Preserving Privacy in Social Networks Against Neighborhood Attacks Bin Zhou Jian Pei School of Computing Science, Simon Fraser University 8888 University Drive, Burnaby, B.C., V5A1S6 Canada { bzhou, jpei } @cs.sfu.ca Dell Ed Abstract — Recently, as more and more social network data Bob Cathy has been published in one way or another, preserving privacy in publishing social network data becomes an important con- George cern. With some local knowledge about individuals in a social Fred Ada network, an adversary may attack the privacy of some victims easily. Unfortunately, most of the previous studies on privacy Harry Irene preservation can deal with relational data only, and cannot be applied to social network data. In this paper, we take an initiative (a) the social network (b) the network with anonymous nodes towards preserving privacy in social network data. We identify an essential type of privacy attacks: neighborhood attacks. If an adversary has some knowledge about the neighbors of a target Ada victim and the relationship among the neighbors, the victim may be re-identified from a social network even if the victim’s identity is preserved using the conventional anonymization techniques. We (c) the 1−neighborhood show that the problem is challenging, and present a practical solution to battle neighborhood attacks. The empirical study graph of Ada (d) privacy−preserved anonymous network indicates that anonymized social networks generated by our method can still be used to answer aggregate network queries Fig. 1. Neighborhood attacks in a social network. with high accuracy. I. I NTRODUCTION Ada and Bob, an adversary can even know from the released Recently, as more and more social network data has been social network (Figure 1(b)) that Ada and Bob are close made publicly available [1], [2], [3], [4], preserving privacy in friends, and they share one common close friend. Other private publishing social network data becomes an important concern. information can be further derived such as how well a victim Is it possible that releasing social network data, even with is connected to the rest of the network and the relative position individuals in the network aonymized, still intrudes privacy? of the victim to the center of the network. To protect the privacy satisfactorily, one way is to guaran- A. Motivation Example tee that any individual cannot be identified correctly in the With some local knowledge about individual vertices in a anonymized social network with a probability higher than 1 k , social network, an adversary may attack the privacy of some where k is a user-specified parameter carrying the same spirit victims. As a concrete example, consider a synthesized social in the k -anonymity model [5]. By adding a noise edge linking network of “close-friends” shown in Figure 1(a). Each vertex Harry and Irene, the 1 -neighborhood graph of every vertex in in the network represents a person. An edge links two persons Figure 1(d) is not unique. An adversary with the knowledge who are close friends. of 1 -neighborhood cannot identify any individual from this Suppose the network is to be published. To preserve privacy, anonymous graph with a confidence higher than 1 2 . is it sufficient to remove all identities as shown in Figure 1(b)? Unfortunately, if an adversary has some knowledge about the B. Challenges neighbors of an individual, the privacy may still be leaked. Although privacy preservation in data publishing has been If an adversary knows that Ada has two close friends who studied extensively and several important models such as k - know each other, and has another two close friends who do not know each other, i.e., the 1 -neighborhood graph of anonymity [5] and l -diversity [6] as well as many efficient algorithms have been proposed, most of the existing studies Ada as shown in Figure 1(c), then the vertex representing Ada can be identified uniquely in the network since no other can deal with relational data only. Those methods cannot be vertices have the same 1 -neighborhood graph. Similarly, Bob applied to social network data straightforwardly. can be identified in Figure 1(b) if the adversary knows the As elaborated in Section I-A, privacy may be leaked if a 1 -neighborhood graph of Bob. social network is released improperly to public. In practice, we Identifying individuals from released social networks in- need a systematic method to anonymize social network data trudes privacy immediately. In this example, by identifying before it is released. However, anonymizing social network
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