For various services, OTP (One-Time Password) is increasingly employed to sign in services. The most popular OTP scheme is S/KEY. However, S/KEY scheme is vulnerable to hash collision. In order to solve this problem, Choi and Kim proposed an OTP scheme based on pairing operation. This scheme overcame hash collision problem. Unfortunately, the scheme is vulnerable against insider attack. In this paper, we propose insider attack-resistant OTP scheme based on pairing operation. Our scheme employed zero-knowledge proof to generate OTP values. In short, our scheme sends an OTP and two random numbers encoded with XOR; any adversary has no sense about the random numbers. Our scheme authenticates entities with an OTP and gain a hint on next OTP value from one of random numbers. Consequently, we present insider attack-resistant OTP scheme by eliminating shared parameter among insider (e.g. time stamp).
In many applications, the password is sent as cleartext to the server to be authenticated thus providing the eavesdropper with opportunity to steal valuable data. This paper presents a simple protocol based on zero knowledge proof by which the user can prove to the authentication server that he has the password without having to send the password to the server as either cleartext or in encrypted format. Thus the user can authenticate himself without having to actually reveal the password to the server. Also, another version of this protocol has been proposed which makes use of public key cryptography thus adding one more level of security to the protocol and enabling mutual authentication between the client & server.
In this thesis we present two new type systems for verifying the security of cryptographic protocol models expressed in a spi-calculus and, respectively, of protocol implementations expressed in a concurrent lambda calculus. In this thesis we present two new type systems for verifying the security of cryptographic protocol models expressed in a spi-calculus and, respectively, of protocol implementations expressed in a concurrent lambda calculus. The two type systems combine prior work on refinement types with union and intersection types and with the novel ability to reason statically about the disjointness of types. The increased expressivity enables the analysis of important protocol classes that were previously out of scope for the type-based analyses of cryptographic protocols. In particular, our type systems can statically analyze protocols that are based on zero-knowledge proofs, even in scenarios when certain protocol participants are compromised. The analysis is scalable and provides security proofs for an unbounded number of protocol executions. The two type systems come with mechanized proofs of correctness and efficient implementations.
George Danezis, Markulf Kohlweiss, Benjamin Livshits, Alfredo Rial
Abstract. Nowadays, service providers gather fine-grained data about users to deliver personalized services, for example, through the use of third-party cookies or social network profiles. This poses a threat both to privacy, since the amount of information obtained is excessive for the purpose of customization, and authenticity, because those methods employed to gather data can be blocked and fooled. In this paper we propose privacy-preserving profiling techniques, in which users perform the profiling task locally, reveal to service providers the result and prove its correctness. We address how our approach applies to tasks of both classification and pattern recognition. For the former, we describe client-side profiling based on random forests, where users, based on certified input data representing their activity, resolve a random forest and reveal the classification result to service providers. For the latter, we show how to match a stream of user activity to a regular expression, or how to assign it a probability using a hidden Markov model. Our techniques, based on the use of zero-knowledge proofs, can be composed with other protocols as part of the certification of a larger computation. 1
Experts predict that in the next 10 to 100 years scientists will succeed in creating human-level artificial general intelligence. While it is most likely that this task will be accomplished by a government agency or a large corporation, the possibility remains that it will be done by a single inventor or a small team of researchers. In this paper, we address the question of safeguarding a discovery which could without hesitation be said to be worth trillions of dollars. Specifically, we propose a method based on the combination of zero knowledge proofs and provably AI-complete CAPTCHA problems to show that a superintelligent system has been constructed without having to reveal the system itself.
Matteo Maffei, Giulio Malavolta, Manuel Reinert, Dominique Schröder
The existing (election) voting systems, e.g., representative democracy, have many limitations and often fail to serve the best interest of the people in collective decision making. To address this issue, the concept of liquid democracy has been emerging as an alternative decision-making model to make better use of "the wisdom of crowds". Very recently, a few liquid democracy implementations, e.g. Google Votes and Decentralized Autonomous Organization (DAO), are released; however, those systems only focus on the functionality aspect, as no privacy/anonymity is considered. In this work, we, for the first time, provide a rigorous study of liquid democracy under the Universal Composability (UC) frame- work. In the literature, liquid democracy was achieved via two separate stages -- delegation and voting. We propose an efficient liquid democracy e-voting scheme that uni es these two stages. At the core of our design is a new voting concept called statement voting, which can be viewed as a natural extension of the conventional voting approaches. We remark that our statement voting can be extended to enable more complex voting and generic ledger-based non-interactive multi-party computation. We believe that the statement voting concept opens a door for constructing a new class of e-voting schemes.
Gilles Barthe, Daniel Hedin, Santiago Zanella-Béguelin, Benjamin Grégoire · 5 authors
Zero-knowledge proofs have a vast applicability in the domain of cryptography, stemming from the fact that they can be used to force potentially malicious parties to abide by the rules of a protocol, without forcing them to reveal their secrets. Σ-protocols are a class of zero-knowledge proofs that can be implemented efficiently and that suffice for a great variety of practical applications. This paper presents a first machine-checked formalization of a comprehensive theory of Σ-protocols. The development includes basic definitions, relations between different security properties that appear in the literature, and general composability theorems. We show its usefulness by formalizing—and proving the security—of concrete instances of several well-known protocols. The formalization builds on CertiCrypt, a framework that provides support to reason about cryptographic systems in the Coq proof assistant, and that has been previously used to formalize security proofs of encryption and signature schemes.
We devise an abstraction of zero-knowledge protocols that is accessible to a fully mechanized analysis. The abstraction is formalized within the applied pi-calculus using a novel equational theory that abstractly characterizes the cryptographic semantics of zero-knowledge proofs. We present an encoding from the equational theory into a convergent rewriting system that is suitable for the automated protocol verifier ProVerif. The encoding is sound and fully automated. We successfully used ProVerif to obtain the first mechanized analysis of (a simplified variant of) the Direct Anonymous Attestation (DAA) protocol. This required us to devise novel abstractions of sophisticated cryptographic security definitions based on interactive games. The analysis reported a novel attack on DAA that was overlooked in its existing cryptographic security proof. We propose a revised variant of DAA that we successfully prove secure using ProVerif.
We proposed a new zero-knowledge proof of identity protocol based on Mandelbrot and Julia Fractal sets. The Fractal based zero-knowledge protocol was possible because of the intrinsic connection between the Mandelbrot and Julia Fractal sets. In the proposed protocol, the private key was used as an input parameter for Mandelbrot Fractal function to generate the corresponding public key. Julia Fractal function was then used to calculate the verified value based on the existing private key and the received public key. The proposed protocol was designed to be resistant against attacks. Fractal based zero-knowledge protocol was an attractive alternative to the traditional number theory zero-knowledge protocol.
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.
Esoteric protocols, such as electronic cash, electronic voting and selective disclosure protocols, use special message constructors that are not widely used in other types of protocols (for example, in authentication protocols). These message constructors include blind signatures, commitments and zero-knowledge proofs. Furthermore, a standard formalization of the Dolev-Yao intruder [6] does not take into account these message constructors, nor does it consider some types of attacks (such as privacy attacks, brute-force dictionary attacks and known-plaintext attacks) that esoteric as well as other types of protocols are designed to protect against. This paper aims to present an extension of typed MSR [3, 4] in order to formally specify the needed message constructors, as well as the capabilities of a Dolev-Yao intruder designed to attack esoteric protocols.
Counterfeit products, especially in the pharmaceutical sector, have plagued the international community for decades. To combat this problem, many anti-counterfeiting approaches have been proposed. They use either Radio Frequency Identification (RFID) or Near Field Communication (NFC) physical tags affixed to the products. Current anti-counterfeiting approaches detect two counterfeiting attacks: (1) modifications to a product's tag details, such as changing the expiration date; and (2) cloning of a genuine product's details to reuse on counterfeit products. In addition, these anti-counterfeiting approaches track-and-trace the physical locations of products as the products flow through supply chains. Existing approaches suffer from two main drawbacks. They cannot detect tag reapplication attacks, wherein a counterfeiter removes a legitimate tag from a genuine product and reapplies it to a counterfeit or expired product. Second, most existing approaches typically rely on a central server to authenticate products. This is not scalable and creates tremendous processing burden on the server, since significant volumes of products flood through the supply chain's nodes. In addition, centralized supply chains require substantial data storage to store authentication records for all products. Moreover, as with centralized systems, traditional supply chains inherently have the problem of a single-point of failure. The thesis of this dissertation is that a robust, scalable, counterfeiting-resistant supply chain that addresses the above drawbacks and can be simultaneously achieved by (i) using a combination of NFC tags on products and a distributed ledger such as blockchain for reapplication-proof, decentralized, and transparent product authentication (ii) a novel game-theoretical consensus protocol for enforcing true decentralization, and enhancing the protocol's security and performance. In this dissertation, we first propose a new Tag Reapplication Detection (TRD) system to detect reapplication attacks using low-cost NFC tags and public key cryptography. To detect reapplication attacks, TRD tracks the number of times a tag has been read in the supply chain using a 'central' authentication server. Second, leveraging the blockchain technology, we propose the Block-Supply Chain, a transformation of TRD into a decentralized supply chain. In this chain, each node maintains a blockchain (distributed public ledger) per product. This blockchain comprises chained blocks, where each is an authentication event. The Block-Supply Chain can detect tag reapplication attacks and can replace the centralized supply chain design, thus overcoming the centralization issues. One of the fundamental characteristics of blockchain technology is the consensus protocol. Consensus protocols ensure that all nodes in the blockchain network agree on the validity of a
William A. Wulf, Alec Yasinsac, Katie S. Oliver, Ramesh Peri
Distributed systems have long relied on shared secrets to ensure the authenticity of principals. Public key systems and zero knowledge proofs of identity have reduced this reliance. We offer a method of remote authentication that can be used with no advance shared knowledge by parties, and that allows parties to increase their confidence in the authenticity of a suspicious party to an arbitrary level. Note: Abstract extracted from PDF text