384 research outputs found
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
A Characterization of Chameleon Hash Functions and New, Efficient Designs
This paper shows that chameleon hash functions and Sigma
protocols are equivalent. We provide a transform of any suitable Sigma protocol
to a chameleon hash function, and also show that any chameleon hash function is
the result of applying our transform to some suitable Sigma protocol. This
enables us to unify previous designs of chameleon hash functions, seeing them
all as emanating from a common paradigm, and also obtain new designs that are
more efficient than previous ones. In particular, via a modified version of the
Fiat-Shamir protocol, we obtain the fastest known chameleon hash function with
a proof of security based on the STANDARD factoring assumption.
The increasing number of applications of
chameleon hash functions,
including on-line/off-line signing, chameleon signatures, designated-verifier
signatures and conversion from weakly-secure to fully-secure
signatures, make our work of
contemporary interest
Hardware Implementations of a Variant of the ZĂ©mor-Tillich Hash Function: Can a Provably Secure Hash Function be very efficient ?
Hash functions are widely used in Cryptography, and hardware implementations of hash functions are of interest in a variety of contexts such as speeding up the computations of a network server or providing authentication in small electronic devices such as RFID tags. Provably secure hash functions, the security of which relies
on the hardness of a mathematical problem, are particularly appealing for security, but they used to be too inefficient in practice. In this paper, we study the efficiency
in hardware of ZT\u27, a provably secure hash function based on the ZĂ©mor-Tillich hash function. We consider three kinds of implementations targeting a high throughput and a low area in different ways. We first present a high-speed implementation of ZT\u27 on
FPGA that is nearly half as efficient as state-of-the-art SHA implementations in terms of throughput per area. We then focus on area reduction and present an ASIC implementation of ZT\u27 with much smaller area costs than SHA-1 and even than SQUASH, which was specially designed for low-cost RFID tags. Between these two extreme implementations, we show that the throughput and area can be traded with a lot of flexibility. Finally, we show that the inherent parallelism of ZT\u27 makes it particularly suitable for applications requiring high speed hashing of very long messages. Our work,
together with existing reasonably efficient software implementations, shows that this variant of the ZĂ©mor-Tillich hash function is in fact very practical for a wide range of applications, while having a security related to the hardness of a mathematical problem
and significant additional advantages such as scalability and parallelism
NEW SECURE SOLUTIONS FOR PRIVACY AND ACCESS CONTROL IN HEALTH INFORMATION EXCHANGE
In the current digital age, almost every healthcare organization (HCO) has moved from storing patient health records on paper to storing them electronically. Health Information Exchange (HIE) is the ability to share (or transfer) patients’ health information between different HCOs while maintaining national security standards like the Health Insurance Portability and Accountability Act (HIPAA) of 1996. Over the past few years, research has been conducted to develop privacy and access control frameworks for HIE systems. The goal of this dissertation is to address the privacy and access control concerns by building practical and efficient HIE frameworks to secure the sharing of patients’ health information.
The first solution allows secure HIE among different healthcare providers while focusing primarily on the privacy of patients’ information. It allows patients to authorize a certain type of health information to be retrieved, which helps prevent any unintentional leakage of information. The privacy solution also provides healthcare providers with the capability of mutual authentication and patient authentication. It also ensures the integrity and auditability of health information being exchanged. The security and performance study for the first protocol shows that it is efficient for the purpose of HIE and offers a high level of security for such exchanges.
The second framework presents a new cloud-based protocol for access control to facilitate HIE across different HCOs, employing a trapdoor hash-based proxy signature in a novel manner to enable secure (authenticated and authorized) on-demand access to patient records. The proposed proxy signature-based scheme provides an explicit mechanism for patients to authorize the sharing of specific medical information with specific HCOs, which helps prevent any undesired or unintentional leakage of health information. The scheme also ensures that such authorizations are authentic with respect to both the HCOs and the patient. Moreover, the use of proxy signatures simplifies security auditing and the ability to obtain support for investigations by providing non-repudiation. Formal definitions, security specifications, and a detailed theoretical analysis, including correctness, security, and performance of both frameworks are provided which demonstrate the improvements upon other existing HIE systems
PROPYLA: Privacy Preserving Long-Term Secure Storage
An increasing amount of sensitive information today is stored electronically
and a substantial part of this information (e.g., health records, tax data,
legal documents) must be retained over long time periods (e.g., several decades
or even centuries). When sensitive data is stored, then integrity and
confidentiality must be protected to ensure reliability and privacy. Commonly
used cryptographic schemes, however, are not designed for protecting data over
such long time periods. Recently, the first storage architecture combining
long-term integrity with long-term confidentiality protection was proposed
(AsiaCCS'17). However, the architecture only deals with a simplified storage
scenario where parts of the stored data cannot be accessed and verified
individually. If this is allowed, however, not only the data content itself,
but also the access pattern to the data (i.e., the information which data items
are accessed at which times) may be sensitive information. Here we present the
first long-term secure storage architecture that provides long-term access
pattern hiding security in addition to long-term integrity and long-term
confidentiality protection. To achieve this, we combine information-theoretic
secret sharing, renewable timestamps, and renewable commitments with an
information-theoretic oblivious random access machine. Our performance analysis
of the proposed architecture shows that achieving long-term integrity,
confidentiality, and access pattern hiding security is feasible.Comment: Few changes have been made compared to proceedings versio
Concurrent Knowledge-Extraction in the Public-Key Model
Knowledge extraction is a fundamental notion, modelling machine possession of
values (witnesses) in a computational complexity sense. The notion provides an
essential tool for cryptographic protocol design and analysis, enabling one to
argue about the internal state of protocol players without ever looking at this
supposedly secret state. However, when transactions are concurrent (e.g., over
the Internet) with players possessing public-keys (as is common in
cryptography), assuring that entities ``know'' what they claim to know, where
adversaries may be well coordinated across different transactions, turns out to
be much more subtle and in need of re-examination. Here, we investigate how to
formally treat knowledge possession by parties (with registered public-keys)
interacting over the Internet. Stated more technically, we look into the
relative power of the notion of ``concurrent knowledge-extraction'' (CKE) in
the concurrent zero-knowledge (CZK) bare public-key (BPK) model.Comment: 38 pages, 4 figure
A GENERALIZED FRAMEWORK FOR CRISP COMMITMENT SCHEMES
Crisp Commitment schemes are very useful building blocks in the design of high-level cryptographic protocols. They are used as a mean of flipping fair coins between two players and others. In this paper an attempt has been made to give a generalized framework for Crisp Commitment schemes is called an Ordinary Crisp Commitment Scheme (OCCS). The Hiding and Binding properties of OCCS are well defined. We also review some the existing of different Crisp Commitment schemes and we show how it is follow our presenting framework
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