Dmitriy Kuptsov

Distributed user authentication in wireless LANs

In this paper, we present a linear programming formulation for the throughput optimization problem in wireless networks that support multi-packet reception (MPR) capability. The formulation takes into account the use of both directional and omni-directional antennas as well as the use of multiple transmitter interfaces per node. The joint routing and scheduling problem is decoupled into routing and scheduling subproblems. We show that the scheduling subproblem is intractable, and propose a polynomial time scheduling algorithm to solve it. We further demonstrate that, for certain type of networks, the completion time of the scheduling algorithm is at most two times the completion time of the the optimal scheduler, which is unknown. We use the proposed scheme for a preliminary study of several design parameters on the performance of MPR-capable networks, including the number of interfaces, the MPR capability and the beamwidth of the antennas.An increasing number of mobile devices, including smartphones, use WLAN for accessing the Internet. Existing WLAN authentication mechanisms are either disruptive, such as presenting a captive web page prompting for password, or unreliable, enabling a malicious user to attack a part of operators infrastructure. In this paper, we present a distributed authentication architecture for WLAN users providing instant network access without manual interactions. It supports terminal mobility across WLAN access points with the Host Identity Protocol (HIP), at the same time protecting the operators infrastructure from external attacks. User data sent over a wireless link is protected by the IPsec ESP protocol. We present our architecture design and implementation experience on two OpenWrt WLAN access points, followed by measurement results of the working prototype. The system is being deployed into pilot use in the city-wide panOULU WLAN.

Cooperative security in distributed networks

We consider a distributed network in which faulty nodes can pose serious threats as they can subvert the correct operation of basic functionalities, such as, routing or data aggregation. As a setoff to such nodes, we suggest that trust management between nodes is an essential part of a distributed system. In particular, benign nodes shall communicate with trusted nodes only and misbehaving nodes must be rapidly removed from the system. This paper formalizes the concept and properties of cooperative security - a protocol which allows implementing trust management by means of two voting procedures. During the first voting - admission procedure - each node gains trust by distributing revocation information to its neighbors. These neighbors form the nodes trusted entourage. If the node cooperates and discloses enough information, it is admitted and can communicate with the rest of the network; otherwise it is rejected. If the admitted node tries to endanger the network the second revocation voting procedure takes place. In this case, if the nodes entourage agrees upon act of misbehavior they revoke the node network-wide using previously disclosed revocation information.

How penalty leads to improvement

Despite much theoretical work, different modifications of backoff protocols in 802.11 networks lack empirical evidence demonstrating their real-life performance. To fill the gap we have set out to experiment with performance of exponential backoff by varying its backoff factor. Despite the satisfactory results for throughput, we have witnessed poor fairness manifesting in severe capture effect. The design of standard backoff protocol allows already successful nodes to remain successful, giving little chance to those nodes that failed to capture the channel in the beginning. With this at hand, we ask a conceptual question: Can one improve the performance of wireless backoff by introducing a mechanism of self-penalty, when overly successful nodes are penalized with big contention windows? Our real-life measurements using commodity hardware demonstrate that in many settings such mechanism not only allows to achieve better throughput, but also assures nearly perfect fairness. We further corroborate these results with simulations and an analytical model. Finally, we present a backoff factor selection protocol which can be implemented in access points to enable deployment of the penalty backoff protocol to consumer devices.

On application of Host Identity Protocol in wireless sensor networks

Recent advances in development of low-cost wireless sensor platforms open up opportunities for novel wireless sensor network (WSN) applications. Likewise emerge security concerns of WSNs receiving closer attention of research community. Well known security threats in WSNs range from Denial-of-Service (DoS), Replay and Sybil attacks to those targeted at violating data integrity and confidentiality. Public-key cryptography (PKC) as a countermeasure to potential attacks, although originally treated infeasible for resource-constrained sensor nodes, has shown its eligibility for WSNs in the past few years. However, different security and performance requirements, energy consumption issues, as well as varying hardware capabilities of sensor motes pose a challenge of finding the most efficient security protocol for a particular WSN application and scenario. In this paper, we propose to use the Host Identity Protocol (HIP) as the main component for building network-layer security in WSNs. Combining PKC signatures to authenticate wireless nodes, a Diffie-Hellman key exchange to create a pairwise secret key, a puzzle mechanism to protect against DoS attacks and the IPsec protocol for optional encryption of sensitive application data, HIP provides a standardized solution to many security problems of WSNs. We discuss how HIP can strengthen security of WSNs, suggest possible alternatives to its heavy components in particular WSN applications and evaluate their computational and energy costs on a Linux-based Imote2 wireless sensor platform.

Performance of Host Identity Protocol on Symbian OS

The Host Identity Protocol (HIP) has been specified by the IETF as a new solution for secure host mobility and multihoming in the Internet. HIP uses self-certifying public-private key pairs in combination with IPsec to authenticate hosts and protect user data. While there are three open-source HIP implementations, little experience is available with running HIP on lightweight hardware such as a mobile phone. Limited computational power and battery lifetime of lightweight devices raise concerns if HIP can be used there at all. This paper describes the porting process of HIP on Linux (HIPL) and OpenHIP implementations to Symbian OS, as well as performance measurements of HIP over WLAN using Nokia E51 and N80 smartphones. We found that with 1024-bit keys, the HIP base exchange with a server varies from 1.68 to 3.31 seconds depending on whether the mobile phone is in standby or active state respectively. After analyzing HIP performance in different scenarios we make conclusions and recommendations on using IP security on lightweight hardware clients.

SAVAH: Source Address Validation with Host Identity Protocol

Explosive growth of the Internet and lack of mechanisms that validate the authenticity of a packet source produced serious security and accounting issues. In this paper, we propose validating source addresses in LAN using Host Identity Protocol (HIP) deployed in a first-hop router. Compared to alternative solutions such as CGA, our approach is suitable both for IPv4 and IPv6. We have implemented SAVAH in Wi-Fi access points and evaluated its overhead for clients and the first-hop router.

Brief announcement: distributed trust management and revocation

Fair node and network operation is a key to ensure the correct system operation. The problem arises when some nodes become compromised or faulty endangering the overall system. This is especially challenging in sensor networks because they are often deployed in hostile environments and have to endure both passive and active attacks. Therefore, a node should only communicate with trusted nodes, while non-trusted nodes should be removed from the system to prevent them from further disrupting its normal operation. To address such threats, we introduce the Efficient Cooperative Security (ECoSec) - a distributed and adaptive protocol that allows a network to control the admission and revocation of nodes in a cooperative and democratic way during two voting rounds. Whereas the contributions of the protocol to the family of cooperative security protocols are two fold. First, it introduces the use of polynomial-based votes showing that its operation, and in general, operation of cooperative security protocols, can endure up to 33% of misbehaving nodes. Second, the protocol applies correlated keying material structures to verify the node admission and node revocation voting procedures reducing the overall communication overhead.

Demand-aware flow allocation in data center networks

In this work we consider a relatively large and highly dynamic data center network in which flows have small interarrival times and different demands for the network resources. Taking into account the properties and specifics of such networks we consider the problem of flow placement, i.e. assignment of an outgoing port for flows at each hop from source to destination. Using the characteristics of modern data centers from previous measurement studies, in this work we first simulate the flow allocation using several algorithms with and without global knowledge. We find that in all settings local forwarding decisions are almost as good as decisions made with global information at hand. This finding enables us to propose a fully distributed mechanism that relies only on local knowledge and allows to achieve fair and demand aware flow allocation in the data center network. The mechanism has low complexity and performs better than naive random flow allocation.

A novel demand-aware fairness metric for IEEE 802.11 wireless networks

Even though literature that focuses on improving fairness among wireless stations in single hop IEEE 802.11 networks is rife, little is discussed on how to measure fairness in such networks when stations have unequal demands for resources. Typically, the performance of such protocols is measured assuming that all stations have equal resource demands under full channel saturation. But if these protocols are evaluated in real environments, where such assumption may not hold, measuring fairness with off the shelf metrics may give inaccurate and inadequate results. To account for these settings, we propose a demand-aware fairness index (DA-index). We argue that the suggested metric is a useful tool for investigating fairness in single-hop IEEE 802.11 networks where resource allocation is governed with backoff protocols. We demonstrate the merits of the proposed metrics with analysis and empirical evaluation.