Hannes Hartenstein

Bio: Hannes Hartenstein is an academic researcher from Karlsruhe Institute of Technology. The author has contributed to research in topics: Vehicular ad hoc network & Wireless ad hoc network. The author has an hindex of 55, co-authored 234 publications receiving 14515 citations. Previous affiliations of Hannes Hartenstein include University of Mannheim & University of Freiburg.

Positionsbasiertes Routing für die Kommunikation zwischen Fahrzeugen (Position-Based Routing for Inter-Vehicle Communication)

Abstract: In the near future communication between vehicles by means of wireless technology will enhance both safety and comfort of the passengers. One main challenge in realizing this communication will be the routing of messages from one sender to one or more receivers. In this paper we propose a position-based ad-hoc routing protocol which solves this problem. In this protocol all vehicles work together, thus no pre-established infrastructure is required. As a consequence, the resulting network is inexpensive and robust. In order to prove the viability of the approach, a simulation study was performed using the ns-2 network simulator. As a basis for this study realistic car movement patterns were used. The study shows that even over large distances requiring message forwarding by multiple vehicles, high success rates for the delivery of messages are achieved.

ETHTID: Deployable Threshold Information Disclosure on Ethereum

Abstract: We address the Threshold Information Disclosure (TID) problem on Ethereum: An arbitrary number of users commit to the scheduled disclosure of their individual messages recorded on the Ethereum blockchain if and only if all such messages are disclosed. Before a disclosure, only the original sender of each message should know its contents. To accomplish this, we task a small council with executing a distributed generation and threshold sharing of an asymmetric key pair. The public key can be used to encrypt messages which only become readable once the threshold-shared decryption key is reconstructed at a predefined point in time and recorded on-chain. With blockchains like Ethereum, it is possible to coordinate such procedures and attach economic stakes to the actions of participating individuals. In this paper, we present ETHTID, an Ethereum smart contract application to coordinate Threshold Information Disclosure. We base our implementation on ETHDKG [1], a smart contract application for distributed key generation and threshold sharing, and adapt it to fit our differing use case as well as add functionality to oversee a scheduled reconstruction of the decryption key. For our main cost saving optimisation, we show that the security of the underlying cryptographic scheme is maintained. We evaluate how the execution costs depend on the size of the council and the threshold and show that the presented protocol is deployable on Ethereum with a council of more than 200 members with gas savings of 20--40\% compared to ETHDKG.

Self-optimization of DHT lookups through run-time performance analysis

Abstract: Distributed Hash Tables (DHTs) provide information lookup within a Peer-to-Peer (P2P) network. A multitude of distributed applications leverages DHTs for offering more advanced services such as distributed file systems, web caches or distributed DNS. For such DHT-based applications, lookup performance is highly important. However, lookup performance is severely affected by network characteristics, i.e., churn and connectivity issues due to NAT routers. As those characteristics are heavily influenced by user behavior, changes are not only likely but also hard to predict. Although DHTs are known for their self-organization, current implementations often do not adapt optimally to variation in network characteristics. In this paper, we propose to dynamically optimize the client through tuning its parameters at run-time. For doing so, different configurations are tested and compared automatically. To reduce overhead, requests sent to other peers are recorded and replayed by a simulation engine, if the same peer is queried again using the same parameter. We evaluated our approach at two exemplary scenarios of the future state of the BitTorrent Mainline DHT (MDHT), one of the most widely used public DHTs. In these scenarios, the lookups of a client using static parameters were more than three times slower and had a 25% higher network overhead than those of an adaptive client. With only 4 additional UDP packets sent per second and a one-digit CPU load, the proposed approach also induces minimal overhead.

Cost-based region growing for fractal image compression

Abstract: For application in fractal coding we investigate image partitionings that are derived by a merge process starting with a uniform partition. At each merging step one would like to opt for the rate-distortion optimal choice. Unfortunately, this is computationally infeasible when efficient coders for the partition information are employed. Therefore, one has to use a model for estimating the coding costs. We discuss merging criteria that depend on variance or collage error and on the Euclidean length of the partition boundaries. Preliminary tests indicate that improved coding costs estimators may be of crucial importance for the success of our approach.

Random graphs

Abstract: We will review some of the major results in random graphs and some of the more challenging open problems. We will cover algorithmic and structural questions. We will touch on newer models, including those related to the WWW.

Spray and wait: an efficient routing scheme for intermittently connected mobile networks

Abstract: Intermittently connected mobile networks are sparse wireless networks where most of the time there does not exist a complete path from the source to the destination. These networks fall into the general category of Delay Tolerant Networks. There are many real networks that follow this paradigm, for example, wildlife tracking sensor networks, military networks, inter-planetary networks, etc. In this context, conventional routing schemes would fail.To deal with such networks researchers have suggested to use flooding-based routing schemes. While flooding-based schemes have a high probability of delivery, they waste a lot of energy and suffer from severe contention, which can significantly degrade their performance. Furthermore, proposed efforts to significantly reduce the overhead of flooding-based schemes have often be plagued by large delays. With this in mind, we introduce a new routing scheme, called Spray and Wait, that "sprays" a number of copies into the network, and then "waits" till one of these nodes meets the destination.Using theory and simulations we show that Spray and Wait outperforms all existing schemes with respect to both average message delivery delay and number of transmissions per message delivered; its overall performance is close to the optimal scheme. Furthermore, it is highly scalable retaining good performance under a large range of scenarios, unlike other schemes. Finally, it is simple to implement and to optimize in order to achieve given performance goals in practice.

Dedicated Short-Range Communications (DSRC) Standards in the United States

Abstract: Wireless vehicular communication has the potential to enable a host of new applications, the most important of which are a class of safety applications that can prevent collisions and save thousands of lives. The automotive industry is working to develop the dedicated short-range communication (DSRC) technology, for use in vehicle-to-vehicle and vehicle-to-roadside communication. The effectiveness of this technology is highly dependent on cooperative standards for interoperability. This paper explains the content and status of the DSRC standards being developed for deployment in the United States. Included in the discussion are the IEEE 802.11p amendment for wireless access in vehicular environments (WAVE), the IEEE 1609.2, 1609.3, and 1609.4 standards for Security, Network Services and Multi-Channel Operation, the SAE J2735 Message Set Dictionary, and the emerging SAE J2945.1 Communication Minimum Performance Requirements standard. The paper shows how these standards fit together to provide a comprehensive solution for DSRC. Most of the key standards are either recently published or expected to be completed in the coming year. A reader will gain a thorough understanding of DSRC technology for vehicular communication, including insights into why specific technical solutions are being adopted, and key challenges remaining for successful DSRC deployment. The U.S. Department of Transportation is planning to decide in 2013 whether to require DSRC equipment in new vehicles.

PORs: Proofs of Retrievability for Large Files

Abstract: In this paper, we define and explore proofs of retrievability (PORs). A POR scheme enables an archive or back-up service (prover) to produce a concise proof that a user (verifier) can retrieve a target file F, that is, that the archive retains and reliably transmits file data sufficient for the user to recover F in its entirety.A POR may be viewed as a kind of cryptographic proof of knowledge (POK), but one specially designed to handle a large file (or bitstring) F. We explore POR protocols here in which the communication costs, number of memory accesses for the prover, and storage requirements of the user (verifier) are small parameters essentially independent of the length of F. In addition to proposing new, practical POR constructions, we explore implementation considerations and optimizations that bear on previously explored, related schemes.In a POR, unlike a POK, neither the prover nor the verifier need actually have knowledge of F. PORs give rise to a new and unusual security definition whose formulation is another contribution of our work.We view PORs as an important tool for semi-trusted online archives. Existing cryptographic techniques help users ensure the privacy and integrity of files they retrieve. It is also natural, however, for users to want to verify that archives do not delete or modify files prior to retrieval. The goal of a POR is to accomplish these checks without users having to download the files themselves. A POR can also provide quality-of-service guarantees, i.e., show that a file is retrievable within a certain time bound.

Securing vehicular ad hoc networks

Abstract: Vehicular networks are very likely to be deployed in the coming years and thus become the most relevant form of mobile ad hoc networks. In this paper, we address the security of these networks. We provide a detailed threat analysis and devise an appropriate security architecture. We also describe some major design decisions still to be made, which in some cases have more than mere technical implications. We provide a set of security protocols, we show that they protect privacy and we analyze their robustness and efficiency.