4,198 research outputs found
Chameleon dark energy models with characteristic signatures
In chameleon dark energy models, local gravity constraints tend to rule out
parameters in which observable cosmological signatures can be found. We study
viable chameleon potentials consistent with a number of recent observational
and experimental bounds. A novel chameleon field potential, motivated by f(R)
gravity, is constructed where observable cosmological signatures are present
both at the background evolution and in the growth-rate of the perturbations.
We study the evolution of matter density perturbations on low redshifts for
this potential and show that the growth index today gamma_0 can have
significant dispersion on scales relevant for large scale structures. The
values of gamma_0 can be even smaller than 0.2 with large variations of gamma
on very low redshifts for the model parameters constrained by local gravity
tests. This gives a possibility to clearly distinguish these chameleon models
from the Lambda-Cold-Dark-Matter model in future high-precision observations.Comment: 16 pages, 8 figure
Chameleons with Field Dependent Couplings
Certain scalar-tensor theories exhibit the so-called chameleon mechanism,
whereby observational signatures of scalar fields are hidden by a combination
of self-interactions and interactions with ambient matter. Not all
scalar-tensor theories exhibit such a chameleon mechanism, which has been
originally found in models with inverse power run-away potentials and field
independent couplings to matter. In this paper we investigate field-theories
with field-dependent couplings and a power-law potential for the scalar field.
We show that the theory indeed is a chameleon field theory. We find the
thin-shell solution for a spherical body and investigate the consequences for
E\"ot-Wash experiments, fifth-force searches and Casimir force experiments.
Requiring that the scalar-field evades gravitational tests, we find that the
coupling is sensitive to a mass-scale which is of order of the Hubble scale
today.Comment: 17 pages, 20 figure
Cosmology of Chameleons with Power-Law Couplings
In chameleon field theories a scalar field can couple to matter with
gravitational strength and still evade local gravity constraints due to a
combination of self-interactions and the couplings to matter. Originally, these
theories were proposed with a constant coupling to matter, however, the
chameleon mechanism also extends to the case where the coupling becomes
field-dependent. We study the cosmology of chameleon models with power-law
couplings and power-law potentials. It is found that these generalized
chameleons, when viable, have a background expansion very close to LCDM, but
can in some special cases enhance the growth of the linear perturbations at low
redshifts. For the models we consider it is found that this region of the
parameter space is ruled out by local gravity constraints. Imposing a coupling
to dark matter only, the local constraints are avoided, and it is possible to
have observable signatures on the linear matter perturbations.Comment: 12 pages, 5 figures. ApJ in prin
Chameleon Signature from Bilinear Pairing
Chameleon signatures are non-interactive signatures based on a hash-and-sign paradigm, and similar in efficiency to regular signatures. The distinguishing characteristic of chameleon signatures is that there are non-transferable, with only the designated recipient capable of asserting its validity. In this paper, we introduce a new ID-based chameleon hash function based on bilinear pairing and build the ID-based chameleon signature scheme. Compared with the conventional chameleon hashing functions, the owner of a public hash key in the ID-based chameleon hashing scheme does not necessarily need to retrieve the associated secret key. The scheme enjoys all the attributes in the normal chameleon signature and the added characteristics of ID-based cryptography based on bilinear pairing
Towards secure end-to-end data aggregation in AMI through delayed-integrity-verification
The integrity and authenticity of the energy usage data in Advanced Metering Infrastructure (AMI) is crucial to ensure the correct energy load to facilitate generation, distribution and customer billing. Any malicious tampering to the data must be detected immediately. This paper introduces secure end-to-end data aggregation for AMI, a security protocol that allows the concentrators to securely aggregate the data collected from the smart meters, while enabling the utility back-end that receives the aggregated data to verify the integrity and data originality. Compromise of concentrators can be detected. The aggregated data is protected using Chameleon Signatures and then forwarded to the utility back-end for verification, accounting, and analysis. Using the Trapdoor Chameleon Hash Function, the smart meters can periodically send an evidence to the utility back-end, by computing an alternative message and a random value (m', r) such that m' consists of all previous energy usage measurements of the smart meter in a specified period of time.
By verifying that the Chameleon Hash Value of (m', r) and that the energy usage matches those aggregated by the concentrators, the utility back-end is convinced of the integrity and authenticity of the data from the smart meters. Any data anomaly between smart meters and concentrators can be detected, thus indicating potential compromise of concentrators
A Characterization of Chameleon Hash Functions and New, Efficient Designs
This paper shows that chameleon hash functions and Sigma
protocols are equivalent. We provide a transform of any suitable Sigma protocol
to a chameleon hash function, and also show that any chameleon hash function is
the result of applying our transform to some suitable Sigma protocol. This
enables us to unify previous designs of chameleon hash functions, seeing them
all as emanating from a common paradigm, and also obtain new designs that are
more efficient than previous ones. In particular, via a modified version of the
Fiat-Shamir protocol, we obtain the fastest known chameleon hash function with
a proof of security based on the STANDARD factoring assumption.
The increasing number of applications of
chameleon hash functions,
including on-line/off-line signing, chameleon signatures, designated-verifier
signatures and conversion from weakly-secure to fully-secure
signatures, make our work of
contemporary interest
Key-Exposure Free Chameleon Hashing and Signatures Based on Discrete Logarithm Systems
Chameleon signatures simultaneously provide the properties of
non-repudiation and non-transferability for the signed message.
However, the initial constructions of chameleon signatures suffer
from the problem of key exposure. This creates a strong
disincentive for the recipient to forge signatures, partially
undermining the concept of non-transferability. Recently, some
specific constructions of discrete logarithm based chameleon
hashing and signatures without key exposure are presented, while
in the setting of gap Diffile-Hellman groups with pairings.
\indent \,\, In this paper, we propose the first key-exposure free
chameleon hash and signature scheme based on discrete logarithm
systems, without using the gap Diffile-Hellman groups. This
provides more flexible constructions of efficient key-exposure
free chameleon hash and signature schemes. Moreover, one
distinguishing advantage of the resulting chameleon signature
scheme is that the property of ``message hiding or ``message
recovery can be achieved freely by the signer, the signer
can efficiently prove which message was the original one if he
desires
Making Existential-Unforgeable Signatures Strongly Unforgeable in the Quantum Random-Oracle Model
Strongly unforgeable signature schemes provide a more stringent security
guarantee than the standard existential unforgeability. It requires that not
only forging a signature on a new message is hard, it is infeasible as well to
produce a new signature on a message for which the adversary has seen valid
signatures before. Strongly unforgeable signatures are useful both in practice
and as a building block in many cryptographic constructions.
This work investigates a generic transformation that compiles any
existential-unforgeable scheme into a strongly unforgeable one, which was
proposed by Teranishi et al. and was proven in the classical random-oracle
model. Our main contribution is showing that the transformation also works
against quantum adversaries in the quantum random-oracle model. We develop
proof techniques such as adaptively programming a quantum random-oracle in a
new setting, which could be of independent interest. Applying the
transformation to an existential-unforgeable signature scheme due to Cash et
al., which can be shown to be quantum-secure assuming certain lattice problems
are hard for quantum computers, we get an efficient quantum-secure strongly
unforgeable signature scheme in the quantum random-oracle model.Comment: 15 pages, to appear in Proceedings TQC 201
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