Fordham University            The Jesuit University of New York

CIS Department Talk - December 7, 2009

The Department of Computer and Information Science Present

Speaker:Dr. Dah-Yoh Lim
Topic: The Paradigm of Partial Erasures
Date:December 7, 2009, 6:00PM
Place:Lincoln Center Campus, Lowenstein, Room 311


Erasing old data and keys is an important tool in cryptographic protocol design. It is useful in many settings, including proactive security, adaptive security, forward security, and intrusion resilience. Protocols for all these settings typically assume the ability to perfectly erase information. Unfortunately, as amply demonstrated in the systems literature, perfect erasures are hard to implement in practice. We propose a model of partial erasures where erasure instructions leave almost all the data erased intact, thus giving the honest players only a limited capability for disposing of old data. Nonetheless, we provide a general compiler that transforms any secure protocol using perfect erasures into one that maintains the same security properties when only partial erasures are available. The key idea is a new redundant representation of secret data which can still be computed on, and yet is rendered useless when partially erased. We prove that any such a compiler must incur a cost in additional storage, and that our compiler is near optimal in terms of its storage overhead. This talk will focus on the practical implications and applicability of the work.

Dr. Dah-Yoh Lim received his B.B.A. in Finance and B.S. in Computer Science and Information Engineering from National Taiwan University, Taipei, Taiwan in 2001, and his S.M. and Ph.D. in Computer Science from MIT in 2004 and 2008 respectively. His research interests include supply chains, rank aggregation, and cryptography and network security. He is now a software developer.

For More Information Contact: Ms. Danielle Aprea 718-817-4480 or Email:


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