1,440 research outputs found
Key-Homomorphic Signatures: Definitions and Applications to Multiparty Signatures and Non-Interactive Zero-Knowledge
Key-homomorphic properties of cryptographic objects, i.e., homomorphisms on their key space, have proven to be useful, both from a theoretical as well as a practical perspective. Important cryptographic objects such as pseudorandom functions or (public key) encryption have been studied previously with respect to key-homomorphisms. Interestingly, however, signature schemes have not been explicitly investigated in this context so far.
We close this gap and initiate the study of key-homomorphic signatures, which turns out to be an interesting and versatile concept. In doing so, we firstly propose a definitional framework for key-homomorphic signatures distilling various natural flavours of key-homomorphic properties. Those properties aim to classify existing signature schemes and thus allow to infer general statements about signature schemes from those classes by simply making black-box use of the respective properties. We apply our definitional framework to show elegant and simple compilers from classes of signature schemes admitting different types of key-homomorphisms to a number of other interesting primitives such as ring signature schemes, (universal) designated verifier signature schemes, simulation-sound extractable non-interactive zero-knowledge (NIZK) arguments, and multisignature schemes. Additionally, using the formalisms provided by our framework, we can prove a tight implication from single-user security to key-prefixed multi-user security for a class of schemes admitting a certain key-homomorphism.
Finally, we discuss schemes that provide homomorphic properties on the message space of signatures under different keys in context of key-homomorphisms and present some first constructive results from key-homomorphic schemes
A New Cryptosystem Based On Hidden Order Groups
Let be a cyclic multiplicative group of order . It is known that the
Diffie-Hellman problem is random self-reducible in with respect to a
fixed generator if is known. That is, given and
having oracle access to a `Diffie-Hellman Problem' solver with fixed generator
, it is possible to compute in polynomial time (see
theorem 3.2). On the other hand, it is not known if such a reduction exists
when is unknown (see conjuncture 3.1). We exploit this ``gap'' to
construct a cryptosystem based on hidden order groups and present a practical
implementation of a novel cryptographic primitive called an \emph{Oracle Strong
Associative One-Way Function} (O-SAOWF). O-SAOWFs have applications in
multiparty protocols. We demonstrate this by presenting a key agreement
protocol for dynamic ad-hoc groups.Comment: removed examples for multiparty key agreement and join protocols,
since they are redundan
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Cryptography
The Oberwolfach workshop Cryptography brought together scientists from cryptography with mathematicians specializing in the algorithmic problems underlying cryptographic security. The goal of the workshop was to stimulate interaction and collaboration that enables a holistic approach to designing cryptography from the mathematical foundations to practical applications. The workshop covered basic computational problems such as factoring and computing discrete logarithms and short vectors. It addressed fundamental research results leading to innovative cryptography for protecting security and privacy in cloud applications. It also covered some practical applications
Revealing the Landscape of Privacy-Enhancing Technologies in the Context of Data Markets for the IoT: A Systematic Literature Review
IoT data markets in public and private institutions have become increasingly
relevant in recent years because of their potential to improve data
availability and unlock new business models. However, exchanging data in
markets bears considerable challenges related to disclosing sensitive
information. Despite considerable research focused on different aspects of
privacy-enhancing data markets for the IoT, none of the solutions proposed so
far seems to find a practical adoption. Thus, this study aims to organize the
state-of-the-art solutions, analyze and scope the technologies that have been
suggested in this context, and structure the remaining challenges to determine
areas where future research is required. To accomplish this goal, we conducted
a systematic literature review on privacy enhancement in data markets for the
IoT, covering 50 publications dated up to July 2020, and provided updates with
24 publications dated up to May 2022. Our results indicate that most research
in this area has emerged only recently, and no IoT data market architecture has
established itself as canonical. Existing solutions frequently lack the
required combination of anonymization and secure computation technologies.
Furthermore, there is no consensus on the appropriate use of blockchain
technology for IoT data markets and a low degree of leveraging existing
libraries or reusing generic data market architectures. We also identified
significant challenges remaining, such as the copy problem and the recursive
enforcement problem that-while solutions have been suggested to some extent-are
often not sufficiently addressed in proposed designs. We conclude that
privacy-enhancing technologies need further improvements to positively impact
data markets so that, ultimately, the value of data is preserved through data
scarcity and users' privacy and businesses-critical information are protected.Comment: 49 pages, 17 figures, 11 table
Distributed Protocols at the Rescue for Trustworthy Online Voting
While online services emerge in all areas of life, the voting procedure in
many democracies remains paper-based as the security of current online voting
technology is highly disputed. We address the issue of trustworthy online
voting protocols and recall therefore their security concepts with its trust
assumptions. Inspired by the Bitcoin protocol, the prospects of distributed
online voting protocols are analysed. No trusted authority is assumed to ensure
ballot secrecy. Further, the integrity of the voting is enforced by all voters
themselves and without a weakest link, the protocol becomes more robust. We
introduce a taxonomy of notions of distribution in online voting protocols that
we apply on selected online voting protocols. Accordingly, blockchain-based
protocols seem to be promising for online voting due to their similarity with
paper-based protocols
Private Multi-party Matrix Multiplication and Trust Computations
This paper deals with distributed matrix multiplication. Each player owns
only one row of both matrices and wishes to learn about one distinct row of the
product matrix, without revealing its input to the other players. We first
improve on a weighted average protocol, in order to securely compute a
dot-product with a quadratic volume of communications and linear number of
rounds. We also propose a protocol with five communication rounds, using a
Paillier-like underlying homomorphic public key cryptosystem, which is secure
in the semi-honest model or secure with high probability in the malicious
adversary model. Using ProVerif, a cryptographic protocol verification tool, we
are able to check the security of the protocol and provide a countermeasure for
each attack found by the tool. We also give a randomization method to avoid
collusion attacks. As an application, we show that this protocol enables a
distributed and secure evaluation of trust relationships in a network, for a
large class of trust evaluation schemes.Comment: Pierangela Samarati. SECRYPT 2016 : 13th International Conference on
Security and Cryptography, Lisbonne, Portugal, 26--28 Juillet 2016. 201
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