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MissionStatement
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RISC Seminar
2008 seminars
Special DIAMANT/RISC seminar on Algebraic Function Fields and Their Cryptographic Applications.
| Date: | Tuesday 21.10.08 |
| Location: | CWI Amsterdam, Room M280 |
| Program: |
| 13:00-13:45h | Ignacio Cascudo Pueyo (U. de Oviedo):
Reducing the difference between the thresholds in AG-based secret sharing schemes
Abstract:
We take a closer look at the strongly multiplicative algebraic
geometric ramp schemes introduced by Chen and Cramer in 2006, and discuss
some situations where, by carefully selecting the parameters of the
scheme, the difference between the privacy and reconstruction thresholds
can be made smaller (joint work with H. Chen, R. Cramer and C. Xing).
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| 14:00-14:45h | Oriol Farràs (UPC Barcelona): On the access structure of Algebraic Geometric Schemes
Abstract:
Chen and Cramer proposed a new family of linear secret sharing schemes
(LSSS), constructed from algebraic geometric Goppa codes, that provide
multiparty computation (MPC) protocols over small fields. In this talk, we
analyze how these algebraic geometric LSSS can be used to obtain secure MPC
protocols. Specifically, we study the (strong) multiplication property of
these schemes and we give a characterization of the access structure of the
schemes defined by hyperelliptic curves. Combining these results, we present
non-threshold adversary structures for which is not possible to build secure
MPC protocol by composing threshold schemes, but it is possible by using
algebraic LSSS. Joint work with Carles Padro' and Iwan Duursma.
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| 15:15-16:00h | Ruud Pellikaan (TU/e): Efficient construction of algebraic geometry codes; the q-th power algorithm
Abstract:
A survey of the parameters and the construction of algebraic geometry
codes will be given. The q-th power algorithm for the computation of
the integral closure of a ring in finite characteristic will be
explained in some detail.
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| 16:15-17:00h | Alp Bassa (EPFL Lausanne): A new tower over cubic finite fields
Abstract:
After a short introduction to towers of algebraic function fields, I
will introduce a new explicit tower over cubic finite fields, whose
limit attains Zink's lower bound. Many features of this tower are very
similar to those of an optimal tower of Garcia-Stichtenoth over
quadratic finite fields, whose modularity was shown by Elkies.
This is joint work with A. Garcia and H. Stichtenoth.
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Special RISC seminar on Quantum Information Theory.
| Date: | Thursday 09.10.08 |
| Location: | CWI Amsterdam, Room M279 |
| Program: |
| 14:00-14:45h | Serge Fehr (CWI):
High-Order Entropic Uncertainty Relations
Abstract:
We study the uncertainty of the measurement outcome when measuring an arbitrary n-qubit quantum state in a basis that is chosen at random from some fixed family of bases. We discuss several canonical cases and obtain (tight) lower bounds on the uncertainty of the measurement outcome, where the uncertainty is measured in terms of the min-entropy. Finally, we briefly point out how these quantum uncertainty relations can be used for designing quantum cryptographic scheme.
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| 14:45-15:30h | David Pérez García (Universidad Complutense de Madrid): Unbounded Violation of Tripartite Bell Inequalities
Abstract:
We will introduce new techniques coming from pure Functional Analysis in the study of correlation Bell inequalities. As a result we will be able to show that there are tripartite Bell inequalities allowing an arbitrarily large quantum violation, solving and old question of Tsirelson. We will also discuss some of the implications of our result, for instance in the problem of measuring the Hilbert space dimension of a quantum system.
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| 16:00-16:45h | Richard D. Gill (Leiden University): Polish poker and the Bell inequality
Abstract:
I will show that the Bell inequality can be recast in a form
appropriate to Bell-type experiments with any number of outcomes in
the two wings of the experiment. It is then interesting to study the
maximal violation possible by quantum mechanics, as the number of
outcomes increases (or if you like, as the dimension of the Hilbert
spaces increase). I will present numerical evidence for the optimal
quantum measurements and the optimal quantum state for larger and
larger dimension. It appears that quantum mechanics can asymptotically
do as well as is allowed by the mere requirement of non-signalling,
which is: perfectly. The main aim of my talk is to interest the
readers in the many open problems which are suggested by this work.
Reference: arXiv:quant-ph/0612020, joint work with Stefan Zohren,
appeared 2008 in PRL.
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| 16:45-17:30h | Christian Schaffner (CWI): The Operational Meaning of Min- and Max-entropy
Abstract:
We show that the conditional min-entropy Hmin(A|B) of a bipartite state
rho_AB is directly related to the maximum achievable overlap with a
maximally entangled state if only local actions on the B-part of rho_AB
are allowed. In the special case where A is classical, this overlap
corresponds to the probability of guessing A given B. In a similar vein,
we connect the conditional max-entropy Hmax(A|B) to the maximum fidelity
of rho_AB with a product state that is completely mixed on A. In the
case where A is classical, this corresponds to the security of A when
used as a secret key in the presence of an adversary holding B. Because
min- and max-entropies are known to characterize information-processing
tasks such as randomness extraction and state merging, our results
establish a direct connection between these tasks and basic operational
problems. For example, they imply that the (logarithm of the)
probability of guessing A given B is a lower bound on the number of
uniform secret bits that can be extracted from A relative to an
adversary holding B. (Joint work with Renato Renner and Robert Koenig)
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Special RISC seminar: "Cryptography Applied!".
| Date: | Thursday 02.10.08 |
| Location: | CWI Amsterdam, Room M279 |
| Program: |
| 13:00-13:45h | Ivan Damgård (Aarhus):
Multi-Party Computation Goes Live
Abstract:
We report on the first large-scale and practical application of
multiparty computation, which took place in January 2008. Details are
given on the background and motivation for the application, as well as
on the actual system that was employed. We end with some thoughts on
the future potential of multiparty computation in practice.
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| 14:00-14:45h | Tomas Toft (CWI/TU/e): Solving linear programming problems using MPC -- theory vs practice
Abstract:
There are many real-world situations, where there is much to be gained
by having access to a trusted third party. Yet typically this is
either expensive or even not possible at all. Multiparty computation
(MPC) eliminate this dilemma by providing a virtual trusted third
party, who performs the desired computation.
Practical MPC is still in its infancy, yet has been shown feasible in
real life. One interesting problem is that of solving linear
programming (LP) problems. Such problems occurs naturally, e.g. in
economics, which gives rise to a large number of motivating examples.
A relatively simple yet feasible solution to this problem is
presented. The secure computation has been implemented and solves
(small) problem instances in a reasonable amount of time. This
implementation provides a starting point for a discussion of the
differences between theory and practice.
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| 15:00-15:45h | Jan Camenisch (IBM Zurich): Crypto in Practice: Private Authentication
Abstract:
Our privacy is put at risk as more and more of our daily transactions
are done electronically and they all require one to reveal personal
information without being able to control what for this data is used
by whom. This is even made worse storing and mining data becomes ever
easier. In this talk we will discuss how technology can help users to
regain and retain control over their personal data. In particular, we
will see how one can authenticate without identify oneself. We will
conclude with a discussion of open problems.
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| 16:00-16:45h | Ivan Damgård (Aarhus): Theory and Practice of Personal Digital Signatures
Abstract:
We take a step towards a more realistic modeling of personal digital
signatures, where the human user, his mobile equipment, his PC and a
server where he may have an account, are all considered as independent
players in the protocol, and where only the human user is assumed
incorruptible. We then propose a protocol for issuing digital
signatures on behalf of the user. This protocol is proactively
UC-secure assuming at most one player is corrupted in every
operational phase. The protocol allows for mobile units with very
small computing power by securely outsourcing computation to the PC
and is also mobile in that it allows usage of any PC that can
communicate properly. Finally, we report on the results of a prototype
implementation of our solution.
Joint work with Gert Mikkelsen
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