Cooperative Epistemic Multi-Agent Planning for Implicit Coordination

Epistemic planning can be used for decision making in multi-agent situations with distributed knowledge and capabilities. Recently, Dynamic Epistemic Logic (DEL) has been shown to provide a very natural and expressive framework for epistemic planning. We extend the DEL-based epistemic planning framework to include perspective shifts, allowing us to define new notions of sequential and conditional planning with implicit coordination. With these, it is possible to solve planning tasks with joint goals in a decentralized manner without the agents having to negotiate about and commit to a joint policy at plan time. First we define the central planning notions and sketch the implementation of a planning system built on those notions. Afterwards we provide some case studies in order to evaluate the planner empirically and to show that the concept is useful for multi-agent systems in practice.Comment: In Proceedings M4M9 2017, arXiv:1703.0173

Combinatorial Solutions Providing Improved Security for the Generalized Russian Cards Problem

We present the first formal mathematical presentation of the generalized Russian cards problem, and provide rigorous security definitions that capture both basic and extended versions of weak and perfect security notions. In the generalized Russian cards problem, three players, Alice, Bob, and Cathy, are dealt a deck of $n$ cards, each given $a$, $b$, and $c$ cards, respectively. The goal is for Alice and Bob to learn each other's hands via public communication, without Cathy learning the fate of any particular card. The basic idea is that Alice announces a set of possible hands she might hold, and Bob, using knowledge of his own hand, should be able to learn Alice's cards from this announcement, but Cathy should not. Using a combinatorial approach, we are able to give a nice characterization of informative strategies (i.e., strategies allowing Bob to learn Alice's hand), having optimal communication complexity, namely the set of possible hands Alice announces must be equivalent to a large set of $t-(n, a, 1)$-designs, where $t=a-c$. We also provide some interesting necessary conditions for certain types of deals to be simultaneously informative and secure. That is, for deals satisfying $c = a-d$ for some $d \geq 2$, where $b \geq d-1$ and the strategy is assumed to satisfy a strong version of security (namely perfect $(d-1)$-security), we show that $a = d+1$ and hence $c=1$. We also give a precise characterization of informative and perfectly $(d-1)$-secure deals of the form $(d+1, b, 1)$ satisfying $b \geq d-1$ involving $d-(n, d+1, 1)$-designs

Dynamic epistemic verification of security protocols: framework and case study

We propose a dynamic epistemic framework for the verification of security protocols. First, we introduce a dynamic epistemic logic equipped with iteration and cryptographic supplements in which we can formalize and check (epistemic) requirements of security protocols. On top of this, we give a general guide how to go from a protocol specification to its representation in our framework. We demonstrate this by checking requirements of a simplified version of a protocol for confidential message comparison

Crossing Hands in the Russian Cards Problem

When communicating using an unconditionally secure protocol, a sender and receiver is able to transmit secret information over a public, insecure channel without fear of the secret being intercepted by a third party. The Russian cards problem is an example of an unconditionally secure protocol where the communication is fully understandable for everyone listening in. Even though everyone can understand what is being said, only the sender and receiver are able to uncover the secrets being transmitted. In this thesis we investigate the interaction among the communicating parties. By extending existing problem-specific software we are able to more efficiently analyze protocols, and we are therefore able to provide an answer to an open problem in the literature. We provide a completely new solution to the Russian cards protocol and show that it fulfills all requirements by the problem. Discovering this new solution provides the person initiating the protocol two new strategies to choose from when constructing the initial announcement of the protocol.Masteroppgave i informasjonsvitenskapINFO39