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5,430 results · page 221 of 227
Tsz Hon Yuen, Qiong Huang, Yi Mu, Willy Susilo · 6 authors
No abstract is available for this record.
Rafael Pass, Wei-Lung Dustin Tseng, Douglas Wikström
We show that only languages in BPP have public-coin black-box zero-knowledge protocols that are secure under an unbounded (polynomial) number of parallel repetitions. This result holds both in the plain model (without any setup) and in the bare public key model (where the prover and the verifier have registered public keys). We complement this result by constructing a public-coin black-box zero-knowledge proof based on one-way functions that remains secure under any a priori bounded number of concurrent executions. A key step (of independent interest) in the analysis of our lower bound shows that any public-coin protocol, when repeated sufficiently in parallel, satisfies a notion of “resettable soundness” if the verifier picks its random coins using a pseudorandom function.
Ronald Cramer, Ivan Damgård, Marcel Keller
No abstract is available for this record.
Mira Belenkiy, Jan Camenisch, Melissa Chase, Markulf Kohlweiss · 6 authors
No abstract is available for this record.
Aggelos Kiayias, Hong-Sheng Zhou
No abstract is available for this record.
Yehuda Lindell, Hila Zarosim
Abstract. In the setting of secure computation, a set of parties wish to securely compute some function of their inputs, in the presence of an adversary. The adversary in question may be static (meaning that it con-trols a predetermined subset of the parties) or adaptive (meaning that it can choose to corrupt parties during the protocol execution and based on what it sees). In this paper, we study two fundamental questions relating to the basic zero-knowledge and oblivious transfer protocol problems: – Adaptive zero-knowledge proofs: We ask whether it is possible to con-struct adaptive zero-knowledge proofs (with unconditional sound-ness). Beaver (STOC 1996) showed that known zero-knowledge proofs are not adaptively secure, and in addition showed how to construct zero-knowledge arguments (with computational soundness). – Adaptively secure oblivious transfer: All known protocols for adap-tively secure oblivious transfer rely on seemingly stronger hardness assumptions than for the case of static adversaries. We ask whether this is inherent, and in particular, whether it is possible to construct adaptively secure oblivious transfer from enhanced trapdoor permu-tations alone. We provide surprising answers to the above questions, showing that achieving adaptive security is sometimes harder than achieving static se-curity, and sometimes not. First, we show that assuming the existence of one-way functions only, there exist adaptive zero-knowledge proofs for all languages in NP. In order to prove this, we overcome the problem that all adaptive zero-knowledge protocols known until now used equivocal commitments (which would enable an all-powerful prover to cheat). Sec-ond, we prove a black-box separation between adaptively secure oblivious transfer and enhanced trapdoor permutations. As a corollary, we derive a black-box separation between adaptively and statically securely obliv-ious transfer. This is the first black-box separation to relate to adaptive security and thus the first evidence that it is indeed harder to achieve security in the presence of adaptive adversaries than in the presence of static adversaries. 1
Yuval Ishai, Eyal Kushilevitz, Rafail Ostrovsky, Amit Sahai
A zero-knowledge proof allows a prover to convince a verifier of an assertion without revealing any further information beyond the fact that the assertion is true. Secure multiparty computation allows n mutually suspicious players to jointly compute a function of their local inputs without revealing to any t corrupted players additional information beyond the output of the function. We present a new general connection between these two fundamental notions. Specifically, we present a general construction of a zero-knowledge proof for an NP relation $R(x,w)$, which makes only a black-box use of any secure protocol for a related multiparty functionality f. The latter protocol is required only to be secure against a small number of “honest but curious” players. We also present a variant of the basic construction that can leverage security against a large number of malicious players to obtain better efficiency. As an application, one can translate previous results on the efficiency of secure multiparty computation to the domain of zero-knowledge, improving over previous constructions of efficient zero-knowledge proofs. In particular, if verifying R on a witness of length m can be done by a circuit C of size s, and assuming that one-way functions exist, we get the following types of zero-knowledge proof protocols: (1) Approaching the witness length. If C has constant depth over $\wedge,\vee,\oplus,\neg$ gates of unbounded fan-in, we get a zero-knowledge proof protocol with communication complexity $m\cdot{poly}(k)\cdot{polylog}(s)$, where k is a security parameter. (2) “Constant-rate” zero-knowledge. For an arbitrary circuit C of size s and a bounded fan-in, we get a zero-knowledge protocol with communication complexity $O(s)+{poly}(k,\log s)$. Thus, for large circuits, the ratio between the communication complexity and the circuit size approaches a constant. This improves over the $O(ks)$ complexity of the best previous protocols.
Andrew Chi-Chih Yao, Frances Yao, Yunlei Zhao
No abstract is available for this record.
Laicheng Cao
Most of the current trust models in peer-to-peer (P2P) networks are identity based, which means that in order for one peer to trust another, it needs to know the other peer's identity. In addition, the conventional access control mechanism is not suitable because the P2P networks is decentralize and dynamic one. We propose a neighborhood key method, authentication scheme base on zero-knowledge proof without leaking any sensitive information, each peer shares secrets only with authenticated neighbors, which generate verifiable pseudonym instead of their real identity from using a one-way Hash function. Security analysis proves that this method makes authentication can't be impersonated, while achieving better anonymity for peers, malicious peers cannot deduce a real identity. And also shows well defending man-in-middle attacks.
Chris Peikert, Vinod Vaikuntanathan
No abstract is available for this record.
Ning Ding, Dawu Gu
No abstract is available for this record.
Jacek Cichoń, Marek Klonowski, Mirosław Kutyłowski
No abstract is available for this record.
Rafael Pass, Wei-Lung Dustin Tseng, Muthuramakrishnan Venkitasubramaniam
Few techniques for obtaining concurrent zero-knowledge exist; all require a complex and subtle analysis. We provide an arguably simpler and more general analysis of the oblivious simulation technique of Kilian and Petrank (STOC’01) while achieving the same bounds as Prabhakaran, Rosen and Sahai (FOCS’02). Using this analysis, and relying on tools recently developed by Ong and Vadhan (Eurocrypt’07, TCC’08) we are able to establish the following unconditional results: • every language inNP which has a ZK proof (resp. ZK argument, statistical ZK argument) also has a black-box concurrent ZK proof (resp. ZK argument, statistical ZK argument). • every languge which has a statistical ZK proof also has an ω(log n)-round black-box con-current statistical ZK proof.
Vipul Goyal, Payman Mohassel, Adam Smith
No abstract is available for this record.
Dario Catalano, Mario Di Raimondo, Dario Fiore, Mariagrazia Messina
Zero knowledge sets (ZKS), introduced by Micali, Rabin, and Kilian in 2003, allow a prover to commit to a secret set$S$in a way such that it can later prove, non interactively, statements of the form$x\in S$(or$x\notin S$), without revealing any further information (on top of what explicitly revealed by the inclusion/exclusion statements above) on$S$, not even its size. Later, Chaseabstracted away the Micali, Rabin, and Kilian's construction by introducing an elegant new variant of commitments that they called (trapdoor) mercurial commitments. Using this primitive, it was shown how to construct zero knowledge sets from a variety of assumptions (both general and number theoretic). This paper introduces the notion of trapdoor$q$-mercurial commitments (${\ssr qTMC}$s), a notion of mercurial commitment that allows the sender to commit to an ordered sequence of exactly$q$messages, rather than to a single one. Following the previous work, it is shown how to construct ZKS from${\ssr qTMC}$s and collision resistant hash functions. Then, it is presented an efficient realization of${\ssr qTMC}$s that is secure under the so called Strong Diffie Hellman (SDH) assumption, a number theoretic conjecture recently introduced by Boneh and Boyen. Using such scheme as basic building block, it is obtained a construction of ZKS that allows for proofs that are much shorter with respect to the best previously known implementations. In particular, for an appropriate choice of the parameters, our proofs are up to 33% shorter for the case of proofs of membership, and up to 73% shorter for the case of proofs of nonmembership. Experimental tests confirm practical time performances.
Rafael Pass, Muthuramakrishnan Venkitasubramaniam
No abstract is available for this record.
Θεόδωρος Μπαλόπουλος
Η διατριβή αυτή ασχολείται με την προδιαγραφή και υλοποίηση πρωτοκόλλων ασφάλειας με απαιτήσεις διασφάλισης ιδιωτικότητας, όπως για παράδειγμα τα πρωτόκολλα ηλεκτρονικών μετρητών, ηλεκτρονικής ψηφοφορίας και επιλεκτικής αποκάλυψης δεδομένων. Ο στόχος, όσον αφορά την προδιαγραφή τους, είναι αυτή να γίνει με τυπική μέθοδο (formal method), και, όσον αφορά την υλοποίησή τους, να βασίζεται στην προδιαγραφή τους και να διασφαλίζει τις περί ιδιωτικότητας απαιτήσεις. Το υπάρχον ερευνητικό έργο στη διεθνή βιβλιογραφία σε τυπικές μεθόδους δεν καλύπτει επαρκώς τα πρωτόκολλα ασφάλειας με απαιτήσεις διασφάλισης ιδιωτικότητας όσο άλλων ειδών πρωτόκολλα ασφάλειας, όπως τα πρωτόκολλα αυθεντικοποίησης. Στην παρούσα διατριβή υποστηρίζεται ότι οι λόγοι για αυτή την ανεπάρκεια μελέτης είναι οι εξής: Πρώτον, ότι τα πρωτόκολλα με απαιτήσεις διασφάλισης ιδιωτικότητας βασίζονται σε πιο εξειδικευμένη κρυπτογραφία, όπως η δέσμευση (commitment), η τυφλή υπογραφή (blind signature), η απόδειξη μηδενικής γνώσης (zero-knowledge proof), η ομομορφική κρυπτογραφία (homomorphic encryption), το mix του Chaum και το onion routing. Δεύτερον, ότι είναι απαραίτητη η διαφοροποίηση στη μοντελοποίηση της κλασικής κρυπτογραφίας (συμμετρική και ασύμμετρη κρυπτογράφηση και ψηφιακές υπογραφές) που τα πρωτόκολλα αυτά χρησιμοποιούν από κοινού με τα υπόλοιπα πρωτόκολλα. Η διατριβή αυτή χρησιμοποιεί ως βάση τη γλώσσα προδιαγραφής πρωτοκόλλων Typed MSR [14, 15], καθώς και την προηγούμενη εργασία μας στην ίδια [10, 7, 9, 8, 6] ερευνητική κατεύθυνση και στοχεύει με τροποποιήσεις και προσθήκες να την μετατρέψει σε κατάλληλη, αφενός για την προδιαγραφή πρωτοκόλλων με απαιτήσεις διασφάλισης ιδιωτικότητας, αφετέρου για την προδιαγραφή ενός κατά Dolev-Yao επιτιθέμενου [19] σχεδιασμένου για επίθεση σε πρωτόκολλα τέτοιου είδους. Επιπλέον, χρησιμοποιεί ως βάση τη γλώσσα Jif [30, 31, 29], καθώς και την προηγούμενη εργασία μας [6] στην ίδια ερευνητική κατεύθυνση και στοχεύει να επιδείξει πως η γλώσσα αυτή, που διαθέτει σύστημα τύπων για απαιτήσεις ασφάλειας, μπορεί να χρησιμοποιηθεί με τέτοιον τρόπο ώστε οι αδυναμίες στην υλοποίηση πρωτοκόλλων ασφαλείας όσον αφορά τη συνδεσιμότητα (linkability) να μπορούν να ανιχνευτούν με ένα συνδυασμό στατικών και δυναμικών (runtime) ελέγχων. Τα βασικά συμπεράσματα της διατριβής αυτής είναι τα ακόλουθα: 1. Προκειμένου η Typed MSR να είναι κατάλληλη για την προδιαγραφή πρωτοκόλλων ασφάλειας με απαιτήσεις ιδιωτικότητας, δεν θα πρέπει να μοντελοποιεί τη συμμετρική και την ασύμμετρη κρυπτογράφηση ως αιτιοκρατική. Μια τέτοια απλούστευση μπορεί να μη δημιουργεί προβλήματα στη μοντελοποίηση άλλων πρωτοκόλλων, αλλά οδηγεί σε ανύπαρκτες αδυναμίες διασύνδεσης στα πρωτόκολλα που μελετούμε στην παρούσα διατριβή. 2. Μπορούμε να κατασκευάσουμε υψηλού επιπέδου μοντελοποιήσεις για κρυπτογραφία πιο σύνθετη από την κλασική, όπως είναι η δέσμευση, η τυφλή υπογραφή, η απόδειξη μηδενικής γνώσης και η ομομορφική κρυπτογραφία. 3. Η χρήση μη διαδραστικών μοντελοποιήσεων για τις αποδείξεις μηδενικής γνώσης οδηγεί στην απλοποίηση τόσο της προδιαγραφής των πρωτοκόλλων, όσο και της μετατροπής αυτής σε υλοποίησή τους. 4. Με βάση τις προαναφερθείσες αλλαγές και προσθήκες, η Typed MSR γίνεται κατάλληλη για την προδιαγραφή πρωτοκόλλων ασφάλειας με απαιτήσεις ιδιωτικότητας, όπως δείχνει η προδιαγραφή των δύο πρωτοκόλλων ηλεκτρονικής ψηφοφορίας που περιέχονται στην παρούσα διατριβή. 5. Ένα απλό σύστημα τύπων, που χρησιμοποιείται παράλληλα με το σύστημα τύπων της Typed MSR, αποτρέπει συγκεκριμένες εσφαλμένες χρήσεις της κρυπτογραφίας που μπορεί να οδηγήσουν σε αδυναμίες συνδεσιμότητας, καθώς και να παρακολουθήσει την απειλή συνδεσιμότητας που προκύπτει από κάθε πιθανή χρήση της κρυπτογραφίας. 6. Είναι απαραίτητη η ενημέρωση του εκφρασμένου σε Typed MSR μοντέλου του κατά Dolev-Yao επιτιθέμενου με βάση τα παραπάνω, ώστε να μπορεί πλέον να επιτεθεί στα πρωτόκολλα τα οποία μελετάμε. 7. Η ενημερωμένη αυτή έκδοση του κατά Dolev-Yao επιτιθέμενου δημιουργεί ένα τυπικό (formal) περιβάλλον, στο οποίο μπορούν να εκφραστούν αδυναμίες διασύνδεσης των πρωτοκόλλων. 8. Τα παραπάνω μπορούν να αποτελέσουν τη βάση για τη χρήση της γλώσσας Jif με τέτοιο τρόπο, ώστε οι αδυναμίες στην υλοποίηση πρωτοκόλλων ασφαλείας όσον αφορά τη συνδεσιμότητα να μπορούν να ανιχνευτούν με ένα συνδυασμό στατικών και δυναμικών ελέγχων. 9. Η συνδεσιμότητα δεν είναι δυνατό να ελεγχθεί στατικά στη γενική περίπτωση, αλλά μπορεί να ελέγχεται δυναμικά κατά την εκτέλεση των πρωτοκόλλων. 10. Οι κανόνες της Typed MSR με τους οποίους παράγονται τα καινούρια μηνύματα τα οποία μπορεί να σχηματίσει ο κατά Dolev-Yao επιτιθέμενος από ένα σύνολο γνωστών μηνυμάτων χωρίζονται σε δύο κατηγορίες, ανάλογα με το αν χρησιμοποιούνται στη φάση αποδόμησης των γνωστών μηνυμάτων ή στη φάση κατασκευής των καινούριων. Συγκεκριμένα μηνύματα που βασίζονται στην κρυπτογραφία της διατριβής αυτής δεν μπορούν όμως να χωριστούν σε μία από τις δύο κατηγορίες, καθώς είναι ωφέλιμη η χρήση τους και στις δύο αυτές φάσεις.
Yuanyuan Yang
This article focuses on a kind of MP2P(Mobile P2P)network,a hybrid architecture,based on mobile computing,where the mobile terminals with Ad Hoc connections can communicate with each other via the P2P technology.The paper mainly makes a study on the secure communication in the mobile P2P network,with One-Round Zero-Knowledge Proofs for the identity authentication.Also the relative performances and efficiency of the system are discussed.
Bao Li
Traditional definition of signature of knowledge can not prevent steganographic communication.To solve this problem,we introduce and formally define the notion of fairness of the signature of knowledge.We then construct a fair signature of knowledge scheme by use of fair zero-knowledge proofs of knowledge,and finally prove that this scheme indeed guarantees the fairness and can efficiently prevent steganographic communication.
Sebastian Faust, Emilia Käsper, Stefan Lucks
We present an efficient simultaneous broadcast protocol ν-SimCast that allows n players to announce independently chosen values, even if up to t < n players are corrupt. Independence is guaranteed in the partially syn-2 chronous communication model, where communication is structured into rounds, while each round is asynchronous. The ν-SimCast protocol is more efficient than previous constructions. For repeated executions, we reduce the communication and computation complexity by a factor O(n). Combined with a deterministic extractor, ν-SimCast provides a particularly efficient solution for distributed coin-flipping. The protocol does not require any zero-knowledge proofs and is shown to be secure in the standard model under the Decisional Diffie Hellman assumption.
Dennis Hofheinz
The selective decommitment problem can be described as follows: assume an adversary receives a number of commitments and then may request openings of, say, half of them. Do the unopened commitments remain secure? Although this question arose more than twenty years ago, no satisfactory answer could be presented so far. We answer the question in several ways: 1. If simulation-based security is desired (i.e., if we demand that the adversary's output can be simulated by a machine that does not see the unopened commitments), then security is not achievable for non-interactive or perfectly binding commitment schemes via black-box reductions to standard cryptographic assumptions. However, we show how to achieve security in this sense with interaction and a non-black-box reduction to one-way permutations. 2. If only indistinguishability of the unopened commitments from random commitments is desired, then security is not achievable for (interactive or non-interactive) perfectly binding commitment schemes, via black-box reductions to standard cryptographic assumptions. However, any statistically hiding scheme does achieve security in this sense. Our results give an almost complete picture when and how security under selective openings can be achieved. Applications of our results include: • Essentially, an encryption scheme must be non-committing in order to achieve provable security against an adaptive adversary. • When implemented with our secure commitment scheme, the interactive proof for graph 3-coloring due to Goldreich et al. becomes zero-knowledge under parallel composition. On the technical side, we develop a technique to show very general impossibility results for black-box proofs.
Federica Paci, Elisa Bertino, Sam Kerr, Aaron Lint · 6 authors
No abstract is available for this record.
Shangyuan Guan, Xiaoshe Dong, Yiduo Mei, Weiguo Wu · 5 authors
Exchange of attribute certificates is a means to establish mutual trust between strangers wishing to share resources or conduct business transactions. Automated trust negotiation (ATN) is a promising approach to regulating the exchange of sensitive information during this process. It has been a fundamental but challenging problem to preserve the privacy of the two negotiation parties during the period of ATN. We present the enhanced hidden credentials and improved concurrent zero-knowledge proof protocol. Based on the above technologies, we propose an ATN for e-business applications, named CASTLE. CASTLE can not only enable the oblivious and selective usage of an attribute or a certificate, but also be resistible for many attacks, especially conspiracy attack. We illustrate the usage of CASTLE through a typical example.
Yi Deng
Abstract. We construct resettably-sound resettable zero knowledge arguments for NP based on standard hardness assumption (the existence of claw-free permutations) in the plain model. This proves the simultaneous resettability conjecture posed by Barak et al. in [FOCS 2001]. Our construction, inspired by the paradigm for designing concurrent zero knowledge protocols, makes crucial use of a tool called instance-dependent resettably-sound resettable WI argument of knowledge (IDWIAOK (and a special-purpose variant), introduced recently by Deng and Lin in [Eurocrypt 2007]). Roughly speaking, for a NP statement of the form x0 ∨ x1, IDWIAOK is an argument for which resettable WI property holds when both x0 and x1 are YES instances, and resettably-sound argument of knowledge property holds when x0 is a NO instance. The heart of the simulator for our protocol is a new technique that allows us to embed the (non-black-box) straight-line simulation strategy in the (black-box) recursive rewinding simulation strategy. 1 The problem and our result It is well known that randomness is essential to zero knowledge proofs/arguments[17]. Moreover,