International Association
for Cryptologic Research

We focus on the problem of Dynamic Searchable Encryption (DSE) with efficient (optimal/quasi-optimal) search in the presence of deletions. Towards that end, we first propose OSSE, the first DSE scheme that can achieve asymptotically optimal search time, linear to the result size and independent of any prior deletions, improving the previous state of the art by a multiplicative logarithmic factor. We then propose our second scheme LLSE, that achieves a sublogarithmic search overhead ($\log\log i_w$, where $i_w$ is the number or prior insertions for a keyword) compared to the optimal achieved by OSSE. While this is slightly worse than our first scheme, it still outperforms prior works, while also achieving faster deletions and asymptotically smaller server storage. Both schemes have standard leakage profiles and are forward-and-backward private. Our experimental evaluation is very encouraging as it shows our schemes consistently outperform the prior state-of-the-art DSE by $1.3$-$6.4\times$ in search computation time, while also requiring just a single roundtrip to receive the search result. Even compared with prior simpler and very efficient constructions in which all deleted records are returned as part of the result, our OSSE achieves better performance for deletion rates ranging from 45-55%, while the previous state-of-the-art quasi-optimal scheme achieves this for 65-75% deletion rates.

In this paper, we present the quantum implementation and analysis of the recently proposed block cipher, DEFAULT. DEFAULT is consisted of two components, namely DEFAULT-LAYER and DEFAULT-CORE. Two instances of DEFAULT-LAYER is used before and after DEFAULT-CORE (the so-called `sandwich construction').

We discuss about the the various choices made to keep the cost for the basic quantum circuit and that of the Grover's oracle search, and compare it with the levels of quantum security specified by the United States' National Institute of Standards and Technology (NIST). All in all, our work nicely fits in the research trend of finding the possible quantum vulnerability of symmetric key ciphers.

In 1986, A.Yao introduced the notion of garbled circuits, designed to verify the correctness of computations performed on an untrusted server. However, correctness is guaranteed for only one input, meaning that a new garbled circuit must be created for each new input. To address this drawback, in 2010 Gennaro et al. performed the evaluation of the garbled circuit homomorphically using Fully Homomorphic Encryption scheme, allowing to reuse the same garbled circuit for new inputs. Their solution requires to encrypt the garbled circuit at every new input. In this paper, we propose a verifiable-computation scheme allowing to verify the correctness of computations performed by an untrusted server for multiple inputs, where the garbled circuit is homomorphically encrypted only once. Hence, we have a faster scheme comparing to Gennaro’s solution, since for each new input, we reduce the computations by the size of the circuit representing the function to be computed, for the same security level. The key point to obtain this speed-up is to rely on Multi-Key Homomorphic Encryption (MKHE) and then to encrypt only once the garbled circuit.

Secure multi-party computation (MPC) protocols that are resilient to a dishonest majority allow the adversary to get the output of the computation while, at the same time, forcing the honest parties to abort. Aumann and Lindell introduced the enhanced notion of security with identifiable abort, which still allows the adversary to trigger an abort but, at the same time, it enables the honest parties to agree on the identity of the party that led to the abort. More recently, in Eurocrypt 2016, Garg et al. showed that, assuming access to a simultaneous message exchange channel for all the parties, at least four rounds of communication are required to securely realize non-trivial functionalities in the plain model.

Following Garg et al., a sequence of works has matched this lower bound, but none of them achieved security with identifiable abort. In this work, we close this gap and show that four rounds of communication are also sufficient to securely realize any functionality with identifiable abort using standard and generic polynomial-time assumptions. To achieve this result we introduce the new notion of bounded-rewind secure MPC that guarantees security even against an adversary that performs a mild form of reset attacks. We show how to instantiate this primitive starting from any MPC protocol and by assuming trapdoor-permutations.

The notion of bounded-rewind secure MPC allows for easier parallel composition of MPC protocols with other (interactive) cryptographic primitives. Therefore, we believe that this primitive can be useful in other contexts in which it is crucial to combine multiple primitives with MPC protocols while keeping the round complexity of the final protocol low.

Eindhoven University of Technology (TU/e), our Coding Theory and Cryptology (CC) group of the Discrete Mathematics (DM) cluster of the Department of Mathematics and Computer Science (M&CS) are looking for an (tenure-track) assistant professor in Cryptology. This vacancy is part of the Irène Curie Fellowship and is currently only open for female candidates.

The position will be part of the Coding Theory and Cryptology (CC) group, within the Discrete Mathematics (DM) cluster. The other group in DM is Discrete Algebra and Geometry. The CC group consists of one full professor (Lange), two associate professors (Schoenmakers and de Weger), and three assistant professors (Hülsing Ravagnani, and Schäge). CC provides undergraduate and graduate courses in cryptology, coding theory, algebra and number theory, as well as service teaching.

The ideal candidate has research experience complementing the existing strengths in CC and a background in mathematics but candidates from all areas of cryptology are encouraged to apply.

We look forward to your application and will screen it as soon as we have received it. Screening will continue until the position has been filled. We expect the first round of interviews in early July, so apply before June 20 to be considered in this round.

Closing date for applications:

Contact: Tanja Lange

More information: https://jobs.tue.nl/nl/vacature/assistant-professor-in-cryptology-936431.html

Event date: 10 July to 14 July 2023

Event date: 1 August to 4 August 2022

In previous years there has been an increased interest in designing threshold signature schemes. Most of the recent works focus on constructing threshold versions of ECDSA or Schnorr signature schemes due to their appealing usage in blockchain technologies. Additionally, a lot of research is being done on cryptographic schemes that are resistant against quantum computer attacks. Presently, the most popular family of post-quantum algorithms is lattice-based cryptography, because its structure allows creation of cryptographic protocols that go beyond encryption and digital signature schemes.

In this work, we propose a new version of the two-party Crystals-Dilithium signature scheme. The security of our scheme is based on the hardness of Module-LWE and Module-SIS problems. In our construction, we follow a similar logic as Damgård et al. (PKC 2021) and use an additively homomorphic commitment scheme. However, compared to them, our protocol uses signature compression techniques from the original Crystals-Dilithium signature scheme which makes it closer to the version submitted to the NIST PQC

In this study, we accelerate Matsui's search algorithm to search for the best differential and linear trails of AES-like ciphers. Our acceleration points are twofold. The first exploits the structure and branch number of an AES-like round function to apply strict pruning conditions to Matsui's search algorithm. The second employs permutation characteristics in trail search to reduce the inputs that need to be analyzed. We demonstrate the optimization of the search algorithm by obtaining the best differential and linear trails of existing block ciphers: AES, LED, MIDORI-64, CRAFT, SKINNY, PRESENT, and GIFT. In particular, our search program finds the full-round best differential and linear trails of GIFT-64 (in approx. 1 s and 10 s) and GIFT-128 (in approx. 89 h and 452 h), respectively. For a more in-depth application, we leverage the acceleration to investigate the optimal DC/LC resistance that GIFT-variants, called BOGI-based ciphers, can achieve. To this end, we identify all the BOGI-based ciphers and reduce them into 41,472 representatives. Deriving 16-, 32-, 64-, and 128-bit BOGI-based ciphers from the representatives, we obtain their best trails until 15, 15, 13, and 11 rounds, respectively. The investigation shows that 12 rounds are the minimum threshold for a 64-bit BOGI-based cipher to prevent efficient trails for DC/LC, whereas GIFT-64 requires 14 rounds. Moreover, it is shown that GIFT can provide better resistance by only replacing the existing bit permutation. Specifically, the bit permutation variants of GIFT-64 and GIFT-128 require fewer rounds, one and two, respectively, to prevent efficient differential and linear trails.

The introduction of Statistical Ineffective Fault Attacks (SIFA) has led to a renewed interest in fault attacks. SIFA requires minimal knowledge of the concrete implementation and is effective even in the presence of common fault or power analysis countermeasures. However, further investigations reveal that undesired and frequent ineffective events, which we refer to as the noise phenomenon, are the bottleneck of SIFA that can considerably diminish its strength. This includes noise associated with the attack’s setup and caused by the countermeasures utilized in the implementation. This research aims to address this significant drawback. We present two novel statistical fault attack variants that are far more successful in dealing with these noisy conditions. The first variant is the Statistical Effective Fault Attack (SEFA), which exploits the non-uniform distribution of intermediate variables in circumstances when the induced faults are effective. The idea behind the second proposed method, dubbed Statistical Hybrid Fault Attacks (SHFA), is to take advantage of the biased distributions of both effective and ineffective cases simultaneously. Our experimental results in various case studies, including noise-free and noisy setups, back up our reasoning that SEFA surpasses SIFA in several instances and that SHFA outperforms both or is at least as efficient as the best of them.

Event date: to
Submission deadline: 1 September 2022
Notification: 15 January 2023

Event date: 4 July to 8 July 2022

Cryptography, Security & Privacy Research Group at Koç University has one opening at the post-doctoral researcher level. Accepted applicants may receive competitive salary, housing (accommodation) support, health insurance, computer, travel support, and lunch meal card.

Your duties include performing research on cryptography, security, and privacy in line with our research group's focus, as well as directing graduate and undergraduate students in their research and teaching. The project funding is related to cryptography, game theory and mechanism design, and blockchain technologies.

Applicants are expected to have already obtained their Ph.D. degrees in Computer Science or related discipline with a thesis topic related to the duties above.

For more information about joining our group and projects, visit

https://crypto.ku.edu.tr/work-with-us/

Submit your application via email including

• full CV,
• transcripts of all universities attended,
• 1-3 sample publications where you are the main author,
• a detailed research proposal,
• 2-3 reference letters sent directly by the referees.

Application and start dates are flexible.

Closing date for applications:

Contact: Assoc. Prof. Alptekin Küpçü
https://member.acm.org/~kupcu

More information: https://crypto.ku.edu.tr/work-with-us/

Cryptography, Security & Privacy Research Group at Koç University has multiple openings at every level. Accepted Computer Science and Engineering applicants may receive competitive scholarships including monthly stipend, tuition waiver, housing (accommodation) support, health insurance, computer, travel support, and lunch meal card.

Your duties include performing research on cryptography, security, and privacy in line with our research group's focus, assist teaching, as well as collaborating with other graduate and undergraduate students. Computer Science, Mathematics, Cryptography, or related background is necessary.

For applying online, and questions about the application-process for M.Sc. and Ph.D. positions, visit

https://gsse.ku.edu.tr/en/admissions/application-requirements

All applications must be completed online. Applications with missing documents will not be considered. Applications via e-mail will not be considered. Application Requirements:

1. CV
2. Recommendation Letters (2 for MSc, 3 for PhD)
3. TOEFL (for everyone whose native language is not English, Internet Based: Minimum Score 80)
4. GRE score
5. Official transcripts from all the universities attended
6. Statement of Purpose
7. Area of Interest Form filled online

https://gsse.ku.edu.tr/en/admissions/how-to-apply/

We also have a non-thesis paid Cyber Security M.Sc. program:

https://cybersecurity.ku.edu.tr/

For more information about joining our group and projects, visit

https://crypto.ku.edu.tr/work-with-us/

Closing date for applications:

Contact: https://gsse.ku.edu.tr/en/admissions/how-to-apply/

More information: https://gsse.ku.edu.tr/en/prospective-students/how-to-apply/

Blockchains are not private enough for safe use by citizens, corporations, or dissidents. Heliax is looking for a cryptographer & researcher interested in zero-knowledge cryptographic protocols and their application to distributed ledger technology to work with us to design, evaluate, and implement zero-knowledge proof constructions such as zkSNARKs and zkSTARKs, distributed cryptographic protocols such as threshold encryption and distributed key generation, and cryptographic primitives such as elliptic curves and hash functions, then put this cryptography into practice in order to realise privacy and scalability capabilities required by the next generation of blockchain networks. This role offers the chance to work closely with a small team on compelling cross-disciplinary problems in theoretical computer science, cryptography, game theory, economics, and systems design, and enjoy a high degree of independence in working conditions and task prioritization.

Closing date for applications:

Contact: Heliax HR

More information: https://heliax.dev/jobs/zero-knowledge-cryptographer-protocol-developer/

Blockchains are not private enough for safe use by citizens, corporations, or dissidents. Heliax is looking for a research cryptographer interested in fully-homomorphic encryption protocols and their application to distributed ledger technology to work with us to design, evaluate, and implement FHE constructions, then put this cryptography into practice in order to realise privacy and scalability capabilities required by the next generation of blockchain networks. This role offers the chance to work closely with a small team on compelling cross-disciplinary problems in theoretical computer science, cryptography, game theory, economics, and systems design, and enjoy a high degree of independence in working conditions and task prioritization.

Closing date for applications:

Contact: Heliax HR Team

More information: https://heliax.dev/jobs/research-cryptographer-FHE/

Passive physical attacks represent a threat to microelectronics systems by exploiting leakages through side-channels, such as power consumption and electromagnetic radiation. In this context, masking is a sound countermeasure against side-channel attacks, which splits the secret data into several randomly uniform data, achieving independence between the data processing and the secret variable. However, a secure masking scheme requires additional implementation costs. Furthermore, glitches and early evaluation can temporally weaken a masked implementation in hardware, creating a potential source of exploitable leakages.

This work shows how to create register-free masking schemes that avoid the early evaluation effect with the help of the dual-rail logic. Moreover, we employ monotonic functions with the purpose of eliminating the occurrence of glitches in combinational circuits. Finally, we evaluate different 2-share masked implementations of the PRESENT and AES S-boxes in a noiseless scenario in order to detect potential first-order leakages and to determine data propagation profiles correlated to the secret variables.

Digital ledger technologies supporting smart contracts usually does not ensure any privacy for user transactions or state. Most solutions to this problem either use private network setups, centralized parties, hardware enclaves, or cryptographic primitives, which are novel, complex, and computationally expensive. This paper looks into an alternative way of implementing smart contracts. Our construction of a protocol for smart contracts employs an overlay protocol design pattern for decentralized applications, which separates transaction ordering from transaction validation. This enables consensus on application state while revealing only encrypted versions of transactions to public consensus protocol network. UTXO-based smart contract model allows partitioning state of distributed ledger in a way that participants would need to decrypt and reach consensus only on those transactions, which are relevant to them. We present security analysis, which shows that, assuming presence of a secure consensus protocol, our construction achieves consensus on UTXO-based transactions, while hiding most of transaction details from all protocol parties, except a limited subset of parties, which need particular transactions for construction of their state.

Cryptosystems have been developed over the years under the typical prevalent setting which assumes that the receiver’s key is kept secure from the adversary, and that the choice of the message to be sent is freely performed by the sender and is kept secure from the adversary as well. Under these fundamental and basic operational assumptions, modern Cryptography has flourished over the last half a century or so, with amazing achievements: New systems (including public-key Cryptography), beautiful and useful models (including security definitions such as semantic security), and new primitives (such as zero-knowledge proofs) have been developed. Furthermore, these fundamental achievements have been translated into actual working systems, and span many of the daily human activities over the Internet.

However, in recent years, there is an overgrowing pressure from many governments to allow the government itself access to keys and messages of encryption systems (under various names: escrow encryption, emergency access, communication decency acts, etc.). Numerous non-direct arguments against such policies have been raised, such as "the bad guys can utilize other encryption system" so all other cryptosystems have to be declared illegal, or that "allowing the government access is an ill-advised policy since it creates a natural weak systems security point, which may attract others (to masquerade as the government)." It has remained a fundamental open issue, though, to show directly that the above mentioned efforts by a government (called here “a dictator” for brevity) which mandate breaking of the basic operational assumption (and disallowing other cryptosystems), is, in fact, a futile exercise. This is a direct technical point which needs to be made and has not been made to date.

In this work, as a technical demonstration of the futility of the dictator’s demands, we invent the notion of “Anamorphic Encryption” which shows that even if the dictator gets the keys and the messages used in the system (before anything is sent) and no other system is allowed, there is a covert way within the context of well established public-key cryptosystems for an entity to immediately (with no latency) send piggybacked secure messages which are, in spite of the stringent dictator conditions, hidden from the dictator itself! We feel that this may be an important direct technical argument against the nature of governments’ attempts to police the use of strong cryptographic systems, and we hope to stimulate further works in this direction.

The celebrated result by Gentry and Wichs established a theoretical barrier for succinct non-interactive arguments (SNARGs), showing that for (expressive enough) hard-on-average languages we must assume non-falsifiable assumptions. We further investigate those barriers by showing new negative and positive results related to extractability and to the preprocessing model. 1. We first ask the question “are there further barriers to SNARGs that are knowledge-sound (SNARKs) and with a black-box extractor?”. We show it is impossible to have such SNARKs in the standard model. This separates SNARKs in the random oracle model (which can have black-box extraction) and those in the standard model. 2. We find positive results regarding the same question in the non-adaptive setting. Under the existence of SNARGs (without extractability) and from standard assumptions, it is possible to build SNARKs with black-box extractability for a non-trivial subset of NP. 3. On the other hand, we show that (under some mild assumptions) all NP languages cannot have SNARKs with black-box extractability even in the non-adaptive setting. 4. The Gentry-Wichs result does not account for the preprocessing model, under which fall several efficient constructions. We show that also in the preprocessing model it is impossible to construct SNARGs that rely on falsifiable assumptions in a black-box way. Along the way, we identify a class of non-trivial languages, which we dub “trapdoor languages”, that bypass some of these impossibility results.