Keeping Authorities "Honest or Bust" with Decentralized Witness Cosigning

The secret keys of critical network authorities - such as time, name, certificate, and software update services - represent high-value targets for hackers, criminals, and spy agencies wishing to use these keys secretly to compromise other hosts. To protect authorities and their clients proactively from undetected exploits and misuse, we introduce CoSi, a scalable witness cosigning protocol ensuring that every authoritative statement is validated and publicly logged by a diverse group of witnesses before any client will accept it. A statement S collectively signed by W witnesses assures clients that S has been seen, and not immediately found erroneous, by those W observers. Even if S is compromised in a fashion not readily detectable by the witnesses, CoSi still guarantees S's exposure to public scrutiny, forcing secrecy-minded attackers to risk that the compromise will soon be detected by one of the W witnesses. Because clients can verify collective signatures efficiently without communication, CoSi protects clients' privacy, and offers the first transparency mechanism effective against persistent man-in-the-middle attackers who control a victim's Internet access, the authority's secret key, and several witnesses' secret keys. CoSi builds on existing cryptographic multisignature methods, scaling them to support thousands of witnesses via signature aggregation over efficient communication trees. A working prototype demonstrates CoSi in the context of timestamping and logging authorities, enabling groups of over 8,000 distributed witnesses to cosign authoritative statements in under two seconds.Comment: 20 pages, 7 figure

The U.S. Response to Human Trafficking: An Unbalanced Approach

The United States' anti-trafficking efforts formally began with the passage of the Trafficking Victims Protection Act (TVPA) of 2000. Since then, the U.S. Government has poured billions of dollars into prevention efforts overseas and prosecution and protection efforts at home. In many ways it provides a model to other countries that are trying to address human trafficking. This report is focused on the United States' efforts to protect trafficked persons found in the United States. Under the TVPA, protections, services and benefits are only offered to trafficked persons who are witnesses assisting law enforcement. This system presents its own challenges in accessing benefits and services, particularly due to law enforcement's anipulation of the system. This is not a case of unforeseen implementation struggles that can be fixed. Instead, at issue is the entire conceptual framework of trafficking as a law enforcement issue and only a law enforcement issue. The results of six years of this approach are becoming startlingly clear -- few trafficked persons coming forward to work with law enforcement. Those who are discovered by law enforcement but refuse or are unable to recount their experiences are not offered any protections and are instead deported. This is an acute problem in particular for trafficked children. The Women's Commission for Refugee Women and Children (Women's Commission) believes that this is an unbalanced approach and that the consequences are grave. While prosecuting traffickers is a just and necessary goal, it should not be accomplished at the expense of the trafficked person. Both objectives can be achieved successfully by adopting a rights-based approach, which entails providing protections to all trafficked persons. It is increasingly acknowledged and recognized even among law enforcement officials that a trafficked person who receives assistance is more likely, willing and able to work with law enforcement. Another issue throwing trafficking protections off balance is the United States' policy which focuses government trafficking efforts on eradicating prostitution, which it conflates with sex trafficking. Efforts at addressing contributing factors to trafficking are laudable but should not be pursued to the exclusion of other efforts. There is a need for immigration and labor reform that would yield dramatic results in protections for trafficked and exploited persons in the informal economy

Generalized qudit Choi maps

Following the linear programming prescription of Ref. \cite{PRA72}, the $d\otimes d$ Bell diagonal entanglement witnesses are provided. By using Jamiolkowski isomorphism, it is shown that the corresponding positive maps are the generalized qudit Choi maps. Also by manipulating particular $d\otimes d$ Bell diagonal separable states and constructing corresponding bound entangled states, it is shown that thus obtained $d\otimes d$ BDEW's (consequently qudit Choi maps) are non-decomposable in certain range of their parameters.Comment: 22 page

Efficient Optimally Lazy Algorithms for Minimal-Interval Semantics

Minimal-interval semantics associates with each query over a document a set of intervals, called witnesses, that are incomparable with respect to inclusion (i.e., they form an antichain): witnesses define the minimal regions of the document satisfying the query. Minimal-interval semantics makes it easy to define and compute several sophisticated proximity operators, provides snippets for user presentation, and can be used to rank documents. In this paper we provide algorithms for computing conjunction and disjunction that are linear in the number of intervals and logarithmic in the number of operands; for additional operators, such as ordered conjunction and Brouwerian difference, we provide linear algorithms. In all cases, space is linear in the number of operands. More importantly, we define a formal notion of optimal laziness, and either prove it, or prove its impossibility, for each algorithm. We cast our results in a general framework of antichains of intervals on total orders, making our algorithms directly applicable to other domains.Comment: 24 pages, 4 figures. A preliminary (now outdated) version was presented at SPIRE 200

Facial structures for various notions of positivity and applications to the theory of entanglement

In this expository note, we explain facial structures for the convex cones consisting of positive linear maps, completely positive linear maps, decomposable positive linear maps between matrix algebras, respectively. These will be applied to study the notions of entangled edge states with positive partial transposes and optimality of entanglement witnesses.Comment: An expository note. Section 7 and Section 8 have been enlarge

Disentanglement in Bipartite Continuous-Variable Systems

Entanglement in bipartite continuous-variable systems is investigated in the presence of partial losses, such as those introduced by a realistic quantum communication channel, e.g. by propagation in an optical fiber. We find that entanglement can vanish completely for partial losses, in a situa- tion reminiscent of so-called entanglement sudden death. Even states with extreme squeezing may become separable after propagation in lossy channels. Having in mind the potential applications of such entangled light beams to optical communications, we investigate the conditions under which entanglement can survive for all partial losses. Different loss scenarios are examined and we derive criteria to test the robustness of entangled states. These criteria are necessary and sufficient for Gaussian states. Our study provides a framework to investigate the robustness of continuous-variable entanglement in more complex multipartite systems.Comment: Phys. Rev. A (in press