<p>Correct certificate revocation practices are essential to each public-key infrastructure. While there exist a number of protocols to achieve revocation in PKI systems, there has been very little work on the theory behind it: Which different types of revocation can be identified? What is the intended effect of a specific revocation type to the knowledge base of each entity?</p><p>As a first step towards a methodology for the development of reliable models, we present a graph-based formalism for specification and reasoning about the distribution and revocation of public keys and certificates. The model is an abstract generalization of existing PKIs and distributed in nature; each entity can issue certificates for public keys that they have confidence in, and distribute or revoke these to and from other entities.</p><p>Each entity has its own public-key base and can derive new knowledge by combining this knowledge with certificates signed with known keys. Each statement that is deduced or quoted within the system derives its support from original knowledge formed outside the system. When such original knowledge is removed, all statements that depended upon it are removed as well. Cyclic support is avoided through the use of support sets.</p><p>We define different revocation reasons and show how they can be modelled as specific actions. Revocation by removal, by inactivation, and by negation are all included. By policy, negative statements are the strongest, and positive are the weakest. Collisions are avoided by removing the weaker statement and, when necessary, its support.</p><p>Graph transformation rules are the chosen formalism. Rules are either interactive changes that can be applied by entities, or automatically applied deductions that keep the system sound and complete after the application of an interactive rule.</p><p>We show that the proposed model is sound and complete with respect to our definition of a valid state.</p> / Report code: LIU-TEK-LIC-2006:1

Because of the popularity of wireless communication technologies, people can access servers without the restriction of place and time. With the rapid development of mobile devices, such as smart phones and iPads, the frequency of wireless networks have increased. Roaming services ensure service provision without location constraints. A secure roaming authentication protocol is critical for the security and privacy of users when accessing services by roaming. It ensures the authenticity of mobile users, and foreign and home servers. After authentication, the session key for the mobile user and the foreign server is established for secure communication. In addition, a secure roaming protocol may provide anonymity for mobile users. When the mobile user requests a service, the server is unable to identify two requests from the same user. For the current anonymous authentication protocols, the foreign server must fulfill the revocation check by the computation linear to the number of revoked users. It makes the protocol infeasible in practical environments. This thesis proposes a strong anonymous authentication protocol, using two-stage authentication, in which the home server is involved in the initial authentication to eliminate the revocation list and issues a timely anonymous credential for subsequent authentication after successful authentication. It reduces the computation costs for the revocation check and minimizes the size of the revocation list. Finally, this thesis also provides security proofs and comparisons of the proposed authentication mechanism.

Thèse Droit, Fribourg (Suisse), 1970.

Title from title screen (viewed April 17,2010). / "March 2010." "The Harlem Parole Reentry Court was established in June of 2001 in response to the high concentration of parolees returning to the East Harlem neighborhood of Manhattan. Created by the Center for Court Innovation in cooperation with the New York State Division of Criminal Justice Services and the Division of Parole, the Reentry Court provides intensive judicial oversight, supervision and services to new parolees during the first six months following release from state prison. The goal of the program is to stabilize returning parolees in the initial phase of their reintegration by helping them to find jobs, secure housing, remain drug-free and assume familial and personal responsibilties. Following graduation, participants are transferred to traditional parole supervision, where they may continue to receive case management services voluntarily through the Reentry Court." -- Executive summary. "The Reentry Court seems to have had a positive effect with regard to preventing new crimes as measured by rearrests and reconvictions. However, participants were found to have higher rates of revocations. In particular, program participants were more likely to be revoked for technical violations of parole conditions. Given the lower caseload and greater intensity of the program, it is assumed that :"supervision effects" are partially responsible for the higher rate of technical violations. In other words, the Harlem Parole Reentry Court may be detecting violations that might otherwise have gone unnoticed. This suggests that reentry courts may want to explore enhancing the use of alternative sanctions in lieu of revocation. Furthermore, reentry courts should explore the possibility of providing greater feedback to parole officers and case managers, making them aware of potential unintended consequences when supervision is increased." -- Executive summary. Includes bibliographical references (p. 35-40).

Title from title screen (viewed April 17,2010). / "March 2010." "The Harlem Parole Reentry Court was established in June of 2001 in response to the high concentration of parolees returning to the East Harlem neighborhood of Manhattan. Created by the Center for Court Innovation in cooperation with the New York State Division of Criminal Justice Services and the Division of Parole, the Reentry Court provides intensive judicial oversight, supervision and services to new parolees during the first six months following release from state prison. The goal of the program is to stabilize returning parolees in the initial phase of their reintegration by helping them to find jobs, secure housing, remain drug-free and assume familial and personal responsibilties. Following graduation, participants are transferred to traditional parole supervision, where they may continue to receive case management services voluntarily through the Reentry Court." -- Executive summary. "The Reentry Court seems to have had a positive effect with regard to preventing new crimes as measured by rearrests and reconvictions. However, participants were found to have higher rates of revocations. In particular, program participants were more likely to be revoked for technical violations of parole conditions. Given the lower caseload and greater intensity of the program, it is assumed that :"supervision effects" are partially responsible for the higher rate of technical violations. In other words, the Harlem Parole Reentry Court may be detecting violations that might otherwise have gone unnoticed. This suggests that reentry courts may want to explore enhancing the use of alternative sanctions in lieu of revocation. Furthermore, reentry courts should explore the possibility of providing greater feedback to parole officers and case managers, making them aware of potential unintended consequences when supervision is increased." -- Executive summary. Includes bibliographical references (p. 35-40).

Through application of modern technology, aviation systems are becoming more automated and are relying less on antiquated air traffic control (ATC) voice systems. Aircraft are now able to wirelessly broadcast and receive identity and location information using transponder technology. This helps reduce controller workload and allows the aircraft to take more responsibility for maintaining safe separation. However, these systems lack source authentication methods or the ability to check the integrity of message content. This opens the door for hackers to potentially create fraudulent messages or manipulate message content. This thesis presents a solution to handling many of the potential security issues in aircraft data communication. This is accomplished through the implementation of a Dual Path PKI (DPP) design which includes a novel approach to handling certificate revocation through session certificates. DPP defines two authentication protocols, one between aircraft and another between aircraft and ATC, to achieve source authentication. Digital signature technology is utilized to achieve message content and source integrity as well as enable bootstrapping DPP into current ATC systems. DPP employs cutting-edge elliptic curve cryptography (ECC) algorithms to increase performance and reduce overhead. T is found that the DPP design successfully mitigates several of the cyber security concerns in aircraft and ATC data communications. An implementation of the design shows that anticipated ATC systems can accommodate the additional processing power and bandwidth required by DPP to successfully achieve system integrity and security. / Master of Science

In his seminal work Strangers in Our Midst (2016a.), David Miller develops his version of liberal nationalism, where he argues for liberal states being justified in requiring immigrants to integrate themselves culturally before giving them access to formal citizenship equal to native citizens. Elsewhere, Miller (2016b.) has also expressed that there are instances when states are justified in revoking citizenships for national security reasons. This paper argues that these positions held by Miller are inconsistent with each other. To make the case against Miller for why this is, three arguments are presented. Firstly, the strict immigration policy suggested in liberal nationalism is permissible because once it is successfully completed, the naturalised citizen gains equal standing in citizenship to native born citizens. If denationalisation is applied in conjunction, but only to some, then their citizenship statis is not equal, and thus the justification for liberal nationalist immigration policy is undermined. Secondly, while it might otherwise be plausible that this injustice is permissible by viewing dual citizens secondary citizenship as a protective privilege, the necessary integration in liberal nationalism makes this response less believable. Finally, one of the most important objectives in liberal nationalism is to promote trust between members. If dual citizens are the only ones who can have their citizenship revoked, and the only reason for this is on suspicion of terrorism, then this risk promoting mistrust against these individuals, making the combination of liberal nationalism and denationalisation self-defeating.

Donation is not only a transfer of property, but it is a proof of certain relationship between the donor and the donee, which results from the liberality and altruism of the donor. Therefore it is understandable that majority of donations take place in the frame of family relations, they appear almost every day and they present a highly used contractual type in all legal orders. The legal regulation of donation has been significantly extended by the new civil code (Act no. 89/2012 coll. civil code) compared to the previous regulation and therefore is more compact and detailed, it has been also extended of another reason for revocation of donation, namely for impoverishment of the donor, furthermore the donatio mortis causa, which has been forbidden by the previous civil code has returned to the current regulation. In spite of enactment of new regulation some questions remain unsolved or new questions arise which will have to be answered by the currently non-existent specialized literature and judicial decisions. The aim of the submitted diploma thesis was to evaluate, whether the current legal regulation of donation contract can stand in comparison with the other European regulations, contained it civil codes with long-standing tradition whether it exceeds them in some directions, which deficiencies...

Anonymous communications networks help to solve the real and important problem of enabling users to communicate privately over the Internet. However, by doing so, they also introduce an entirely new problem: How can service providers on the Internet---such as websites, IRC networks and mail servers---allow anonymous access while protecting themselves against abuse by misbehaving anonymous users? Recent research efforts have focused on using anonymous blacklisting systems (also known as anonymous revocation systems) to solve this problem. As opposed to revocable anonymity systems, which enable some trusted third party to deanonymize users, anonymous blacklisting systems provide a way for users to authenticate anonymously with a service provider, while enabling the service provider to revoke access from individual misbehaving anonymous users without revealing their identities. The literature contains several anonymous blacklisting systems, many of which are impractical for real-world deployment. In 2006, however, Tsang et al. proposed Nymble, which solves the anonymous blacklisting problem very efficiently using trusted third parties. Nymble has inspired a number of subsequent anonymous blacklisting systems. Some of these use fundamentally different approaches to accomplish what Nymble does without using third parties at all; so far, these proposals have all suffered from serious performance and scalability problems. Other systems build on the Nymble framework to reduce Nymble's trust assumptions while maintaining its highly efficient design. The primary contribution of this thesis is a new anonymous blacklisting system built on the Nymble framework---a nimbler version of Nymble---called Nymbler. We propose several enhancements to the Nymble framework that facilitate the construction of a scheme that minimizes trust in third parties. We then propose a new set of security and privacy properties that anonymous blacklisting systems should possess to protect: 1) users' privacy against malicious service providers and third parties (including other malicious users), and 2) service providers against abuse by malicious users. We also propose a set of performance requirements that anonymous blacklisting systems should meet to maximize their potential for real-world adoption, and formally define some optional features in the anonymous blacklisting systems literature. We then present Nymbler, which improves on existing Nymble-like systems by reducing the level of trust placed in third parties, while simultaneously providing stronger privacy guarantees and some new functionality. It avoids dependence on trusted hardware and unreasonable assumptions about non-collusion between trusted third parties. We have implemented all key components of Nymbler, and our measurements indicate that the system is highly practical. Our system solves several open problems in the anonymous blacklisting systems literature, and makes use of some new cryptographic constructions that are likely to be of independent theoretical interest.

Anonymous communications networks help to solve the real and important problem of enabling users to communicate privately over the Internet. However, by doing so, they also introduce an entirely new problem: How can service providers on the Internet---such as websites, IRC networks and mail servers---allow anonymous access while protecting themselves against abuse by misbehaving anonymous users? Recent research efforts have focused on using anonymous blacklisting systems (also known as anonymous revocation systems) to solve this problem. As opposed to revocable anonymity systems, which enable some trusted third party to deanonymize users, anonymous blacklisting systems provide a way for users to authenticate anonymously with a service provider, while enabling the service provider to revoke access from individual misbehaving anonymous users without revealing their identities. The literature contains several anonymous blacklisting systems, many of which are impractical for real-world deployment. In 2006, however, Tsang et al. proposed Nymble, which solves the anonymous blacklisting problem very efficiently using trusted third parties. Nymble has inspired a number of subsequent anonymous blacklisting systems. Some of these use fundamentally different approaches to accomplish what Nymble does without using third parties at all; so far, these proposals have all suffered from serious performance and scalability problems. Other systems build on the Nymble framework to reduce Nymble's trust assumptions while maintaining its highly efficient design. The primary contribution of this thesis is a new anonymous blacklisting system built on the Nymble framework---a nimbler version of Nymble---called Nymbler. We propose several enhancements to the Nymble framework that facilitate the construction of a scheme that minimizes trust in third parties. We then propose a new set of security and privacy properties that anonymous blacklisting systems should possess to protect: 1) users' privacy against malicious service providers and third parties (including other malicious users), and 2) service providers against abuse by malicious users. We also propose a set of performance requirements that anonymous blacklisting systems should meet to maximize their potential for real-world adoption, and formally define some optional features in the anonymous blacklisting systems literature. We then present Nymbler, which improves on existing Nymble-like systems by reducing the level of trust placed in third parties, while simultaneously providing stronger privacy guarantees and some new functionality. It avoids dependence on trusted hardware and unreasonable assumptions about non-collusion between trusted third parties. We have implemented all key components of Nymbler, and our measurements indicate that the system is highly practical. Our system solves several open problems in the anonymous blacklisting systems literature, and makes use of some new cryptographic constructions that are likely to be of independent theoretical interest.