Thomas Y. Woo

A semantic model for authentication protocols

The authors specify authentication protocols as formal objects with precise syntax and semantics, and define a semantic model that characterizes protocol executions. They have identified two basic types of correctness properties, namely, correspondence and secrecy; that underlie the correctness concerns of authentication protocols. Assertions for specifying these properties, and a formal semantics for their satisfaction in the semantic model are defined. The Otway-Rees protocol is used to illustrate the semantic model and the basic correctness properties.<<ETX>>

A modular approach to packet classification: algorithms and results

The ability to classify packets according to pre-defined rules is critical to providing many sophisticated value-added services, such as security, QoS, load balancing, traffic accounting, etc. Various approaches to packet classification have been studied in the literature with accompanying theoretical bounds. Practical studies with results applying to large number of filters (from 8K to 1 million) are rare. In this paper, we take a practical approach to the problem of packet classification. Specifically, we propose and study a novel approach to packet classification which combines a heuristic tree search with the use of filter buckets. Besides high performance and a reasonable storage requirement, our algorithm is unique in the sense that it can adapt to the input packet distribution by taking into account the relative filter usage. To evaluate our algorithms, we have developed realistic models of large scale filter tables, and used them to drive extensive experimentation. The results demonstrate the practicality of our algorithms for up to even 1 million filters.

Authorization in Distributed Systems: A New Approach

In most existing systems, authorization is specified using some low-level system-specific mechanisms, e.g., protection bits, capabilities and access control lists. We argue that authorization is an independent semantic concept that must be separated from implementation mechanisms and given a precise semantics. We propose a logical approach to representing and evaluating authorization. Specifically, we introduce a language for specifying policy bases. A policy base encodes a set of authorization requirements and is given a precise semantics based upon a formal notion of authorization policy. The semantics is computable, thus providing a basis for authorization evaluation.

A lesson on authentication protocol design

The purpose of this note is to describe a useful lesson we learned on authentication protocol design. In a recent article [9], we presented a simple authentication protocol to illustrate the concept of a trusted server. The protocol has a flaw, which was brought to our attention by Mart~n Abadi of DEC. In what follows, we first describe the protocol and its flaw, and how the flaw-was introduced in the process of deriving the protocol from its correct full information version. We then introduce a principle, called the Principle of Full Information, and explain how its use could have prevented the protocol flaw. We believe the Principle of Full Information is a useful authentication protocol design principle, and advocate its use. Lastly, we present several heuristics for simplifying full information protocols and illustrate their application to a mutual authentication protocol.

CloudStream: Delivering high-quality streaming videos through a cloud-based SVC proxy

Existing media providers such as YouTube and Hulu deliver videos by turning it into a progressive download. This can result in frequent video freezes under varying network dynamics. In this paper, we present CloudStream: a cloud-based video proxy that can deliver high-quality streaming videos by transcoding the original video in real time to a scalable codec which allows streaming adaptation to network dynamics. The key is a multi-level transcoding parallelization framework with two mapping options (Hallsh-based Mapping and Lateness-first Mapping) that optimize transcoding speed and reduce the transcoding jitters while preserving the encoded video quality. We evaluate the performance of CloudStream on our campus cloud testbed.

CloudIQ: a framework for processing base stations in a data center

The cellular industry is evaluating architectures to distribute the signal processing in radio access networks. One of the options is to process the signals of all base stations on a shared pool of compute resources in a central location. In this centralized architecture, the existing base stations will be replaced with just the antennas and a few other active RF components, and the remainder of the digital processing including the physical layer will be carried out in a central location. This model has potential benefits that include a reduction in the cost of operating the network due to fewer site visits, easy upgrades, and lower site lease costs, and an improvement in the network performance with joint signal processing techniques that span multiple base stations. Further there is a potential to exploit variations in the processing load across base stations, to pool the base stations into fewer compute resources, thereby allowing the operator to either reduce energy consumption by turning the remaining processors off or reducing costs by provisioning fewer compute resources. We focus on this aspect in this paper. Specifically, we make the following contributions in the paper. Based on real-world data, we characterise the potential savings if shared homogeneous compute resources are used to process the signals from multiple base stations in the centralized architecture. We show that the centralized architecture can potentially result in savings of at least 22 % in compute resources by exploiting the variations in the processing load across base stations. These savings are achievable with statistical guarantees on successfully processing the base stations signals. We also design a framework that has two objectives: (i) partitioning the set of base stations into groups that are simultaneously processed on a shared homogeneous compute platform for a given statistical guarantee, and (ii) scheduling the set of base stations allocated to a platform in order to meet their real-time processing requirements. This partitioning and scheduling framework saves up to 19 % of the compute resources for a probability of failure of one in 100 million. We refer to this solution as CloudIQ. Finally we implement and extensively evaluate the CloudIQ framework with a 3GPP compliant implementation of 5 MHz LTE.

Authentication for distributed systems

A number of protocols used to authenticate users, hosts and processes are described. The three main types of authentication in a distributed computing system-message content authentication, message origin authentication, and general identity authentication-are explained. Authentication exchanges are identified, and paradigms of authentication protocols are presented. Authentication protocol failures are addressed, and an authentication framework is provided. As case studies, two authentication services, Kerberos and SPX, are examined. >

On the Detection of Signaling DoS Attacks on 3G Wireless Networks

Third generation (3G) wireless networks based on the CDMA2000 and UMTS standards are now increasingly being deployed throughout the world. Because of their complex signaling and relatively limited bandwidth, these 3G networks are generally more vulnerable than their wireline counterparts, thus making them fertile ground for new attacks. In this paper, we identify and study a novel denial of service (DoS) attack, called signaling attack, that exploits the unique vulnerabilities of the signaling/control plane in 3G wireless networks. Using simulations driven by real traces, we are able to demonstrate the impact of a signaling attack. Specifically, we show how a well-timed low-volume signaling attack can potentially overload the control plane and detrimentally affect the key elements in a 3G wireless infrastructure. The low-volume nature of the signaling attack allows it to avoid detection by existing intrusion detection algorithms, which are often signature or volume-based. As a counter-measure, we present and evaluate an online early detection algorithm based on the statistical CUSUM method. Through the use of extensive trace-driven simulations, we demonstrate that the algorithm is robust and can identify an attack in its inception, before significant damage is done.

Authorization in distributed systems: a formal approach

It is argued that authorization is an independent semantic concept that must be separated from implementation mechanisms and given a precise semantics. A logical approach to representing and evaluating authorization is proposed. Specifically, a language for specifying policy bases is introduced. A policy base encodes a set of authorization requirements and is given a precise semantics based on a formal notion of authorization policy. The semantics is computable, thus providing a basis for authorization evaluation. Two composition operators for policy bases which are appropriate for modeling distributed systems with multiple administrative domains are introduced.<<ETX>>

Cache-based compaction: a new technique for optimizing Web transfer

We propose and study a new technique, which we call cache-based compaction for reducing the latency of Web browsing over a slow link. The compaction technique trades computation for bandwidth. The key observation is that an object can be coded in a highly compact form for transfer if similar objects that have been transferred earlier can be used as references. The contributions of this paper are: (1) an efficient selection algorithm for selecting similar objects as references, and (2) an encoding/decoding algorithm that reduces the size of a Web object by exploiting its similarities with the reference objects. We verify the efficacy of our proposal through detailed experimental evaluations. This compaction technique significantly generalizes previous work on optimizing Web transfer using compression or differencing, and provides a systematic foundation that ties together caching, compression and prefetching.