Approximate Constrained Bipartite Edge Coloring

International audienceWe study the following Constrained Bipartite Edge Coloring (CBEC) problem: We are given a bipartite graph G(U,V,E) of maximum degree l with n vertices, in which some of the edges have been legally colored with c colors. We wish to complete the coloring of the edges of G minimizing the total number of colors used. The problem has been proved to be NP-hard event for bipartite graphs of maximum degree three

User privacy issues regarding certificates and the TLS protocol

The aim of this paper is two-fold. 1) We raise concerns regarding possible violations of user privacy relative to the use of X509 Certificates and the Transport Layer Security protocol. We stress that this approach to secure network transactions, while preserving the interests of service providers, neglects to consider the right to privacy of the users. 2) We propose the concept of a crypto certificate and the Secure and Private Socket Layer protocol (SPSL protocol, in short) and show their effectiveness in preserving user privacy and, at the same time, protecting the interests of service providers. Focusing on the particular case of web transactions, we describe a system based on SPSL for secure and private web navigation. Our implementation includes an SPSL-proxy for an SSL-enabled web client and a module for the Apache web server along with administrative tools for the server side. The system has been developed starting from the implementation of an API for the SPSL protocol that we describe in the paper. Experimental results show that SPSL is an effective and efficient solution to the problem of privacy in web transaction. The protocol we propose and, consequently, the implementation we describe are fully dynamic and provide an adjustable level of privacy.

A Secure and Private System for Subscription-Based Remote Services

In this paper we study privacy issues regarding the use of the SSL/TLS protocol and X.509 certificates. Our main attention is placed on subscription-based remote services (e.g., subscription to newspapers and databases) where the service manager charges a flat fee for a period of time independent of the actual number of times the service is requested. We start by pointing out that restricting the access to such services by using X.509 certificates and the SSL/TLS protocol, while preserving the interests of the service managers, neglects the right to privacy of the users. We then propose the concept of a crypto certificate and the Secure and Private Socket Layer protocol (SPSL protocol, in short) and show how they can be used to preserve user privacy and, at the same time, protecting the interests of the service managers. The SPSL protocol only requires the user to have a standard X.509 certificate (with an RSA key) and does not require the user to get any special ad-hoc certificate. Finally, we show the viability of the proposed solution by describing a system based on SPSL for secure and private access to subscription-based web services. Our implementation includes an SPSL-proxy for a TLS-enabled web client and a module for the Apache web server along with administrative tools for the server side. The system has been developed starting from the implementation of an API for the SPSL protocol that we describe in the paper

Optimal Pebble Motion on a Tree

In this paper we consider the following pebble coordination problem. Consider a tree with n vertices and k pebbles located at distinct vertices of the tree. Each pebble can be moved from its current position to an adjacent unoccupied vertex. Among the k pebbles, one distinguished pebbles has been assigned a destination. We give an O(n 5 ) algorithm for the problem of designing the shortest sequence of moves that takes the distinguished pebble from its original position to its destination. Our algorithm improves the running time of the best previously presented algorithm that needed to solve O(n 6 ) min-cost ow problems on graphs of size O(n). Our algorithm does not resort to reduction to ow but is instead based on a novel dynamic programming approach. A preliminary version of this paper appeared as \A New Approach to Optimal Motion Planning on Trees with Obstacles" in Proceedings of 4{European Symposium on Algorithms (LNCS 1136), pp. 529-545. This work was partially supporte..

A New Approach to Optimal Planning of Robot Motion on a Tree with Obstacles

. In this paper we study the Graph Motion Planning of 1 Robot problem (GMP1R) on a tree. This problem consists in computing a minimum cost plan for moving a robot from one vertex to another in a tree whose vertices can have movable obstacles. Papadimitriou et alt. [FOCS 94] introduced the problem and gave an algorithm for the GMP1R on a tree. Their approach is based on flow arguments and yields an algorithm that solves O(n 6 ) mincost flow problems on graphs with O(n) vertices. They also give a 7 approximation algorithm that solves O(n) mincost flow problems on graphs with O(n) vertices. We propose a new dynamic programming approach to GMP1R on a tree. Based on this approach we give a O(n 4 ) algorithm for the GMP1R on a tree. Moreover, we give an O(n 3 ) approximation algorithm that obtains a solution that is within a 7 factor from the optimum. We also discuss extensions of our work and pose a new open problem. 1 Introduction Consider the following optimization problem introdu..

Secure Dependency Enforcement in Package Management Systems

Package management systems play an essential role in pursuing systems dependability by ensuring that software is correctly installed and kept up-to-date according to vendor-defined installation policies. Circumventing such policies could make the system unhealthy and insecure and can constitute a serious security threat. In many application scenarios, e.g., distribution of commercial software, the confidentiality of the software must be guaranteed against non-authorized players. In some cases, the installation policy itself is considered a sensitive information, e.g., when it reveals required hardware in military contexts. In this paper we address the problem of strongly enforcing software dependencies in package management systems, to prevent that a malicious user forces the system to install any package despite its requirements are not completely fulfilled. The enforcement is strong in the sense that the encrypted software package cannot be even decrypted if the dependencies are not satisfied. Once a new package is decrypted and installed, our protocol non-interactively updates the key material on the target device. This key update will allow the decryption of further packages that depend on the newly installed one. We further present “policy-hiding” variants of our protocol. Finally we provide an experimental evaluation of the system performance

Wavelength Routing of Symmetric Communication Requests in Directed Fiber Trees

We focus on a special version of the problem of allocating bandwidth for a set of directed communication requests in tree--shaped optical networks. We consider patterns of requests that are symmetric, e.g. for each request originating from a node v 1 and destined to a node v 2 , there also exists its symmetric, a request that originates from v 2 and destines to v 1 . The problem can be viewed as coloring of undirected paths in trees, but we cannot hope for optimal solutions even when the network is a binary tree, a case for which the undirected problem is in P . In this paper we investigate the relation of this special case with both the undirected problem and the general (non--symmetric) version of the directed problem. We prove that the problem is NP--hard for arbitrary tree topologies and present lower and upper bounds on the number of wavelengths