Crypto Seminar

— 5:30pm

In Person and Virtual - ET - Blelloch-Skees Conference Room, Gates Hillman 8115 and Zoom

SURYA MATHIALAGAN , Ph.D. Student, Computer Science / Theory Group, Massachusetts Institute of Technology

Optimal Oblivious RAM with Integrity

Oblivious RAM (ORAM), introduced by Goldreich and Ostrovsky (J. ACM '96), is a primitive that allows a client to perform RAM computations on a server without revealing any information about the underlying data, even via the access pattern. For a database of size N, well-known lower bounds show that a multiplicative overhead of Omega(\log N) in the number of RAM operations is necessary assuming O(1) client storage. A long sequence of works culminated in the asymptotically optimal construction of Asharov, Komargodski, Lin, and Shi (CRYPTO 2021) with O(\log N) worst-case overhead and O(1) client storage. However, this optimal ORAM construction is only known to be secure in the semi-honest setting, where an adversary is allowed to observe the access patterns but not modify the contents of the database. In the malicious setting, if an adversary is allowed to tamper with the database, this construction and many others in fact become insecure. In this work, we construct an ORAM protocol with worst-case O(\log N) overhead and O(1) client storage that protects against tampering adversaries. By the Omega(\log N) ORAM lower bound, our construction is asymptotically optimal. We can also interpret our construction as an online memory checker that matches the bandwidth of the best known online memory checkers while additionally hiding the access pattern. To achieve this, we intricately interleave the ORAM construction of Asharov et al. with online and offline memory checking techniques. In Person and Zoom Participation. See announcement.

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