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12 October 2021

University of Connecticut, Computer Science and Engineering Dept.
Job Posting
Several PhD student openings in the domains of cryptography, computer security, privacy, and blockchain-based systems, are available at the University of Connecticut (UConn), CSE dept., led by Prof. Ghada Almashaqbeh. Start date can be as early as Spring 2022 or later for Fall 2022.

The positions provide a great opportunity for students with interest in interdisciplinary projects that combine knowledge from various fields towards the design of secure systems and protocols. We target real-world timely problems and aim to provide secure and practical solutions backed by rigorous foundations and efficient implementations/thorough performance testing. We are also interested in conceptual projects that contribute in bridging the gap between theory and practice of Cryptography.

Closing date for applications:

Campus George Charpak Provence, Mines Saint Etienne, Gardanne, France
Job Posting
Job role: One year-Post-doctoral position as a product Security Engineer

Department:
R&D – Product Security Location / Working place Meyreuil, France
SAS Campus George Charpak Provence, Gardanne, France

Mission:
Participate in security certifications: hardware and software platforms
Porting post-quantum cryptographic libraries to Wisekey’s components
Implement side channel / deep learning attacks in Wisekey’s security lab
Maintain Wisekey’s attack benches

Main responsabilities:
Standardization follow-up on post-quantum algorithms
Implement an attack bench on component using post-quantum cryptographic libraries
Keep abreast of new attacks (conferences, fairs, scientific articles)

Requirements:
Educational background / diplomas: PhD
Skills: Cryptography, Safety of embedded systems, Security certifications (CC, EMVCo, FIPS), Development on embedded systems
Starting date: ASAP
To apply please send your CV, a cover letter, and contact information of 2 references

Closing date for applications:

Jean-Pierre Enguent (VP-R&D Wisekey), jpenguent@WISEKEY.COM

CryptoLux Group, University of Luxembourg
Job Posting
The University of Luxembourg invites applications from M.Sc. holders in the general area of applied cryptography. Cryptolux.org is a team of cryptographers and security researchers interested in applied cryptography, cryptanalysis, privacy, network security, cryptographic blockchains and is led by Prof. Alex Biryukov. We are affiliated to the Department of Computer Science (DCS) and to the interdisciplinary Security and Trust center (SnT).

Area (potential topics of the thesis)

• Cryptanalysis and design of cryptographic primitives, ex. Lightweight block ciphers, hash functions, authenticated encryption schemes
• Privacy Enhancing Technology (Tor-like networks, privacy for cryptocurrencies)
• Cryptography for blockchains
• White-box cryptography
The University offers a Ph.D. study program with an initial contract of 36 months, with a further possible 1-year extension if required. The University offers highly competitive salaries and is an equal opportunity employer. You will work in one of the most international universities in the world and will participate in the development of a large information security research center.

Starting date 1-Jan-2022 or later upon agreement. Early submission is encouraged; applications will be processed upon receipt.

Closing date for applications:

Contact: Prof. Alex Biryukov

Thomas Attema, Serge Fehr, Michael Klooß
ePrint Report
The celebrated Fiat-Shamir transformation turns any public-coin interactive proof into an non-interactive one, which inherits the main security properties (in the random oracle model) of the interactive version. While originally considered in the context of 3-move public-coin interactive proofs, i.e., so-called $\Sigma$-protocols, it is now applied to multi-round protocols as well. Unfortunately, the security loss for a $(2\mu + 1)$-move protocol is, in general, $Q^\mu$, where $Q$ is the number of oracle queries performed by the attacker. In general, this is the best one can hope for, as it is easy to see that this loss applies to the $\mu$-fold sequential repetition of $\Sigma$-protocols, but it raises the question whether certain (natural) classes of interactive proofs feature a milder security loss.

In this work, we give positive and negative results on this question. On the positive side, we show that for $(k_1, \ldots, k_\mu)$-special-sound protocols (which cover a broad class of use cases), the knowledge error degrades linearly in $Q$ (instead of $Q^\mu$). On the negative side, we show that for $t$-fold parallel repetitions of typical $(k_1, \ldots, k_\mu)$-special-sound protocols, there is an attack which results in a security loss of about $(Q/\mu)^\mu \mu^{-t}$, assuming for simplicity that $t$ is an integer multiple of $\mu$.
Ivan Damgård, Daniel Escudero, Antigoni Polychroniadou
ePrint Report
We consider the task of designing secure computation protocols in an unstable network where honest parties can drop out at any time, according to a schedule provided by the adversary. This type of setting, where even honest parties are prone to failures, is more realistic than traditional models, and has therefore gained a lot of attention recently. Unlike previous works in the literature, we allow parties to return to the computation according to an adversarially chosen schedule and, moreover, we do not assume that these parties receive the messages that were sent to them while being offline. However, we do assume an upper bound on the number of rounds that an honest party can be off-line---otherwise protocols in this setting cannot guarantee termination within a bounded number of rounds.

We study the settings of perfect, statistical and computational security and design MPC protocols in each of these scenarios. We assume that the intersection of online-and-honest parties from one round to the next is at least $2t+1$, $t+1$ and $1$ respectively, where $t$ is the number of (actively) corrupt parties. We show the intersection requirements to be optimal. Our (positive) results are obtained in a way that may be of independent interest: we implement a traditional stable network on top of the unstable one, which allows us to plug in \textit{any} MPC protocol on top. This approach adds a necessary overhead to the round count of the protocols, which is related to the maximal number of rounds an honest party can be offline. We also present a novel, perfectly secure MPC protocol that avoids this overhead by following a more direct'' approach rather than building a stable network on top. We introduce our network model in the UC-framework and prove the security of our protocols within this setting.
Elizabeth Crites, Chelsea Komlo, Mary Maller
ePrint Report
In this paper, we present new techniques for proving the security of multi- and threshold signature schemes under discrete logarithm assumptions in the random oracle model. The purpose is to provide a simple framework for analyzing the relatively complex interactions of these schemes in a concurrent model, thereby reducing the risk of attacks. We make use of proofs of possession and prove that a Schnorr signature suffices as a proof of possession in the algebraic group model without any tightness loss. We introduce and prove the security of a simple, three-round multisignature $\mathsf{SimpleMuSig}$.

Using our new techniques, we prove the concurrent security of a variant of the $\mathsf{MuSig2}$ multisignature scheme that includes proofs of possession as well as the $\mathsf{FROST}$ threshold signature scheme. These are currently the most efficient schemes in the literature for generating Schnorr signatures in a multiparty setting. Our variant of $\mathsf{MuSig2}$, which we call $\mathsf{SpeedyMuSig}$, has faster key aggregation due to the proofs of possession.
Marcel Nageler, Christoph Dobraunig, Maria Eichlseder
ePrint Report
Differential fault analysis (DFA) is a very powerful attack vector on implementations of symmetric cryptography. Most countermeasures are applied at the implementation level. At ASIACRYPT 2021, Baksi et al. proposed a design strategy that aims to provide inherent cipher level resistance against DFA by using S-boxes with linear structures. They argue that in their instantiation, the block cipher DEFAULT, a DFA adversary can learn at most 64 of the 128 key bits, so the remaining brute-force complexity of $2^{64}$ is impractical.

In this paper, we show that a DFA adversary can combine information across rounds to recover the full key, invalidating their security claim. In particular, we observe that such ciphers exhibit large classes of equivalent keys that can be represented efficiently in normalized form using linear equations. We exploit this in combination with the specifics of DEFAULT's strong key schedule to recover the key using less than 100 faulty computation and negligible time complexity. Moreover, we show that even an idealized version of DEFAULT with independent round keys is vulnerable to our information-combining attacks based on normalized keys.
ePrint Report
We present a new OT-based two-party multiplication protocol that is almost as efficient as Gilboa's semi-honest protocol (Crypto '99), but has a high-level of security against malicious adversaries without further compilation. The achieved security suffices for many applications, and, assuming DDH, can be cheaply compiled into full security.
Eugene Frimpong, Reyhaneh Rabbaninejad, Antonis Michalas
ePrint Report
Drone-based applications continue to garner a lot of attention due to their significant potential in both commercial and non-commercial use. Owing to this increasing popularity, researchers have begun to pay attention to the communication security requirements involved in deploying drone-based applications and services on a large scale, with particular emphasis on group communication. The majority of existing works in this field focus on the use of symmetric key cryptographic schemes or group key agreement schemes. However, in this paper, we propose a pairing-free certificateless group authenticated key distribution protocol for drone-based applications which takes into consideration drones with varying computational resources. The proposed scheme ensures key freshness, group key secrecy, forward secrecy, and backward secrecy while ensuring that the scheme is lightweight enough to be implemented on very resource-constrained drones or smart devices. We extensively prove the security of our scheme and demonstrate its real-world applicability by evaluating its performance on three different kinds of drone boards (UP Xtreme i7 board, SamL11-Xpro board, and a Zolertia Re-mote Revb board).
Kyoichi Asano, Keita Emura, Atsushi Takayasu, Yohei Watanabe
ePrint Report
Attribute-based encryption with equality test ($\mathsf{ABEET}$) is an extension of the ordinary attribute-based encryption ($\mathsf{ABE}$), where trapdoors enable us to check whether two ciphertexts are encryptions of the same message. Thus far, several CCA-secure $\mathsf{ABEET}$ schemes have been proposed for monotone span programs satisfying selective security under $q$-type assumptions. In this paper, we propose a generic construction of CCA-secure $\mathsf{ABEET}$ from delegatable $\mathsf{ABE}$. Specifically, our construction is an attribute-based extension of Lee et al.'s generic construction of identity-based encryption with equality test from hierarchical identity-based encryption. Even as far as we know, there are various delegatable $\mathsf{ABE}$ schemes. Therefore, we obtain various $\mathsf{ABEET}$ schemes with new properties that have not been achieved before such as various predicates, adaptive security, standard assumptions, compact ciphertexts/secret keys, and lattice-based constructions.
Dimitris Mouris, Nektarios Georgios Tsoutsos
ePrint Report
In crowd-sourced data aggregation, participants share their data points with curators. However, the lack of privacy guarantees may discourage participation, which motivates the need for privacy-preserving aggregation protocols. Unfortunately, existing solutions do not support public auditing without revealing the participants' data. In real-world applications, there is a need for public verifiability (i.e., verifying the protocol correctness) while preserving the privacy of the participants' inputs since the participants do not always trust the data curator. Likewise, public distributed ledgers (e.g., blockchains) provide public auditing but may reveal sensitive information.

We present Masquerade, a novel protocol for computing private statistics, such as sum, average, and histograms without revealing anything about participants' data. We propose a tailored multiplicative commitment scheme to ensure the integrity of data aggregations and publish all the participants' commitments on a ledger to provide public verifiability. We complement our methodology with two zero-knowledge proof protocols that detect potentially untrusted participants who attempt to poison the aggregation results. Thus, Masquerade ensures the validity of shared data points before being aggregated, enabling a broad range of numerical and categorical. In our experiments, we evaluate our protocol's runtime and communication overhead using homomorphic ciphertexts and commitments for a variable number of participants.
Rami Elkhatib, Brian Koziel, Reza Azarderakhsh
ePrint Report
In the third round of the NIST PQC standardization process, the only isogeny-based candidate, SIKE, suffers from slow performance when compared to other contenders. The large-degree isogeny computation performs a series of isogenous mappings between curves, to account for about 80% of SIKE’s latency. Here, we propose, implement, and evaluate a new method for computing large-degree isogenies of an odd power. Our new strategy for this computation avoids expensive recomputation of temporary isogeny results.We modified open-source libraries targeting x86, ARM64, and ARM32 platforms. Across each of these implementations, our new method achieves 10% and 5% speedups in SIKE’s key encapsulation and decapsulation operations, respectively. Additionally, these implementations use 3% less stack space at only a 48 byte increase in code size. Given the benefit and simplicity of our approach, we recommend this method for current and emerging SIKE implementations.
Kai-Min Chung, Yao-Ching Hsieh, Mi-Ying Huang, Yu-Hsuan Huang, Tanja Lange, Bo-Yin Yang
ePrint Report
Group signatures are an important cryptographic primitive providing both anonymity and accountability to signatures. Accountable ring signatures combine features from both ring signatures and group signatures, and can be directly transformed to group signatures. While there exists extensive work on constructing group signatures from various post-quantum assumptions, there has not been any using isogeny-based assumptions. In this work, we propose the first construction of isogeny-based group signatures, which is a direct result of our isogeny-based accountable ring signature. This is also the first construction of accountable ring signatures based on post-quantum assumptions. Our schemes are based on the decisional CSIDH assumption (D-CSIDH) and are proven secure under the random oracle model (ROM).
Avinash Vijayarangan, K.R. Sekar, R. Srikanth
ePrint Report
With the fast-growing technology and emerging innovations in the research arena, privacy and preservation of data predominantly in the medical field are highly essential. At the same time, there is a need for minimized storage of voluminous data in the medical repository. The inspiration for this research work to formulate the hybrid methodologies using improved Steganography, wavelet transform, and lossless compression for privacy and preservation of medical big data images and patient information in the medical big data repositories. The novelty of the work focuses on the preservation of patient’s information using enhanced security and optimized big data image storage, which helps the pharmacology professionals to store double the amount of information in the same storage space of the medical big data repository. The secure storage, fast retrieval of image, and minimum computation are the basic ideology of the work. The research work adopts a fast and optimized approach of the Knight Tour algorithm for embedding the patient’s data in their medical image and a Discrete Wavelet Transform (DWT) for the safeguarding of the cover image. Furthermore, a lossless wavelet packet compression is applied to minimize the storage size and to maximize storage efficiency. The outcome of the work achieves a higher level of data security without loss in the quality of the image. In addition, the preservation of the reduced size image will be easy to accommodate and can store bountiful images in the repository. A proposed hybrid method of compression in order to get high resolution on spatial and frequency domains will provide an edge.
Ward Beullens, Samuel Dobson, Shuichi Katsumata, Yi-Fu Lai, Federico Pintore
ePrint Report
We construct an efficient dynamic group signature (or more generally an accountable ring signature) from isogeny and lattice assumptions. Our group signature is based on a simple generic construction that can be instantiated by cryptographically hard group actions such as the CSIDH group action or an MLWE-based group action. The signature is of size $O(\log N)$, where $N$ is the number of users in the group. Our idea builds on the recent efficient OR-proof by Beullens, Katsumata, and Pintore (Asiacrypt'20), where we efficiently add a proof of valid ciphertext to their OR-proof and further show that the resulting non-interactive zero-knowledge proof system is online extractable.

Our group signatures satisfy more ideal security properties compared to previously known constructions, while simultaneously having an attractive signature size. The signature size of our isogeny-based construction is an order of magnitude smaller than all previously known post-quantum group signatures (e.g., 6.6 KB for 64 members). In comparison, our lattice-based construction has a larger signature size (e.g., either 126 KB or 89 KB for 64 members depending on the satisfied security property). However, since the $O(\cdot)$-notation hides a very small constant factor, it remains small even for very large group sizes, say $2^{20}$.
Yi-Fu Lai, Samuel Dobson
ePrint Report
Both ring signatures and group signatures are useful privacy tools, allowing signers to hide their identities within a set of other public keys, while allowing their signatures to be validated with respect to the entire set. Group signature schemes and revocable ring signature schemes both provide the additional ability for certain authorized members to revoke the anonymity on a signature and reveal the true signer—allowing management of abuse in the scheme. This work consists of two parts. Firstly, we introduce a stronger security notion—collusion resistance—for revocable ring signatures and show how to derive a group signature scheme from it, which provides a new approach to obtaining group signatures. This improves on the existing weak security model (e.g. with selfless anonymity) which fails to guarantee anonymity of members whose keys are exposed. Our stronger notion requires that the scheme remains secure against full key exposure in the anonymity game, and allows collusion among arbitrary members in the revocability game. Secondly (and more concretely), we construct a practical collusion-resistant revocable ring signature scheme based on hard homogenous spaces (HHS), and thus obtain a group signature scheme based on isogenies. To the best of our knowledge, the schemes given in this work are the first efficient post-quantum (collusion-resistant) revocable ring signature scheme, and the first efficient isogeny-based group signature scheme in the literature.
We focus on the multiple persistent faults analysis in this paper to fill existing gaps in its application in a variety of scenarios. Our major contributions are twofold. First, we propose a novel technique to apply persistent fault apply in the multiple persistent faults setting that decreases the number of survived keys and the required data. We demonstrate that by utilizing 1509 and 1448 ciphertexts, the number of survived keys after performing persistent fault analysis on AES in the presence of eight and sixteen faults can be reduced to only $2^9$ candidates, whereas the best known attacks need 2008 and 1643 ciphertexts, respectively, with a time complexity of $2^{50}$. Second, we develop generalized frameworks for retrieving the key in the ciphertext-only model. Our methods for both performing persistent fault attacks and key-recovery processes are highly flexible and provide a general trade-off between the number of required ciphertexts and the time complexity. To break AES with 16 persistent faults in the Sbox, our experiments show that the number of required ciphertexts can be decreased to 477 while the attack is still practical with respect to the time complexity. To confirm the accuracy of our methods, we performed several simulations as well as experimental validations on the ARM Cortex-M4 microcontroller with electromagnetic fault injection on AES and LED, which are two well-known block ciphers to validate the types of faults and the distribution of the number of faults in practice.