The Internet of Things (IoT) technology has ex- panded widely across the world, promising new data management opportunities for industries, companies and individuals in different sectors, such as health services or transport logistics. The exponentially increasing number of IoT devices, their origin diversity, their limited capabilities in terms of resources, as well as the ever-increasing amount of data, raise new challenges for security and privacy protection, precluding traditional access control solutions to be integrated to this new environment. In this paper, we propose a reliable, server-aided, policy-based access control mechanism, named CHARIOT, that enables an IoT platform to verify credentials of different devices requesting access to the data stored within it. CHARIOT enables IoT devices to authenticate themselves to the platform without compromising their privacy by using attribute-based signatures. Our solution also allows secure delegation of costly computational operations to a cloud server, hence relieving the workload at IoT devices' side.

Abstract Searchable Encryption (SE) allows a user to upload data to the cloud and to search it in a remote fashion while preserving the privacy of both the data and the queries. Recent research results describe attacks on SE schemes using the access pattern, denoting the ids of documents matching search queries, which most SE schemes reveal during query processing. However SE schemes usually leak more than just the access pattern, and this extra leakage can lead to attacks (much) more harmful than the ones using basic access pattern leakage only. We remark that in the special case of Multi-User Searchable Encryption (MUSE), where many users upload and search data in a cloud-based infrastructure, a large number of existing solutions have a common leakage in addition to the well-studied access pattern leakage. We show that this seemingly small extra leakage allows a very simple yet powerful attack, and that the privacy degree of the affected schemes have been overestimated. We also show that this new vulnerability affects existing software. Finally we formalize the newly identified leakage profile and show how it relates to previously defined ones.

With the advent of cloud computing, individuals and companies alike are looking for opportunities to leverage cloud resources not only for storage but also for computation. Nevertheless, the reliance on the cloud to perform computation raises the unavoidable challenge of how to assure the correctness of the delegated computation. In this regard, we introduce two cryptographic protocols for publicly verifiable computation that allow a lightweight client to securely outsource to a cloud server the evaluation of high-degree univariate polynomials and the multiplication of large matrices. Similarly to existing work, our protocols follow the amortized verifiable computation approach. Furthermore, by exploiting the mathematical properties of polynomials and matrices, they are more efficient and give way to public delegatability. Finally, besides their efficiency, our protocols are provably secure under well-studied assumptions.

In this paper, we address the problem of privacy preserving delegated word search in the cloud. We consider a scenario where a data owner outsources its data to a cloud server and delegates the search capabilities to a set of third party users. In the face of semi-honest cloud servers, the data owner does not want to disclose any information about the outsourced data; yet it still wants to benefit from the highly parallel cloud environment. In addition, the data owner wants to ensure that delegating the search functionality to third parties does not allow these third parties to jeopardize the confidentiality of the outsourced data, neither does it prevent the data owner from efficiently revoking the access of these authorized parties. To these ends, we propose a word search protocol that builds upon techniques of keyed hash functions, oblivious pseudo-random functions and Cuckoo hashing to construct a searchable index for the outsourced data, and uses private information retrieval of short information to guarantee that word search queries do not reveal any information about the data to the cloud server. Moreover, we combine attribute-based encryption and oblivious pseudo-random functions to achieve an efficient revocation of authorized third parties. The proposed scheme is suitable for the cloud as it can be easily parallelized.

Existing privacy controls based on access control techniques do not prevent massive dissemination of private data by unauthorized users. We suggest a usage control enforcement scheme that allows users to gain control over their data during its entire lifetime. The scheme is based on a peer-to-peer architecture whereby a different set of peers is randomly selected for data assignment. Usage control is achieved based on the assumption that at least t out of any set of n peers will not behave maliciously. Such a system would still suffer from re-injection attacks whereby attackers can gain ownership of data and the usage policy thereof by simply re-storing data after slight modification of the content. In order to cope with re-injection attacks the scheme relies on a similarity detection mechanism. The robustness of the scheme has been evaluated in an experimental setting using a variety of re-injection attacks.

With the continuous and exponential increase of the number of users and the size of their data, data deduplication becomes more and more a necessity for cloud storage providers. By storing a unique copy of duplicate data, cloud providers greatly reduce their storage and data transfer costs. The advantages of deduplication unfortunately come with a high cost in terms of new security and privacy challenges. We propose ClouDedup, a secure and efficient storage service which assures block-level deduplication and data confidentiality at the same time. Although based on convergent encryption, ClouDedup remains secure thanks to the definition of a component that implements an additional encryption operation and an access control mechanism. Furthermore, as the requirement for deduplication at block-level raises an issue with respect to key management, we suggest to include a new component in order to implement the key management for each block together with the actual deduplication operation. We show that the overhead introduced by these new components is minimal and does not impact the overall storage and computational costs.

Special issue on "security and privacy in pervasive and ubiquitous computing and communication systems"Pervasive computing and communications are emerging rapidly as an exciting new paradigm to provide data collection, computing, and communication services all the time and everywhere.As new pervasive and ubiquitous computing applications are launched, new security threats emerge, and new security and privacy measures are in urgent need before the corresponding cyber attacks make these new applications too risky to run or use.This special issue focuses on addressing the emerging security threats in pervasive and ubiquitous computing and communication systems.In particular, this special issue contains substantially extended versions of four outstanding papers selected from the program of the 4th International Conference on Security and Privacy in Communication Networks (SecureComm), which received 124 submissions.The review process is rigorous.Every submission is reviewed by at least three reviewers.Based on the review comments, most of the accepted papers have gone through two rounds of revision to achieve best quality.The richness of this special issue comes from the fact that the four papers address different emerging security threats.In particular, paper "DISA: Detection and Isolation of Sneaky Attackers in Locally-Monitored Multi-hop Wireless Networks" addresses an emerging threat in wireless networks, paper "Architecture and Performance Evaluation of a Hybrid Intrusion Detection System for IP Telephony" addresses the emerging threats in IP telephony networks, paper "Attacking the Kad Network -Real World Evaluation and High Fidelity Simulation using DVN" studies a new attack in peer-to-peer file sharing networks, paper "Agent-Based Modeling of Malware Dynamics in Heterogeneous Environments" presents an emulation framework for studying emerging malware, and paper "SMM Rootkits: A New Breed of OS Independent Malware" addresses a new rootkit threat.This special issue was successful, thanks to the efforts of a host of individuals who volunteered their time and energy in putting it together.We are thus grateful to all the reviewers for all their effort and patience in the paper evaluation.We are also grateful to Editor-in-Chief Prof.

Cloud and IT service providers should act as responsible stewards for the data of their customers and users. However, the current absence of accountability frameworks for distributed IT services makes it difficult for users to understand, influence and determine how their service providers honour their obligations. The A4Cloud project will create solutions to support users in deciding and tracking how their data is used by cloud service providers. By combining methods of risk analysis, policy enforcement, monitoring and compliance auditing with tailored IT mechanisms for security, assurance and redress, A4Cloud aims to extend accountability across entire cloud service value chains, covering personal and business sensitive information in the cloud.

Counterfeit detection in RFID-based supply chains aims at preventing adversaries from injecting fake products that do not meet quality standards. This paper introduces CHECKER, a new protocol for counterfeit detection in RFID-based supply chains through on-site checking. While RFID-equipped products travel through the supply chain, RFID readers can verify product genuineness by checking the validity of the product's path. CHECKER uses a polynomial-based encoding to represent paths in the supply chain. Each tag T in CHECKER stores an IND-CCA encryption of T's identifier ID and a signature of ID using the polynomial encoding of T's path as secret key. CHECKER is provably secure and privacy preserving. An adversary can neither inject fake products into the supply chain nor trace products. Moreover, RFID tags in CHECKER can be cheap read/write only tags that do not perform any computation. Per tag, only 120 Bytes storage are required.

As RFID applications are entering our daily life, many new security and privacy challenges arise. However, current research in RFID security focuses mainly on simple authentication and privacy-preserving identification. In this paper, we discuss the possibility of widening the scope of RFID security and privacy by introducing a new application scenario. The suggested application consists of computing statistics on private properties of individuals stored in RFID tags. The main requirement is to compute global statistics while preserving the privacy of individual readings. PPS assures the privacy of properties stored in each tag through the combination of homomorphic encryption and aggregation at the readers. Re-encryption is used to prevent tracking of users. The readers scan tags and forward the aggregate of their encrypted readings to the back-end server. The back-end server then decrypts the aggregates it receives and updates the global statistics accordingly. PPS is provably privacy-preserving. Moreover, tags can be very simple as they are not required to perform any computation, but only to store data.

Many incentive mechanisms have been proposed to foster cooperation among nodes in Peer-to-Peer (P2P) networks. Unfortunately, most of existing solutions rely on the existence of an online centralized authority that is in charge of a fair distribution and transaction of credits (incentives) between peers. Such centralized mechanisms mainly suffer from privacy leakage and single point of failure problems. To cope with these problems, we propose to take advantage of the distributed nature of P2P networks in order for the peers to take care of credit-based operations. Cheating and other DoS attacks are prevented thanks to a threshold security mechanism where the operation should be approved by a predefined certain number of peers. The main novelty of the proposed mechanism is the fact that a “credit” is assigned to some peers using distributed hash tables, hence, peers can follow and control the history of operations with respect to this credit, only. Thanks to this new approach, a malicious node cannot easily keep track of all operations originating from a single node and the impact of cheating or similar attacks would be strongly reduced.

The extremely widespread adoption of Online Social Networks (OSNs) raises many questions on privacy and access control. Regardless of the particular centralized or de-centralized nature of the OSN, the achievable security and privacy degree strongly depends on the graph-theoretical properties of the social graph representing the real friendship relations between the users. In this paper, we analyze the relationship between the social network graph topology and the achievable privacy. We observe three metrics, namely degree distribution, clustering coefficient and mixing time, and show that they give fundamental insights on the privacy degree of the OSN. We propose how to exploit these insight for the design of future privacy-friendly OSN.

Jamming attacks can severely affect the performance of Wireless Sensor Networks (WSNs) due to their broadcast nature. The most reliable solution to reduce the impact of such attacks is to detect and localize the source of the attack. In this paper, we investigate the feasibility of localizing an omni-antenna jammer. We propose Catch the Jammer (CJ), an efficient jammer localization scheme whereby victim nodes at the border of the jammed region share their location information with their one-hop neighbor nodes which further collaborate to find the position of the jammer. This new localization technique first computes a convex hull for the set of victim nodes and further extracts the corresponding minimum covering circle. Simulation results show that CJ outperforms most of the existing localization algorithms depending on the variation of the jammer's transmission range and the position of the jammer.

Online Social Network (OSN) applications and services such as picture sharing, wall posting, and the like, nowadays have a strong impact on the way users interact with each other. Catering for a broad range of users of all ages, and a vast difference in social, educational, and national background, these applications and services allow even users with limited technical skills to share a wide range of personal information with a theoretically unlimited number of partners. This advantage comes at the cost of increased security and privacy exposures for users for two main reasons: first of all, users tend to disclose private personal information with little guard, and secondly, existing OSN applications severely suffer from vulnerabilities in their privacy protection or the lack thereof. The exploitation of these vulnerabilities can lead a malicious user to launch many different types of attacks such as Id theft, profile cloning or secondary data collection. Furthermore, even assuming a perfect protection from such malicious users, legitimate users are still exposed to a major orthogonal privacy threat, since in all existing OSN applications, the service provider has access to all the data including some private information stored and managed by the application itself and can misuse such information easily. Since the access to users' private data is the underpinning of a promising business model, current OSN services are not likely to address this problem in the near future. Researchers recently proposed to design the OSN application based on a peer-to-peer architecture in order to avoid centralized control over users' data. While in one hand a peer-to-peer model seems to be a good candidate to build a privacy preserving solution that avoids centralized control, on the other hand it lacks any a priori trust relationships among parties.

As the organizing committee, it is our pleasure to present the proceedings of the 2ndIEEE International Workshop on Data Security and PrivAcy in wireless Networks (D-SPAN), held on June 20, 2011, in Lucca, Italy. The goal of this one-day workshop, organized in conjunction with the 12thIEEE WoWMoM 2011, is to exchange cutting-edge ideas for securing the next-generation wireless networks, systems and applications. The scope of D-SPAN includes a wide variety of topics, including security and privacy of data collection, transmission, storage, publishing, and sharing in wireless networks broadly defined - such as cellular and mobile ad hoc networks (MANET), vehicular ad hoc networks (VANET), cognitive and sensor networks - to applying data analytics techniques to address security and privacy challenges in these networks. D-SPAN provides a forum for academic and industry researchers to present research ideas that build bridges across three communities: wireless networks and databases, and security.

In this paper, we present the design of the lightweight F_f family of privacy-preserving authentication protocols for RFID-systems. F_f results from a systematic design based on a new algebraic framework focusing on the security and privacy of RFID authentication protocols. F_f offers user-adjustable, strong authentication, and privacy against known algebraic attacks and recently popular SAT-solving attacks. In contrast to related work, F_f achieves these security properties without requiring an expensive cryptographic hash function. F_f is designed for a challenge-response protocol, where the tag sends random nonces and the results of HMAC-like computations of one of the nonces together with its secret key back to the reader. In this paper, the authentication and privacy of F_f is evaluated using analytical and experimental methods.

Social networking services (SNS), which provide the application with the most probably highest growth rates in the Internet today, raise serious security concerns, especially with respect to the privacy of their users. Multiple studies have shown the vulnerability of these services to breaches of privacy and to impersonation attacks mounted by third parties, however the centralized storage at the providers of SNS represents an additional quite significant weakness that so far has not satisfyingly been addressed. In this paper we show the feasibility of ldquoSafebookrdquo, our proposal for the provision of a competitive social networking service, which solves these vulnerabilities by its decentralized design, leveraging on the real life relationships of its users and means of cryptography.

Autonomic and opportunistic communications require specific routing algorithms, like replication-based algorithms or context-based forwarding. Privacy is a major concern for protocols which disseminate the context of their destination. In this paper, we focus on the privacy issue inherent to context-based protocols, in the framework of an original epidemic forwarding scheme, which uses context as a heuristic to limit the replication of messages. We define the achievable privacy level with respect to the trusted communities assumption, and the security implications. Indeed, privacy in such an environment raises challenging problems, which lead us to a solution based on two refinements of identity-based encryption, namely searchable encryption and policy-based encryption. This new solution enables forwarding while preserving privacy by allowing secure partial matches in the header and by enforcing confidentiality of the payload.

Abstract Hop‐by‐hop data aggregation is a very important technique used to reduce the communication overhead and energy expenditure of sensor nodes during the process of data collection in a wireless sensor network (WSN). However, the unattended nature of WSNs calls for data aggregation techniques to be secure. Indeed, sensor nodes can be compromised to mislead the base station (BS) by injecting bogus data into the network during both forwarding and aggregation of data. Moreover, data aggregation might increase the risk of confidentiality violations: If sensors close to the BS are corrupted, an adversary could easily access to the results of the ‘in network’ computation performed by the WSN. Further, nodes can also fail due to random and non‐malicious causes (e.g., battery exhaustion), hence availability should be considered as well. In this paper we tackle the above issues that affect data aggregation techniques by proposing a mechanism that: (i)provides both confidentiality and integrity of the aggregated data so that for any compromised sensor in the WSN the information acquired could only reveal the readings performed by a small, constant number of neighboring sensors of the compromised one; (ii) detects bogus data injection attempts; (iii) provides high resilience to sensor failures. Our protocol is based on the concept of delayed aggregation and peer monitoring and requires local interactions only. Hence, it is highly scalable and introduces small overhead; detailed analysis supports our findings. Copyright © 2009 John Wiley & Sons, Ltd.

Although very developed in many sectors (databases, filesystems), access control schemes are still somewhat elusive when it comes to wireless sensor networks. However, it is clear that many WSN systems - such as healthcare and automotive ones - need a controlled access to data that sensor nodes produce, given its high sensitivity. Enforcing access control in wireless sensor networks is a particularly difficult task due to the limited computational capacity of wireless sensor nodes. In this paper we present a full-fledged access control scheme for wireless sensor data. We enforce access control through data encryption, thus embedding access control in sensor data units. We also propose a lightweight key generation mechanism, based on cryptographic hash functions, that allows for hierarchical key derivation. The suggested protocol only relies on simple operations, does not require interactions between nodes and data consumers and has minimal storage requirements.

As opposed to centralized workflow management systems, the distributed execution of workflows can not rely on a trusted centralized point of coordination. As a result, basic security features including compliance of the overall sequence of workflow operations with the pre-defined workflow execution plan or traceability become critical issues that are yet to be addressed. Besides, the detection of security inconsistencies during the execution of a workflow usually implies the complete failure of the workflow although it may be possible in some situations to recover from the latter. In this paper, we present security solutions supporting the secure execution of distributed workflows. These mechanisms capitalize on onion encryption techniques and security policy models to assure the integrity of the distributed execution of workflows, to prevent business partners from being involved in a workflow instance forged by a malicious peer and to provide business partners identity traceability for sensitive workflow instances. Moreover, we specify how these security mechanisms can be combined with a transactional coordination framework to recover from faults that may be caught during their execution. The defined solutions can easily be integrated into distributed workflow management systems as our design is strongly coupled with the runtime specification of decentralized workflows.

Workflow technologies are becoming pervasive in that they enable the execution of business processes in distributed and ubiquitous computing environments. As long-running transactions, the execution of workflows in environments without dedicated infrastructures raises transactional requirements due to the dynamicity of resources available to run a workflow instance and the integration of relaxed atomicity constraints at both design and instantiation time. In this paper, we propose an adaptive transactional protocol for the pervasive workflow model developed in a previous work to support the execution of business processes in the pervasive setting. The execution of this protocol takes place in two phases. First, candidate business partners are assigned to tasks using an algorithm wherein the selection process is based on both functional and transactional requirements. The workflow execution further proceeds through a hierarchical coordination protocol managed by the workflow initiator and controlled based on a decision table computed as an outcome of the business partner assignment procedure. The resulting workflow execution is compliant with the defined consistency requirements, and the coordination decisions depend on the transactional characteristics offered by the partners assigned to each task. An implementation of our theoretical results relying on ontology Web Language for Series and Business Process Execution Language technologies is further detailed as a proof of concept.

E-business and e-government implementations are becoming more and more widespread with growing number users depending on availability, accuracy and security of such e-services. The users must be able to trust these services, otherwise they will be reluctant to embrace the new opportunities and will not be able to reap the potential benefits. In addition, the end users wish to use the e-services in the simplest way possible and to have them ldquoon taprdquo 24times7 as other conventional utilities. For this to become possible, a robust interoperability fabric among the involved institutions needs to be established. This means having a lot of collaborative interactions invisible to the end-user (a business or an individual citizen) in order to fulfill the promise of e-services. Such interactions become more complex when the organizations belong to different countries, act according different laws in different languages. This paper presents the work being done to create an efficient, secure and trusted interoperability framework for public sector agencies of European Union member countries.

Several cooperation enforcement schemes based on rewarding mechanisms such as electronic cash or online credits have lately been proposed to prevent selfish behavior in ad-hoc networks. However, these schemes suffer from the lack of fairness guarantees or the reliance on costly mechanisms such as tamper- proof hardware or the requirement for trusted third parties (TTPs) that are not suitable for ad-hoc networks. In this paper, we present a new cooperation-enforcement scheme that is perfectly suitable for ad-hoc delay-tolerant networks. The protocol is based on a simple technique called hot- potato forwarding whereby in order to receive a packet, potential recipients must first deliver an advance reward to the sender prior to the transmission of the packet. Thanks to this technique cooperation among nodes becomes mandatory and poisoning attacks and cheating actions are inherently prevented. The second contribution in our scheme is an optimistic fair exchange protocol that solves the fairness problem that is inherent to peer rewarding schemes. The protocol achieves total fairness with the help of a TTP and is optimistic in that the TTP is only involved in case of conflict between peer nodes. Correct execution of the protocol does not require any access to the TTP, so fairness is achieved without any impact on well-behaving nodes. The fairness of the protocol is validated through the exhaustive analysis of all possible protocol traces.

The concept of policy-based cryptography is a promising paradigm for trust establishment and authorization in largescale open environments like the Internet and Mobile Networks. It aims at providing a framework for performing cryptographic operations with respect to policies formalized as monotone Boolean expressions written in standard normal forms. A policy involves conjunctions and disjunctions of conditions where each condition is fulfilled by a digital credential representing the signature of a specific credential issuer on a set of statements about a certain entity. Therefore, an entity fulfills a policy if any only if it has been issued a set of credentials fulfilling the combination of conditions specified by the policy.In this work, we focus on policy-based encryption schemes which allow to encrypt a message according to a policy so that only entities fulfilling the policy are able to decrypt the message. More generally, policy-based encryption belongs to an emerging family of encryption schemes sharing the ability to integrate encryption with access control structures. This ability is mainly enabled by bilinear pairings over elliptic curves and allows for several interesting applications in different contexts.A policy-based encryption scheme has to fulfill two primary requirements: on one hand, provable security under well defined attack models. On the other hand, efficiency, especially when dealing with the conjunctions and disjunctions of credential-based conditions.The contributions of our research work are twofold:1. The standard acceptable notion of security for public-key encryption schemes is indistinguishability against chosen ciphertext attacks. Hence, it is natural to require that a policy-based encryption scheme also satisfies this strong notion of security. However, the definition of this security notion must be adapted to the policy-based setting. Our first contribution is the definition of policy-oriented security model for policy-based encryption schemes as well as the development of an efficient policy-based encryption scheme that is provably secure under our security model in the random oracle model.2. Policy-based encryption schemes may suffer from the key-escrow property i.e. in addition to the legitimate holder of the credentials fulfilling the encryption policy, any collusion of credential issuers who are able to issue a set of credentials fulfilling the policy can decrypt the message. Our second contribution is to address this issue through the notion of policy-based public-key encryption. The latter allows encrypting a message not only with respect to a policy but also according to a public-key so that only an entity fulfilling the policy and having access to the corresponding private-key is able to decrypt the message. We developed a policy-based public-key encryption scheme from bilinear pairings and proved its security under the corresponding security model. Our proposal improves related work in terms of both security and efficiency.

Workflow technologies are becoming pervasive in that they enable the execution of business processes in distributed and ubiquitous computing environments. The execution of pervasive workflows raises transactional requirements due to their dynamicity and the need for relaxed atomicity. In this paper, we propose an adaptive transactional protocol for the pervasive workflow model developed in a previous work. The execution of this protocol takes place in two phases. First devices are assigned to tasks using an algorithm whereby workflow partners are selected based on functional and transactional requirements. The workflow execution further proceeds through a hierarchical coordination protocol managed by the workflow initiator and controlled based on a decision table computed as an outcome of the device assignment procedure. The resulting workflow execution is compliant with the defined consistency requirements and the coordination decisions depend on the transactional characteristics of the devices assigned to each task

Current Web services composition approaches do not take into account transactional requirements defined by designers. The transactional challenges raised by the composition of Web services are twofold: relaxed atomicity and dynamicity. In this paper, we propose a new process to automate the design of transactional composite Web services. Our solution enables the composition of Web services not only according to functional requirements but also to transactional ones defined using the acceptable termination states model. The resulting composite Web service is compliant with the consistency requirements expressed by designers and its execution can easily be coordinated using the coordination rules provided as an outcome of our approach

As opposed to existing workflow management systems, the distributed execution of workflows in pervasive environments can not rely on centralized control. The dynamic nature of the pervasive environments on the other hand does not allow a permanent assignment of roles to devices. In this paper, we suggest an architecture supporting distributed execution of workflows in pervasive environments based on a fully decentralized control and dynamic assignment of roles to devices. The architecture is defined in terms of data structures associated with the workflow execution plan and dynamic information, a protocol for the exchange of the workflow data among devices and a new function called role discovery dealing with the dynamic assignment of roles to devices. This architecture is applied in the context of Web services using BPEL as workflow description language

Even though group rekeying is one of the most visited areas in network security, solutions still are severely lacking with respect to reliability and real customer expectations. We first classify secure multicast applications with regard to these expectations and suggest a new approach that defines different recipient categories based on their "loyalty" and that treats each category differently by offering better service to more loyal recipients. We propose to restructure the logical key hierarchy (LKH) scheme by separately regrouping members based on their membership duration, aiming at preserving members with long duration membership from the impact of rekeying operations caused by arrivals or departures of short-lived members. We then describe an extensive method for computing system parameters, like rekeying intervals, based on customer satisfaction criteria.

Networks integrating satellite shared access, such as DVB-S/RCS, are particularly exposed to denial of service (DoS) attacks through which a satellite terminal can maliciously use the Network Control Center (NCC) resources by submitting a high number of bogus requests. Anti-clogging techniques used in terrestrial mesh networks to thwart DoS attacks fall short of solving DoS problems in the case of satellite networks due to the inherent broadcast capability of the communication medium. We suggest a generic mechanism to prevent DoS attacks in control plane protocols. The principle behind this mechanism is an efficient identification technique that allows the satellite servers to quickly discard bogus requests. Thanks to this technique, intruders controlling the total bandwidth of the up-link can only consume a very small fraction of the NCC's resources.

This paper introduces and solves a security problem of pervasive computing: how to define authorizations for off-line interactions when trust relationships among entities do not exist. A new type of capability is proposed to assure that user interactions are not traceable and that misbehaving users automatically lose some money they deposited as a guarantee of their loyalty. The solution inspired by electronic cash is based on a new version of the cut-and-choose protocol adapted for open environments.

We propose a new stream authentication scheme that is suitable for live packet streams distributed over a lossy channel, such as an IP-multicast group. Packets are signed together in a block and the recipient can authenticate this block if the loss rate per block is lower than a certain threshold, which can be chosen based on the characteristic of the communication channel. This scheme provides both integrity and non repudiation of origin, and in a majority of situations, it performs with less overhead in bytes per packet than previously proposed practical live stream authentication schemes.

In this article we propose a new framework for multicast security based on distributed computation of security transforms by intermediate nodes. The involvement of intermediate nodes in the security process causes a new type of dependency between group membership and the topology of the multicast network. Thanks to this dependency, the containment of security exposures in large multicast groups is ensured. The framework also ensures both the scalability for large dynamic groups and the security of individual members. Two different key distribution protocols complying with the framework are introduced: an extension of the EIGamal encryption scheme, and one based on a multiexponent version of RSA.

In this paper we propose a new framework for multicast security based on distributed computation of security transforms by intermediate nodes. The involvement of intermediate nodes in the security process causes a new type of dependency between group membership and the topology of the multicast network. Thanks to this dependency, the containment of security exposures in large multicast groups is assured. The framework also assures both the scalability for large dynamic groups and the security of individual members. Two different key distribution protocols complying with the framework are introduced. The first protocol is an extension of the El Gamal encryption scheme whereas the second is based on a multi-exponent version of RSA.

A communication platform is described that supports the fast implementation of networked multimedia applications with conference character and collaboration features. The platform exhibits the notion of a site as one of its main abstractions. A site is a collection of workstations, media input, and output devices that are, in terms of control, tightly coupled. Connection and application control is centralized within one site, but distributed among different sites. The platform exports a programming interface with high-level abstractions for session and connection control, allowing application developers to concentrate on scenario and user interface design. The platform was implemented in the course of the European Beteus (Broadband Exchange for Trans-European Usage) project. A tele-meeting application and a tele-teaching application were developed on top of it. Platform components and applications were tested on the European asynchronous transfer mode (ATM) pilot network over a period of nine months. The paper first describes platform architecture and programming interface, then talks about the implementation of platform and applications and their deployment in the harsh environment of a trans-national broadband pilot network.

We present IDAMN (intrusion detection architecture for mobile networks), a distributed system whose main functionality is to track and detect mobile intruders in real time. IDAMN includes two algorithms which model the behavior of users in terms of both telephony activity and migration pattern. The main novelty of our architecture is its ability to perform intrusion detection in the visited location and within the duration of a typical call, as opposed to existing designs that require the reporting of all call data to the home location in order to perform the actual detection. The algorithms and the components of IDAMN have been designed in order to minimize the overhead incurred in the fixed part of the cellular network.

This paper presents, a new technique for compression and secure image coding that is based on the iterated function system (IFS). A multi-resolution access control algorithm based on the convergence control of an iterative image reconstruction process is investigated. For multimedia applications an icon representation of low image quality is extracted directly from the encrypted data flow thanks to the partial self-affinity properties inherent to the local-IFS. The robustness of our scheme is due to the inherent high correlation of image data and to the non-linear decoding process.

This paper discusses issues and idiosyncrasies associated with changing passwords and keys in distributed computer systems. Current approaches are often complicated and fail to provide the desired level of security and fault tolerance. A novel and ve

User mobilityis a feature that raises many new security-related issues and concerns.One of them is the disclosure of a mobile user's reai identity during the authentication process, or other procedures specific to mobile networks.Such disclosure allows an unauthorized third-party to track the m.obile user's movements and current whereabouts.Depending ou the context, access to auy information related to a mobile user's location without his consent can be a serious violation of his privacy.This new issue might be seen as a conflicting requirement with respect to authentication: untraceability requires hiding the user's identity while authentication requires the user's identity to be revealed in order to be proved.What is needed is a single mechanism reconciling both authentication and privacy of a mobile user's identification.The basic :solution to this problem is the use of uliases.Aliases insure untraceability by hiding the user's real identity as well as his relationship with domain authorities.In this paper, we present a classification scheme to identify the various degrees of untraceability requirements.We then present an efficient method for the computation of aliases and apply It to a new set of inter-domain authentication protocols.We demonstrate that these protocols can be designed to meet various degrees of untraceability requirements.In designing these protocols, we try to avoid the drawbacks of authentication protoc:ols in existing mobile network architectures such as CDPD and GSM.

An essential function for achieving security in computer networks is reliable authentication of communicating parties and network components. Such authentication typically relies on exchanges of cryptographic messages between the involved parties, which in turn implies that these parties be able to acquire shared secret keys or certified public keys. Provision of authentication and key distribution functions in the primitive and resource-constrained environments of low-function networking mechanisms, portable, or wireless devices presents challenges in terms of resource usage, system management, ease of use, efficiency, and flexibility that are beyond the capabilities of previous designs such as Kerberos or X.509. This paper presents a family of light-weight authentication and key distribution protocols suitable for use in the low layers of network architectures. All the protocols are built around a common two-way authentication protocol. The paper argues that key distribution may require substantially different approaches in different network environments and shows that the proposed family of protocols offers a flexible palette of compatible solutions addressing many different networking scenarios. The mechanisms are minimal in cryptographic processing and message size, yet they are strong enough to meet the needs of secure key distribution for network entity authentication. The protocols presented have been implemented as part of comprehensive security subsystem prototype called KryptoKnight.>

This paper describes an access control mechanism that enforces at the network level an access control decision that is taken at the application level. The mechanism is based on the pre-computation of encrypted counters called tickets. An access enforcement device verifies the existence of a valid ticket in each packet that is subject to access control and kills unauthorized packets. Tickets are not computed as a function of the user data. Due to the timing constraints of shared media LANs the presence of a valid ticket in a packet proves that the operation implied by the user data has been authorized. The access control mechanism is elaborated for Internet protocols over Ethernet and we discuss its properties for internetworking and multicasting.

The authors describe a novel authentication method whereby the fixed relationship between the user and the device is avoided. They present a method whereby the authentication device, which is a token card, is used solely to provide a secure channel between a human user and an authentication server. Since the communication channel is secured by the card, the user can still utilize weak secrets such as passwords and personal identification numbers for authentication purposes, but, without any risk of exposure. Furthermore, the card's and the user's secrets are mutually independent, i.e., the card is impersonal, it can be freely shared by several users. This eliminates the high cost of administration which is typical of existing designs requiring fixed user-device relationship. The method does not require any coupling between the token card and the workstation, which would be difficult to implement on a global scale and retrofit onto existing equipment.>

Most existing designs for two-way cryptographic authentication protocols suffer from one or more limitations. Among other things, they require synchronization of local clocks, they are subject to export restrictions because of the way they use cryptographic functions, and they are not amenable to use in lower layers of network protocols because of the size and complexity of messages they use. Designing suitable cryptographic protocols that cater to large and dynamic network communities but do not suffer from these problems presents substantial problems. It is shown how a few simple protocols, including one proposed by ISO, can easily be broken, and properties that authentication protocols should exhibit are derived. A methodology for systematically building and testing the security of a family of cryptographic two-way authentication protocols that are as simple as possible yet resistant to a wide class of attacks, efficient, easy to implement and use, and amenable to many different networking environments is described. Examples of protocols of that family that presents various advantages in specific distributed system scenarios are discussed.>