform this mapping only after verifying that two potentially communicating devices are truly within each other's physical proximity. This system prevents malicious parties from mapping messages or profile information to a specific user. **Privacy leakage**: While phishing attacks involve a malicious entity attempting to trick users, privacy leaks ostensibly occur with the user's permission. Both malicious and non-malicious entities can leverage this phenomenon. For example, a health insurance company might notice that a potential insuree's social networking profile is public, and look at that profile for information regarding the potential insuree's medical state. Though possible in any social network, the increased amount of personal information available to CAMSN services (and social networking services in general) dictates that such privacy leaks might have far greater consequences. For example, a website leveraging privacy leakage in CAMSN services has been released [27]. This website examines users' locations on CAMSN services and identifies users who are not in their home. By identifying users who are not at home, the site potentially aids malicious persons in finding empty homes to burglarize. The site _only_ makes use of publicly available information; users who appear on the site have _chosen_ to make their location publicly available (though, likely, without sufficient consideration). Sufficient documentation must be provided by mobile social networking services to ensure users are able to alter privacy settings. Default service privacy settings are of critical importance in battling privacy leakage, as even with documentation users might not understand how to alter privacy settings. **Network-based attacks**: Mobile social networking services are susceptible to attacks on their infrastructure.