Sealed containers in Z

Physical means of securing information, such as sealed envelopes and scratch cards, can be used to achieve cryptographic objectives. Reasoning about this has so far been informal. We give a model of distinguishable sealed envelopes in Z, exploring design decisions and further analysis and development of such models

Growth dynamics of different species in a Araucaria Forest remnant.

IUFROLAT 2013. Disponibilizado online. Resumen

Dinâmica de crescimento de espécies de um remanescente de Floresta Ombrófila Mista em Colombo, PR.

Estudos visando o uso adequado dos recursos da floresta são indispensáveis para o manejo e conservação de remanescentes florestais, como os da Floresta Ombrófila Mista. Tendo em vista a necessidade de se aprimorar conhecimentos sobre o crescimento de espécies em regiões subtropicais, o presente trabalho teve por objetivo monitorar o crescimento diamétrico intra-anual de espécies arbóreas em Colombo, Paraná. Em novembro de 2009 foram instaladas faixas dendrométricas em árvores adultas (de 15 a 25 indivíduos) de 9 espécies dentre as mais frequentes em um remanescente de Floresta Ombrófila Mista. As medições de incremento diamétrico foram feitas mensalmente, até junho de 2011. Ocotea bicolor se diferenciou das outras espécies, apresentando crescimento superior e constante. Isto pode ser atribuído ao menor recobrimento da copa das árvores, favorecendo o acesso à luz pela espécie e consequentemente o seu crescimento. O maior crescimento de todas as espécies estudadas ocorreu no outono de 2011, estação antecedida por um inverno de baixa precipitação (inverno de 2010), em que a luminosidade esteve mais disponível para a produção fotossintética

Planejamento do manejo de florestas naturais da Amazônia visando o segundo ciclo.

Resumo

Considerações sobre o manejo da estrutura diamétrica do cumarú-ferro (Dipteryx odorata), em empresa no estado do Acre.

bitstream/item/81146/1/CT298.pd

Supressão dos maciços florestais no município de Araucária, PR entre os anos de 2005 e 2012.

Resumo

Insured MPC: Efficient Secure Computation with Financial Penalties

Fairness in Secure Multiparty Computation (MPC) is known to be impossible to achieve in the presence of a dishonest majority. Previous works have proposed combining MPC protocols with Cryptocurrencies in order to financially punish aborting adversaries, providing an incentive for parties to honestly follow the protocol. This approach also yields privacy-preserving Smart Contracts, where private inputs can be processed with MPC in order to determine the distribution of funds given to the contract. The focus of existing work is on proving that this approach is possible and unfortunately they present monolithic and mostly inefficient constructions. In this work, we put forth the first modular construction of ``Insured MPC\u27\u27, where either the output of the private computation (which describes how to distribute funds) is fairly delivered or a proof that a set of parties has misbehaved is produced, allowing for financial punishments. Moreover, both the output and the proof of cheating are publicly verifiable, allowing third parties to independently validate an execution. We present a highly efficient compiler that uses any MPC protocol with certain properties together with a standard (non-private) Smart Contract and a publicly verifiable homomorphic commitment scheme to implement Insured MPC. As an intermediate step, we propose the first construction of a publicly verifiable homomorphic commitment scheme achieving composability guarantees and concrete efficiency. Our results are proven in the Global Universal Composability framework using a Global Random Oracle as the setup assumption. From a theoretical perspective, our general results provide the first characterization of sufficient properties that MPC protocols must achieve in order to be efficiently combined with Cryptocurrencies, as well as insights into publicly verifiable protocols. On the other hand, our constructions have highly efficient concrete instantiations, allowing for fast implementations

Quantum key distribution with delayed privacy amplification and its application to security proof of a two-way deterministic protocol

Privacy amplification (PA) is an essential post-processing step in quantum key distribution (QKD) for removing any information an eavesdropper may have on the final secret key. In this paper, we consider delaying PA of the final key after its use in one-time pad encryption and prove its security. We prove that the security and the key generation rate are not affected by delaying PA. Delaying PA has two applications: it serves as a tool for significantly simplifying the security proof of QKD with a two-way quantum channel, and also it is useful in QKD networks with trusted relays. To illustrate the power of the delayed PA idea, we use it to prove the security of a qubit-based two-way deterministic QKD protocol which uses four states and four encoding operations.Comment: 11 pages, 3 figure

A method for making password-based key exchange resilient to server compromise

Abstract. This paper considers the problem of password-authenticated key exchange (PAKE) in a client-server setting, where the server authenticates using a stored password file, and it is desirable to maintain some degree of security even if the server is compromised. A PAKE scheme is said to be resilient to server compromise if an adversary who compromises the server must at least perform an offline dictionary attack to gain any advantage in impersonating a client. (Of course, offline dictionary attacks should be infeasible in the absence of server compromise.) One can see that this is the best security possible, since by definition the password file has enough information to allow one to play the role of the server, and thus to verify passwords in an offline dictionary attack. While some previous PAKE schemes have been proven resilient to server compromise, there was no known general technique to take an arbitrary PAKE scheme and make it provably resilient to server compromise. This paper presents a practical technique for doing so which requires essentially one extra round of communication and one signature computation/verification. We prove security in the universal composability framework by (1) defining a new functionality for PAKE with resilience to server compromise, (2) specifying a protocol combining this technique with a (basic) PAKE functionality, and (3) proving (in the random oracle model) that this protocol securely realizes the new functionality.