810 resultados para Secret


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We consider in this thesis the problem of information reconciliation in the context of secret key distillation between two legitimate parties. In some scenarios of interest this problem can be advantageously solved with low density parity check (LDPC) codes optimized for the binary symmetric channel. In particular, we demonstrate that our method leads to a significant efficiency improvement, with respect to earlier interactive reconciliation methods. We propose a protocol based on LDPC codes that can be adapted to changes in the communication channel extending the original source. The efficiency of our protocol is only limited by the quality of the code and, while transmitting more information than needed to reconcile Alice’s and Bob’s sequences, it does not reveal any more information on the original source than an ad-hoc code would have revealed.---ABSTRACT---En esta tesis estudiamos el problema de la reconciliación de información en el contexto de la destilación de secreto entre dos partes. En algunos escenarios de interés, códigos de baja densidad de ecuaciones de paridad (LDPC) adaptados al canal binario simétrico ofrecen una buena solución al problema estudiado. Demostramos que nuestro método mejora significativamente la eficiencia de la reconciliación. Proponemos un protocolo basado en códigos LDPC que puede ser adaptado a cambios en el canal de comunicaciones mediante una extensión de la fuente original. La eficiencia de nuestro protocolo está limitada exclusivamente por el código utilizado y no revela información adicional sobre la fuente original que la que un código con la tasa de información adaptada habría revelado.

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We report on a variant of the so-called Cascade protocol that is well-known for its usage as information reconciliation protocol in quantum cryptography. A theoretical analysis of the optimal size of the parity check blocks is provided. We obtain a very small leakage which is for block sizes of 2^16 typically only 2.5% above the Shannon limit, and notably, this holds for a QBER between 1% and 50%. For a QBER between 1% and 6% the leakage is only 2% above the Shannon limit. As comparison, the leakage of the original Cascade algorithm is 20% (40%) above the Shannon limit for a QBER of 10% (35%).

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To provide more efficient and flexible alternatives for the applications of secret sharing schemes, this paper describes a threshold sharing scheme based on exponentiation of matrices in Galois fields. A significant characteristic of the proposed scheme is that each participant has to keep only one master secret share which can be used to reconstruct different group secrets according to the number of threshold values.

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This study provides a comparative analysis of the national legal regimes and practices governing the use of intelligence information as evidence in the United Kingdom, France, Germany, Spain, Italy, the Netherlands and Sweden. It explores notably how national security can be invoked to determine the classification of information and evidence as 'state secrets' in court proceedings and whether such laws and practices are fundamental rights- and rule of law-compliant. The study finds that, in the majority of Member States under investigation, the judiciary is significantly hindered in effectively adjudicating justice and guaranteeing the rights of the defence in ‘national security’ cases. The research also illustrates that the very term ‘national security’ is nebulously defined across the Member States analysed, with no national definition meeting legal certainty and “in accordance with the law” standards and a clear risk that the executive and secret services may act arbitrarily. The study argues that national and transnational intelligence community practices and cooperation need to be subject to more independent and effective judicial accountability and be brought into line with EU 'rule of law' standards.

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Cover-title.

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The chronicles of Michael Danevitch of the Russian secret service.-- The clue of the dead hand.

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Mode of access: Internet.

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Disbound Original Held in Oak Street Library Facility.