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29 June 2021
Gaëtan Cassiers, Sebastian Faust, Maximilian Orlt, François-Xavier Standaert
Zichen Gui, Kenneth G. Paterson, Sikhar Patranabis
We present the first leakage-abuse attacks that achieve practically efficient and highly scalable query reconstruction against state-of-the-art STE schemes with perturbed leakage profiles while relying only no noisy co-occurrence pattern leakage and without making strong assumptions on the auxiliary information available to the adversary. Our attacks subvert the query privacy guarantees of STE schemes with differentially private access patterns (Chen et al., INFOCOM'18) and STE schemes built in a naturally efficient manner from volume-hiding encrypted multi-maps (Kamara and Moataz, Eurocrypt'19 and Patel et al., CCS'19).
Many existing leakage-abuse attacks only work in a strong known-data model where the auxiliary information available to the adversary is either an exact replica of or a "noise-free" subset of the target database. Our attacks are the first to work in a weaker and more realistic inference model where the auxiliary information available to the adversary is sampled independently from but statistically close to the target database. Compared to (a handful of) existing inference attacks, our attacks make significantly relaxed assumptions about the nature of auxiliary information available to the adversary.
Technically, our attacks exploit insufficiencies in existing leakage-perturbation techniques as well as novel observations surrounding inevitable system-wide leakage from efficient realizations of STE. We model the attacks as optimization problems with carefully designed objective functions that are maximized via simulated annealing. We demonstrate the practical effectiveness of our attacks via extensive experimentation over real-world databases. Our attacks achieve up to 90% query reconstruction against STE implementations using recommended security parameters, with 5x greater scalability than any existing attack exploiting access pattern leakage.
Yuan Yao, Pantea Kiaei, Richa Singh, Shahin Tajik, Patrick Schaumont
Aritra Banerjee
Onur Gunlu, Joerg Kliewer, Rafael F. Schaefer, Vladimir Sidorenko
Sara Stadler, Vitor Sakaguti, Harjot Kaur, Anna Lena Fehlhaber
Bo-Yeon Sim, Aesun Park, Dong-Guk Han
Yanqi Gu, Stanislaw Jarecki, Hugo Krawczyk
In addition to resilience to OPRF compromise, a DH-based implementation of KHAPE (using HMQV) offers the best performance among aPAKE protocols in terms of exponentiations with less than the cost of an exponentiation on top of an UNauthenticated Diffie-Hellman exchange. KHAPE uses three messages if the server initiates the exchange or four when the client does (one more than OPAQUE in the latter case).
All results in the paper are proven within the UC framework in the ideal cipher model. Of independent interest is our treatment of key-hiding AKE which KHAPE uses as a main component as well as our UC proofs of AKE security for protocols 3DH (a basis of Signal), HMQV and SKEME, that we use as efficient instantiations of KHAPE.
David Chaum, Mario Larangeira, Mario Yaksetig, William Carter
Our main motivation is that in case of leakage of the secret key, established techniques based on zero-knowledge proofs of knowledge are void since the key becomes public. On the other hand, the ``back up key'', which is secret, can be used to generate a ``proof of ownership'', i.e., only the real owner of this secret key can generate such a proof. To the best of our knowledge, this extra level of security is novel, and could have already been used in practice, if available, in digital wallets for cryptocurrencies that suffered massive leakage of account private keys. In this work, we formalize the notion of ``Proof of Ownership'' and ``Fallback'' as new properties. Then, we introduce our construction, which is compatible with major designs for wallets based on ECDSA, and adds a $\mbox{W-OTS}^{+}$ signing key as a ``back up key''. Thus offering a quantum secure fallback. This design allows the hiding of any quantum secure signature key pair, and is not exclusive to $\mbox{W-OTS}^{+}$. Finally, we briefly discuss the construction of multiple generations of proofs of ownership.
Vipul Goyal, Yifan Song, Akshayaram Srinivasan
We introduce a new primitive called as Traceable Secret Sharing to tackle this problem. In particular, a traceable secret sharing scheme guarantees that a cheating server always runs the risk of getting traced and prosecuted by providing a valid evidence (which can be examined in a court of law) implicating its dishonest behavior. We explore various definitional aspects and show how they are highly non-trivial to construct (even ignoring efficiency aspects). We then give an efficient construction of traceable secret sharing assuming the existence of a secure two-party computation protocol. We also show an application of this primitive in constructing traceable protocols for multi-server delegation of computation.
28 June 2021
NXP Semiconductors
Closing date for applications:
Contact: Ulrich Althen
More information: https://nxp.wd3.myworkdayjobs.com/careers/job/Gratkorn/Principal-Cryptographer--m-f-d-_R-10028227
Nanjing City, China, 17 December - 19 December 2021
Submission deadline: 8 August 2021
Notification: 12 September 2021
University of Surrey
The Department of Computer Science at the University of Surrey is seeking to appoint two Lecturers / Senior Lecturers in Cyber Security to strengthen its research within the Surrey Centre for Cyber Security (SCCS) and to support the Department’s ambitious strategic growth in this area. The appointments are on a full-time and permanent basis.
Of particular interest are the following research areas: applied cryptography, privacy enhancing technologies (incl. anonymisation, secure multi-party computation, computing on encrypted data), software security (e.g., malware analysis), system security (incl., security of autonomous or cyber-physical systems), security architectures (incl., trusted computing, TEEs), security protocols for blockchain and/or machine learning, or tool-assisted formal verification of security and privacy.
The Department of Computer Science has a world-class reputation in cyber security and regularly publishes at top-tier conferences and journals. The Department is home to Surrey Centre for Cyber Security (SCCS) and Surrey is only one of four institutions in the UK holding recognition from the National Cyber Security Centre as an Academic Centre of Excellence in both Cyber Security Research and in Cyber Security Education (Gold).
SCCS maintains close links with leading industries, the public sector and governmental bodies, leading to a strong heritage of real-world impact. The Department has made significant investment in its facilities with a new 200-seater computer science teaching laboratory, a virtual cloud computing platform, a secure systems facility and an HPC cluster for research.
We are interested in outstanding candidates with a strong record of publications in top-tier cyber security venues and, in particular for the Senior Lecturer post, with an established network of international collaborators from academia and/or industry and experience in attracting sustainable research funding.
Closing date for applications:
Contact:
Head of Department: Dr Mark Manulis (m.manulis@surrey.ac.uk).
Director of SCCS: Prof Steve Schneider (s.schneider@surrey.ac.uk)
More information: https://jobs.surrey.ac.uk/vacancy.aspx?ref=027721
Institute for Infocomm Research, Singapore
Closing date for applications:
Contact: Singee
More information: https://careers.a-star.edu.sg/jobdetails.aspx?ID=4147
24 June 2021
Jan Ferdinand Sauer, Alan Szepieniec
Panagiotis Chatzigiannis, Foteini Baldimtsi
Nicolai Müller, Thorben Moos, Amir Moradi
Cécile Delerablée, Lénaïck Gouriou, David Pointcheval
To this aim, we define a new primitive with switchable attributes, in both the ciphertexts and the keys, and new indistinguishability properties. We then provide concrete and efficient instantiations with adaptive security under the sole SXDH assumption in the standard model.
Balthazar Bauer, Georg Fuchsbauer, Antoine Plouviez
Despite its wide use, surprisingly, OMDL is lacking any rigorous analysis; there is not even a proof that it holds in the generic group model (GGM). (We show that a claimed proof is flawed.) In this work we give a formal proof of OMDL in the GGM. We also prove a related assumption, the one-more computational Diffie-Hellman assumption, in the GGM. Our proofs deviate from prior proofs in the GGM and replace the use of the Schwartz-Zippel Lemma by a new argument.
Iggy van Hoof, Elena Kirshanova, Alexander May
In this work we consider quantum combinatorial attacks on ternary LWE. Our algorithms are based on the quantum walk framework of Magniez-Nayak-Roland-Santha. At the heart of our algorithms is a combinatorial tool called the representation technique that appears in algorithms for the subset sum problem. This technique can also be applied to ternary LWE resulting in faster attacks. The focus of this work is quantum speed-ups for such representation-based attacks on LWE.
When expressed in terms of the search space $\mathcal{S}$ for LWE keys, the asymptotic complexity of the representation attack drops from $\mathcal{S}^{0.24}$ (classical) down to $\mathcal{S}^{0.19}$ (quantum). This translates into noticeable attack's speed-ups for concrete NTRU instantiations like NTRU-HRSS and NTRU Prime. Our algorithms do not undermine current security claims for NTRU or other ternary LWE based schemes, yet they can lay ground for improvements of the combinatorial subroutines inside hybrid attacks on LWE.