68 research outputs found
Secure Datastructures based on Multiparty Computation
The problem of secure multiparty computation -- performing some computation based on distributed, private inputs -- has been studied intensively for more than twenty years. This work includes both ``one shot\u27\u27 applications as well as reactive tasks, where the exact computation is not known in advance. We extend this line of work by asking whether it is possible to \emph{efficiently} both update and query secret data. A clearer formulation is, perhaps, to ask whether is it possible to construct efficient datastructures based on secure multiparty computation primitives.
It is possible to construct arbitrary secure datastructures based on an oblivious RAM (ORAM). However, current state of the art information theoretically secure solutions incur a poly-logarithmic overhead on both secure computation and memory. The overhead is much smaller when considering computationally secure solutions, however, this requires secure evaluation of a one-way function as a primitive, which may reintroduce a considerable overhead.
By constructing a secure priority queue we show that practical datastructures are possible. The ideas are radically different than those used in any ORAM implementation: The present solution accesses data in a \emph{deterministic} manner, whereas all ORAMs \emph{randomize} the access pattern in order to hide it. The priority queue operations -- insertion into the structure and deletion of the minimal element contained therein -- both require \bigo(\log^2 n) invocations of the cryptographic primitives (secure arithmetic and comparison) amortized in rounds amortized, where is the overall number of operations performed
Adding Query Privacy to Robust DHTs
Interest in anonymous communication over distributed hash tables (DHTs) has
increased in recent years. However, almost all known solutions solely aim at
achieving sender or requestor anonymity in DHT queries. In many application
scenarios, it is crucial that the queried key remains secret from intermediate
peers that (help to) route the queries towards their destinations. In this
paper, we satisfy this requirement by presenting an approach for providing
privacy for the keys in DHT queries.
We use the concept of oblivious transfer (OT) in communication over DHTs to
preserve query privacy without compromising spam resistance. Although our
OT-based approach can work over any DHT, we concentrate on communication over
robust DHTs that can tolerate Byzantine faults and resist spam. We choose the
best-known robust DHT construction, and employ an efficient OT protocol
well-suited for achieving our goal of obtaining query privacy over robust DHTs.
Finally, we compare the performance of our privacy-preserving protocols with
their more privacy-invasive counterparts. We observe that there is no increase
in the message complexity and only a small overhead in the computational
complexity.Comment: To appear at ACM ASIACCS 201
Deterministic, Stash-Free Write-Only ORAM
Write-Only Oblivious RAM (WoORAM) protocols provide privacy by encrypting the
contents of data and also hiding the pattern of write operations over that
data. WoORAMs provide better privacy than plain encryption and better
performance than more general ORAM schemes (which hide both writing and reading
access patterns), and the write-oblivious setting has been applied to important
applications of cloud storage synchronization and encrypted hidden volumes. In
this paper, we introduce an entirely new technique for Write-Only ORAM, called
DetWoORAM. Unlike previous solutions, DetWoORAM uses a deterministic,
sequential writing pattern without the need for any "stashing" of blocks in
local state when writes fail. Our protocol, while conceptually simple, provides
substantial improvement over prior solutions, both asymptotically and
experimentally. In particular, under typical settings the DetWoORAM writes only
2 blocks (sequentially) to backend memory for each block written to the device,
which is optimal. We have implemented our solution using the BUSE (block device
in user-space) module and tested DetWoORAM against both an encryption only
baseline of dm-crypt and prior, randomized WoORAM solutions, measuring only a
3x-14x slowdown compared to an encryption-only baseline and around 6x-19x
speedup compared to prior work
Benchmarking 6DOF Outdoor Visual Localization in Changing Conditions
Visual localization enables autonomous vehicles to navigate in their
surroundings and augmented reality applications to link virtual to real worlds.
Practical visual localization approaches need to be robust to a wide variety of
viewing condition, including day-night changes, as well as weather and seasonal
variations, while providing highly accurate 6 degree-of-freedom (6DOF) camera
pose estimates. In this paper, we introduce the first benchmark datasets
specifically designed for analyzing the impact of such factors on visual
localization. Using carefully created ground truth poses for query images taken
under a wide variety of conditions, we evaluate the impact of various factors
on 6DOF camera pose estimation accuracy through extensive experiments with
state-of-the-art localization approaches. Based on our results, we draw
conclusions about the difficulty of different conditions, showing that
long-term localization is far from solved, and propose promising avenues for
future work, including sequence-based localization approaches and the need for
better local features. Our benchmark is available at visuallocalization.net.Comment: Accepted to CVPR 2018 as a spotligh
Secure Computing, Economy, and Trust: A Generic Solution for Secure Auctions with Real-World Applications
In this paper we consider the problem of constructing secure auctions based on techniques from modern cryptography. We combine knowledge from economics, cryptography and security engineering and develop and implement secure auctions for practical real-world problems. In essence this paper is an overview of the research project SCET--Secure Computing, Economy, and Trust-- which attempts to build auctions for real applications using secure multiparty computation. The main contributions of this project are: A generic setup for secure evaluation of integer arithmetic including comparisons; general double auctions expressed by such operations; a real world double auction tailored to the complexity and performance of the basic primitives '+' and
Fast Multiparty Multiplications from shared bits
We study the question of securely multiplying N-bit integers that are stored in binary representation, in the context of protocols for dishonest majority with preprocessing. We achieve communication complexity O(N) using only secure operations over small fields F_2 and F_p with log(p) \approx log(N). For semi-honest security we achieve communication O(N)2^{O(log∗(N))} using only secure operations over F_2. This improves over the straightforward solution of simulating a Boolean multiplication circuit, both asymptotically and in practice
Better Preprocessing for Secure Multiparty Computation
We present techniques and protocols for the preprocessing of secure multiparty computation (MPC), focusing on the so-called SPDZ MPC scheme SPDZ and its derivatives. These MPC schemes consist of a so-called preprocessing or offline phase where correlated randomness is generated that is independent of the inputs and the evaluated function, and an online phase where such correlated randomness is consumed to securely and efficiently evaluate circuits. In the recent years, it has been shown that such protocols turn out to be very efficient in practice.
While much research has been conducted towards optimizing the online phase of the MPC protocols, there seems to have been less focus on the offline phase of such protocols. With this work, we want to close this gap and give a toolbox of techniques that aim at optimizing the preprocessing.
We support both instantiations over small fields and large rings using somewhat homomorphic encryption and the Paillier cryptosystem, respectively. In the case of small fields, we show how the preprocessing overhead can basically be made independent of the field characteristic and present a more efficient (amortized) zero-knowledge proof of plaintext knowledge. In the case of large rings, we present a protocol based on the Paillier cryptosystem which has a lower message complexity than previous protocols and employs more efficient zero-knowledge proofs that, to the best of our knowledge, were not presented in previous work
Pygmy resonance and low-energy enhancement in the -ray strength functions of Pd~isotopes
An unexpected enhancement in the -ray strength function, as compared
to the low energy tail of the Giant Dipole Resonance (GDR), has been observed
for Sc, Ti, V, Fe and Mo isotopes for MeV. This enhancement was
not observed in subsequent analyses on Sn isotopes, but a Pygmy Dipole
Resonance (PDR) centered at MeV was however detected. The
-ray strength functions measured for Cd isotopes exhibit both features
over the range of isotopes, with the low-energy enhancement decreasing- and PDR
strength increasing as a function of neutron number. This suggests a
transitional region for the onset of low-energy enhancement, and also that the
PDR strength depends on the number of neutrons. The -ray strength
functions of Pd have been measured in order to further explore the
proposed transitional region. Experimental data were obtained at the Oslo
Cyclotron Laboratory by using the charged particle reactions (He,
He) and (He, ) on Pd
target foils. Particle coincidence measurements provided information
on initial excitation energies and the corresponding -ray spectra,
which were used to extract the level densities and -ray strength
functions according to the Oslo method. The -ray strength functions
indicate a sudden increase in magnitude for MeV, which is
interpreted as a PDR centered at MeV. An enhanced
-ray strength at low energies is also observed for Pd, which is
the lightest isotope measured in this work. Further, the results correspond and
agree very well with the observations from the Cd isotopes, and support the
suggested transitional region for the onset of low-energy enhancement with
decreasing mass number. The neutron number dependency of the PDR strength is
also evident
Efficient RSA Key Generation and Threshold Paillier in the Two-Party Setting
The problem of generating an RSA composite in a distributed manner without leaking its factorization is particularly challenging and useful in many cryptographic protocols. Our first contribution is the first non-generic fully simulatable protocol for distributively generating an RSA composite with security against malicious behavior. Our second contribution is complete Paillier [Pai99] threshold encryption scheme in the two-party setting with security against malicious behavior. Furthermore, we describe how to extend our protocols to the multiparty setting with dishonest majority.
Our RSA key generation is comprised of the following: (i) a distributed protocol for generation of an RSA composite, and (ii) a biprimality test for verifying the validity of the generated composite. Our Paillier threshold encryption scheme uses the RSA composite as public key and is comprised of: (i) a distributed generation of the corresponding secret-key shares and, (ii) a distributed decryption protocol for decrypting according to Paillier
Long-Term Visual Localization Revisited
Visual localization enables autonomous vehicles to navigate in their surroundings and augmented reality applications to link virtual to real worlds. Practical visual localization approaches need to be robust to a wide variety of viewing conditions, including day-night changes, as well as weather and seasonal variations, while providing highly accurate six degree-of-freedom (6DOF) camera pose estimates. In this paper, we extend three publicly available datasets containing images captured under a wide variety of viewing conditions, but lacking camera pose information, with ground truth pose information, making evaluation of the impact of various factors on 6DOF camera pose estimation accuracy possible. We also discuss the performance of state-of-the-art localization approaches on these datasets. Additionally, we release around half of the poses for all conditions, and keep the remaining half private as a test set, in the hopes that this will stimulate research on long-term visual localization, learned local image features, and related research areas. Our datasets are available at visuallocalization.net, where we are also hosting a benchmarking server for automatic evaluation of results on the test set. The presented state-of-the-art results are to a large degree based on submissions to our server
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