5,575 research outputs found
Semantic Security and Indistinguishability in the Quantum World
At CRYPTO 2013, Boneh and Zhandry initiated the study of quantum-secure
encryption. They proposed first indistinguishability definitions for the
quantum world where the actual indistinguishability only holds for classical
messages, and they provide arguments why it might be hard to achieve a stronger
notion. In this work, we show that stronger notions are achievable, where the
indistinguishability holds for quantum superpositions of messages. We
investigate exhaustively the possibilities and subtle differences in defining
such a quantum indistinguishability notion for symmetric-key encryption
schemes. We justify our stronger definition by showing its equivalence to novel
quantum semantic-security notions that we introduce. Furthermore, we show that
our new security definitions cannot be achieved by a large class of ciphers --
those which are quasi-preserving the message length. On the other hand, we
provide a secure construction based on quantum-resistant pseudorandom
permutations; this construction can be used as a generic transformation for
turning a large class of encryption schemes into quantum indistinguishable and
hence quantum semantically secure ones. Moreover, our construction is the first
completely classical encryption scheme shown to be secure against an even
stronger notion of indistinguishability, which was previously known to be
achievable only by using quantum messages and arbitrary quantum encryption
circuits.Comment: 37 pages, 2 figure
The Poset of Hypergraph Quasirandomness
Chung and Graham began the systematic study of k-uniform hypergraph
quasirandom properties soon after the foundational results of Thomason and
Chung-Graham-Wilson on quasirandom graphs. One feature that became apparent in
the early work on k-uniform hypergraph quasirandomness is that properties that
are equivalent for graphs are not equivalent for hypergraphs, and thus
hypergraphs enjoy a variety of inequivalent quasirandom properties. In the past
two decades, there has been an intensive study of these disparate notions of
quasirandomness for hypergraphs, and an open problem that has emerged is to
determine the relationship between them.
Our main result is to determine the poset of implications between these
quasirandom properties. This answers a recent question of Chung and continues a
project begun by Chung and Graham in their first paper on hypergraph
quasirandomness in the early 1990's.Comment: 43 pages, 1 figur
The descriptive theory of represented spaces
This is a survey on the ongoing development of a descriptive theory of
represented spaces, which is intended as an extension of both classical and
effective descriptive set theory to deal with both sets and functions between
represented spaces. Most material is from work-in-progress, and thus there may
be a stronger focus on projects involving the author than an objective survey
would merit.Comment: survey of work-in-progres
Computational Soundness for Dalvik Bytecode
Automatically analyzing information flow within Android applications that
rely on cryptographic operations with their computational security guarantees
imposes formidable challenges that existing approaches for understanding an
app's behavior struggle to meet. These approaches do not distinguish
cryptographic and non-cryptographic operations, and hence do not account for
cryptographic protections: f(m) is considered sensitive for a sensitive message
m irrespective of potential secrecy properties offered by a cryptographic
operation f. These approaches consequently provide a safe approximation of the
app's behavior, but they mistakenly classify a large fraction of apps as
potentially insecure and consequently yield overly pessimistic results.
In this paper, we show how cryptographic operations can be faithfully
included into existing approaches for automated app analysis. To this end, we
first show how cryptographic operations can be expressed as symbolic
abstractions within the comprehensive Dalvik bytecode language. These
abstractions are accessible to automated analysis, and they can be conveniently
added to existing app analysis tools using minor changes in their semantics.
Second, we show that our abstractions are faithful by providing the first
computational soundness result for Dalvik bytecode, i.e., the absence of
attacks against our symbolically abstracted program entails the absence of any
attacks against a suitable cryptographic program realization. We cast our
computational soundness result in the CoSP framework, which makes the result
modular and composable.Comment: Technical report for the ACM CCS 2016 conference pape
Identifying the Information Gain of a Quantum Measurement
We show that quantum-to-classical channels, i.e., quantum measurements, can
be asymptotically simulated by an amount of classical communication equal to
the quantum mutual information of the measurement, if sufficient shared
randomness is available. This result generalizes Winter's measurement
compression theorem for fixed independent and identically distributed inputs
[Winter, CMP 244 (157), 2004] to arbitrary inputs, and more importantly, it
identifies the quantum mutual information of a measurement as the information
gained by performing it, independent of the input state on which it is
performed. Our result is a generalization of the classical reverse Shannon
theorem to quantum-to-classical channels. In this sense, it can be seen as a
quantum reverse Shannon theorem for quantum-to-classical channels, but with the
entanglement assistance and quantum communication replaced by shared randomness
and classical communication, respectively. The proof is based on a novel
one-shot state merging protocol for "classically coherent states" as well as
the post-selection technique for quantum channels, and it uses techniques
developed for the quantum reverse Shannon theorem [Berta et al., CMP 306 (579),
2011].Comment: v2: new result about non-feedback measurement simulation, 45 pages, 4
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