International Association for Cryptologic Research

Ph.D. Database

The aim of the IACR Ph.D. database is twofold. On the first hand, we want to offer an overview of Ph.D. already completed in the domain of cryptology. Where possible, this should also include a subject classification, an abstract, and access to the full text. On the second hand, it deals with Ph.D. subjects currently under investigation. This way, we provide a timely map of contemporary research in cryptology. All entries or changes need to be approved by an editor. You can contact them via phds (at)


Nishanth Chandran (#706)
Name Nishanth Chandran
Personal Homepage
Topic of his/her doctorate. Theoretical Foundations of Position-Based Cryptography
Category cryptographic protocols
Ph.D. Supervisor(s) Rafail Ostrovsky, Amit Sahai
Year of completion 2011
Abstract In this thesis, we initiate the study of cryptographic protocols where the identity, or other credentials and inputs, of a party are derived from its \emph{geographic location}. We start by considering the central task in this setting, i.e., securely verifying the position of a device. Despite much work in this area, we show that in the Vanilla (or standard) model, this above task (i.e., of secure positioning) is impossible to achieve, even if we assume that the adversary is computationally bounded. In light of the above impossibility result, we then turn to Dziembowski's Bounded Retrieval Model (a variant of Maurer's Bounded Storage Model) and formalize and construct information theoretically secure protocols for two fundamental tasks: \begin{itemize} \item[-] Secure Positioning; and \item[-] Position-Based Key Exchange. \end{itemize} We then show that these tasks are in fact {\em universal\/} in this setting -- we show how we can use them to realize Secure Multi-Party Computation. The main contribution of this thesis is threefold: to place the problem of secure positioning on a sound theoretical footing; to prove a strong impossibility result that simultaneously shows the insecurity of previous attempts at the problem; and to present positive results showing that the bounded-retrieval framework is a fruitful one to study the foundations of position-based cryptography. This thesis is based on joint works with Vipul Goyal, Ryan Moriarty, and Rafail Ostrovsky.
E-Mail Address nish (at)
Last Change 2011-10-25 13:31:16
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