79 research outputs found
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
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
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 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
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
Cryptography Based on Correlated Data: Foundations and Practice
Correlated data can be very useful in cryptography. For instance, if a uniformly random key is available to Alice and Bob, it can be used as an one-time pad to transmit a message with perfect security. With more elaborate forms of correlated data, the parties can achieve even more complex cryptographic tasks, such as secure multiparty computation. This thesis explores (from both a theoretical and a practical point of view) the topic of cryptography based on correlated data
- …