462 research outputs found
A Fault Analytic Method against HB+
The search for lightweight authentication protocols suitable for low-cost
RFID tags constitutes an active and challenging research area. In this context,
a family of protocols based on the LPN problem has been proposed: the so-called
HB-family. Despite the rich literature regarding the cryptanalysis of these
protocols, there are no published results about the impact of fault analysis
over them. The purpose of this paper is to fill this gap by presenting a fault
analytic method against a prominent member of the HB-family: HB+ protocol. We
demonstrate that the fault analysis model can lead to a flexible and effective
attack against HB-like protocols, posing a serious threat over them
On the Commitment Capacity of Unfair Noisy Channels
Noisy channels are a valuable resource from a cryptographic point of view.
They can be used for exchanging secret-keys as well as realizing other
cryptographic primitives such as commitment and oblivious transfer. To be
really useful, noisy channels have to be consider in the scenario where a
cheating party has some degree of control over the channel characteristics.
Damg\r{a}rd et al. (EUROCRYPT 1999) proposed a more realistic model where such
level of control is permitted to an adversary, the so called unfair noisy
channels, and proved that they can be used to obtain commitment and oblivious
transfer protocols. Given that noisy channels are a precious resource for
cryptographic purposes, one important question is determining the optimal rate
in which they can be used. The commitment capacity has already been determined
for the cases of discrete memoryless channels and Gaussian channels. In this
work we address the problem of determining the commitment capacity of unfair
noisy channels. We compute a single-letter characterization of the commitment
capacity of unfair noisy channels. In the case where an adversary has no
control over the channel (the fair case) our capacity reduces to the well-known
capacity of a discrete memoryless binary symmetric channel
Commitment and Oblivious Transfer in the Bounded Storage Model with Errors
The bounded storage model restricts the memory of an adversary in a
cryptographic protocol, rather than restricting its computational power, making
information theoretically secure protocols feasible. We present the first
protocols for commitment and oblivious transfer in the bounded storage model
with errors, i.e., the model where the public random sources available to the
two parties are not exactly the same, but instead are only required to have a
small Hamming distance between themselves. Commitment and oblivious transfer
protocols were known previously only for the error-free variant of the bounded
storage model, which is harder to realize
A CCA2 Secure Variant of the McEliece Cryptosystem
The McEliece public-key encryption scheme has become an interesting
alternative to cryptosystems based on number-theoretical problems. Differently
from RSA and ElGa- mal, McEliece PKC is not known to be broken by a quantum
computer. Moreover, even tough McEliece PKC has a relatively big key size,
encryption and decryption operations are rather efficient. In spite of all the
recent results in coding theory based cryptosystems, to the date, there are no
constructions secure against chosen ciphertext attacks in the standard model -
the de facto security notion for public-key cryptosystems. In this work, we
show the first construction of a McEliece based public-key cryptosystem secure
against chosen ciphertext attacks in the standard model. Our construction is
inspired by a recently proposed technique by Rosen and Segev
On the Oblivious Transfer Capacity of Generalized Erasure Channels against Malicious Adversaries
Noisy channels are a powerful resource for cryptography as they can be used
to obtain information-theoretically secure key agreement, commitment and
oblivious transfer protocols, among others. Oblivious transfer (OT) is a
fundamental primitive since it is complete for secure multi-party computation,
and the OT capacity characterizes how efficiently a channel can be used for
obtaining string oblivious transfer. Ahlswede and Csisz\'{a}r (\emph{ISIT'07})
presented upper and lower bounds on the OT capacity of generalized erasure
channels (GEC) against passive adversaries. In the case of GEC with erasure
probability at least 1/2, the upper and lower bounds match and therefore the OT
capacity was determined. It was later proved by Pinto et al. (\emph{IEEE Trans.
Inf. Theory 57(8)}) that in this case there is also a protocol against
malicious adversaries achieving the same lower bound, and hence the OT capacity
is identical for passive and malicious adversaries. In the case of GEC with
erasure probability smaller than 1/2, the known lower bound against passive
adversaries that was established by Ahlswede and Csisz\'{a}r does not match
their upper bound and it was unknown whether this OT rate could be achieved
against malicious adversaries as well. In this work we show that there is a
protocol against malicious adversaries achieving the same OT rate that was
obtained against passive adversaries.
In order to obtain our results we introduce a novel use of interactive
hashing that is suitable for dealing with the case of low erasure probability
()
A Framework for Efficient Adaptively Secure Composable Oblivious Transfer in the ROM
Oblivious Transfer (OT) is a fundamental cryptographic protocol that finds a
number of applications, in particular, as an essential building block for
two-party and multi-party computation. We construct a round-optimal (2 rounds)
universally composable (UC) protocol for oblivious transfer secure against
active adaptive adversaries from any OW-CPA secure public-key encryption scheme
with certain properties in the random oracle model (ROM). In terms of
computation, our protocol only requires the generation of a public/secret-key
pair, two encryption operations and one decryption operation, apart from a few
calls to the random oracle. In~terms of communication, our protocol only
requires the transfer of one public-key, two ciphertexts, and three binary
strings of roughly the same size as the message. Next, we show how to
instantiate our construction under the low noise LPN, McEliece, QC-MDPC, LWE,
and CDH assumptions. Our instantiations based on the low noise LPN, McEliece,
and QC-MDPC assumptions are the first UC-secure OT protocols based on coding
assumptions to achieve: 1) adaptive security, 2) optimal round complexity, 3)
low communication and computational complexities. Previous results in this
setting only achieved static security and used costly cut-and-choose
techniques.Our instantiation based on CDH achieves adaptive security at the
small cost of communicating only two more group elements as compared to the
gap-DH based Simplest OT protocol of Chou and Orlandi (Latincrypt 15), which
only achieves static security in the ROM
Round and Communication Balanced Protocols for Oblivious Evaluation of Finite State Machines
We propose protocols for obliviously evaluating finite-state machines, i.e.,
the evaluation is shared between the provider of the finite-state machine and
the provider of the input string in such a manner that neither party learns the
other's input, and the states being visited are hidden from both. For alphabet
size , number of states , and input length , previous
solutions have either required a number of rounds linear in or
communication . Our solutions require 2 rounds
with communication . We present two different
solutions to this problem, a two-party one and a setting with an untrusted but
non-colluding helper
On the Composability of Statistically Secure Random Oblivious Transfer
We show that random oblivious transfer protocols that are statistically secure according to a definition based on a list of information-theoretical properties are also statistically universally composable. That is, they are simulatable secure with an unlimited adversary, an unlimited simulator, and an unlimited environment machine. Our result implies that several previous oblivious transfer protocols in the literature that were proven secure under weaker, non-composable definitions of security can actually be used in arbitrary statistically secure applications without lowering the security
Weakly supervised deep learning for the detection of domain generation algorithms
Domain generation algorithms (DGAs) have become commonplace in malware that seeks to establish command and control communication between an infected machine and the botmaster. DGAs dynamically and consistently generate large volumes of malicious domain names, only a few of which are registered by the botmaster, within a short time window around their generation time, and subsequently resolved when the malware on the infected machine tries to access them. Deep neural networks that can classify domain names as benign or malicious are of great interest in the real-time defense against DGAs. In contrast with traditional machine learning models, deep networks do not rely on human engineered features. Instead, they can learn features automatically from data, provided that they are supplied with sufficiently large amounts of suitable training data. Obtaining cleanly labeled ground truth data is difficult and time consuming. Heuristically labeled data could potentially provide a source of training data for weakly supervised training of DGA detectors. We propose a set of heuristics for automatically labeling domain names monitored in real traffic, and then train and evaluate classifiers with the proposed heuristically labeled dataset. We show through experiments on a dataset with 50 million domain names that such heuristically labeled data is very useful in practice to improve the predictive accuracy of deep learning-based DGA classifiers, and that these deep neural networks significantly outperform a random forest classifier with human engineered features
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