Cryptography for Efficiency : New Directions in Authenticated Data Structures

of “Cryptography for Efficiency: New Directions in Authenticated Data Structures” by Charalampos Papamanthou, Ph.D., Brown University, May 2011. Cloud computing has emerged as an important new computational and storage medium and is increasingly being adopted both by companies and individuals as a means of reducing operational and maintenance costs. However, remotely-stored sensitive data may be lost or modified and third-party computations may not be performed correctly due to errors, opportunistic behavior, or malicious attacks. Thus, while the cloud is an attractive alternative to local trusted computational resources, users need integrity guarantees in order to fully adopt this new paradigm. Specifically, they need to be assured that uploaded data has not been altered and outsourced computations have been performed correctly. Tackling the above problems requires the design of protocols that, on the one hand, are provably secure and at the same time remain highly efficient, otherwise the main purpose of adopting cloud computing, namely efficiency and scalability, is defeated. It is therefore essential that expertise in cryptography and efficient algorithmics be combined to achieve these goals. This thesis studies techniques allowing the efficient verification of data integrity and computations correctness in such adversarial environments. Towards this end, several new authenticated data structures for fundamental algorithmics and computation problems, e.g., hash table queries and set operations, are proposed. The main novelty of this work lies in employing advanced cryptography such as lattices and bilinear maps, towards achieving high efficiency, departing from traditional hash-based primitives. As such, the proposed techniques lead to efficient solutions that introduce minimal asymptotic overhead and at the same time enable highly-desirable features such as optimal verification mechanisms and parallel authenticated data structures algorithms. The small asymptotic overhead does translate into significant practical savings, yielding efficient protocols and system prototypes. Cryptography for Efficiency: New Directions in Authenticated Data Structures by Charalampos Papamanthou B.Sc., Applied Informatics, University of Macedonia, 2003 M.Sc., Computer Science, University of Crete, 2005 M.Sc., Computer Science, Brown University, 2007 A dissertation submitted in partial fulfillment of the requirements for the Degree of Doctor of Philosophy in the Department of Computer Science at Brown University Providence, Rhode Island May 2011 c © Copyright 2011 by Charalampos Papamanthou This dissertation by Charalampos Papamanthou is accepted in its present form by the Department of Computer Science as satisfying the dissertation requirement for the degree of Doctor of Philosophy. Date Roberto Tamassia, Director Recommended to the Graduate Council Date Michael T. Goodrich, Reader University of California, Irvine Date Anna Lysyanskaya, Reader Date Franco P. Preparata, Reader Approved by the Graduate Council Date Peter M. Weber Dean of the Graduate School iii