63 research outputs found
07381 Abstracts Collection -- Cryptography
From 16.09.2007 to 21.09.2007 the Dagstuhl Seminar 07381 ``Cryptography\u27\u27 was held
in the International Conference and Research Center (IBFI), Schloss Dagstuhl.
During the seminar, several participants presented their current
research, and ongoing work and open problems were discussed. Abstracts of
the presentations given during the seminar as well as abstracts of
seminar results and ideas are put together in this paper. The first section
describes the seminar topics and goals in general.
Links to extended abstracts or full papers are provided, if available
Leftover Hashing Against Quantum Side Information
The Leftover Hash Lemma states that the output of a two-universal hash
function applied to an input with sufficiently high entropy is almost uniformly
random. In its standard formulation, the lemma refers to a notion of randomness
that is (usually implicitly) defined with respect to classical side
information. Here, we prove a (strictly) more general version of the Leftover
Hash Lemma that is valid even if side information is represented by the state
of a quantum system. Furthermore, our result applies to arbitrary delta-almost
two-universal families of hash functions. The generalized Leftover Hash Lemma
has applications in cryptography, e.g., for key agreement in the presence of an
adversary who is not restricted to classical information processing
Quantum entropic security and approximate quantum encryption
We present full generalisations of entropic security and entropic
indistinguishability to the quantum world where no assumption but a limit on
the knowledge of the adversary is made. This limit is quantified using the
quantum conditional min-entropy as introduced by Renato Renner. A proof of the
equivalence between the two security definitions is presented. We also provide
proofs of security for two different cyphers in this model and a proof for a
lower bound on the key length required by any such cypher. These cyphers
generalise existing schemes for approximate quantum encryption to the entropic
security model.Comment: Corrected mistakes in the proofs of Theorems 3 and 6; results
unchanged. To appear in IEEE Transactions on Information Theory
Short seed extractors against quantum storage
Some, but not all, extractors resist adversaries with limited quantum
storage. In this paper we show that Trevisan's extractor has this property,
thereby showing an extractor against quantum storage with logarithmic seed
length
A Hypercontractive Inequality for Matrix-Valued Functions with Applications to Quantum Computing and LDCs
The Bonami-Beckner hypercontractive inequality is a powerful tool in Fourier
analysis of real-valued functions on the Boolean cube. In this paper we present
a version of this inequality for matrix-valued functions on the Boolean cube.
Its proof is based on a powerful inequality by Ball, Carlen, and Lieb. We also
present a number of applications. First, we analyze maps that encode
classical bits into qubits, in such a way that each set of bits can be
recovered with some probability by an appropriate measurement on the quantum
encoding; we show that if , then the success probability is
exponentially small in . This result may be viewed as a direct product
version of Nayak's quantum random access code bound. It in turn implies strong
direct product theorems for the one-way quantum communication complexity of
Disjointness and other problems. Second, we prove that error-correcting codes
that are locally decodable with 2 queries require length exponential in the
length of the encoded string. This gives what is arguably the first
``non-quantum'' proof of a result originally derived by Kerenidis and de Wolf
using quantum information theory, and answers a question by Trevisan.Comment: This is the full version of a paper that will appear in the
proceedings of the IEEE FOCS 08 conferenc
Sampling of min-entropy relative to quantum knowledge
Let X_1, ..., X_n be a sequence of n classical random variables and consider
a sample of r positions selected at random. Then, except with (exponentially in
r) small probability, the min-entropy of the sample is not smaller than,
roughly, a fraction r/n of the total min-entropy of all positions X_1, ...,
X_n, which is optimal. Here, we show that this statement, originally proven by
Vadhan [LNCS, vol. 2729, Springer, 2003] for the purely classical case, is
still true if the min-entropy is measured relative to a quantum system. Because
min-entropy quantifies the amount of randomness that can be extracted from a
given random variable, our result can be used to prove the soundness of locally
computable extractors in a context where side information might be
quantum-mechanical. In particular, it implies that key agreement in the
bounded-storage model (using a standard sample-and-hash protocol) is fully
secure against quantum adversaries, thus solving a long-standing open problem.Comment: 48 pages, late
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