1,710 research outputs found
How Practical is Public-Key Encryption Based on LPN and Ring-LPN?
We conduct a study of public-key cryptosystems based on variants of the Learning Parity with Noise (LPN) problem. The main LPN variant in consideration was introduced by Alekhnovich (FOCS 2003), and we describe several improvements to the originally proposed scheme, inspired by similar existing variants of Regev\u27s LWE-based cryptosystem. To achieve further efficiency, we propose the first public-key cryptosystem based on the ring-LPN problem, which is a more recently introduced LPN variant that makes for substantial improvement in terms of both time and space. We also introduce a variant of this problem called the transposed Ring-LPN problem. Our public-key scheme based on this problem is even more efficient. For all cases, we compute the parameters required for various security levels in practice, given the best currently known attacks.
Our conclusion is that the basic LPN-based scheme is in several respects not competitive with existing practical schemes, as the public key, ciphertexts and encryption time become very large already for 80-bit security. On the other hand, the scheme based on transposed Ring-LPN is far better in all these respects. Although the public key and ciphertexts are still larger than for, say, RSA at comparable security levels, they are not prohibitively large; moreover, for decryption, the scheme outperforms RSA for security levels of 112 bits or more. The Ring-LPN based scheme is less efficient, however. Thus, LPN-based public-key cryptography seems to be somewhat more promising for practical use than has been generally assumed so far
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
Chosen-ciphertext security from subset sum
We construct a public-key encryption (PKE) scheme whose
security is polynomial-time equivalent to the hardness of the Subset Sum problem. Our scheme achieves the standard notion of indistinguishability against chosen-ciphertext attacks (IND-CCA) and can be used to encrypt messages of arbitrary polynomial length, improving upon a previous construction by Lyubashevsky, Palacio, and Segev (TCC 2010) which achieved only the weaker notion of semantic security (IND-CPA) and whose concrete security decreases with the length of the message being encrypted. At the core of our construction is a trapdoor technique which originates in the work of Micciancio and Peikert (Eurocrypt 2012
Tree Parity Machine Rekeying Architectures
The necessity to secure the communication between hardware components in
embedded systems becomes increasingly important with regard to the secrecy of
data and particularly its commercial use. We suggest a low-cost (i.e. small
logic-area) solution for flexible security levels and short key lifetimes. The
basis is an approach for symmetric key exchange using the synchronisation of
Tree Parity Machines. Fast successive key generation enables a key exchange
within a few milliseconds, given realistic communication channels with a
limited bandwidth. For demonstration we evaluate characteristics of a
standard-cell ASIC design realisation as IP-core in 0.18-micrometer
CMOS-technology
Authenticated tree parity machine key exchange
The synchronisation of Tree Parity Machines (TPMs), has proven to provide a
valuable alternative concept for secure symmetric key exchange. Yet, from a
cryptographer's point of view, authentication is at least as important as a
secure exchange of keys. Adding an authentication via hashing e.g. is
straightforward but with no relation to Neural Cryptography. We consequently
formulate an authenticated key exchange within this concept. Another
alternative, integrating a Zero-Knowledge protocol into the synchronisation, is
also presented. A Man-In-The-Middle attack and even all currently known
attacks, that are based on using identically structured TPMs and
synchronisation as well, can so be averted. This in turn has practical
consequences on using the trajectory in weight space. Both suggestions have the
advantage of not affecting the previously observed physics of this interacting
system at all.Comment: This work directly relates to cond-mat/0202112 (see also
http://arxiv.org/find/cond-mat/1/au:+Kinzel/0/1/0/all/0/1
Affine Determinant Programs: A Framework for Obfuscation and Witness Encryption
An affine determinant program ADP: {0,1}^n → {0,1} is specified by a tuple (A,B_1,...,B_n) of square matrices over F_q and a function Eval: F_q → {0,1}, and evaluated on x \in {0,1}^n by computing Eval(det(A + sum_{i \in [n]} x_i B_i)).
In this work, we suggest ADPs as a new framework for building general-purpose obfuscation and witness encryption. We provide evidence to suggest that constructions following our ADP-based framework may one day yield secure, practically feasible obfuscation.
As a proof-of-concept, we give a candidate ADP-based construction of indistinguishability obfuscation (iO) for all circuits along with a simple witness encryption candidate. We provide cryptanalysis demonstrating that our schemes resist several potential attacks, and leave further cryptanalysis to future work. Lastly, we explore practically feasible applications of our witness encryption candidate, such as public-key encryption with near-optimal key generation
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
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