A GENERALIZED FRAMEWORK FOR CRISP COMMITMENT SCHEMES

Crisp Commitment schemes are very useful building blocks in the design of high-level cryptographic protocols. They are used as a mean of flipping fair coins between two players and others. In this paper an attempt has been made to give a generalized framework for Crisp Commitment schemes is called an Ordinary Crisp Commitment Scheme (OCCS). The Hiding and Binding properties of OCCS are well defined. We also review some the existing of different Crisp Commitment schemes and we show how it is follow our presenting framework

Reexamination of Quantum Bit Commitment: the Possible and the Impossible

Bit commitment protocols whose security is based on the laws of quantum mechanics alone are generally held to be impossible. In this paper we give a strengthened and explicit proof of this result. We extend its scope to a much larger variety of protocols, which may have an arbitrary number of rounds, in which both classical and quantum information is exchanged, and which may include aborts and resets. Moreover, we do not consider the receiver to be bound to a fixed "honest" strategy, so that "anonymous state protocols", which were recently suggested as a possible way to beat the known no-go results are also covered. We show that any concealing protocol allows the sender to find a cheating strategy, which is universal in the sense that it works against any strategy of the receiver. Moreover, if the concealing property holds only approximately, the cheat goes undetected with a high probability, which we explicitly estimate. The proof uses an explicit formalization of general two party protocols, which is applicable to more general situations, and a new estimate about the continuity of the Stinespring dilation of a general quantum channel. The result also provides a natural characterization of protocols that fall outside the standard setting of unlimited available technology, and thus may allow secure bit commitment. We present a new such protocol whose security, perhaps surprisingly, relies on decoherence in the receiver's lab.Comment: v1: 26 pages, 4 eps figures. v2: 31 pages, 5 eps figures; replaced with published version; title changed to comply with puzzling Phys. Rev. regulations; impossibility proof extended to protocols with infinitely many rounds or a continuous communication tree; security proof of decoherence monster protocol expanded; presentation clarifie

Smooth Projective Hashing and Two-Message Oblivious Transfer

We present a general framework for constructing two-message oblivious transfer protocols using a modification of Cramer and Shoup\u27s notion of smooth projective hashing (2002). This framework is an abstraction of the two-message oblivious transfer protocols of Naor and Pinkas (2001) and Aiello et al. (2001), whose security is based on the Decisional Diffie Hellman Assumption. In particular, we give two new oblivious transfer protocols. The security of one is based on the Quadratic Residuosity Assumption, and the security of the other is based on the $N$\u27th Residuosity Assumption. Compared to other applications of smooth projective hashing, in our context we must deal also with maliciously chosen parameters, which raises new technical difficulties. We also improve on prior constructions of factoring-based smooth universal hashing, in that our constructions *do not require that the underlying RSA modulus is a product of safe primes*. (This holds for the schemes based on the Quadratic Residuosity Assumption as well as the ones based on the $N$\u27th Residuosity Assumption.) In fact, we observe that the safe-prime requirement is unnecessary for many prior constructions. In particular, the factoring-based CCA secure encryption schemes due to Cramer-Shoup, Gennaro-Lindell, and Camenisch-Shoup remain secure even if the underlying RSA modulus is not a product of safe primes

Informationsübertragung durch Quantenkanäle

This PhD thesis represents work done between Aug. 2003 and Dec. 2006 in Reinhard F. Werner's quantum information theory group at Technische Universität Braunschweig, and Artur Ekert's Centre for Quantum Computation at the University of Cambridge. Quantum information science combines ideas from physics, computer science and information theory to investigate how quintessentially quantum mechanical effects such as superposition and entanglement can be employed for the handling and transfer of information. My thesis falls into the field of abstract quantum information theory, which is concerned with the fundamental resources for quantum information processing and their interconversion and tradeoffs. Every such processing of quantum information can be represented as a quantum channel: a completely positive and trace-preserving map between observable algebras associated to physical systems. This work investigates both fundamental properties of quantum channels (mostly in Chs. 3 and 4) and their asymptotic capacities for classical as well as quantum information transfer (in Chs. 5 through 8).Diese Dissertation zur Erlangung des Grades eines Doktors der Naturwissenschaften (Dr. rer. nat.) entstand zwischen August 2003 und Dezember 2006 in Prof. Reinhard F. Werners Arbeitsgruppe Quanteninformationstheorie an der Technischen Universität Braunschweig und Prof. Artur Ekerts Centre for Quantum Computation an der Universität Cambridge. Die Quanteninformationswissenschaft untersucht mit den Ideen und Methoden der Physik, der Informatik und der Informationstheorie, wie sich charakteristisch quantenphysikalische Effekte, beispielsweise Superposition und Verschränkung, zur Verarbeitung und Übertragung von Information nutzbar machen lassen. Die vorliegende Dissertation fällt in das Gebiet der abstrakten Quanteninformationstheorie, die die grundlegenden Ressourcen für die Verarbeitung von Quanteninformation sowie deren Wechselbeziehungen und Abhängigkeiten untersucht. Eine jede solche Verarbeitung von Quanteninformation läßt sich mathematisch beschreiben als sogenannter Quantenkanal, eine vollständig positive und spurerhaltende Abbildung zwischen den physikalischen Systemen zugeordneten Observablen-Algebren. In dieser Arbeit werden sowohl grundlegende Eigenschaften solcher Quantenkanäle (vor allem in den Kap. 3 und Kap. 4) als auch ihre asymptotischen Kapazitäten für die Übertragung von klassischer Information und Quanteninformation (in Kap. 5 bis 8) untersucht