Honest Parties Research Articles

Mining Association Rule for Horizontally Partitioned Databases Using CK Secure Sum Technique

The security of the large database becomes a serious issue while sharing the data to the network against unauthorised access. However in order to provide the security many researchers cited the issue of Secured Multiparty Computation (SMC) that allows multiple parties to compute some function of their inputs without disclosing the actual input to one another. Secure sum computation method is popularly and widely accepted due to its simple and thorough solution. The outcomes of our proposed procedure provide a significant result so that it becomes impossible for semi honest party to know the private data of some other sites.

Multipartite Entanglement Verification Resistant against Dishonest Parties

Future quantum information networks will consist of quantum and classical agents, who have the ability to communicate in a variety of ways with trusted and untrusted parties and securely delegate computational tasks to untrusted large-scale quantum computing servers. Multipartite quantum entanglement is a fundamental resource for such a network and, hence, it is imperative to study the possibility of verifying a multipartite entanglement source in a way that is efficient and provides strong guarantees even in the presence of multiple dishonest parties. In this Letter, we show how an agent of a quantum network can perform a distributed verification of a source creating multipartite Greenberger-Horne-Zeilinger (GHZ) states with minimal resources, which is, nevertheless, resistant against any number of dishonest parties. Moreover, we provide a tight tradeoff between the level of security and the distance between the state produced by the source and the ideal GHZ state. Last, by adding the resource of a trusted common random source, we can further provide security guarantees for all honest parties in the quantum network simultaneously.

Affiliation-Hiding Authenticated Asymmetric Group Key Agreement

We introduce the concept of Affiliation-Hiding Authenticated Asymmetric Group Key Agreement (AH-AAGKA) and construct a concrete one-round AH-AAGKA protocol. An AH-AAGKA protocol allows the participants of a group to establish a common encryption key associated with several decryption keys; each of which can only be computed by the corresponding legitimate group member. An AH-AAGKA protocol has the following privacy feature. For a member i of a group G, if i participates in an AH-AAGKA protocol, any protocol participant j cannot learn whether i is a member of G, unless j himself is a member of group G. Our scheme demonstrates new features in comparison with other existing AH-AGKA protocols. If non-group members participate in our protocol, honest parties can identify these non-group members. Our scheme also captures Unlinkability and Perfect Forward Secrecy (PFS), which are missing in other existing schemes. We propose a novel security model to prove that our protocol holds PFS and present a new privacy model to prove that our scheme meets Affiliation-Hiding property.

Cheating Resistance of a Secure Incentive Protocol for Mobile Ad Hoc Networks

The idea of rewarding good behaviour instead of penalizing bad or selfish nodes is the underlying concept behind the design of protocols to encourage intermediary nodes in multi-hop mobile ad hoc networks to forward packets from source to destination. We investigate the security of such a secure incentive protocol and show that contrary to its design objective, the protocol allows adversaries to cheat honest parties and furthermore falls to an attack on its entity authentication and key establishment. We analyze the design choices to explore why the protocol exhibits these limitations.

Unconditional Security From Noisy Quantum Storage

We consider the implementation of two-party cryptographic primitives based on the sole assumption that no large-scale reliable quantum storage is available to the cheating party. We construct novel protocols for oblivious transfer and bit commitment, and prove that realistic noise levels provide security even against the most general attack. Such unconditional results were previously only known in the so-called bounded-storage model which is a special case of our setting. Our protocols can be implemented with present-day hardware used for quantum key distribution. In particular, no quantum storage is required for the honest parties.

Efficient Secret Handshaking Protocol

Secret handshaking protocols allow two members of the same group to identify each other secretly, i.e., any two parties who are members of the same group will recognize each other as members, yet, a party which is not a member of this group cannot tell, by engaging some party in the handshaking protocol, whether that party is a member of this group. Unlinkability is one of the main merits of secret handshaking protocols, that is, a party engaged in at least two handshakes must not be able to link any two different handshakes to a particular party. To achieve unlinkability, almost all protocols proposed so far rely on the one-time credentials technique, where each party can use her credential only once. Hence, each party must hold enough credentials allowing her to engage in the handshakes for enough period of time (e.g. a month) without referring to the group authority for renewal. There is a severe security problem when one-time credentials are employed, that is, an active adversary may initialize with an honest party as many handshaking sessions as she can and hence, depletes all the credentials held by this party, once a party runs out of credentials she will not be able to engage in handshaking no more (Denial of Service attack, DoS). At the same time, the group authority must be able to manage enormous number of issued credentials in data structures and certificate revocation lists (CRL). Thus, on the large scale implementation (large group population), one-time credentials become impractical. In this paper, we propose a provably secure two-party secret handshaking protocol which realizes the unlinkability property using only one permanent credential for each member and avoiding the inefficient one-time credentials. At the same time, our protocol provides immediate revocation of members by the group authority without relying heavily on CRL structures. Keywords: Secret handshakes, authentication, one-time credentials, unlinkability, revocation, denial of service, anonymous RSA, mediated PKI.

Quantum Cryptography with Several Cloning Attacks

Problem statement: In a previous research, we investigated the quantum key distribution of the well known BB84 protocol with several intercept and resend attacks. In the present research, we studied the effect of many eavesdroppers cloning at tacks of the Bennett-Brassard cryptographic protocol on the quantum error and mutual informatio n between honest parties and information with sender for each eavesdropper. Approach: The quantum error and the mutual information were calculated analytically and computed for arbitrary number of cloning attacks. Our objective in this study was to know if the number of the eavesdropper s and their angle of cloning act on the safety of information. Results: It was found that the quantum error and the secure d/no secured transition depend strongly on the number of eavesdropper and their an gle of attacks. The particular cases where all eavesdroppers collaborate were also investigated. Conclusion: Furthermore, the cloning attack's quantum error is lower than the intercept and resen ds attacks one, which means that the cloning attack s is the optimal one for arbitrary number of eavesdro pper.

Implementation of two-party protocols in the noisy-storage model

The noisy-storage model allows the implementation of secure two-party protocols under the sole assumption that no large-scale reliable quantum storage is available to the cheating party. No quantum storage is thereby required for the honest parties. Examples of such protocols include bit commitment, oblivious transfer and secure identification. Here, we provide a guideline for the practical implementation of such protocols. In particular, we analyze security in a practical setting where the honest parties themselves are unable to perform perfect operations and need to deal with practical problems such as errors during transmission and detector inefficiencies. We provide explicit security parameters for two different experimental setups using weak coherent, and parametric down conversion sources. In addition, we analyze a modification of the protocols based on decoy states.

A non-distillability criterion for secret correlations

Within entanglement theory there are criteria which certify that some quantum states cannot be distilled into pure entanglement. An example is the positive partial transposition criterion. Here we present, for the first time, the analogous thing for secret correlations. We introduce a computable criterion which certifies that a probability distribution between two honest parties and an eavesdropper cannot be (asymptotically) distilled into a secret key. The existence of non-distillable correlations with positive secrecy cost, also known as bound information, is an open question. This criterion may be the key for finding bound information. However, if it turns out that this criterion does not detect bound information, then, a very interesting consequence follows: any distribution with positive secrecy cost can increase the secrecy content of another distribution. In other words, all correlations with positive secrecy cost constitute a useful resource.

QUANTUM KEY DISTRIBUTION WITH SEVERAL INTERCEPTS AND RESEND ATTACKS

The effect of several eavesdroppers intercept-resend attacks on the quantum error and mutual information between honest parties of a quantum channel chain is investigated within the BB84 (Bennett and Brassard, 1984). The quantum error and the mutual information are computed for arbitrary number of attacks. It is found that the quantum error and the secured–no secured transition depend strongly on the number N of eavesdroppers and their probabilities of intercepting attacks. For N = 3, numerical calculations show that the quantum error exhibits three kinds of different behaviors as a function of the probability of attack ω1of the first eavesdropper namely: (i) the quantum error remains constant for sufficiently small ω1, (ii) exhibits a plateau for intermediate values of ω1, (iii) increases, passes through a maximum and decreases when increasing ω1. However, depending on the probabilities of attack, phase diagrams present several kinds of topologies, in good agreement with the quantum error behavior. Moreover, in the particular case where all eavesdroppers intercept with identical probabilities ω, the quantum error increases as a nonlinear function with the number of eavesdroppers before reaching an upper limit of ≈ 0.475 for sufficiently large N. Besides, it is shown that the secured–no secured transition occurs under the effect of the number of eavesdroppers.

Performance Analysis of Secure Multiparty Computation Protocol

In this paper we address the issue related to privacy, security, complexity and Implementation, various adversaries exist which hamper the secure multiparty computation. In the secure multiparty computation, a set of parties wishes to jointly compute some function of their inputs. Such a computation must preserve certain security properties, like privacy and correctness, even if some of the participating parties or an external adversary colludes to attack the honest parties.

Security Against Covert Adversaries: Efficient Protocols for Realistic Adversaries

In the setting of secure multiparty computation, a set of mutually distrustful parties wish to securely compute some joint function of their private inputs. The computation should be carried out in a secure way, meaning that no coalition of corrupted parties should be able to learn more than specified or somehow cause the result to be “incorrect.” Typically, corrupted parties are either assumed to be semi-honest (meaning that they follow the protocol specification) or malicious (meaning that they may deviate arbitrarily from the protocol). However, in many settings, the assumption regarding semi-honest behavior does not suffice and security in the presence of malicious adversaries is excessive and expensive to achieve. In this paper, we introduce the notion of covert adversaries, which we believe faithfully models the adversarial behavior in many commercial, political, and social settings. Covert adversaries have the property that they may deviate arbitrarily from the protocol specification in an attempt to cheat, but do not wish to be “caught” doing so. We provide a definition of security for covert adversaries and show that it is possible to obtain highly efficient protocols that are secure against such adversaries. We stress that in our definition, we quantify over all (possibly malicious) adversaries and do not assume that the adversary behaves in any particular way. Rather, we guarantee that if an adversary deviates from the protocol in a way that would enable it to “cheat” (meaning that it can achieve something that is impossible in an ideal model where a trusted party is used to compute the function), then the honest parties are guaranteed to detect this cheating with good probability. We argue that this level of security is sufficient in many settings.

Device-independent quantum key distribution secure against collective attacks

Device-independent quantum key distribution (DIQKD) represents a relaxation of the security assumptions made in usual quantum key distribution (QKD). As in usual QKD, the security of DIQKD follows from the laws of quantum physics, but contrary to usual QKD, it does not rely on any assumptions about the internal working of the quantum devices used in the protocol. In this paper, we present in detail the security proof for a DIQKD protocol introduced in Acín et al (2008 Phys. Rev. Lett. 98 230501). This proof exploits the full structure of quantum theory (as opposed to other proofs that exploit only the no-signaling principle), but only holds against collective attacks, where the eavesdropper is assumed to act on the quantum systems of the honest parties independently and identically in each round of the protocol (although she can act coherently on her systems at any time). The security of any DIQKD protocol necessarily relies on the violation of a Bell inequality. We discuss the issue of loopholes in Bell experiments in this context.

Asymptotic security of binary modulated continuous-variable quantum key distribution under collective attacks

We estimate a lower bound to the secret key rate of a binary modulated continuous variable quantum key distribution scheme. We consider the collective attack scenario with quantum channels that impose arbitrary noise on the exchanged signals. The analysis is done in the infinite key limit. Bob performs ideal homodyne measurements on the received states and the two honest parties employ a reverse reconciliation procedure in the classical postprocessing step of the protocol.

T-Private and t-Secure Auctions

In most of the auction systems the values of bids are known to the auctioneer. This allows him to manipulate the outcome of the auction. Hence, one might be interested in hiding these values. Some cryptographically secure protocols for electronic auctions have been presented in the last decade. Our work extends these protocols in several ways. On the basis of garbled circuits, i.e., encrypted circuits, we present protocols for sealed-bid auctions that fulfill the following requirements: 1) protocols are information-theoretically t-private for honest but curious parties; 2) the number of bits that can be learned by malicious adversaries is bounded by the output length of the auction; 3) the computational requirements for participating parties are very low: only random bit choices and bitwise computation of the XOR-function are necessary. Note that one can distinguish between the protocol that generates a garbled circuit for an auction and the protocol to evaluate the auction. In this paper we address both problems. We will present a t-private protocol for the construction of a garbled circuit that reaches the lower bound of 2t + 1 parties, and a more randomness efficient protocol for (t + 1)2 parties. Finally, we address the problem of bid changes in an auction.

Key Distillation and the Secret-Bit Fraction

We consider distillation of secret bits from partially secret noisy correlations PABE, shared between two honest parties and an eavesdropper. The most studied distillation scenario consists of joint operations on a large number of copies of the distribution (PABE)N, assisted with public communication. Here we consider distillation with only one copy of the distribution, and instead of rates, the ?quality? of the distilled secret bits is optimized, where the ?quality? is quantified by the secret-bit fraction of the result. The secret-bit fraction of a binary distribution is the proportion which constitutes a secret bit between Alice and Bob. With local operations and public communication the maximal extractable secret-bit fraction from a distribution PABE is found, and is denoted by ?[PABE]. This quantity is shown to be nonincreasing under local operations and public communication, and nondecreasing under eavesdropper's local operations: ? is a secrecy monotone. It is shown that if ? [PABE] > 1/2 then PABE is distillable, thus providing a sufficient condition for distillability. A simple expression for ?[PABE] is found when the eavesdropper is decoupled, and when the honest parties' information is binary and the local operations are reversible. Intriguingly, for general distributions the (optimal) operation requires local degradation of the data.

Cryptography in the Bounded-Quantum-Storage Model

We initiate the study of two-party cryptographic primitives with unconditional security, assuming that the adversary's quantum memory is of bounded size. We show that oblivious transfer and bit commitment can be implemented in this model using protocols where honest parties need no quantum memory, whereas an adversarial player needs quantum memory of size at least $n/2$ in order to break the protocol, where n is the number of qubits transmitted. This is in sharp contrast to the classical bounded-memory model, where we can only tolerate adversaries with memory of size quadratic in honest players' memory size. Our protocols are efficient and noninteractive and can be implemented using today's technology. On the technical side, a new entropic uncertainty relation involving min-entropy is established.

Security of coherent-state quantum cryptography in the presence of Gaussian noise

We investigate the security against collective attacks of a continuous variable quantum key distribution scheme in the asymptotic key limit for a realistic setting. The quantum channel connecting the two honest parties is assumed to be lossy and imposes Gaussian noise on the observed quadrature distributions. Secret key rates are given for direct and reverse reconciliation schemes including post-selection in the collective attack scenario. The effect of a nonideal error correction and two-way communication in the classical post-processing step is also taken into account.

Applications of LDPC Codes to the Wiretap Channel

With the advent of quantum key distribution (QKD) systems, perfect (i.e., information-theoretic) security can now be achieved for distribution of a cryptographic key. QKD systems and similar protocols use classical error-correcting codes for both error correction (for the honest parties to correct errors) and privacy amplification (to make an eavesdropper fully ignorant). From a coding perspective, a good model that corresponds to such a setting is the wire tap channel introduced by Wyner in 1975. In this correspondence, we study fundamental limits and coding methods for wire tap channels. We provide an alternative view of the proof for secrecy capacity of wire tap channels and show how capacity achieving codes can be used to achieve the secrecy capacity for any wiretap channel. We also consider binary erasure channel and binary symmetric channel special cases for the wiretap channel and propose specific practical codes. In some cases our designs achieve the secrecy capacity and in others the codes provide security at rates below secrecy capacity. For the special case of a noiseless main channel and binary erasure channel, we consider encoder and decoder design for codes achieving secrecy on the wiretap channel; we show that it is possible to construct linear-time decodable secrecy codes based on low-density parity-check (LDPC) codes that achieve secrecy.

Constant-Round Oblivious Transfer in the Bounded Storage Model

We present the first constant-round protocol for Oblivious Transfer in Maurer's bounded storage model. In this model, a long random string R is initially transmitted and each of the parties stores only a small portion of R. Even though the portions stored by the honest parties are small, security is guaranteed against any malicious party that remembers almost the entire string R (but not all of it). Previous constructions for oblivious transfer in the bounded storage model required polynomially many rounds of interaction. In contrast, our protocol uses only five messages. In addition we also improve other parameters, such as the number of bits transferred and the probability of immaturely aborting the protocol due to failure. Our techniques utilize explicit constructions from the theory of derandomization. In particular, we achieve the constant round complexity of our oblivious transfer protocol by constructing a novel four-message protocol for Interactive Hashing, in place of the well-known protocol by Naor et al. (known as the NOVY protocol) which involves many rounds of interaction. Our four-message interactive hashing protocol is constructed by use of t-wise independent permutations and may be of independent interest. For achieving constant-round complexity we also construct a new subset encoding scheme that is dense; namely, guarantees that almost every string in the image of the encoding function has a preimage. Other tools we employ include randomness extractors and averaging samplers.