Topic: "On the Design of Secure Codes at Finite Lengths for Wiretap Channel"
Speaker: Prof. Jeongseok Ha
Affiliation: Korea Advanced Institute of Science and Technology (KAIST)

Summary:
Ozarow and Wyner proposed a secrecy code design scheme using a linear code and its cosets. It was shown that when a wiretap channel has a noiseless main channel and an eavesdropper taps a subset of coded bits through a wiretapper’s channel, the eavesdropper’s equivocation is readily obtained by analyzing a parity-check matrix of the linear code. However, for wiretap codes at finite lengths, the complexity to find the equivocation grows rapidly and becomes prohibitive with the increasing length of codewords. In this talk, we introduce a tight lower bound on the equivocation that can be available by simple manipulations when a secrecy code is transmitted over a perfect-BEC wiretap channel of type-I. The lower bound provides a guaranteed secrecy performance for various linear codes at any lengths over perfect-BEC wiretap channels of type-I. It will be demonstrated that the lower bound can be applied to design of secrecy codes for wiretap channels of type-I with Gaussian main and wiretapper’s channels.
In this talk, we also discuss a binary erasure wiretap channel of type II in which the number of eavesdropped bits becomes available a posteriori. We aim at achieving perfect secrecy over such a channel model. The most appropriate application is a secret key agreement scheme. We present a secret key agreement scheme that adopts the formulation S = HX of Wyner-Ozarows’s linear coset coding. The scheme is based on the following simple observation: even if some information on a secret message S leaked out, it is still possible to have perfect secrecy for some subsequence of S. Our secret key agreement scheme achieves perfect secrecy by taking only those subsequences that are independent of the eavesdropped bits. Our secret key agreement scheme naturally leads to defining a security measure D for parity-check matrices such that the eavesdropper gets zero information on the subsequence as long as the length of the subsequence is less than the security measure D. Possible applications of the key agreement scheme will also be introduce.
 
Bio:
Jeongseok Ha received the B.E. degree in electronics from Kyungpook National University, Taegu, Korea in 1992, the M.S. degree in electronic and electrical engineering from Pohang University of Science and Technology, Pohang, Korea, in 1994, and the Ph.D. degree in electrical and computer engineering from Georgia Institute of Technology, Atlanta, in 2003. He is now with Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea, as an associate professor. His research interests include theories and applications of error-control codes and physical layer security.

For more information:

Hyoungsuk Jeon, h.jeon@gatech.edu

Cordai Farrar, cordai.farrar@ece.gatech.edu, 404-894-7890