On Secure Capacity of Multiple Unicast Traffic over Separable Networks This paper studies the problem of information theoretic secure communication when a source has private messages to transmit to m destinations, in the presence of a passive adversary who eavesdrops an unknown set of k edges. The information theoretic secure capacity is derived over unitedge capacity separable networks, for the cases when k  1 and m is arbitrary, or m  3 and k is arbitrary. This is achieved by first showing that there exists a secure polynomialtime code construction that matches an outer bound over twolayer networks, followed by a deterministic mapping between twolayer and arbitrary separable networks.

Private Authentication: Optimal Information Theoretic Schemes The main security service in the connected world of cyber physical systems necessitates to authenticate a large number of nodes privately. In this paper, the private authentication problem is considered, that consists of a certificate authority, a verifier, many legitimate users (prover) and any arbitrary number of illegitimate users. Each legitimate user wants to be authenticated (using his personal key) by the verifier, while simultaneously wants to stay completely anonymous (even to the verifier and the CA). On the other hand, an illegitimate user must fail to authenticate himself. We analyze this problem from an information theoretical perspective. First, we propose a general interactive informationtheoretic model for the problem. As a metric to measure the reliability, we consider the authentication key rate whose rate maximization has a tradeoff with establishing privacy. Then, we analyze the problem in two different regimes: finite size regime (i.e., the variables are elements of a finite field) and asymptotic regime (i.e., the variables are considered to have large enough length). For both regimes, we propose schemes that satisfy the completeness, soundness and privacy properties. In finite size regime, the idea is to generate the authentication keys according to a secret sharing scheme. In asymptotic regime, we use a random binning based scheme which relies on the joint typicality to generate the authentication keys. Moreover, providing the converse proof, we show that our scheme achieves capacity in the asymptotic regime. For finite size regime our scheme achieves capacity for large field size.