Secret key agreement (SKA) is a basic cryptographic primitive that establishes a shared secret key between parties. In the two-party source model of SKA, Alice and Bob want to share a secret key. They each have private samples of two correlated variables that are partially leaked to Eve. In a one-way SKA protocol, Alice sends a single message to Bob over a public channel, allowing the two parties to calculate a shared secret key that will be essentially unknown to Eve. The length of the key is a function of the number of samples$n$. In this paper, we prove a tight second-order asymptotic approximation of the key length of one-way SKA protocols, and propose an approach to construct a computationally efficient one-way SKA protocol with near-optimum finite key length. We compare our results with related work, and discuss future research directions.

In secret key agreement (SKA) in multiterminal channel model, terminals are connected by a noisy discrete memoryless channel (DMC) with multiple input and multiple outputs. Terminals can use the DMC to obtain correlated randomness, and communicate over a noiseless public channel to establish a shared secret key among a designated subset of terminals. We focus on a special class of multiterminal channel models, called wiretapped Polytree-PIN, in which the noisy channel consists of a set of independent point-to-point channels whose underlying undirected connectivity graph forms a tree. We consider a wiretap setting, where the output of each point-to-point channel is partially leaked to a passive wiretapper adversary, Eve, through a second independent noisy channel. A secure SKA protocol generates a group secret key such that Eve has no information about it. In this paper, we derive the wiretap secret key capacity, which is the largest achievable secret key rate, of the wiretapped PolytreePIN model. Our result also implies the key capacity of the non-wiretapped Polytree-PIN model, that is the case when there is no leakage from point-to-point channels to Eve.

Secret key agreement (SKA) is an essential primitive in cryptography and information security. In a multiterminal key agreement problem, there are a set of terminals each having access to a component of a vector random variable, and the goal of the terminals is to establish a shared key among a designated subset of terminals. This problem has been studied under different assumptions about the adversary. In the most general model, the adversary has access to a random variable Z, that is correlated with all terminals' variables. The single-letter characterization of the secret key capacity of this model, known as the wiretap secret key capacity, is not known for an arbitrary Z. In this paper, we calculate the wiretap secret key capacity of a Tree-PIN, when Z consists of noisy version of terminals' variables. We also derive an upper bound and a lower bound for the wiretap secret key capacity of a PIN, and prove their tightness for some special cases.

Moving target defense (MTD) strategies have been widely studied for securing computer systems. We consider using MTD strategies to provide long-term cryptographic security for message transmission against an eavesdropping adversary who has access to a quantum computer. In such a setting, today’s widely used cryptographic systems including Diffie-Hellman key agreement protocol and RSA cryptosystem will be insecure and alternative solutions are needed. We will use a physical assumption, existence of multiple communication paths between the sender and the receiver, as the basis of security, and propose a cryptographic system that uses this assumption and an MTD strategy to guarantee efficient long-term information theoretic security even when only a single path is not eavesdropped. Following the approach of Maleki et al., we model the system using a Markov chain, derive its transition probabilities, propose two security measures, and prove results that show how to calculate these measures using transition probabilities. We define two types of attackers that we call risk-taking and risk-averse and compute our proposed measures for the two types of adversaries for a concrete MTD strategy. We will use numerical analysis to study tradeoffs between system parameters, discuss our results, and propose directions for future research.