Data Leakage Detection

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IEEE TRANSACTIONS ON KNOWLEDGE AND DATA ENGINEERING,

VOL. 23,

NO. 1,

JANUARY 2011

51

Data Leakage Detection
Panagiotis Papadimitriou, Student Member, IEEE, and Hector Garcia-Molina, Member, IEEE Abstract—We study the following problem: A data distributor has given sensitive data to a set of supposedly trusted agents (third parties). Some of the data are leaked and found in an unauthorized place (e.g., on the web or somebody’s laptop). The distributor must assess the likelihood that the leaked data came from one or more agents, as opposed to having been independently gathered by other means. We propose data allocation strategies (across the agents) that improve the probability of identifying leakages. These methods do not rely on alterations of the released data (e.g., watermarks). In some cases, we can also inject “realistic but fake” data records to further improve our chances of detecting leakage and identifying the guilty party. Index Terms—Allocation strategies, data leakage, data privacy, fake records, leakage model.

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1 INTRODUCTION
we study the following scenario: After giving a set of objects to agents, the distributor discovers some of those same objects in an unauthorized place. (For example, the data may be found on a website, or may be obtained through a legal discovery process.) At this point, the distributor can assess the likelihood that the leaked data came from one or more agents, as opposed to having been independently gathered by other means. Using an analogy with cookies stolen from a cookie jar, if we catch Freddie with a single cookie, he can argue that a friend gave him the cookie. But if we catch Freddie with five cookies, it will be much harder for him to argue that his hands were not in the cookie jar. If the distributor sees “enough evidence” that an agent leaked data, he may stop doing business with him, or may initiate legal proceedings. In this paper, we develop a model for assessing the “guilt” of agents. We also present algorithms for distributing objects to agents, in a way that improves our chances of identifying a leaker. Finally, we also consider the option of adding “fake” objects to the distributed set. Such objects do not correspond to real entities but appear realistic to the agents. In a sense, the fake objects act as a type of watermark for the entire set, without modifying any individual members. If it turns out that an agent was given one or more fake objects that were leaked, then the distributor can be more confident that agent was guilty. We start in Section 2 by introducing our problem setup and the notation we use. In Sections 4 and 5, we present a model for calculating “guilt” probabilities in cases of data leakage. Then, in Sections 6 and 7, we present strategies for data allocation to agents. Finally, in Section 8, we evaluate the strategies in different data leakage scenarios, and check whether they indeed help us to identify a leaker.

N the course of doing business, sometimes sensitive data must be handed over to supposedly trusted third parties. For example, a hospital may give patient records to researchers who will devise new treatments. Similarly, a company may have partnerships with other companies that require sharing customer data. Another enterprise may outsource its data processing, so data must be given to various other companies. We call the owner of the data the distributor and the supposedly trusted third parties the agents. Our goal is to detect when the distributor’s sensitive data have been leaked by agents, and if possible to identify the agent that leaked the data. We consider applications where the original sensitive data cannot be perturbed. Perturbation is a very useful technique where the data are modified and made “less sensitive” before being handed to agents. For example, one can add random noise to certain attributes, or one can replace exact values by ranges [18]. However, in some cases, it is important not to alter the...
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