81 research outputs found
Trusted-HB: a low-cost version of HB+ secure against Man-in-The-Middle attacks
Since the introduction at Crypto'05 by Juels and Weis of the protocol HB+, a
lightweight protocol secure against active attacks but only in a detection
based-model, many works have tried to enhance its security. We propose here a
new approach to achieve resistance against Man-in-The-Middle attacks. Our
requirements - in terms of extra communications and hardware - are surprisingly
low.Comment: submitted to IEEE Transactions on Information Theor
A New Algorithm for Solving Ring-LPN with a Reducible Polynomial
The LPN (Learning Parity with Noise) problem has recently proved to be of
great importance in cryptology. A special and very useful case is the RING-LPN
problem, which typically provides improved efficiency in the constructed
cryptographic primitive. We present a new algorithm for solving the RING-LPN
problem in the case when the polynomial used is reducible. It greatly
outperforms previous algorithms for solving this problem. Using the algorithm,
we can break the Lapin authentication protocol for the proposed instance using
a reducible polynomial, in about 2^70 bit operations
Solving the LPN problem in cube-root time
In this paper it is shown that given a sufficient number of (noisy) random
binary linear equations, the Learning from Parity with Noise (LPN) problem can
be solved in essentially cube root time in the number of unknowns. The
techniques used to recover the solution are known from fast correlation attacks
on stream ciphers. As in fast correlation attacks, the performance of the
algorithm depends on the number of equations given. It is shown that if this
number exceeds a certain bound, and the bias of the noisy equations is
polynomial in number of unknowns, the running time of the algorithm is reduced
to almost cube root time compared to the brute force checking of all possible
solutions. The mentioned bound is explicitly given and it is further shown that
when this bound is exceeded, the complexity of the approach can even be further
reduced
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
An Improved BKW Algorithm for LWE with Applications to Cryptography and Lattices
In this paper, we study the Learning With Errors problem and its binary
variant, where secrets and errors are binary or taken in a small interval. We
introduce a new variant of the Blum, Kalai and Wasserman algorithm, relying on
a quantization step that generalizes and fine-tunes modulus switching. In
general this new technique yields a significant gain in the constant in front
of the exponent in the overall complexity. We illustrate this by solving p
within half a day a LWE instance with dimension n = 128, modulus ,
Gaussian noise and binary secret, using
samples, while the previous best result based on BKW claims a time
complexity of with samples for the same parameters. We then
introduce variants of BDD, GapSVP and UniqueSVP, where the target point is
required to lie in the fundamental parallelepiped, and show how the previous
algorithm is able to solve these variants in subexponential time. Moreover, we
also show how the previous algorithm can be used to solve the BinaryLWE problem
with n samples in subexponential time . This
analysis does not require any heuristic assumption, contrary to other algebraic
approaches; instead, it uses a variant of an idea by Lyubashevsky to generate
many samples from a small number of samples. This makes it possible to
asymptotically and heuristically break the NTRU cryptosystem in subexponential
time (without contradicting its security assumption). We are also able to solve
subset sum problems in subexponential time for density , which is of
independent interest: for such density, the previous best algorithm requires
exponential time. As a direct application, we can solve in subexponential time
the parameters of a cryptosystem based on this problem proposed at TCC 2010.Comment: CRYPTO 201
Security problems of systems of extremely weak devices
In this paper we discuss some fundamental security issues of distributed systems of weak devices.
We briefly describe two extreme kinds of such systems - the sensor network and theRadio
Frequency IDentification (RFID) system from the point of view of security mechanisms
designer. We describe some most important particularities and issues (including unsolved
problems) that have to be taken into account in security design and analysis. Finally we
present some fundamental concepts and paradigms of research on security of weak devices. In
the paper we also give a brief survey of ultra–light HB/HB+ - family of encryption schemes
and so-called predistribution protocols
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