16,381 research outputs found
Distributed Cryptography Based on the Proofs of Work
Motivated by the recent success of Bitcoin we study the question of constructing distributed cryptographic protocols in a fully peer-to-peer scenario (without any trusted setup) under the assumption that the adversary has limited computing power. We propose a formal model for this scenario and then we construct the following protocols working in it:
(i) a broadcast protocol secure under the assumption that the honest parties have computing power that is some non-negligible fraction of computing power of the adversary (this fraction can be small, in particular it can be much less than 1/2),
(ii) a protocol for identifying a set of parties such that the majority of them is honest, and every honest party belongs to this set (this protocol works under the assumption that the majority of computing power is controlled by the honest parties).
Our broadcast protocol can be used to generate an unpredictable beacon (that can later serve, e.g., as a genesis block for a new cryptocurrency). The protocol from Point (ii) can be used to construct arbitrary multiparty computation protocols. Our main tool for checking the computing power of the parties are the Proofs of Work (Dwork and Naor, CRYPTO 92). Our broadcast protocol is built on top of the classical protocol of Dolev and Strong (SIAM J. on Comp. 1983). Although our motivation is mostly theoretic, we believe that our ideas can lead to practical implementations (probably after some optimizations and simplifications). We discuss some possible applications of our protocols at the end of the paper
Cloud Data Auditing Using Proofs of Retrievability
Cloud servers offer data outsourcing facility to their clients. A client
outsources her data without having any copy at her end. Therefore, she needs a
guarantee that her data are not modified by the server which may be malicious.
Data auditing is performed on the outsourced data to resolve this issue.
Moreover, the client may want all her data to be stored untampered. In this
chapter, we describe proofs of retrievability (POR) that convince the client
about the integrity of all her data.Comment: A version has been published as a book chapter in Guide to Security
Assurance for Cloud Computing (Springer International Publishing Switzerland
2015
Using quantum key distribution for cryptographic purposes: a survey
The appealing feature of quantum key distribution (QKD), from a cryptographic
viewpoint, is the ability to prove the information-theoretic security (ITS) of
the established keys. As a key establishment primitive, QKD however does not
provide a standalone security service in its own: the secret keys established
by QKD are in general then used by a subsequent cryptographic applications for
which the requirements, the context of use and the security properties can
vary. It is therefore important, in the perspective of integrating QKD in
security infrastructures, to analyze how QKD can be combined with other
cryptographic primitives. The purpose of this survey article, which is mostly
centered on European research results, is to contribute to such an analysis. We
first review and compare the properties of the existing key establishment
techniques, QKD being one of them. We then study more specifically two generic
scenarios related to the practical use of QKD in cryptographic infrastructures:
1) using QKD as a key renewal technique for a symmetric cipher over a
point-to-point link; 2) using QKD in a network containing many users with the
objective of offering any-to-any key establishment service. We discuss the
constraints as well as the potential interest of using QKD in these contexts.
We finally give an overview of challenges relative to the development of QKD
technology that also constitute potential avenues for cryptographic research.Comment: Revised version of the SECOQC White Paper. Published in the special
issue on QKD of TCS, Theoretical Computer Science (2014), pp. 62-8
Quantum Cryptography Beyond Quantum Key Distribution
Quantum cryptography is the art and science of exploiting quantum mechanical
effects in order to perform cryptographic tasks. While the most well-known
example of this discipline is quantum key distribution (QKD), there exist many
other applications such as quantum money, randomness generation, secure two-
and multi-party computation and delegated quantum computation. Quantum
cryptography also studies the limitations and challenges resulting from quantum
adversaries---including the impossibility of quantum bit commitment, the
difficulty of quantum rewinding and the definition of quantum security models
for classical primitives. In this review article, aimed primarily at
cryptographers unfamiliar with the quantum world, we survey the area of
theoretical quantum cryptography, with an emphasis on the constructions and
limitations beyond the realm of QKD.Comment: 45 pages, over 245 reference
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