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27 February 2023
Bertram Poettering, Simon Rastikian
We hence investigate generalizations of the KEM abstraction that allow a considerably simplified construction of the above primitives. In particular, we study VKEMs and KDFEMs, which augment classic KEMs by label inputs, encapsulation handle outputs, and key derivation features, and we demonstrate that they can be transformed into KEM combiners and key transport schemes without requiring auxiliary components. We finally show that all four finalist KEMs of the NIST competition are effectively KDFEMs. Our conclusion is that only very mild adjustments are necessary to significantly increase their versatility.
Phillip Gajland, Bor de Kock, Miguel Quaresma, Giulio Malavolta, Peter Schwabe
In this work, we provide the first evidence against this folklore belief. We construct a practical lattice-based NIKE whose security is based on the standard module learning with errors (M-LWE) problem in the quantum random oracle model. Our scheme is obtained in two steps: (i) A passively-secure construction that achieves a strong notion of correctness, coupled with (ii) a generic compiler that turns any such scheme into an actively secure one. To substantiate our efficiency claim, we present an optimised implementation of our construction in Rust and Jasmin, demonstrating its applicability to real-world scenarios. For this we obtain public keys of approximately 220 KBs and the computation of shared keys takes than 12 million cycles on an Intel Skylake CPU at a post-quantum security level of more than 120 bits.
24 February 2023
osaka, Japan, 23 March 2023
Submission deadline: 25 March 2023
Notification: 25 April 2023
Messina, Italy, 2 July - 8 July 2023
Submission deadline: 5 March 2023
Notification: 23 April 2023
CSEM, Neuchâtel, Switzerland
As part of an experienced team in security and software, you will contribute to the development of security features for future generation of sustainable IoT applications leveraging distributed architectures, edge AI capabilities and advanced cryptography (e.g. post quantum, threshold cryptography). You will be working closely with a diverse team of engineers and researchers, and you will take a leading role in transforming a vision into tangible IPs.
Your responsibilities- Implement cryptography and security primitives for embedded devices.
- Develop Proof of concepts based on advanced cryptography topics.
- Harden the security modules against side channel attacks, software attacks and other relevant threats.
- Adopt a holistic approach to design robust (end to end) security features.
- Propose innovative security IPs and challenge them against state of the art and review them with peers.
- Build demonstrators and share results/knowledge with your colleagues.
- Continuously keep aware of the state of the art.
- Contribute to the supervision of interns.
You are a PhD graduate or an MSc graduate with >=2 years experience. You have background in applied cryptography or embedded security and experience in embedded development. You are motivated to progress within applied cryptography and embedded security. Programming languages: C, Python. ML frameworks, VHDL would be an advantage.
Closing date for applications:
Contact: To apply, please follow the link to the job description by clicking on the job title above. (If not working, paste https://www.csem.ch/en/jobs/cryptography-engineer to your browser.)
More information: https://www.csem.ch/en/jobs/cryptography-engineer
23 February 2023
Benny Applebaum, Niv Konstantini
Along the way, we construct a highly-efficient Vector Oblivious Linear Evaluation (VOLE) protocol and present several practical and theoretical optimizations, as well as a prototype implementation. Our most efficient variant can achieve an asymptotic rate of $1/4$ (i.e., for vectors of length $w$ we send roughly $4w$ elements of $F$), which is only slightly worse than the passively-secure protocol whose rate is $1/3$. The protocol seems to be practically competitive over fast networks, even for relatively small fields $F$ and relatively short vectors. Specifically, our VOLE protocol has 3 rounds, and even for 10K-long vectors, it has an amortized cost per entry of less than 4 OT's and less than 300 arithmetic operations. Most of these operations (about 200) can be pre-processed locally in an offline non-interactive phase. (Better constants can be obtained for longer vectors.) Some of our optimizations rely on a novel intractability assumption regarding the non-malleability of noisy linear codes that may be of independent interest.
Our technical approach employs two new ingredients. First, we present a new information-theoretic construction of Conditional Disclosure of Secrets (CDS) and show how to use it in order to immunize the VOLE protocol of Applebaum et al. against active adversaries. Second, by using elementary properties of low-degree polynomials, we show that, for some simple arithmetic functionalities, one can easily upgrade Yao's garbled-circuit protocol to the active setting with a minor overhead while preserving the round complexity.
Emmanuela Orsini, Riccardo Zanotto
Dinh Duy Nguyen, Duong Hieu Phan, David Pointcheval
Florian Hirner, Ahmet Can Mert, Sujoy Sinha Roy
Panos Kampanakis, Tancrède Lepoint
This vision paper motivates more research and possible standards updates related to the upcoming quantum-resistant cryptography migration. It stresses the importance of amplification reflection attacks and congestion control concerns in transport protocols and presents research and standardization takeaways for assessing the impact and the efficacy of potential countermeasures. It emphasizes the need to go beyond the standardization of key encapsulation mechanisms in order to address the numerous protocols and deployments of public-key encryption while avoiding pitfalls. Finally, it motivates the critical need for research in anonymous credentials and blind signatures at the core of numerous deployments and standardization efforts aimed at providing privacy-preserving trust signals.
James Bartusek, Sanjam Garg, Vipul Goyal, Dakshita Khurana, Giulio Malavolta, Justin Raizes, Bhaskar Roberts
This work answers the above questions, providing the first fully (maliciously) secure solution to the question of blind delegation with certified deletion, and the first solution to the question of obfuscation with certified deletion. Unlike prior work on deletion, these settings require security in the presence of repeated access to partial decryptions of encoded data, followed by certified deletion of the (rest of the) encoded data. To enable security, we introduce a powerful new paradigm for secure information-theoretic deletion of data based on quantum \emph{subspace coset states}. We obtain the following results.
Blind Delegation with Certified Deletion - Assuming the quantum hardness of learning with errors, we obtain maliciously-secure blind delegation with certified deletion. This improves upon prior protocols by Poremba (ITCS 2023) and Bartusek and Khurana (arXiv 2022) that we show are insecure against a malicious server. - Assuming sub-exponentially quantum-secure indistinguishability obfuscation, we obtain a \emph{two-message} protocol for blind delegation with certified deletion. All previous protocols required multiple rounds of interaction between the client and server.
Obfuscation with Certified Deletion - Assuming post-quantum indistinguishability obfuscation, we obtain a construction of differing-inputs obfuscation with certified deletion, for a polynomial number of differing inputs. As an immediate corollary, we obtain a strong variant of secure software leasing for every differing-inputs circuit family. - We obtain two flavors of functional encryption with certified deletion, one where ciphertexts can be certifiably deleted, and the other where secret keys can be certifiably deleted, assuming appropriate variants of indistinguishability obfuscation and other standard assumptions. - We show how to prepare an ``oracle with certified deletion'' implementing any efficient classical functionality.
Additional Results - Assuming post-quantum CCA-secure public-key encryption, we obtain a notion of CCA-secure public-key encryption with certified deletion. We view this primarily as a pedagogical tool towards understanding our technique. - Assuming post-quantum indistinguishability obfuscation, we show how to generically add a \emph{publicly-verifiable} certified deletion property to a variety of cryptosystems. Publicly-verifiable deletion schemes prior to our work either relied on unproven conjectures (Poremba, ITCS 2023) or structured oracles (Hiroka et al., Asiacrypt 2021).
All our primitives satisfy {\em everlasting security after deletion}, except for functional encryption with deletion for secret keys, where a computational certified deletion guarantee is inherent.
Shweta Agrawal, Fuyuki Kitagawa, Ryo Nishimaki, Shota Yamada, Takashi Yamakawa
1. Definitions: We introduce the definition of PKE with secure key leasing and formalize a security notion that we call indistinguishability against key leasing attacks (IND-KLA security). We also define a one-wayness notion for PKE-SKL that we call OW-KLA security and show that an OW-KLA secure PKE-SKL scheme can be lifted to an IND-KLA secure one by using the (quantum) Goldreich-Levin lemma. 2. Constructing IND-KLA PKE with Secure Key Leasing: We provide a construction of OW-KLA secure PKE-SKL (which implies IND-KLA secure PKE-SKL as discussed above) by leveraging a PKE scheme that satisfies a new security notion that we call consistent or inconsistent security against key leasing attacks (CoIC-KLA security). We then construct a CoIC-KLA secure PKE scheme using 1-key Ciphertext-Policy Functional Encryption (CPFE) that in turn can be based on any IND-CPA secure PKE scheme.
3. Identity Based Encryption, Attribute Based Encryption and Functional Encryption with Secure Key Leasing: We provide definitions of secure key leasing in the context of advanced encryption schemes such as identity based encryption (IBE), attribute-based encryption (ABE) and functional encryption (FE). Then we provide constructions by combining the above PKE-SKL with standard IBE, ABE and FE schemes.
Notably, our definitions allow the adversary to request distinguishing keys in the security game, namely, keys that distinguish the challenge bit by simply decrypting the challenge ciphertext, so long as it returns them (and they pass the validity test) before it sees the challenge ciphertext. All our constructions satisfy this stronger definition, albeit with the restriction that only a bounded number of such keys be allowed to the adversary in the IBE and ABE (but not FE) security games.
Prior to our work, the notion of single decryptor encryption (SDE) has been studied in the context of PKE (Georgiou and Zhandry, Eprint 2020) and FE (Kitigawa and Nishimaki, Asiacrypt 2022) but all their constructions rely on strong assumptions including indistinguishability obfuscation. In contrast, our constructions do not require any additional assumptions, showing that PKE/IBE/ABE/FE can be upgraded to support secure key leasing for free.
Yanbo Chen
In this work, we propose a lattice-based two-round multi-signature scheme called DualMS. Compared to DOTT, DualMS is likely to significantly reduce signature size, since it replaces an opening to a homomorphic trapdoor commitment with a Dilithium-G response in the signature. Compared to MuSig-L, concrete parameters show that DualMS has smaller public keys, signatures, and lower communication, while the first round cannot be preprocessed offline as in MuSig-L.
The main reason behind such improvements is a trapdoor-free "dual signing simulation" of our scheme. Signature simulation of DualMS is virtually identical the normal signing procedure and does not use lattice trapdoors like DOTT and MuSig-L.
Henri Gilbert, Rachelle Heim Boissier, Louiza Khati, Yann Rotella
Sanjay Bhattacherjee, Julio Hernandez-Castro, Jack Moyler
22 February 2023
Prague, Czechia, 10 September - 14 September 2023
Taipei, Taiwan, 29 November - 2 December 2023
Drew Stone
Guangqiu Lv, Chenhui Jin, Ting Cui
In this paper, we solve this open problem through some techniques to reduce complexity and a transformation technique from matrix multiplication chain to Mixed Integer Quadratically-Constrained Programs (MIQCP). First, the computational complexity of the DL correlation of $\boxplus_2$ is reduced to approximately one-eighth of the state of art, which can be computed by a $2\times2$ matrix multiplication chain of the same length as before. Some methods to further reduce complexity in special cases have been studied. Additionally, we present how to compute the extended (rotational) DL correlations of $\boxplus_k$ for $k\ge 2$, where two output linear masks of the cipher pairs can be different. Second, to ensure that the existing solver Gurobi\footnote{The solver used in this paper is Gurobi, and some ready-made functions in Gurobi are also used, such as LOG\_2 and ABS. The source code is available at \url{https://}. } can compute DL correlations of $\boxplus_2$, we propose a method to transform an arbitrary matrix multiplication chain into a MIQCP, which forms the foundation of our automatic search of DL trails in ARX ciphers. Third, in ARX ciphers, we use a single DL trail under some explicit conditions to give a good estimate of the correlation, which avoids the exhaustion of intermediate differences. We then derive an automatic method for evaluating the DL correlations of ARX, which we apply to Alzette and some versions of SPECK. Experimentally verified results confirm the validity of our method, with the predicted correlations being close to the experimental ones. To the best of our knowledge, this method finds the best DL distinguishers for these ARX primitives currently. Furthermore, we presented the lowest time-complexity attacks against 12-14 rounds of SPECK32 to date.
Jordan Frery, Andrei Stoian, Roman Bredehoft, Luis Montero, Celia Kherfallah, Benoit Chevallier-Mames, Arthur Meyre
More precisely, we explain in this paper how we apply FHE to tree-based models and get state-of-the-art solutions over encrypted tabular data. We show that our method is applicable to a wide range of tree-based models, including decision trees, random forests, and gradient boosted trees, and has been implemented within the Concrete-ML library, which is open-source at https://github.com/zama-ai/concrete-ml. With a selected set of use-cases, we demonstrate that our FHE version is very close to the unprotected version in terms of accuracy.