13480741
Source authentication in group communication systems
Many group communication systems need to enforce a restriction that limits members are authorized to send messages to the group. Receivers therefore need to authenticate message sources before the received messages are accepted. Source authentication in peer-to-peer systems is trivial: the two communication parties can agree on one pair key and use this key to authenticate each other. However, because the group key is shared by all members in a group system, it is quite challenging to identify the sender and determine its authorization. Furthermore, if the authorization can be changed at run-time, source authentication problem can be even harder. This paper presents a source authentication technique called TTA scheme (Transitive Trust Authentication). TTA supports source authentication as well as dynamic authorization change. In addition, its computation and communication overhead is low.
1661187
Siren: catching evasive malware
With the growing popularity of anomaly detection systems, which is due partly to the rise in zero-day attacks, a new class of threats have evolved where the attacker mimics legitimate activity to blend in and avoid detection. We propose a new system called Siren that injects crafted human input alongside legitimate user activity to thwart these mimicry attacks. The crafted input is specially designed to trigger a known sequence of network requests, which Siren compares to the actual traffic. It then flags unexpected messages as malicious. Using this method, we were able to detect ten spyware programs that we tested, many of which attempt to blend in with user activity. This paper presents the design, implementation, and evaluation of the Siren activity injection system, as well as a discussion of its potential limitations
1639134
Towards the theoretical foundation of choreography
With the growth of interest on the web services, people pay increasinglyattention to the choreography, that is, to describe collaborations ofparticipants in accomplishing a common business goal from a globalviewpoint. In this paper, based on a simple choreography language and arole-oriented process language, we study some fundamental issues relatedto choreography, especially those related to implementation, includingsemantics, projection and natural projection, dominant role in choices anditerations, etc. We propose the concept of dominant role and somenovel languages structures related to it. The study reveals some cluesabout the language, the semantics, the specification and theimplementation of choreography.
8778857
On Models for Quantified Boolean Formulas
A quantified Boolean formula is true, if for any existentially quantified variable there exists a Boolean function depending on the preceding universal variables, such that substituting the existential variables by the Boolean functions results in a true formula. We call a satisfying set of Boolean functions a model. In this paper, we investigate for various classes of quantified Boolean formulas and various classes of Boolean functions the problem whether a model exists. Furthermore, for these classes the complexity of the model checking problem – whether a set of Boolean functions is a model for a formula – will be shown. Finally, for classes of Boolean functions we establish some characterizations in terms of quantified Boolean formulas which have such a model. For example, roughly speaking any satisfiable quantified Boolean Horn formula can be satisfied by monomials and vice versa.
1611793
Type Checking Choreography Description Language
The Web Services Choreography Description Language (WS-CDL) is a W3C specification developed for the description of peer-to-peer collaborations of participants from a global viewpoint. Currently WS-CDL has no rigorous static type checking. We believe that introducing a type system will exclude many design and description errors, and ensure desirable properties of the choreography specifications. In this paper, we took a core language CDL, which covers most of the important features of the WS-CDL, and is more convenient for the study. We developed the abstract syntax and operational semantics of CDL, and defined a collection of rules which can be used to check if choreography is well-typed. Moreover, we also proved some type safety theorems for CDL in the sense that well-typed choreography cannot get stuck. We show how the use of type information can allow us to gain confidence in the correctness of choreography.
15922787
Supporting Mobility in MosquitoNet
The goal of the MosquitoNet project is to provide continuous Internet connectivity to mobile hosts. Mobile hosts must be able to take advantage of the best network connectivity available in any location, whether wired or wireless. We have implemented a mobile IP system that supports seamless switching between different networks and communication devices. In contrast to previous approaches to mobile IP, we believe mobile hosts should not assume any explicit mobility support from the networks they visit, aside from basic Internet connectivity. This decision places extra responsibilities on the mobile hosts themselves. In this paper, we describe the design and implications of such a system. Measurements of our implementation show that the inherent overhead to switch networks (below 10ms) is insignificant compared to the time required to bring up a new communication device.
354671
Finding anchors for genomic sequence comparison
Recent sequencing of the human and other mammalian genomes has brought about the necessity to align them, to identify and characterize their commonalities and differences. Programs that align whole genomes generally use a seed-and-extend technique, starting from exact or near-exact matches and selecting a reliable subset of these, called anchors, and then filling in the remaining portions between the anchors using a combination of local and global alignment algorithms, but their choices for the parameters so far have been primarily heuristic. We present a statistical framework and practical methods for selecting a set of matches that is both sensitive and specific and can constitute a reliable set of anchors for a one-to-one mapping of two genomes from which a whole-genome alignment can be built. Starting from exact matches, we introduce a novel per-base repeat annotation, the $Z$-score, from which noise and repeat filtering conditions are explored. Dynamic programming-based chaining algorithms are also evaluated as context-based filters. We apply the methods described here to the comparison of two progressive assemblies of the human genome, NCBI build 28 and build 34 http://genome.ucsc.edu), and show that a significant portion of the two genomes can be found in selected exact matches, with very limited amount of sequence duplication.