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.

Random graphs

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.

/pdf/spray-and-wait-an-efficient-routing-scheme-for-50seq3wqos.pdf

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

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.

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

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.

PORs: Proofs of Retrievability for Large Files

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.

/pdf/securing-vehicular-ad-hoc-networks-4sgegi8hgk.pdf

Securing vehicular ad hoc networks

A fractal coder partitions an image into blocks that are coded via self-references to other parts of the image itself. We present a fractal coder that derives highly image-adaptive partitions and corresponding fractal codes in a time-efficient manner using a region-merging approach. The proposed merging strategy leads to improved rate-distortion performance compared to previously reported pure fractal coders, and it is faster than other state-of-the-art fractal coding methods.

/pdf/region-based-fractal-image-compression-3fqoowoezz.pdf

Region-based fractal image compression

Vehicular Ad Hoc Networks (VANETs) represent an emerging topic in wireless communication and networking VANETs are currently receiving a lot of attention due to their promise of considerably increasing safety and comfort while being on the road High mobility, adverse channel conditions, and market introduction are some of the key challenges one has to deal with when designing these spontaneous networks Inter-Vehicle-Communications Based on Ad Hoc Networking Principles covers results and achievements of the FleetNet project, a project devoted to the design of a vehicular ad hoc network

Inter-Vehicle-Communications - Based on Ad Hoc Networking Principles : The FleetNet Project

We present a simulation model of the Bitcoin peer-to-peer network, a widely deployed distributed electronic currency system. The model enables evaluations of the feasibility and cost of attacks on the Bitcoin network at full scale of 6,000 nodes. The simulation model is based on unmodified code from core segments of the Bitcoin reference implementation used by 99% of nodes. Parametrization of the model is performed based on large-scale measurements of the real-world network. We present preliminary validation results showing a reasonable correspondence of the propagation of messages in the Bitcoin network compared with simulation results. We apply the model to study the feasibility of a partitioning attack on the network and show that the attack is sensitive to the churn of the attacking nodes.

/pdf/a-simulation-model-for-analysis-of-attacks-on-the-bitcoin-vzr8hsnfic.pdf

A simulation model for analysis of attacks on the Bitcoin peer-to-peer network

A simulation study on the performance of mobile IPv6 in a WLAN-based cellular network

New Research Challenges for the Security of Ad Hoc and Sensor Networks.- Public Key Cryptography in Sensor Networks-Revisited.- Exploring Message Authentication in Sensor Networks.- Secure Initialization in Single-Hop Radio Networks.- Some Methods for Privacy in RFID Communication.- Ring Signature Schemes for General Ad-Hoc Access Structures.- Linking Ad Hoc Charging Schemes to AAAC Architectures.- Blind Spontaneous Anonymous Group Signatures for Ad Hoc Groups.- Security for Interactions in Pervasive Networks: Applicability of Recommendation Systems.- Pseudonym Generation Scheme for Ad-Hoc Group Communication Based on IDH.- Secure Overlay for Service Centric Wireless Sensor Networks.- IKE in Ad-Hoc IP Networking.- Advanced Detection of Selfish or Malicious Nodes in Ad Hoc Networks.- A Security Architecture for Mobile Wireless Sensor Networks.- Securely Propagating Authentication in an Ensemble of Personal Devices Using Single Sign-on.- Key Management in Wireless Sensor Networks.- SDD: Secure Directed Diffusion Protocol for Sensor Networks.- Secure AES Hardware Module for Resource Constrained Devices.

Security in Ad-hoc and Sensor Networks: First European Workshop, ESAS 2004, Heidelberg, Germany, August 6, 2004, Revised Selected Papers (Lecture Notes in Computer Science)

Hannes Hartenstein

Papers

Region-based fractal image compression

Inter-Vehicle-Communications - Based on Ad Hoc Networking Principles : The FleetNet Project

A simulation model for analysis of attacks on the Bitcoin peer-to-peer network

A simulation study on the performance of mobile IPv6 in a WLAN-based cellular network

Security in Ad-hoc and Sensor Networks: First European Workshop, ESAS 2004, Heidelberg, Germany, August 6, 2004, Revised Selected Papers (Lecture Notes in Computer Science)