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1. Quantum Key-Revocable Dual-Regev Encryption, Revisited

   Ananth, Prabhanjan; Hu, Zihan; Huang, Zikuan (November 2024, Springer Nature)

   Quantum information can be used to achieve novel cryptographic primitives that are impossible to achieve classically. A recent work by Ananth, Poremba, Vaikuntanathan (TCC 2023) focuses on equipping the dual-Regev encryption scheme, introduced by Gentry, Peikert, Vaikuntanathan (STOC 2008), with key revocation capabilities using quantum information. They further showed that the key-revocable dual-Regev scheme implies the existence of fully homomorphic encryption and pseudorandom functions, with both of them also equipped with key revocation capabilities. Unfortunately, they were only able to prove the security of their schemes based on new conjectures and left open the problem of basing the security of key revocable dual-Regev encryption on well-studied assumptions. In this work, we resolve this open problem. Assuming polynomial hardness of learning with errors (over sub-exponential modulus), we show that key-revocable dual-Regev encryption is secure. As a consequence, for the first time, we achieve the following results: Key-revocable public-key encryption and key-revocable fully-homomorphic encryption satisfying classical revocation security and based on polynomial hardness of learning with errors. Prior works either did not achieve classical revocation or were based on sub-exponential hardness of learning with errors. Key-revocable pseudorandom functions satisfying classical revocation from the polynomial hardness of learning with errors. Prior works relied upon unproven conjectures. 

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2. Public-Key Encryption Resistant to Parameter Subversion and Its Realization from Efficiently-Embeddable Groups

   Auerbach, Benedikt; Bellare, Mihir; Kiltz, Eike (March 2018, Public-Key Cryptography – PKC 2018. PKC 2018. Lecture Notes in Computer Science, vol 10769. Springer, Cham)

   We initiate the study of public-key encryption (PKE) schemes and key-encapsulation mechanisms (KEMs) that retain security even when public parameters (primes, curves) they use may be untrusted and subverted. We define a strong security goal that we call ciphertext pseudo-randomness under parameter subversion attack (CPR-PSA). We also define indistinguishability (of ciphertexts for PKE, and of encapsulated keys from random ones for KEMs) and public-key hiding (also called anonymity) under parameter subversion attack, and show they are implied by CPR-PSA, for both PKE and KEMs. We show that hybrid encryption continues to work in the parameter subversion setting to reduce the design of CPR-PSA PKE to CPR-PSA KEMs and an appropriate form of symmetric encryption. To obtain efficient, elliptic-curve-based KEMs achieving CPR-PSA, we introduce efficiently-embeddable group families and give several constructions from elliptic-curves. 

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3. Reconfigurable Network-on-Chip Security Architecture

   https://doi.org/10.1145/3406661  

   Charles, Subodha; Mishra, Prabhat (October 2020, ACM Transactions on Design Automation of Electronic Systems)

   null (Ed.)

   Growth of the Internet-of-things has led to complex system-on-chips (SoCs) being used in the edge devices in IoT applications. The increased complexity is demanding designers to consider several critical factors, such as dynamic requirement changes, long application life, mass production, and tight time-to-market deadlines. These requirements lead to more complex security concerns. SoC manufacturers outsource some of the intellectual property cores integrated on the SoC to untrusted third-party vendors. The untrusted intellectual properties can contain malicious implants, which can launch attacks using the resources provided by the on-chip interconnection network, commonly known as the network-on-chip (NoC). Existing efforts on securing NoC have considered lightweight encryption, authentication, and other attack detection mechanisms such as denial-of-service and buffer overflows. Unfortunately, these approaches focus on designing statically optimized security solutions. As a result, they are not suitable for many IoT systems with long application life and dynamic requirement changes. There is a critical need to design reconfigurable security architectures that can be dynamically tuned based on changing requirements. In this article, we propose a tier-based reconfigurable security architecture that can adapt to different use-case scenarios. We explore how to design an efficient reconfigurable architecture that can support three popular NoC security mechanisms (encryption, authentication, and denial-of-service attack detection and localization) and implement suitable dynamic reconfiguration techniques. We evaluate our proposed framework by running standard benchmarks enabling different tiers of security and provide a comprehensive analysis of how different levels of security can affect application performance, energy efficiency, and area overhead. 

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4. On Quantum Chosen-Ciphertext Attacks and Learning with Errors

   Alagic, Gorjan; Jeffery, Stacey; Ozols, Maris; Poremba, Alexander (January 2019, Theory of Quantum Computing, Communication, and Cryptography 2019)

   Large-scale quantum computing is a significant threat to classical public-key cryptography. In strong "quantum access" security models, numerous symmetric-key cryptosystems are also vulnerable. We consider classical encryption in a model which grants the adversary quantum oracle access to encryption and decryption, but where the latter is restricted to non-adaptive (i.e., pre-challenge) queries only. We define this model formally using appropriate notions of ciphertext indistinguishability and semantic security (which are equivalent by standard arguments) and call it QCCA1 in analogy to the classical CCA1 security model. Using a bound on quantum random-access codes, we show that the standard PRF- and PRP-based encryption schemes are QCCA1-secure when instantiated with quantum-secure primitives. We then revisit standard IND-CPA-secure Learning with Errors (LWE) encryption and show that leaking just one quantum decryption query (and no other queries or leakage of any kind) allows the adversary to recover the full secret key with constant success probability. In the classical setting, by contrast, recovering the key uses a linear number of decryption queries, and this is optimal. The algorithm at the core of our attack is a (large-modulus version of) the well-known Bernstein-Vazirani algorithm. We emphasize that our results should *not* be interpreted as a weakness of these cryptosystems in their stated security setting (i.e., post-quantum chosen-plaintext secrecy). Rather, our results mean that, if these cryptosystems are exposed to chosen-ciphertext attacks (e.g., as a result of deployment in an inappropriate real-world setting) then quantum attacks are even more devastating than classical ones. 

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5. On the Security of Homomorphic Encryption on Approximate Numbers

   https://doi.org/10.1007/978-3-030-77870-5_23  

   Li, B.; Micciancio, D. (October 2021, Advances in Cryptology – EUROCRYPT 2021)

   Canteaut, A.; Standaert, F. (Ed.)

   We present passive attacks against CKKS, the homomorphic encryption scheme for arithmetic on approximate numbers presented at Asiacrypt 2017. The attack is both theoretically efficient (running in expected polynomial time) and very practical, leading to complete key recovery with high probability and very modest running times. We implemented and tested the attack against major open source homomorphic encryption libraries, including HEAAN, SEAL, HElib and PALISADE, and when computing several functions that often arise in applications of the CKKS scheme to machine learning on encrypted data, like mean and variance computations, and approximation of logistic and exponential functions using their Maclaurin series. The attack shows that the traditional formulation of IND-CPA security (or indistinguishability against chosen plaintext attacks) achieved by CKKS does not adequately capture security against passive adversaries when applied to approximate encryption schemes, and that a different, stronger definition is required to evaluate the security of such schemes. We provide a solid theoretical basis for the security evaluation of homomorphic encryption on approximate numbers (against passive attacks) by proposing new definitions, that naturally extend the traditional notion of IND-CPA security to the approximate computation setting. We propose both indistinguishability-based and simulation-based variants, as well as restricted versions of the definitions that limit the order and number of adversarial queries (as may be enforced by some applications). We prove implications and separations among different definitional variants, and discuss possible modifications to CKKS that may serve as a countermeasure to our attacks. 

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