Flaminia L. Luccio

Feedback vertex set in hypercubes

Abstract Given a graph G=(V,E) , the minimum feedback vertex set V is a subset of vertices of minimum size whose removal induces an acyclic subgraph G′=(V\ V ,E′) . The problem of finding V is NP -hard for general networks but interesting polynomial solutions have been found for particular graph classes. In this paper we find close upper and lower bounds to the size of V in a k -dimensional hypercube.

Sorting and election in anonymous asynchronous rings

In an anonymous ring of n processors, all processors are totally indistinguishable except for their input values. These values are not necessarily distinct, i.e., they form a multiset, and this makes many problems particularly difficult. We consider the problem of distributively sorting such a multiset on the ring, and we give a complete characterization of the relationship with the problems of leader election for vertices and edges. For Boolean input values and prime n, we also establish a lower bound, and a reasonably close upper bound on the message complexity valid for sorting and leader election.

Type-based analysis of PIN processing APIs

We examine some known attacks on the PIN verification framework, based on weaknesses of the security API for the tamperresistant Hardware Security Modules used in the network. We specify this API in an imperative language with cryptographic primitives, and show how its flaws are captured by a notion of robustness that extends the one of Myers, Sabelfeld and Zdancewic to our cryptographic setting. We propose an improved API, give an extended type system for assuring integrity and for preserving confidentiality via randomized and nonrandomized encryptions, and show our new API to be type-checkable.

Mobile agents rendezvous when tokens fail

The mobile agent rendezvous problem consists of k ≥ 2 mobile agents trying to rendezvous or meet in a minimum amount of time on an n node ring network. Tokens and markers have been used successfully to achieve rendezvous when the problem is symmetric, e.g., the network is an anonymous ring and the mobile agents are identical and run the same deterministic algorithm. In this paper, we explore how token failure affects the time required for mobile agent rendezvous under symmetric conditions with different types of knowledge. Our results suggest that knowledge of n is better than knowledge of k in terms of achieving rendezvous as quickly as possible in the faulty token setting.

Guessing Bank PINs by Winning a Mastermind Game

In this paper we formally prove that the problem of cracking, i.e., correctly guessing, bank PINs used for accessing Automated Teller Machines and the problem of solving the Generalized Mastermind Game are strictly related. The Generalized Mastermind Game with N colors and k pegs is an extension of the well known Mastermind game, played with 6 colors and 4 pegs. The rules are the same, one player has to conceal a sequence of k colored pegs behind a screen and another player has to guess the exact position and colors of the pegs using the minimal number of moves. We first introduce a general game, called the Extended Mastermind Game (EMG), and we then formally prove it includes both the Generalized Mastermind Game and the PIN cracking Problem. We then present some experimental results that we have devised using a computer program that optimizes a well known technique presented by Knuth in 1976 for the standard Mastermind game. We finally show that the program improves the as state-of-the-art Mastermind solvers as it is able to compute strategies for cases which were not yet covered. More interestingly, the same solving strategy is adapted also for the solution of the PIN cracking problem.

Contiguous Search Problem in Sierpiński Graphs

In this paper we consider the problem of capturing an intruder in a particular fractal graph, the Sierpiński graph SGn. The problem consists of having a team of mobile software agents that collaborate in order to capture the intruder. The intruder is a mobile entity that escapes from the team of agents, moving arbitrarily fast inside the network, i.e., traversing any number of contiguous nodes as long as no other agent resides on them. The agents move asynchronously and they know the network topology they are in is a Sierpiński graph SGn.We first derive lower bounds on the minimum number of agents, number of moves and time steps required to capture the intruder. We then consider some variations of the model based on the capabilities of the agents: visibility, where the agents can “see” the state of their neighbors and thus can move autonomously; locality, where the agents can only access local information and thus their moves have to be coordinated by a leader. For each model, we design a capturing strategy and we make some observations. One of our goals is to continue a previous study on what is the impact of visibility on complexity: in this topology we are able to reach an optimal bound on the number of agents required by both cleaning strategies. However, the strategy in the visibility model is fully distributed, whereas the other strategy requires a leader. Moreover, the second strategy requires a higher number of moves and time steps.

An introduction to security API analysis

A security API is an Application Program Interface that allows untrusted code to access sensitive resources in a secure way. Examples of security APIs include the interface between the tamper-resistant chip on a smartcard (trusted) and the card reader (untrusted), the interface between a cryptographic Hardware Security Module, or HSM (trusted) and the client machine (untrusted), and the Google maps API (an interface between a server, trusted by Google, and the rest of the Internet).

Visualizing personalized views in virtual museum tours

We propose a multi-agent adaptive system to support tours of virtual museums. The system stores userspsila personalized views in zz-structures, particular data structures capable of representing both hypertext information and contextual interconnections among different information. We present an extension of the standard zz-structure model in terms of computational agents. These agents cooperate and collaborate in order to help users visualizing their personalized views. The power of this new model resides in the (partially limited) level of freedom users have for the dynamical choice, based on some present interest or necessity, of their navigational path inside the virtual museum.

BANANA: a tool for boundary ambients nesting analysis

Banana is a tool for the analysis of information leakage in mobile agent specifications. The language considered is Mobile Ambient calculus, initially proposed by Cardelli and Gordon with the main purpose of explicitly modeling mobility [5]. Sites and agents (i.e., processes) are modeled as nested boxes (i.e., ambients), provided with capabilities for entering, exiting and dissolving other boxes. This specification language provides a very simple framework to reason about information flow and security when mobility is an issue [1].

Routing in Series Parallel Networks

AbstractAbstract. We consider the problem of routing messages between pairs of nodes of a distributed network, along shortest paths. We introduce a new routing technique, called Distance Routing that, due to its structure, is naturally well applicable on a family of networks called Series Parallel Graphs. We compute the time and space complexities of Distance Routing in Series Parallel Graphs, and we compare them with the relative complexities of Interval Routing, showing the improvement of Distance Routing especially in terms of time complexity.