Private Discovery of Common Social Contacts

  • Emiliano De Cristofaro
  • Mark Manulis
  • Bertram Poettering
Part of the Lecture Notes in Computer Science book series (LNCS, volume 6715)


The increasing use of computing devices for social interactions propels the proliferation of online social applications, yet, it prompts a number of privacy concerns. One common problem occurs when two unfamiliar users, in the process of establishing social relationships, want to assess their social proximity by discovering mutual contacts. In this paper, we introduce Private Contact Discovery, a novel cryptographic primitive that lets two users, on input their respective contact lists, learn their common contacts (if any), and nothing else. We present an efficient and provably secure construction, that (i) prevents arbitrary list manipulation by means of contact certification, and (ii) guarantees user authentication and revocability. Following a rigorous cryptographic treatment of the problem, we define the privacy-protecting contact-hiding property and prove it for our solution, under the RSA assumption in the Random Oracle Model (ROM). We also show that other related cryptographic techniques, such as Private Set Intersection and Secret Handshakes, are unsuitable in this context. Experimental analysis attests to the practicality of our technique, which achieves computational and communication overhead (almost) linear in the number of contacts.


Random Oracle Model Contact List Protocol Execution User Versus Anonymous Credential 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2011

Authors and Affiliations

  • Emiliano De Cristofaro
    • 1
  • Mark Manulis
    • 2
  • Bertram Poettering
    • 2
  1. 1.Computer Science DepartmentUniversity of CaliforniaIrvineUSA
  2. 2.Cryptographic Protocols GroupTU Darmstadt & CASEDGermany

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