1. Structure based Data De-anonymization of Social Networks and Mobility Traces Shouling Ji, Weiqing Li, and Raheem Beyah Georgia Institute of Technology Mudhakar Srivatsa IBM T. J. Watson Research Center Jing S. He KSU Presenter: Qin Liu, Chinese University of Hong Kong

2. Ji et al.Structure based Data De-anonymization Introduction Social networking services are a fast-growing business nowadays – Facebook, Twitter, Google+, LiveJournal, YouTube, … When users participate in online social network activities, people’s privacy suffers potential serious threat – Create personal portfolio, post current location, … Countermeasures – Naïve anonymization: removing “Personally Identifiable Information (PII)” – Edge modification – k-anonymity and its varients Still vulnerable to powerful structure-based de-anonymization attacks – Narayanan-Shmatikov attack (IEEE S&P 2009) – Srivatsa-Hicks attack (ACM CCS 2012) – Others

3. Ji et al.Structure based Data De-anonymization Narayanan-Shmatikov attack (IEEE S&P 2009) Anonymized data: Twitter (crawled in late 2007) – A microblogging service – 224K users, 8.5M edges Auxiliary data: Flicker (crawled in late 2007/early 2008) – A photo-sharing service – 3.3M users, 53M edges Result: 30.8% of the users are successfully de-anonymized TwitterFlicker User mapping Heuristics Eccentricity Edge directionality Node degree Revisiting nodes Reverse match

4. Ji et al.Structure based Data De-anonymization Srivatsa-Hicks (ACM CCS 2012) Anonymized data – Mobility traces: St Andrews, Smallblue, and Infocom 2006 Auxiliary data – Social networks: Facebook, and DBLP De-anonymize mobility traces using corresponding social networks Over 80% users can be successfully de-anonymized

5. Ji et al.Structure based Data De-anonymization Other structural de-anonymization attacks Backstrom et al. attack (WWW 2007) – Both active attacks and passive attacks Narayanan et al. attack (IJCNN 2011) – A simplified version Narayanan-Shmatikov attack (IEEE S&P 2009) – For breaching link privacy Pedarsani et al. attack (Allerton 2013) – A Bayesian method based attack

6. Ji et al.Structure based Data De-anonymization Limitations of existing attacks Not scalable – E.g., Backstrom et al. attack (WWW 2007) needs to create Sybil users before anonymized data release, which is not controllable or scalable – E.g., Srivatsa-Hicks attack (CCS 2012) has a complexity of O(k!n 3 ), k is the number seeds, which is not scalable High computational cost – E.g., Narayanan-Shmatikov attack (S&P 2009) has a complexity of O(n k +n 4 ) Not general – E.g., Narayanan-Shmatikov attack (S&P 2009) is designed for directed graph – E.g., Pedarsani et al. attack (Allerton 2013) is good for sparse graphs but bad for dense graphs

7. Ji et al.Structure based Data De-anonymization Our contributions Defined and mesured three de-anonymization metrics – Strucutral similarity, relative distance similarity, and inheritance similarity Proposed a Unified Similarity (US) based De-Anonymization (DA) framework – Iteratively de-anonymize data with accuracy guarantee Generalized DA to an Adaptive De-Anonymization (ADA) framework – To de-anonymize large-scale data without the knowledge on the overlap size between the anonymized data and the auxiliary data Applied the proposed de-anonymization attacks to real world datasets – Successfully de-anonymized three mobility traces: At Andrews, Infocom06, and Smallblue – Successfully de-anonymized three social network datasets: ArnetMiner, Google+, and Facebook

8. Ji et al.Structure based Data De-anonymization Outline Background Preliminaries and Model De-anonymization Generalized Scalable De-anonymization Experiments Conclusion and Future Work

9. Ji et al.Structure based Data De-anonymization Preliminaries and Model Anonymized data graph Auxiliary data graph Attack Model – A de-anonymization attack is a mapping of users from the anonymized graph to the auxiliary graph, i.e.,

10. Ji et al.Structure based Data De-anonymization Datasets – mobility traces Mobility traces (anonymized data) and social networks (auxiliary data) (same as Srivatsa-Hicks attack (ACM CCS 2012)) Preprocess mobility traces to construct anonymized contact graphs (see Srivatsa and Hick’s paper for detail) Use social network as auxiliary data to de-anonymize mobility traces

11. Ji et al.Structure based Data De-anonymization Datasets – social networks ArnetMiner – A coauthor network – A weighted graph with weight indicating the number of coauthored papers – 1,127 authors and 6,690 “coauthor” relationships Google+ – Two Google+ datasets crawled on July 19 and August 6 in 2011, denoted by JUL and AUG, respectively – JUL: 5,200 users, 7,062 connections – AUG: 5,200 users, 7,813 connections Facebook – 63,731 users – 1,269,502 friend relationships

12. Ji et al.Structure based Data De-anonymization Outline Background Preliminaries and Model De-anonymization Generalized Scalable De-anonymization Experiments Conclusion and Future Work

13. Ji et al.Structure based Data De-anonymization De-anonymization High-Level Description – Seed selection – Mapping propagation Seed selection – Identify a small number of seed mappings from the anonymized graph to the auxiliary graph – Bootstrap the de-anonymization Mapping propagation – De- anonymize the anonymized graph using multiple similarity measurements

14. Ji et al.Structure based Data De-anonymization Mapping Propagation Metrics – Structural Similarity – Relative Distance Similarity – Inheritance Similarity – Unified Similarity We also defined the weighted version of these metrics by considering the weights on edges Propagation framework

15. Ji et al.Structure based Data De-anonymization Structural Similarity Degree centrality – The number of ties that a node has in a graph

16. Ji et al.Structure based Data De-anonymization Structural Similarity Closeness centrality – How close a node is to others nodes in a graph

17. Ji et al.Structure based Data De-anonymization Structural Similarity Betweenness centrality – A node’s global structural importance within a graph

18. Ji et al.Structure based Data De-anonymization Structural Similarity Defined as the cosine similarity between two nodes’ degree, closeness, and betweenness centralities

19. Ji et al.Structure based Data De-anonymization Relative Distance Similarity Defined as the cosine similarity between two nodes’ distance vectors to seeds

20. Ji et al.Structure based Data De-anonymization Inheritance Similarity Characterize the knowledge provided by current mapping results – Two nodes have more common mapped neighbors will have high inheritance similarity score

21. Ji et al.Structure based Data De-anonymization Unified Similarity (US) Considering the structural similarity, relative distance similarity, and inheritance similarity Weights US Structural similarity Relative distance similarity Inheritance similarity

22. Ji et al.Structure based Data De-anonymization US based De-Anonymization (DA) Framework Step 1: seed identification by existing techniques Step 2: calculate two candidate node sets C a and C u from the anonymized graph and the auxiliary graph, respectively Step 3: calculate the US of each user from C a to every user in C u, and construct a weighted bipartite graph from C a and C u based on the calculated US scores Step 4: Seek a maximum weighted bipartite matching Step 5: Decide whether to accept a node de-anonymization result in the bipartite mathching Go to step 2 if the end condition is not reached

23. Ji et al.Structure based Data De-anonymization Outline Background Preliminaries and Model De-anonymization Generalized Scalable De-anonymization Experiments Conclusion and Future Work

24. Ji et al.Structure based Data De-anonymization Generalized Scalable De-anonymization Core Matching Subgraph (CMS)

25. Ji et al.Structure based Data De-anonymization Adaptive De-Anonymization (ADA) Identify initial CMS Run DA on initial CMS Update CMS or End

26. Ji et al.Structure based Data De-anonymization Outline Background Preliminaries and Model De-anonymization Generalized Scalable De-anonymization Experiments Conclusion and Future Work

27. Ji et al.Structure based Data De-anonymization Experiments – de-anonymize mobility traces

28. Ji et al.Structure based Data De-anonymization Experiments – de-anonymize ArnetMiner

29. Ji et al.Structure based Data De-anonymization Experiments – de-anonymize Google+

30. Ji et al.Structure based Data De-anonymization Experiments – de-anonymize Facebook

31. Ji et al.Structure based Data De-anonymization Conclusion and Future Work Conclusion – Proposed and examined several structural similarity metrics – Designed a new scalable structural de-anonymization framework for mobility traces and social networks – Validated the proposed de-anonymization framework on multiple mobility traces and social networks Future work – More experiments on large-scale datasets – De-anonymizablity quantification (partially done in our ACM CCS 2014 paper) – Secure data publishing system

32. Ji et al.Structure based Data De-anonymization Thank you and the presenter Qin Liu! Shouling Ji sji@gatech.edu http://users.ece.gatech.edu/sji/