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21 
Quantum Information Processing with Adversarial DevicesMcKague, Matthew 20 May 2010 (has links)
We consider several applications in blackbox quantum computation in which untrusted physical quantum devices are connected together to produce an experiment. By examining the outcome statistics of such an experiment, and comparing them against the desired experiment, we may hope to certify that the physical experiment is implementing the desired experiment. This is useful in order to verify that a calculation has been performed correctly, that measurement outcomes are secure, or that the devices are producing the desired state.
First, we introduce constructions for a family of simulations, which duplicate the outcome statistics of an experiment but are not exactly the same as the desired experiment. This places limitations on how strict we may be with the requirements we place on the physical devices. We identify many simulations, and consider their implications for quantum foundations as well as security related applications.
The most general application of blackbox quantum computing is selftesting circuits, in which a generic physical circuit may be tested against a given circuit. Earlier results were restricted to circuits described on a real Hilbert space. We give new proofs for earlier results and begin work extending them to circuits on a complex Hilbert space with a test that verifies complex measurements.
For security applications of blackbox quantum computing, we consider device independent quantum key distribution (DIQKD). We may consider DIQKD as an extension of QKD (quantum key distribution) in which the model of the physical measurement devices is replaced with an adversarial model. This introduces many technical problems, such as unbounded dimension, but promises increased security since the many complexities hidden by traditional models are implicitly considered. We extend earlier work by proving security with fewer assumptions.
Finally, we consider the case of blackbox state characterization. Here the emphasis is placed on providing robust results with operationally meaningful measures. The goal is to certify that a black box device is producing high quality maximally entangled pairs of qubits using only untrusted measurements and a single statistic, the CHSH value, defined using correlations of outcomes from the two parts of the system. We present several measures of quality and prove bounds for them.

22 
On the orientation of hypergraphsRuizVargas, Andres J. 12 1900 (has links)
This is an expository thesis. In this thesis we study outorientations of hypergraphs, where every hyperarc has one tail vertex. We study hypergraphs that admit outorientations covering supermodulartype connectivity requirements. For this, we follow a paper of Frank.
We also study the Steiner rooted orientation problem. Given a hypergraph and a subset of vertices S ⊆ V, the goal is to give necessary and sufficient conditions for an orientation such that the connectivity between a root vertex and each vertex of S is at least k, for a positive integer k. We follow a paper by Kiraly and Lau, where they prove that every 2khyperedge connected hypergraph has such an orientation.

23 
Analyzing Quantum Cryptographic Protocols Using Optimization TechniquesSikora, Jamie 20 April 2012 (has links)
This thesis concerns the analysis of the unconditional security of quantum cryptographic protocols using convex optimization techniques. It is divided into the study of coinflipping and oblivious transfer. We first examine a family of coinflipping protocols. Almost all of the handful of explicitly described coinflipping protocols are based on bitcommitment. To explore the possibility of finding explicit optimal or nearoptimal protocols, we focus on a class which generalizes such protocols. We call these $\BCCF$protocols, for bitcommitment based coinflipping. We use the semidefinite programming (SDP) formulation of cheating strategies along the lines of Kitaev to analyze the structure of the protocols.
In the first part of the thesis, we show how these semidefinite programs can be used to simplify the analysis of the protocol. In particular, we show that a particular set of cheating strategies contains an optimal strategy. This reduces the problem to optimizing a linear combination of fidelity functions over a polytope which has several benefits. First, it allows one to model cheating probabilities using a simpler class of optimization problems known as secondorder cone programs (SOCPs). Second, it helps with the construction of point games due to Kitaev as described in Mochon's work.
Point games were developed to give a new perspective for studying quantum protocols. In some sense, the notion of point games is dual to the notion of protocols.
There has been increased research activity in optimization concerning generalizing theory and algorithms for linear programming to much wider classes of optimization problems such as semidefinite programming. For example, semidefinite programming provides a tool for potentially improving results based on linear programming or investigating old problems that have eluded analysis by linear programming. In this sense, the history of semidefinite programming is very similar to the history of quantum computation.
Quantum computing gives a generalized model of computation to tackle new and old problems, improving on and generalizing older classical techniques. Indeed, there are striking differences between linear programming and semidefinite programming as there are between classical and quantum computation. In this thesis, we strengthen this analogy by studying a family of classical coinflipping protocols based on classical bitcommitment. Cheating strategies for these ``classical $\BCCF$protocols'' can be formulated as linear programs (LPs) which are closely related to the semidefinite programs for the quantum version. In fact, we can construct point games for the classical protocols as well using the analysis for the quantum case.
Using point games, we prove that every classical $\BCCF$protocol allows exactly one of the parties to entirely determine the outcome. Also, we rederive Kitaev's lower bound to show that only ``classical'' protocols can saturate Kitaev's analysis. Moreover, if the product of Alice and Bob's optimal cheating probabilities is $1/2$, then at least one party can cheat with probability $1$.
The second part concerns the design of an algorithm to search for $\BCCF$protocols with small bias. Most coinflipping protocols with more than three rounds have eluded direct analysis. To better understand the properties of optimal $\BCCF$protocols with four or more rounds, we turn to computational experiments. We design a computational optimization approach to search for the best protocol based on the semidefinite programming formulations of cheating strategies. We create a protocol filter using cheating strategies, some of which build upon known strategies and others are based on convex optimization and linear algebra. The protocol filter efficiently eliminates candidate protocols with too high a bias. Using this protocol filter and symmetry arguments, we perform searches in a matter of days that would have otherwise taken millions of years. Our experiments checked $10^{16}$ four and sixround $\BCCF$protocols and suggest that the optimal bias is $1/4$.
The third part examines the relationship between oblivious transfer, bitcommitment, and coinflipping. We consider oblivious transfer which succeeds with probability $1$ when the two parties are honest and construct a simple protocol with security provably better than any classical protocol. We also derive a lower bound by constructing a bitcommitment protocol from an oblivious transfer protocol. Known lower bounds for bitcommitment then lead to a constant lower bound on the bias of oblivious transfer. Finally, we show that it is possible to use Kitaev's semidefinite programming formulation of cheating strategies to obtain optimal lower bounds on a ``forcing'' variant of oblivious transfer related to coinflipping.

24 
Algebraic Methods and Monotone Hurwitz NumbersGuayPaquet, Mathieu January 2012 (has links)
We develop algebraic methods to solve joincut equations, which are partial differential equations that arise in the study of permutation factorizations. Using these techniques, we give a detailed study of the recently introduced monotone Hurwitz numbers, which count factorizations of a given permutation into a fixed number of transpositions, subject to some technical conditions known as transitivity and monotonicity.
Part of the interest in monotone Hurwitz numbers comes from the fact that they have been identified as the coefficients in a certain asymptotic expansion related to the HarishChandraItzyksonZuber integral, which comes from the theory of random matrices and has applications in mathematical physics. The connection between random matrices and permutation factorizations goes through representation theory, with symmetric functions in the JucysMurphy elements playing a key role.
As the name implies, monotone Hurwitz numbers are related to the more classical Hurwitz numbers, which count permutation factorizations regardless of monotonicity, and for which there is a significant body of work. Our results for monotone Hurwitz numbers are inspired by similar results for Hurwitz numbers; we obtain a genus expansion for the related generating functions, which yields explicit formulas and a polynomiality result for monotone Hurwitz numbers. A significant difference between the two cases is that our methods are purely algebraic, whereas the theory of Hurwitz numbers relies on some fairly deep results in algebraic geometry.
Despite our methods being algebraic, it seems that there should be a connection between monotone Hurwitz numbers and geometry, although this is currently missing. We give some evidence for this connection by identifying some of the coefficients in the monotone Hurwitz genus expansion with coefficients in the classical Hurwitz genus expansion known to be Hodge integrals over the moduli space of curves.

25 
On the Efficiency and Security of Cryptographic PairingsKnapp, Edward 04 December 2012 (has links)
Pairingbased cryptography has been employed to obtain several advantageous cryptographic protocols. In particular, there exist several identitybased variants of common cryptographic schemes. The computation of a single pairing is a comparatively expensive operation, since it often requires many operations in the underlying elliptic curve. In this thesis, we explore the efficient computation of pairings.
Computation of the Tate pairing is done in two steps. First, a Miller function is computed, followed by the final exponentiation. We discuss the stateoftheart optimizations for Miller function computation under various conditions. We are able to shave off a fixed number of operations in the final exponentiation. We consider methods to effectively parallelize the computation of pairings in a multicore setting and discover that the Weil pairing may provide some advantage under certain conditions. This work is extended to the 192bit security level and some unlikely candidate curves for such a setting are discovered.
Electronic Toll Pricing (ETP) aims to improve road tolling by collecting toll fares electronically and without the need to slow down vehicles. In most ETP schemes, drivers are charged periodically based on the locations, times, distances or durations travelled. Many ETP schemes are currently deployed and although these systems are efficient, they require a great deal of knowledge regarding driving habits in order to operate correctly. We present an ETP scheme where pairingbased BLS signatures play an important role.
Finally, we discuss the security of pairings in the presence of an efficient algorithm to invert the pairing. We generalize previous results to the setting of asymmetric pairings as well as give a simplified proof in the symmetric setting.

26 
Quantum Information Processing with Adversarial DevicesMcKague, Matthew 20 May 2010 (has links)
We consider several applications in blackbox quantum computation in which untrusted physical quantum devices are connected together to produce an experiment. By examining the outcome statistics of such an experiment, and comparing them against the desired experiment, we may hope to certify that the physical experiment is implementing the desired experiment. This is useful in order to verify that a calculation has been performed correctly, that measurement outcomes are secure, or that the devices are producing the desired state.
First, we introduce constructions for a family of simulations, which duplicate the outcome statistics of an experiment but are not exactly the same as the desired experiment. This places limitations on how strict we may be with the requirements we place on the physical devices. We identify many simulations, and consider their implications for quantum foundations as well as security related applications.
The most general application of blackbox quantum computing is selftesting circuits, in which a generic physical circuit may be tested against a given circuit. Earlier results were restricted to circuits described on a real Hilbert space. We give new proofs for earlier results and begin work extending them to circuits on a complex Hilbert space with a test that verifies complex measurements.
For security applications of blackbox quantum computing, we consider device independent quantum key distribution (DIQKD). We may consider DIQKD as an extension of QKD (quantum key distribution) in which the model of the physical measurement devices is replaced with an adversarial model. This introduces many technical problems, such as unbounded dimension, but promises increased security since the many complexities hidden by traditional models are implicitly considered. We extend earlier work by proving security with fewer assumptions.
Finally, we consider the case of blackbox state characterization. Here the emphasis is placed on providing robust results with operationally meaningful measures. The goal is to certify that a black box device is producing high quality maximally entangled pairs of qubits using only untrusted measurements and a single statistic, the CHSH value, defined using correlations of outcomes from the two parts of the system. We present several measures of quality and prove bounds for them.

27 
On the orientation of hypergraphsRuizVargas, Andres J. 12 1900 (has links)
This is an expository thesis. In this thesis we study outorientations of hypergraphs, where every hyperarc has one tail vertex. We study hypergraphs that admit outorientations covering supermodulartype connectivity requirements. For this, we follow a paper of Frank.
We also study the Steiner rooted orientation problem. Given a hypergraph and a subset of vertices S ⊆ V, the goal is to give necessary and sufficient conditions for an orientation such that the connectivity between a root vertex and each vertex of S is at least k, for a positive integer k. We follow a paper by Kiraly and Lau, where they prove that every 2khyperedge connected hypergraph has such an orientation.

28 
Analyzing Quantum Cryptographic Protocols Using Optimization TechniquesSikora, Jamie 20 April 2012 (has links)
This thesis concerns the analysis of the unconditional security of quantum cryptographic protocols using convex optimization techniques. It is divided into the study of coinflipping and oblivious transfer. We first examine a family of coinflipping protocols. Almost all of the handful of explicitly described coinflipping protocols are based on bitcommitment. To explore the possibility of finding explicit optimal or nearoptimal protocols, we focus on a class which generalizes such protocols. We call these $\BCCF$protocols, for bitcommitment based coinflipping. We use the semidefinite programming (SDP) formulation of cheating strategies along the lines of Kitaev to analyze the structure of the protocols.
In the first part of the thesis, we show how these semidefinite programs can be used to simplify the analysis of the protocol. In particular, we show that a particular set of cheating strategies contains an optimal strategy. This reduces the problem to optimizing a linear combination of fidelity functions over a polytope which has several benefits. First, it allows one to model cheating probabilities using a simpler class of optimization problems known as secondorder cone programs (SOCPs). Second, it helps with the construction of point games due to Kitaev as described in Mochon's work.
Point games were developed to give a new perspective for studying quantum protocols. In some sense, the notion of point games is dual to the notion of protocols.
There has been increased research activity in optimization concerning generalizing theory and algorithms for linear programming to much wider classes of optimization problems such as semidefinite programming. For example, semidefinite programming provides a tool for potentially improving results based on linear programming or investigating old problems that have eluded analysis by linear programming. In this sense, the history of semidefinite programming is very similar to the history of quantum computation.
Quantum computing gives a generalized model of computation to tackle new and old problems, improving on and generalizing older classical techniques. Indeed, there are striking differences between linear programming and semidefinite programming as there are between classical and quantum computation. In this thesis, we strengthen this analogy by studying a family of classical coinflipping protocols based on classical bitcommitment. Cheating strategies for these ``classical $\BCCF$protocols'' can be formulated as linear programs (LPs) which are closely related to the semidefinite programs for the quantum version. In fact, we can construct point games for the classical protocols as well using the analysis for the quantum case.
Using point games, we prove that every classical $\BCCF$protocol allows exactly one of the parties to entirely determine the outcome. Also, we rederive Kitaev's lower bound to show that only ``classical'' protocols can saturate Kitaev's analysis. Moreover, if the product of Alice and Bob's optimal cheating probabilities is $1/2$, then at least one party can cheat with probability $1$.
The second part concerns the design of an algorithm to search for $\BCCF$protocols with small bias. Most coinflipping protocols with more than three rounds have eluded direct analysis. To better understand the properties of optimal $\BCCF$protocols with four or more rounds, we turn to computational experiments. We design a computational optimization approach to search for the best protocol based on the semidefinite programming formulations of cheating strategies. We create a protocol filter using cheating strategies, some of which build upon known strategies and others are based on convex optimization and linear algebra. The protocol filter efficiently eliminates candidate protocols with too high a bias. Using this protocol filter and symmetry arguments, we perform searches in a matter of days that would have otherwise taken millions of years. Our experiments checked $10^{16}$ four and sixround $\BCCF$protocols and suggest that the optimal bias is $1/4$.
The third part examines the relationship between oblivious transfer, bitcommitment, and coinflipping. We consider oblivious transfer which succeeds with probability $1$ when the two parties are honest and construct a simple protocol with security provably better than any classical protocol. We also derive a lower bound by constructing a bitcommitment protocol from an oblivious transfer protocol. Known lower bounds for bitcommitment then lead to a constant lower bound on the bias of oblivious transfer. Finally, we show that it is possible to use Kitaev's semidefinite programming formulation of cheating strategies to obtain optimal lower bounds on a ``forcing'' variant of oblivious transfer related to coinflipping.

29 
Algebraic Methods and Monotone Hurwitz NumbersGuayPaquet, Mathieu January 2012 (has links)
We develop algebraic methods to solve joincut equations, which are partial differential equations that arise in the study of permutation factorizations. Using these techniques, we give a detailed study of the recently introduced monotone Hurwitz numbers, which count factorizations of a given permutation into a fixed number of transpositions, subject to some technical conditions known as transitivity and monotonicity.
Part of the interest in monotone Hurwitz numbers comes from the fact that they have been identified as the coefficients in a certain asymptotic expansion related to the HarishChandraItzyksonZuber integral, which comes from the theory of random matrices and has applications in mathematical physics. The connection between random matrices and permutation factorizations goes through representation theory, with symmetric functions in the JucysMurphy elements playing a key role.
As the name implies, monotone Hurwitz numbers are related to the more classical Hurwitz numbers, which count permutation factorizations regardless of monotonicity, and for which there is a significant body of work. Our results for monotone Hurwitz numbers are inspired by similar results for Hurwitz numbers; we obtain a genus expansion for the related generating functions, which yields explicit formulas and a polynomiality result for monotone Hurwitz numbers. A significant difference between the two cases is that our methods are purely algebraic, whereas the theory of Hurwitz numbers relies on some fairly deep results in algebraic geometry.
Despite our methods being algebraic, it seems that there should be a connection between monotone Hurwitz numbers and geometry, although this is currently missing. We give some evidence for this connection by identifying some of the coefficients in the monotone Hurwitz genus expansion with coefficients in the classical Hurwitz genus expansion known to be Hodge integrals over the moduli space of curves.

30 
On the Efficiency and Security of Cryptographic PairingsKnapp, Edward 04 December 2012 (has links)
Pairingbased cryptography has been employed to obtain several advantageous cryptographic protocols. In particular, there exist several identitybased variants of common cryptographic schemes. The computation of a single pairing is a comparatively expensive operation, since it often requires many operations in the underlying elliptic curve. In this thesis, we explore the efficient computation of pairings.
Computation of the Tate pairing is done in two steps. First, a Miller function is computed, followed by the final exponentiation. We discuss the stateoftheart optimizations for Miller function computation under various conditions. We are able to shave off a fixed number of operations in the final exponentiation. We consider methods to effectively parallelize the computation of pairings in a multicore setting and discover that the Weil pairing may provide some advantage under certain conditions. This work is extended to the 192bit security level and some unlikely candidate curves for such a setting are discovered.
Electronic Toll Pricing (ETP) aims to improve road tolling by collecting toll fares electronically and without the need to slow down vehicles. In most ETP schemes, drivers are charged periodically based on the locations, times, distances or durations travelled. Many ETP schemes are currently deployed and although these systems are efficient, they require a great deal of knowledge regarding driving habits in order to operate correctly. We present an ETP scheme where pairingbased BLS signatures play an important role.
Finally, we discuss the security of pairings in the presence of an efficient algorithm to invert the pairing. We generalize previous results to the setting of asymmetric pairings as well as give a simplified proof in the symmetric setting.

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