52 research outputs found
Key-Exposure Free Chameleon Hashing and Signatures Based on Discrete Logarithm Systems
Chameleon signatures simultaneously provide the properties of
non-repudiation and non-transferability for the signed message.
However, the initial constructions of chameleon signatures suffer
from the problem of key exposure. This creates a strong
disincentive for the recipient to forge signatures, partially
undermining the concept of non-transferability. Recently, some
specific constructions of discrete logarithm based chameleon
hashing and signatures without key exposure are presented, while
in the setting of gap Diffile-Hellman groups with pairings.
\indent \,\, In this paper, we propose the first key-exposure free
chameleon hash and signature scheme based on discrete logarithm
systems, without using the gap Diffile-Hellman groups. This
provides more flexible constructions of efficient key-exposure
free chameleon hash and signature schemes. Moreover, one
distinguishing advantage of the resulting chameleon signature
scheme is that the property of ``message hiding or ``message
recovery can be achieved freely by the signer, the signer
can efficiently prove which message was the original one if he
desires
Chameleon: a Blind Double Trapdoor Hash Function for Securing AMI Data Aggregation
Data aggregation is an integral part of Advanced Metering Infrastructure (AMI) deployment that is implemented by the concentrator. Data aggregation reduces the number of transmissions, thereby reducing communication costs and increasing the bandwidth utilization of AMI. However, the concentrator poses a great risk of being tampered with, leading to erroneous bills and possible consumer disputes. In this paper, we propose an end-to-end integrity protocol using elliptic curve based chameleon hashing to provide data integrity and authenticity. The concentrator generates and sends a chameleon hash value of the aggregated readings to the Meter Data Management System (MDMS) for verification, while the smart meter with the trapdoor key computes and sends a commitment value to the MDMS so that the resulting chameleon hash value calculated by the MDMS is equivalent to the previous hash value sent by the concentrator. By comparing the two hash values, the MDMS can validate the integrity and authenticity of the data sent by the concentrator. Compared with the discrete logarithm implementation, the ECC implementation reduces the computational cost of MDMS, concentrator and smart meter by approximately 36.8%, 80%, and 99% respectively. We also demonstrate the security soundness of our protocol through informal security analysis
Identity-Based Chameleon Hash Scheme Without Key Exposure
In this paper, we propose the first identity-based chameleon hash
scheme without key exposure, which gives a positive answer for the open problem introduced by Ateniese and de Medeiros in 2004
CONSTRUCTION OF EFFICIENT AUTHENTICATION SCHEMES USING TRAPDOOR HASH FUNCTIONS
In large-scale distributed systems, where adversarial attacks can have widespread impact, authentication provides protection from threats involving impersonation of entities and tampering of data. Practical solutions to authentication problems in distributed systems must meet specific constraints of the target system, and provide a reasonable balance between security and cost. The goal of this dissertation is to address the problem of building practical and efficient authentication mechanisms to secure distributed applications. This dissertation presents techniques to construct efficient digital signature schemes using trapdoor hash functions for various distributed applications. Trapdoor hash functions are collision-resistant hash functions associated with a secret trapdoor key that allows the key-holder to find collisions between hashes of different messages. The main contributions of this dissertation are as follows:
1. A common problem with conventional trapdoor hash functions is that revealing a collision producing message pair allows an entity to compute additional collisions without knowledge of the trapdoor key. To overcome this problem, we design an efficient trapdoor hash function that prevents all entities except the trapdoor key-holder from computing collisions regardless of whether collision producing message pairs are revealed by the key-holder.
2. We design a technique to construct efficient proxy signatures using trapdoor hash functions to authenticate and authorize agents acting on behalf of users in agent-based computing systems. Our technique provides agent authentication, assurance of agreement between delegator and agent, security without relying on secure communication channels and control over an agent’s capabilities.
3. We develop a trapdoor hash-based signature amortization technique for authenticating real-time, delay-sensitive streams. Our technique provides independent verifiability of blocks comprising a stream, minimizes sender-side and receiver-side delays, minimizes communication overhead, and avoids transmission of redundant information.
4. We demonstrate the practical efficacy of our trapdoor hash-based techniques for signature amortization and proxy signature construction by presenting discrete log-based instantiations of the generic techniques that are efficient to compute, and produce short signatures.
Our detailed performance analyses demonstrate that the proposed schemes outperform existing schemes in computation cost and signature size. We also present proofs for security of the proposed discrete-log based instantiations against forgery attacks under the discrete-log assumption
Tightly Secure Chameleon Hash Functions in the Multi-User Setting and Their Applications
We define the security notion of (strong) collision resistance for chameleon hash functions in the multi-user setting ((S-)MU-CR security). We also present three constructions, CHF_dl, CHF_rsa and CHF_fac, and prove their tight S-MU-CR security based on the discrete logarithm, RSA and factoring assumptions, respectively. In applications, our tightly S-MU-CR secure chameleon hash functions help us to lift a signature scheme from (weak) unforgeability to strong unforgeability in the multi-user setting, and the security reduction is tightness preserving. Furthermore, they can also be used to construct tightly secure online/offline signatures, chameleon signatures and proxy signatures, etc., in the multi-user setting
Comments and Improvements on Chameleon Hashing Without Key Exposure Based on Factoring
In this paper, we present some security flaws of the key-exposure
free chameleon hash scheme based on factoring \cite{GWX07}.
Besides, we propose an improved chameleon hash scheme without key
exposure based on factoring which enjoys all the desired security
notions of chameleon hashing
Cryptography for Bitcoin and friends
Numerous cryptographic extensions to Bitcoin have been proposed since Satoshi Nakamoto introduced the revolutionary design in 2008. However, only few proposals have been adopted in Bitcoin and other prevalent cryptocurrencies, whose resistance to fundamental changes has proven to grow with their success. In this dissertation, we introduce four cryptographic techniques that advance the functionality and privacy provided by Bitcoin and similar cryptocurrencies without requiring fundamental changes in their design: First, we realize smart contracts that disincentivize parties in distributed systems from making contradicting statements by penalizing such behavior by the loss of funds in a cryptocurrency. Second, we propose CoinShuffle++, a coin mixing protocol which improves the anonymity of cryptocurrency users by combining their transactions and thereby making it harder for observers to trace those transactions. The core of CoinShuffle++ is DiceMix, a novel and efficient protocol for broadcasting messages anonymously without the help of any trusted third-party anonymity proxies and in the presence of malicious participants. Third, we combine coin mixing with the existing idea to hide payment values in homomorphic commitments to obtain the ValueShuffle protocol, which enables us to overcome major obstacles to the practical deployment of coin mixing protocols. Fourth, we show how to prepare the aforementioned homomorphic commitments for a safe transition to post-quantum cryptography.Seit seiner revolutionären Erfindung durch Satoshi Nakamoto im Jahr 2008 wurden zahlreiche kryptographische Erweiterungen für Bitcoin vorgeschlagen. Gleichwohl wurden nur wenige Vorschläge in Bitcoin und andere weit verbreitete Kryptowährungen integriert, deren Resistenz gegen tiefgreifende Veränderungen augenscheinlich mit ihrer Verbreitung wächst. In dieser Dissertation schlagen wir vier kryptographische Verfahren vor, die die Funktionalität und die Datenschutzeigenschaften von Bitcoin und ähnlichen Kryptowährungen verbessern ohne deren Funktionsweise tiefgreifend verändern zu müssen. Erstens realisieren wir Smart Contracts, die es erlauben widersprüchliche Aussagen einer Vertragspartei mit dem Verlust von Kryptogeld zu bestrafen. Zweitens schlagen wir CoinShuffle++ vor, ein Mix-Protokoll, das die Anonymität von Benutzern verbessert, indem es ihre Transaktionen kombiniert und so deren Rückverfolgung erschwert. Sein Herzstück ist DiceMix, ein neues und effizientes Protokoll zur anonymen Veröffentlichung von Nachrichten ohne vertrauenswürdige Dritte und in der Präsenz von bösartigen Teilnehmern. Drittens kombinieren wir dieses Protokoll mit der existierenden Idee, Geldbeträge in Commitments zu verbergen, und erhalten so das ValueShuffle-Protokoll, das uns ermöglicht, große Hindernisse für den praktischen Einsatz von Mix-Protokollen zu überwinden. Viertens zeigen wir, wie die dabei benutzten Commitments für einen sicheren Übergang zu Post-Quanten-Kryptographie vorbereitet werden können
Chameleon Signature from Bilinear Pairing
Chameleon signatures are non-interactive signatures based on a hash-and-sign paradigm, and similar in efficiency to regular signatures. The distinguishing characteristic of chameleon signatures is that there are non-transferable, with only the designated recipient capable of asserting its validity. In this paper, we introduce a new ID-based chameleon hash function based on bilinear pairing and build the ID-based chameleon signature scheme. Compared with the conventional chameleon hashing functions, the owner of a public hash key in the ID-based chameleon hashing scheme does not necessarily need to retrieve the associated secret key. The scheme enjoys all the attributes in the normal chameleon signature and the added characteristics of ID-based cryptography based on bilinear pairing
CryptoMaze: Atomic Off-Chain Payments in Payment Channel Network
Payment protocols developed to realize off-chain transactions in Payment
channel network (PCN) assumes the underlying routing algorithm transfers the
payment via a single path. However, a path may not have sufficient capacity to
route a transaction. It is inevitable to split the payment across multiple
paths. If we run independent instances of the protocol on each path, the
execution may fail in some of the paths, leading to partial transfer of funds.
A payer has to reattempt the entire process for the residual amount. We propose
a secure and privacy-preserving payment protocol, CryptoMaze. Instead of
independent paths, the funds are transferred from sender to receiver across
several payment channels responsible for routing, in a breadth-first fashion.
Payments are resolved faster at reduced setup cost, compared to existing
state-of-the-art. Correlation among the partial payments is captured,
guaranteeing atomicity. Further, two party ECDSA signature is used for
establishing scriptless locks among parties involved in the payment. It reduces
space overhead by leveraging on core Bitcoin scripts. We provide a formal model
in the Universal Composability framework and state the privacy goals achieved
by CryptoMaze. We compare the performance of our protocol with the existing
single path based payment protocol, Multi-hop HTLC, applied iteratively on one
path at a time on several instances. It is observed that CryptoMaze requires
less communication overhead and low execution time, demonstrating efficiency
and scalability.Comment: 30 pages, 9 figures, 1 tabl
Accountable Trapdoor Sanitizable Signatures
Abstract. Sanitizable signature (SS) allows a signer to partly delegate signing rights to a predeter-mined party, called sanitizer, who can later modify certain designated parts of a message originally signed by the signer and generate a new signature on the sanitized message without interacting with the signer. One of the important security requirements of sanitizable signatures is accountability, which allows the signer to prove, in case of dispute, to a third party that a message was modified by the sanitizer. Trapdoor sanitizable signature (TSS) enables a signer of a message to delegate the power of sanitization to any parties at anytime but at the expense of losing the accountability property. In this paper, we introduce the notion of accountable trapdoor sanitizable signature (ATSS) which lies between SS and TSS. As a building block for constructing ATSS, we also introduce the notion of accountable chameleon hash (ACH), which is an extension of chameleon hash (CH) and might be of independent interest. We propose a concrete construction of ACH and show how to use it to construct an ATSS scheme
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