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 discrete-event simulation (DES) involves the execution of a sequence of event handlers dynamically scheduled at runtime. As a consequence, a priori knowledge of the control flow of the overall simulation program is limited. In particular, powerful optimizations supported by modern compilers can only be applied on the scope of individual event handlers, which frequently involve only a few lines of code. We propose a method that extends the scope for compiler optimizations in discrete-event simulations by generating batches of multiple events that are subjected to compiler optimizations as contiguous procedures. A runtime mechanism executes suitable batches at negligible overhead. Our method does not require any compiler extensions and introduces only minor additional effort during model development. The feasibility and potential performance gains of the approach are illustrated on the example of an idealized proof-ofconcept model. We believe that the applicability of the approach extends to general event-driven programs.

/pdf/enabling-cross-event-optimization-in-discrete-event-56iu0t2mqx.pdf

Enabling Cross-Event Optimization in Discrete-Event Simulation Through Compile-Time Event Batching

Payment channel networks are an approach to improve the scalability of blockchain-based cryptocurrencies. Because payment channel networks are used for transfer of financial value, their security in the presence of adversarial participants should be verified formally. We formalize the protocol of the Lightning Network, a payment channel network built for Bitcoin, and show that the protocol fulfills the expected security properties. As the state space of a specification consisting of multiple participants is too large for model checking, we formalize intermediate specifications and use a chain of refinements to validate the security properties where each refinement is justified either by model checking or by a pen-and-paper proof.

Towards a Formal Verification of the Lightning Network with TLA+

PROBLEM TO BE SOLVED: To provide a method for information dissemination in a communication network, preferably in a vehicular ad hoc network (VANET).SOLUTION: A communication network 1 comprises a plurality of communication nodes N which are aware of the respective geographical position, and the dissemination process is initiated by one of the nodes, an originator node O, by sending a unicast message that includes information to be disseminated to a specific node, a first forwarder node F1, within a relevant area RA in which the information is to be disseminated. Other nodes C1, C2, and C3 in the relevant area RA, which receive the message sent by the originator node O to the first forwarder node F1, elect a forwarder node, respectively, and perform a unicast retransmission of the message to the elected forwarder node on the basis of a timer-based contention process.

Method for information dissemination in communication network, communication node and communication method thereof, and communication network

Ad-Hoc Netzwerke fdie Kommunikation zwischen Fahrzeugen

When sensitive data is outsourced to an untrustworthy cloud storage provider, encryption techniques can be used to enforce data confidentiality. Ideally, such encryption techniques should not only enforce the confidentiality of data at rest but also the confidentiality of data accesses, as database access patterns can leak information about the database’s contents. Oblivious RAM (ORAM) approaches were proposed to hide access patterns, but they currently support a very limited set of database query operations. In this paper, we propose PATCONFDB that supports database query functionalities and hides query access patterns. PATCONFDB represents a construction based on ORAM schemes: when an index (B-tree) is outsourced, multiple ORAM instances are used to maintain access pattern confidentiality. PATCONFDB can make use of up-to-date ORAM schemes, for example an implementation of Burst ORAM is used to significantly boost the performance of accesses. We compare PATCONFDB with a shuffled B-tree protocol, provide a discussion on security properties, and give recommendations of which protocol to use in which usage scenario. We provide a rigorous efficiency evaluation to determine the storage and network overhead as well as query latency. In particular, we show that PATCONFDB with ORAM-based schemes like Burst ORAM only causes a marginal latency overhead when evaluating equality conditions on databases of up to 10 million records. However, the network overhead still remains a challenge.

/pdf/patconfdb-design-and-evaluation-of-access-pattern-fojzpy4xsf.pdf

Hannes Hartenstein

Papers

Enabling Cross-Event Optimization in Discrete-Event Simulation Through Compile-Time Event Batching

Towards a Formal Verification of the Lightning Network with TLA+

Method for information dissemination in communication network, communication node and communication method thereof, and communication network

Ad-Hoc Netzwerke fdie Kommunikation zwischen Fahrzeugen

PATCONFDB: Design and Evaluation of Access Pattern Confidentiality-Preserving Indexes