Results 21-40 of 85.       1 2 3 4 5   User Experience Design for E-Voting: How mental models align with security mechanismsZollinger, Marie-Laure ; Distler, Verena ; Roenne, Peter et alin Electronic Voting (2019, October)This paper presents a mobile application for vote-casting and vote-verification based on the Selene e-voting protocol and explains how it was developed and implemented using the User Experience Design ... [more ▼]This paper presents a mobile application for vote-casting and vote-verification based on the Selene e-voting protocol and explains how it was developed and implemented using the User Experience Design process. The resulting interface was tested with 38 participants, and user experience data was collected via questionnaires and semi-structured interviews on user experience and perceived security. Results concerning the impact of displaying security mechanisms on UX were presented in a complementary paper. Here we expand on this analysis by studying the mental models revealed during the interviews and compare them with theoretical security notions. Finally, we propose a list of improvements for designs of future voting protocols. [less ▲]Detailed reference viewed: 196 (17 UL) A Lightweight Implementation of NTRUEncrypt for 8-bit AVR MicrocontrollersCheng, Hao ; Groszschädl, Johann ; Roenne, Peter et alE-print/Working paper (2019)Introduced in 1996, NTRUEncrypt is not only one of the earliest but also one of the most scrutinized lattice-based cryptosystems and a serious contender in NIST’s ongoing Post-Quantum Cryptography (PQC ... [more ▼]Introduced in 1996, NTRUEncrypt is not only one of the earliest but also one of the most scrutinized lattice-based cryptosystems and a serious contender in NIST’s ongoing Post-Quantum Cryptography (PQC) standardization project. An important criterion for the assessment of candidates is their computational cost in various hardware and software environments. This paper contributes to the evaluation of NTRUEncrypt on the ATmega class of AVR microcontrollers, which belongs to the most popular 8-bit platforms in the embedded domain. More concretely, we present AvrNtru, a carefully-optimized implementation of NTRUEncrypt that we developed from scratch with the goal of achieving high performance and resistance to timing attacks. AvrNtru complies with version 3.3 of the EESS#1 specification and supports recent product-form parameter sets like ees443ep1, ees587ep1, and ees743ep1. A full encryption operation (including mask generation and blinding- polynomial generation) using the ees443ep1 parameters takes 834,272 clock cycles on an ATmega1281 microcontroller; the decryption is slightly more costly and has an execution time of 1,061,683 cycles. When choosing the ees743ep1 parameters to achieve a 256-bit security level, 1,539,829 clock cycles are cost for encryption and 2,103,228 clock cycles for decryption. We achieved these results thanks to a novel hybrid technique for multiplication in truncated polynomial rings where one of the operands is a sparse ternary polynomial in product form. Our hybrid technique is inspired by Gura et al’s hybrid method for multiple-precision integer multiplication (CHES 2004) and takes advantage of the large register file of the AVR architecture to minimize the number of load instructions. A constant-time multiplication in the ring specified by the ees443ep1 parameters requires only 210,827 cycles, which sets a new speed record for the arithmetic component of a lattice-based cryptosystem on an 8-bit microcontroller. [less ▲]Detailed reference viewed: 217 (34 UL) A Critical Security Analysis of the Password-Based Authentication Honeywords System Under Code-Corruption AttackGenç, Ziya Alper ; Lenzini, Gabriele ; Ryan, Peter et alin Information Systems Security and Privacy (2019, July)Password-based authentication is a widespread method to access into systems, thus password files are a valuable resource often target of attacks. To detect when a password file has been stolen, Juels and ... [more ▼]Password-based authentication is a widespread method to access into systems, thus password files are a valuable resource often target of attacks. To detect when a password file has been stolen, Juels and Rivest introduced the Honeywords System in 2013. The core idea is to store the password with a list of decoy words that are indistinguishable'' from the password, called honeywords. An adversary that obtains the password file and, by dictionary attack, retrieves the honeywords can only guess the password when attempting to log in: but any incorrect guess will set off an alarm, warning that file has been compromised. In a recent conference paper, we studied the security of the Honeywords System in a scenario where the intruder also manages to corrupt the server's code (with certain limiting assumptions); we proposed an authentication protocol and proved it secure despite the corruption. In this extended journal version, we detail the analysis and we extend it, under the same attacker model, to the other two protocols of the original Honeywords System, the setup and change of password. We formally verify the security of both of them; further, we discuss that our design suggests a completely new approach that diverges from the original idea of the Honeywords System but indicates an alternative way to authenticate users which is robust to server's code-corruption. [less ▲]Detailed reference viewed: 217 (9 UL) Security – Visible, Yet Unseen? How Displaying Security Mechanisms Impacts User Experience and Perceived SecurityDistler, Verena ; Zollinger, Marie-Laure ; Lallemand, Carine et alin Proceedings of ACM CHI Conference on Human Factors in Computing Systems (CHI2019) (2019, April)An unsolved debate in the field of usable security concerns whether security mechanisms should be visible, or blackboxed away from the user for the sake of usability. However, tying this question to ... [more ▼]An unsolved debate in the field of usable security concerns whether security mechanisms should be visible, or blackboxed away from the user for the sake of usability. However, tying this question to pragmatic usability factors only might be simplistic. This study aims at researching the impact of displaying security mechanisms on user experience (UX) in the context of e-voting. Two versions of an e-voting application were designed and tested using a between-group experimental protocol (N=38). Version D displayed security mechanisms, while version ND did not reveal any security-related information. We collected data on UX using standardised evaluation scales and semi-structured interviews. Version D performed better overall in terms of UX and need fulfilment. Qualitative analysis of the interviews gives further insights into factors impacting perceived security. Our study adds to existing research suggesting a conceptual shift from usability to UX and discusses implications for designing and evaluating secure systems. [less ▲]Detailed reference viewed: 556 (62 UL) How to Assess the Usability Metrics of E-Voting SchemesMarky, Karola; Zollinger, Marie-Laure ; Funk, Markus et alin Lecture Notes in Computer Science (2019, February)Detailed reference viewed: 169 (21 UL) NoCry: No More Secure Encryption Keys for Cryptographic RansomwareGenç, Ziya Alper ; Lenzini, Gabriele ; Ryan, Peter in Proceedings of the Second International Workshop on Emerging Technologies for Authorization and Authentication (2019)Since the appearance of ransomware in the cyber crime scene, researchers and anti-malware companies have been offering solutions to mitigate the threat. Anti-malware solutions differ on the specific ... [more ▼]Since the appearance of ransomware in the cyber crime scene, researchers and anti-malware companies have been offering solutions to mitigate the threat. Anti-malware solutions differ on the specific strategy they implement, and all have pros and cons. However, three requirements concern them all: their implementation must be secure, be effective, and be efficient. Recently, Genç et al. proposed to stop a specific class of ransomware, the cryptographically strong one, by blocking unauthorized calls to cryptographically secure pseudo-random number generators, which are required to build strong encryption keys. Here, in adherence to the requirements, we discuss an implementation of that solution that is more secure (with components that are not vulnerable to known attacks), more effective (with less false negatives in the class of ransomware addressed) and more efficient (with minimal false positive rate and negligible overhead) than the original, bringing its security and technological readiness to a higher level. [less ▲]Detailed reference viewed: 199 (10 UL) An offline dictionary attack against zkPAKE protocolLopez Becerra, José Miguel ; Ryan, Peter ; Sala, Petra et alin An offline dictionary attack against zkPAKE protocol (2019)Password Authenticated Key Exchange (PAKE) allows a user to establish a secure cryptographic key with a server, using only knowledge of a pre-shared password. One of the basic security require- ments of ... [more ▼]Password Authenticated Key Exchange (PAKE) allows a user to establish a secure cryptographic key with a server, using only knowledge of a pre-shared password. One of the basic security require- ments of PAKE is to prevent o ine dictionary attacks. In this paper, we revisit zkPAKE, an augmented PAKE that has been recently proposed by Mochetti, Resende, and Aranha (SBSeg 2015). Our work shows that the zkPAKE protocol is prone to o ine password guess- ing attack, even in the presence of an adversary that has only eavesdrop- ping capabilities. Results of performance evaluation show that our attack is practical and e cient.Therefore, zkPAKE is insecure and should not be used as a password-authenticated key exchange mechanism. [less ▲]Detailed reference viewed: 208 (15 UL) Risk-Limiting TalliesJamroga, Wojciech ; Roenne, Peter ; Ryan, Peter et alin Electronic Voting: Proceedings of E-Vote-ID (2019)Detailed reference viewed: 53 (5 UL) Novel Collaborative Filtering Recommender Friendly to Privacy ProtectionWang, Jun; Tang, Qiang; Delerue Arriaga, Afonso et alin International Joint Conference on Artificial Intelligence (IJCAI 2019), Macao 10-16 August 2019 (2019)Nowadays, recommender system is an indispensable tool in many information services, and a large number of algorithms have been designed and implemented. However, fed with very large datasets, state-of-the ... [more ▼]Nowadays, recommender system is an indispensable tool in many information services, and a large number of algorithms have been designed and implemented. However, fed with very large datasets, state-of-the-art recommendation algorithms often face an efficiency bottleneck, i.e., it takes huge amount of computing resources to train a recommendation model. In order to satisfy the needs of privacy-savvy users who do not want to disclose their information to the service provider, the complexity of most existing solutions becomes prohibitive. As such, it is an interesting research question to design simple and efficient recommendation algorithms that achieve reasonable accuracy and facilitate privacy protection at the same time. In this paper, we propose an efficient recommendation algorithm, named CryptoRec, which has two nice properties: (1) can estimate a new user's preferences by directly using a model pre-learned from an expert dataset, and the new user's data is not required to train the model; (2) can compute recommendations with only addition and multiplication operations. As to the evaluation, we first test the recommendation accuracy on three real-world datasets and show that CryptoRec is competitive with state-of-the-art recommenders. Then, we evaluate the performance of the privacy-preserving variants of CryptoRec and show that predictions can be computed in seconds on a PC. In contrast, existing solutions will need tens or hundreds of hours on more powerful computers. [less ▲]Detailed reference viewed: 34 (3 UL) HoneyPAKEsLopez Becerra, José Miguel ; Roenne, Peter ; Ryan, Peter et alin Security Protocols XXVI: Lecture Notes in Computer Science (2018, November 27)We combine two security mechanisms: using a Password-based Authenticated Key Establishment (PAKE) protocol to protect the password for access control and the Honeywords construction of Juels and Rivest to ... [more ▼]We combine two security mechanisms: using a Password-based Authenticated Key Establishment (PAKE) protocol to protect the password for access control and the Honeywords construction of Juels and Rivest to detect loss of password files. The resulting construction combines the properties of both mechanisms: ensuring that the password is intrinsically protected by the PAKE protocol during transmission and the Honeywords mechanisms for detecting attempts to exploit a compromised password file. Our constructions lead very naturally to two factor type protocols. An enhanced version of our protocol further provides protection against a compromised login server by ensuring that it does not learn the index to the true password. [less ▲]Detailed reference viewed: 141 (14 UL) Revisiting Deniability in Quantum Key Exchange via Covert Communication and Entanglement DistillationAtashpendar, Arash ; Policharla, Guru Vamsi; Roenne, Peter et alin Secure IT Systems, 23rd Nordic Conference, NordSec 2018. Lecture Notes in Computer Science, vol 11252. Springer, Cham (2018, November 02)We revisit the notion of deniability in quantum key exchange (QKE), a topic that remains largely unexplored. In the only work on this subject by Donald Beaver, it is argued that QKE is not necessarily ... [more ▼]We revisit the notion of deniability in quantum key exchange (QKE), a topic that remains largely unexplored. In the only work on this subject by Donald Beaver, it is argued that QKE is not necessarily deniable due to an eavesdropping attack that limits key equivocation. We provide more insight into the nature of this attack and how it extends to other constructions such as QKE obtained from uncloneable encryption. We then adopt the framework for quantum authenticated key exchange, developed by Mosca et al., and extend it to introduce the notion of coercer-deniable QKE, formalized in terms of the indistinguishability of real and fake coercer views. Next, we apply results from a recent work by Arrazola and Scarani on covert quantum communication to establish a connection between covert QKE and deniability. We propose DC-QKE, a simple deniable covert QKE protocol, and prove its deniability via a reduction to the security of covert QKE. Finally, we consider how entanglement distillation can be used to enable information-theoretically deniable protocols for QKE and tasks beyond key exchange. [less ▲]Detailed reference viewed: 230 (56 UL) Electryo, In-person Voting with Transparent Voter Verifiability and Eligibility VerifiabilityRoenne, Peter ; Ryan, Peter ; Zollinger, Marie-Laure E-print/Working paper (2018)Selene is an e-voting protocol that allows voters to directly check their individual vote, in cleartext, in the final tally via a tracker system, while providing good coercion mitigation. This is in ... [more ▼]Selene is an e-voting protocol that allows voters to directly check their individual vote, in cleartext, in the final tally via a tracker system, while providing good coercion mitigation. This is in contrast to conventional, end-to-end verifiable schemes in which the voter verifies the presence of an encryption of her vote on the bulletin board. The Selene mechanism can be applied to many e-voting schemes, but here we present an application to the polling station context, resulting in a voter-verifiable electronic tally with a paper audit trail. The system uses a smartcard-based public key system to provide the individual verifica- tion and universal eligibility verifiability. The paper record contains an encrypted link to the voter’s identity, requiring stronger assumptions on ballot privacy than normal paper voting, but with the benefit of pro- viding good auditability and dispute resolution as well as supporting (comparison) risk limiting audits. [less ▲]Detailed reference viewed: 193 (15 UL) Facilitating Privacy-preserving Recommendation-as-a-Service with Machine LearningWang, Jun ; Delerue Arriaga, Afonso ; Tang, Qiang et alPoster (2018, October)Machine-Learning-as-a-Service has become increasingly popular, with Recommendation-as-a-Service as one of the representative examples. In such services, providing privacy protection for users is an ... [more ▼]Machine-Learning-as-a-Service has become increasingly popular, with Recommendation-as-a-Service as one of the representative examples. In such services, providing privacy protection for users is an important topic. Reviewing privacy-preserving solutions which were proposed in the past decade, privacy and machine learning are often seen as two competing goals at stake. Though improving cryptographic primitives (e.g., secure multi-party computation (SMC) or homomorphic encryption (HE)) or devising sophisticated secure protocols has made a remarkable achievement, but in conjunction with state-of-the-art recommender systems often yields far-from-practical solutions. We tackle this problem from the direction of machine learning. We aim to design crypto-friendly recommendation algorithms, thus to obtain efficient solutions by directly using existing cryptographic tools. In particular, we propose an HE-friendly recommender system, refer to as CryptoRec, which (1) decouples user features from latent feature space, avoiding training the recommendation model on encrypted data; (2) only relies on addition and multiplication operations, making the model straightforwardly compatible with HE schemes. The properties turn recommendation-computations into a simple matrix-multiplication operation. To further improve efficiency, we introduce a sparse-quantization-reuse method which reduces the recommendation-computation time by $9\times$ (compared to using CryptoRec directly), without compromising the accuracy. We demonstrate the efficiency and accuracy of CryptoRec on three real-world datasets. CryptoRec allows a server to estimate a user's preferences on thousands of items within a few seconds on a single PC, with the user's data homomorphically encrypted, while its prediction accuracy is still competitive with state-of-the-art recommender systems computing over clear data. Our solution enables Recommendation-as-a-Service on large datasets in a nearly real-time (seconds) level. [less ▲]Detailed reference viewed: 183 (6 UL) A Proof of Entropy Minimization for Outputs in Deletion Channels via Hidden Word StatisticsAtashpendar, Arash ; Mestel, David ; Roscoe, A.W. (Bill) et alE-print/Working paper (2018)From the output produced by a memoryless deletion channel from a uniformly random input of known length n, one obtains a posterior distribution on the channel input. The difference between the Shannon ... [more ▼]From the output produced by a memoryless deletion channel from a uniformly random input of known length n, one obtains a posterior distribution on the channel input. The difference between the Shannon entropy of this distribution and that of the uniform prior measures the amount of information about the channel input which is conveyed by the output of length m, and it is natural to ask for which outputs this is extremized. This question was posed in a previous work, where it was conjectured on the basis of experimental data that the entropy of the posterior is minimized and maximized by the constant strings 𝟶𝟶𝟶… and 𝟷𝟷𝟷… and the alternating strings 𝟶𝟷𝟶𝟷… and 𝟷𝟶𝟷𝟶… respectively. In the present work we confirm the minimization conjecture in the asymptotic limit using results from hidden word statistics. We show how the analytic-combinatorial methods of Flajolet, Szpankowski and Vall\'ee for dealing with the hidden pattern matching problem can be applied to resolve the case of fixed output length and n→∞, by obtaining estimates for the entropy in terms of the moments of the posterior distribution and establishing its minimization via a measure of autocorrelation. [less ▲]Detailed reference viewed: 183 (45 UL) An Offline Dictionary Attack Against zkPAKE ProtocolLopez Becerra, José Miguel ; Ryan, Peter ; Sala, Petra et alPoster (2018, June)Password Authenticated Key Exchange (PAKE) allows a user to establish a strong cryptographic key with a server, using only knowledge of a pre-shared password. One of the basic security requirements of ... [more ▼]Password Authenticated Key Exchange (PAKE) allows a user to establish a strong cryptographic key with a server, using only knowledge of a pre-shared password. One of the basic security requirements of PAKE is to prevent o ine dictionary attacks. In this paper, we revisit zkPAKE, an augmented PAKE that has been recently proposed by Mochetti, Resende, and Aranha (SBSeg 2015). Our work shows that the zkPAKE protocol is prone to o ine password guessing attack, even in the presence of an adversary that has only eavesdropping capabilities. Therefore, zkPAKE is insecure and should not be used as a password-authenticated key exchange mechanism [less ▲]Detailed reference viewed: 171 (15 UL) Cholesteric Liquid Crystal Shells as Enabling Material for Information-Rich Design and Architecture.Schwartz, Mathew; Lenzini, Gabriele ; Geng, Yong et alin Advanced Materials (2018)The responsive and dynamic character of liquid crystals (LCs), arising from their ability to self-organize into long-range ordered structures while maintaining fluidity, has given them a role as key ... [more ▼]The responsive and dynamic character of liquid crystals (LCs), arising from their ability to self-organize into long-range ordered structures while maintaining fluidity, has given them a role as key enabling materials in the information technology that surrounds us today. Ongoing research hints at future LC-based technologies of entirely different types, for instance by taking advantage of the peculiar behavior of cholesteric liquid crystals (CLCs) subject to curvature. Spherical shells of CLC reflect light omnidirectionally with specific polarization and wavelength, tunable from the UV to the infrared (IR) range, with complex patterns arising when many of them are brought together. Here, these properties are analyzed and explained, and future application opportunities from an inter- disciplinary standpoint are discussed. By incorporating arrangements of CLC shells in smart facades or vehicle coatings, or in objects of high value subject to counterfeiting, game-changing future uses might arise in fields spanning infor- mation security, design, and architecture. The focus here is on the challenges of a digitized and information-rich future society where humans increasingly rely on technology and share their space with autonomous vehicles, drones, and robots. [less ▲]Detailed reference viewed: 347 (14 UL) From Clustering Supersequences to Entropy Minimizing Subsequences for Single and Double DeletionsAtashpendar, Arash ; Beunardeau, Marc; Connolly, Aisling et alE-print/Working paper (2018)A binary string transmitted via a memoryless i.i.d. deletion channel is received as a subsequence of the original input. From this, one obtains a posterior distribution on the channel input, corresponding ... [more ▼]A binary string transmitted via a memoryless i.i.d. deletion channel is received as a subsequence of the original input. From this, one obtains a posterior distribution on the channel input, corresponding to a set of candidate supersequences weighted by the number of times the received subsequence can be embedded in them. In a previous work it is conjectured on the basis of experimental data that the entropy of the posterior is minimized and maximized by the constant and the alternating strings, respectively. In this work, in addition to revisiting the entropy minimization conjecture, we also address several related combinatorial problems. We present an algorithm for counting the number of subsequence embeddings using a run-length encoding of strings. We then describe methods for clustering the space of supersequences such that the cardinality of the resulting sets depends only on the length of the received subsequence and its Hamming weight, but not its exact form. Then, we consider supersequences that contain a single embedding of a fixed subsequence, referred to as singletons, and provide a closed form expression for enumerating them using the same run-length encoding. We prove an analogous result for the minimization and maximization of the number of singletons, by the alternating and the uniform strings, respectively. Next, we prove the original minimal entropy conjecture for the special cases of single and double deletions using similar clustering techniques and the same run-length encoding, which allow us to characterize the distribution of the number of subsequence embeddings in the space of compatible supersequences to demonstrate the effect of an entropy decreasing operation. [less ▲]Detailed reference viewed: 162 (42 UL) A Security Analysis, and a Fix, of a Code-Corrupted Honeywords SystemGenç, Ziya Alper ; Lenzini, Gabriele ; Ryan, Peter et alin Proceedings of the 4th International Conference on Information Systems Security and Privacy (2018)In 2013 Juels and Rivest introduced the Honeywords System, a password-based authentication system designed to detect when a password file has been stolen. A Honeywords System stores passwords together ... [more ▼]In 2013 Juels and Rivest introduced the Honeywords System, a password-based authentication system designed to detect when a password file has been stolen. A Honeywords System stores passwords together with indistinguishable decoy words so when an intruder steals the file, retrieves the words, and tries to log-in, he does not know which one is the password. By guessing one from the decoy words, he may not be lucky and reveal the leak. Juels and Rivest left a problem open: how to make the system secure even when the intruder corrupted the login server’s code. In this paper we study and solve the problem. However, since “code corruption” is a powerful attack, we first define rigorously the threat and set a few assumptions under which the problem is still solvable, before showing meaningful attacks against the original Honeywords System. Then we elicit a fundamental security requirement, implementing which, we are able to restore the honeywords System’s security despite a corrupted login service. We verify the new protocol’s security formally, using ProVerif for this task. We also implement the protocol and test its performance. Finally, at the light of our findings, we discuss whether it is still worth using a fixed honeywords-based system against such a powerful threat, or whether it is better, in order to be resilient against code corruption attacks, to design afresh a completely different password-based authentication solution. [less ▲]Detailed reference viewed: 445 (53 UL) Next Generation Cryptographic RansomwareGenç, Ziya Alper ; Lenzini, Gabriele ; Ryan, Peter in Proceedings of the Secure IT Systems (2018)We are assisting at an evolution in the ecosystem of cryptoware - the malware that encrypts files and makes them unavailable unless the victim pays up. New variants are taking the place once dominated by ... [more ▼]We are assisting at an evolution in the ecosystem of cryptoware - the malware that encrypts files and makes them unavailable unless the victim pays up. New variants are taking the place once dominated by older versions; incident reports suggest that forthcoming ransomware will be more sophisticated, disruptive, and targeted. Can we anticipate how such future generations of ransomware will work in order to start planning on how to stop them? We argue that among them there will be some which will try to defeat current anti-ransomware; thus, we can speculate over their working principle by studying the weak points in the strategies that seven of the most advanced anti-ransomware are currently implementing. We support our speculations with experiments, proving at the same time that those weak points are in fact vulnerabilities and that the future ransomware that we have imagined can be effective. [less ▲]Detailed reference viewed: 337 (13 UL) No Random, No Ransom: A Key to Stop Cryptographic RansomwareGenç, Ziya Alper ; Lenzini, Gabriele ; Ryan, Peter in Proceedings of the 15th Conference on Detection of Intrusions and Malware, and Vulnerability Assessment (2018)To be effective, ransomware has to implement strong encryption, and strong encryption in turn requires a good source of random numbers. Without access to true randomness, ransomware relies on the pseudo ... [more ▼]To be effective, ransomware has to implement strong encryption, and strong encryption in turn requires a good source of random numbers. Without access to true randomness, ransomware relies on the pseudo random number generators that modern Operating Systems make available to applications. With this insight, we propose a strategy to mitigate ransomware attacks that considers pseudo random number generator functions as critical resources, controls accesses on their APIs and stops unauthorized applications that call them. Our strategy, tested against 524 active real-world ransomware samples, stops 94% of them, including WannaCry, Locky, CryptoLocker and CryptoWall. Remarkably, it also nullifies NotPetya, the latest offspring of the family which so far has eluded all defenses. [less ▲]Detailed reference viewed: 626 (28 UL)   1 2 3 4 5