Fast equality test for straight-line compressed strings

The paper describes a simple and fast randomized test for equality of grammar-compressed strings. The thorough running time analysis is done by applying a logarithmic cost measure. Keywords: randomized algorithms, straight line programs, grammar-based compressio

Conditional Allocation of Control Rights in Venture Capital Finance

When a young entrepreneurial firm matures, it is often necessary to replace the founding entrepreneur by a professional manager. This replacement decision can be affected by the private benefits of control enjoyed by the entrepreneur which gives rise to a conflict of interest between the entrepreneur and the venture capitalist. We show that a combination of convertible securities and contingent control rights can be used to resolve this conflict efficiently. This contractual arrangement is frequently observed in venture capital finance.Corporate Finance; Venture Capital; Control Rights; Convertible Securities

Conditional Allocation of Control Rights in Venture Capital Finance

When a young entrepreneurial firm matures, it is often necessary to replace the founding entrepreneur by a professional manager. This replacement decision can be affected by the private benefits of control enjoyed by the entrepreneur which gives rise to a conflict of interest between the entrepreneur and the venture capitalist. We show that a combination of convertible securities and contingent control rights can be used to resolve this conflict efficiently. This contractual arrangement is frequently observed in venture capital finance.Corporate Finance; Venture Capital; Control Rights; Convertible Securities

Broadcasting in Prefix Space: P2P Data Dissemination with Predictable Performance

A broadcast mode may augment peer-to-peer overlay networks with an efficient, scalable data replication function, but may also give rise to a virtual link layer in VPN-type solutions. We introduce a simple broadcasting mechanism that operates in the prefix space of distributed hash tables without signaling. This paper concentrates on the performance analysis of the prefix flooding scheme. Starting from simple models of recursive $k$-ary trees, we analytically derive distributions of hop counts and the replication load. Extensive simulation results are presented further on, based on an implementation within the OverSim framework. Comparisons are drawn to Scribe, taken as a general reference model for group communication according to the shared, rendezvous-point-centered distribution paradigm. The prefix flooding scheme thereby confirmed its widely predictable performance and consistently outperformed Scribe in all metrics. Reverse path selection in overlays is identified as a major cause of performance degradation.Comment: final version for ICIW'0

Monetary Union: European Lessons, Latin American Prospects

In this paper selective issues of long-run sustainability of monetary unions are analyzed. Using theoretical insights and the experience of EMU up to now we argue that empirical evidence on OCA criteria for EMU suggests that benefits for the countries participating in EMU outweigh costs by a relatively large margin although by varying degrees from country to country. We also conclude that the Stability Pact is a sufficient but not a necessary condition for EMU to succeed and that EMU has been driven by political considerations. A sound financial sector is a precondition. With regard to lessons to be drawn for Latin America and the Caribbean we first find that there has been a strong push towards the floating cum inflation-targeting corner and to regional trade integration. Moreover, it seems that, in contrast to EMU, the benefit-cost balance of a move to monetary union is much less favorable in Latin America and the Caribbean and, most important, the political dimension missing.

The Abandoned Side of the Internet: Hijacking Internet Resources When Domain Names Expire

The vulnerability of the Internet has been demonstrated by prominent IP prefix hijacking events. Major outages such as the China Telecom incident in 2010 stimulate speculations about malicious intentions behind such anomalies. Surprisingly, almost all discussions in the current literature assume that hijacking incidents are enabled by the lack of security mechanisms in the inter-domain routing protocol BGP. In this paper, we discuss an attacker model that accounts for the hijacking of network ownership information stored in Regional Internet Registry (RIR) databases. We show that such threats emerge from abandoned Internet resources (e.g., IP address blocks, AS numbers). When DNS names expire, attackers gain the opportunity to take resource ownership by re-registering domain names that are referenced by corresponding RIR database objects. We argue that this kind of attack is more attractive than conventional hijacking, since the attacker can act in full anonymity on behalf of a victim. Despite corresponding incidents have been observed in the past, current detection techniques are not qualified to deal with these attacks. We show that they are feasible with very little effort, and analyze the risk potential of abandoned Internet resources for the European service region: our findings reveal that currently 73 /24 IP prefixes and 7 ASes are vulnerable to be stealthily abused. We discuss countermeasures and outline research directions towards preventive solutions.Comment: Final version for TMA 201

Espèces de plantes associées avec différents niveaux de richesse spécifique et de couverture végétale comme indicatrices de désertification au Burkina Faso (Afrique de l'Ouest)

Im sudano-sahelischen Westafrika stellt Desertifikation einschließlich des damit verbundenen Biodiversitätsverlustes und der Bodenerosion ein großes Problem dar. Der daraus resultierende Verlust an Ökosystemdienstleistungen hat schwere negative Folgen für die ansässige Bevölkerung. Um die Bewertung dieser Aspekte der Desertifikation zu erleichtern, haben wir nach als Indikatoren geeigneten Pflanzenarten gesucht. Auf der Basis einer umfassenden Datenbank von Vegetationsaufnahmen aus Burkina Faso identifizierten wir Arten, deren Vorkommen mit hoher oder geringer Ausprägung von Artenreichtum oder Vegetationsbedeckung assoziiert ist. Die Identifizierung geschah für jede einzelne Art durch Berechnung der entsprechenden Mittelwerte aus sämtlichen Aufnahmen, in denen die Art vertreten war. Um die Unterschiede zwischen den klimatisch-pflanzengeographischen Regionen des Landes zu berücksichtigen, erfolgte eine separate Berechnung für die drei Vegetationszonen Sahel, Nordsudan und Südsudan. Da krautige Arten und Gehölze in den zur Verfügung stehenden Vegetationsaufnahmen in der Regel auf unterschiedlich großen Flächen dokumentiert wurden, behandelten wir auch diese Gruppen separat. Für jede sich auf diese Weise ergebende Kategorie ermittelten wir die jeweils zehn am stärksten mit geringem bzw. hohem Artenreichtum oder geringer bzw. hoher Vegetationsbedeckung assoziierten Arten.Desertification is a major problem in Sudano-sahelian West Africa, including the loss of biodiversity and vegetation cover. The loss of related ecosystem services is having a severe impact on human wellbeing. To facilitate assessments of these aspects of desertification, we decided to find plant species suitable as indicators. Based on a large database of vegetation plot data for Burkina Faso, we identified species associated with high or low levels of species richness and vegetation cover by calculating average values of these measures from vegetation plots on which they occur. To account for the differences between the dry Sahel and the more humid Sudan, we separated the plots of our study area in three vegetation zones (Sahel, North Sudan, South Sudan). Furthermore, herbs and woody plants were analysed separately, as they were usually represented in different plot sizes in the primary data. For each combination of species richness or vegetation cover, vegetation zone and growth form we identified ten species indicating low and another ten species indicating high values and assigned indicator values based on the average values of these species in the relevés.La désertification est un problème majeur dans la région soudano-sahélienne en Afrique de l'Ouest, y compris la perte de la biodiversité et de la couverture végétale. La perte des services écosystémiques a de graves répercussions sur le bien-être humain. Pour faciliter l'évaluation de ces aspects de la désertification, nous avons décidé de proposer des espèces végétales comme indicatrices des différents états de dégradation. A partir d’une grande base de données de la végétation pour le Burkina Faso, nous avons identifié des espèces liées aux niveaux élevés ou faibles de la richesse spécifique et la couverture végétale par le calcul des valeurs moyennes des parcelles de végétation dans lesquelles elles se trouvent. Pour tenir compte des différences entre le Sahel plus sec et le soudanien plus humide, nous avons séparé les parcelles de notre zone d'étude en trois zones de végétation (sahelienne, nord-soudanienne, sud-soudanienne). En outre, les herbacées et les ligneux ont été analysés séparément, car généralement étudiés dans des parcelles de différentes tailles dans les données primaires. For each combination of species richness or vegetation cover, vegetation zone and growth form we identified ten species indicating low and another ten species indicating high values and assigned indicator values based on the average values. Pour chaque combinaison de richesse spécifique ou couverture végétale, zone de vegetation et forme de croissance on a identifié dix espèces indicatrices de valeurs basses et dix espèces indicatrices de valeurs hautes basées sur les valeurs moyens de ces espèces dans les relevés

CAIR: Using Formal Languages to Study Routing, Leaking, and Interception in BGP

The Internet routing protocol BGP expresses topological reachability and policy-based decisions simultaneously in path vectors. A complete view on the Internet backbone routing is given by the collection of all valid routes, which is infeasible to obtain due to information hiding of BGP, the lack of omnipresent collection points, and data complexity. Commonly, graph-based data models are used to represent the Internet topology from a given set of BGP routing tables but fall short of explaining policy contexts. As a consequence, routing anomalies such as route leaks and interception attacks cannot be explained with graphs. In this paper, we use formal languages to represent the global routing system in a rigorous model. Our CAIR framework translates BGP announcements into a finite route language that allows for the incremental construction of minimal route automata. CAIR preserves route diversity, is highly efficient, and well-suited to monitor BGP path changes in real-time. We formally derive implementable search patterns for route leaks and interception attacks. In contrast to the state-of-the-art, we can detect these incidents. In practical experiments, we analyze public BGP data over the last seven years