Matthias Schunter

Optimistic protocols for fair exchange

We describe a generic protocol for fair exchange of electronic goods with non-repudiation. Goods can be signatures (i.e., non-repudiation tokens of public data), confidential data, or payments. The protocol does not involve a third party in the exchange in the fault-less case but only for recovery.

A privacy policy model for enterprises

Privacy is an increasing concern in the marketplace. Although enterprises promise sound privacy practices to their customers, there is no technical mechanism to enforce them internally In this paper we describe a privacy policy model that protects personal data from privacy violations by means of enforcing enterprise-wide privacy, policies. By extending Jajodia et al.s flexible authorization framework (FAF) with grantors and obligations, we create a privacy control language that includes user consent, obligations, and distributed administration. Conditions impose restrictions on the use of the collected data, such as modeling guardian consent and options. Access decisions are extended with obligations, which list a set of activities that must be executed together with the access request. Grantors allow to define a separation of duty between the security officer and the privacy officer.

E-P3P privacy policies and privacy authorization

Enterprises collect large amounts of personal data from their customers. To ease privacy concerns, enterprises publish privacy statements that outline how data is used and shared. The Platform for Enterprise Privacy Practices (E-P3P) defines a fine-grained privacy policy model. A Chief Privacy Officer can use E-P3P to formalize the desired enterprise-internal handling of collected data. A particular data user is then allowed to use certain collected data for a given purpose if and only if the E-P3P authorization engine allows this request based on the applicable E-P3P policy. By enforcing such formalized privacy practices, E-P3P enables enterprises to keep their promises and prevent accidental privacy violations.

Trusting mobile user devices and security modules

The market for devices like mobile phones, multifunctional watches, and personal digital assistants is growing rapidly. Most of these mobile user devices need security for their prospective electronic commerce applications. While new technology has simplified many business and personal transactions, it has also opened the door to high-tech crime. We investigate design options for mobile user devices that are used in legally significant applications.

A Toolkit for Managing Enterprise Privacy Policies

Enterprise privacy enforcement allows enterprises to internally enforce a privacy policy that the enterprise has decided to comply to. An enterprise privacy policy often reflects different legal regulations, promises made to customers, as well as more restrictive internal practices of the enterprise. Further, it may allow customer preferences. Hence it may be authored, maintained, and audited in a distributed fashion.

The ESPRIT Project CAFE - High Security Digital Payment Systems

CAFE (“Conditional Access for Europe”) is an ongoing project in the European Communitys ESPRIT program. The goal of CAFE is to develop innovative systems for conditional access, and in particular, digital payment systems. An important aspect of CAFE is high security of all parties concerned, with the least possible requirements that they are forced to trust other parties (so-called multi-party security). This should give legal certainty to everybody at all times. Moreover, both the electronic money issuer and the individual users are less dependent on the tamper-resistance of devices than in usual digital payment systems. Since CAFE aims at the market of small everyday payments that is currently dominated by cash, payments are offline, and privacy is an important issue.

Security audits of multi-tier virtual infrastructures in public infrastructure clouds

Cloud computing has gained remarkable popularity in the recent years by a wide spectrum of consumers, ranging from small start-ups to governments. However, its benefits in terms of flexibility, scalability, and low upfront investments, are shadowed by security challenges which inhibit its adoption. Managed through a web-services interface, users can configure highly flexible but complex cloud computing environments. Furthermore, users misconfiguring such cloud services poses a severe security risk that can lead to security incidents, e.g., erroneous exposure of services due to faulty network security configurations. In this article we present a novel approach in the security assessment of the end-user configuration of multi-tier architectures deployed on infrastructure clouds such as Amazon EC2. In order to perform this assessment for the currently deployed configuration, we automated the process of extracting the configuration using the Amazon API. In the assessment we focused on the reachability and vulnerability of services in the virtual infrastructure, and presented a way for the visualization and automated analysis based on reachability and attack graphs. We proposed a query and policy language for the analysis which can be used to obtain insights into the configuration and to specify desired and undesired configurations. We have implemented the security assessment in a prototype and evaluated it for practical scenarios. Our approach effectively allows to remediate todays security concerns through validation of configurations of complex cloud infrastructures.

Enhancing grid security using trusted virtualization

Grid applications increasingly have sophisticated functional and security requirements. Current techniques mostly protect the grid resource provider from attacks by the grid user, while leaving the user comparatively dependent on the well-behavior of the provider. We present the key components for a trustworthy grid architecture and address this trust asymmetry by using a combination of trusted computing and virtualization technologies. We propose a scalable offline attestation protocol, which allows the selection of trustworthy partners in the grid with low overhead. By providing multilateral security, i.e., security for both the grid user and the grid provider, our protocol increases the confidence that can be placed on the correctness of a grid computation and on the protection of user-provided assets.

Optimal efficiency of optimistic contract signing

A contract is a non-repudiable agreement on a given contract text, i.e., a contract can be used to prove agreement between its signatories to any verifier. A contract signing scheme is used to fairly compute a contract so that, even if one of the signatories misbehaves, either both or none of the signatories obtain a contract. Optimistic contract signing protocols use a third paay to ensure fairness, but in such a way that the third party is not actively involved in the fault-less case. Since no satisfactory protocols without any third party exist, this seems to be the best one can hope for. We prove tight lower bounds on the message and round complexity of optimistic contract signing on synchronous and asynchronous networks, and present new and efficient protocols based on digital signatures which achieve provably optimal efficiency.

Towards automated provisioning of secure virtualized networks

We describe a secure network virtualization framework that helps realize the abstraction of Trusted Virtual Domains (TVDs), a security-enhanced variant of virtualized network zones. The framework allows groups of related virtual machines running on separate physical machines to be connected together as though there were on their own separate network fabric and, at the same time, helps enforce cross-group security requirements such as isolation, confidentiality, security, and information flow control. The framework uses existing network virtualization technologies, such as Ethernet encapsulation, VLAN tagging, and VPNs, and combines and orchestrates them appropriately to implement TVDs. Our framework aims at automating the instantiation and deployment of the appropriate security mechanism and network virtualization technologies based on an input security model that specifies the required level of isolation and permitted network flows. We have implemented a prototype of the framework based on the Xen hypervisor. Experimental evaluation of the prototype shows that the performance of our virtual networking extensions is comparable to that of the standard Xen configuration.