Repository Community: null

Q-AMT: Multi-Target Security Assessment for Lattice KEMs

2026-06-30T15:00:00Z

Title: Q-AMT: Multi-Target Security Assessment for Lattice KEMs Author(s): Kim, Gwang-Sik; Kim, Young-Sik Abstract: Security reductions for Fujisaki-Okamoto (FO)-style lattice key-encapsulation mechanisms (KEMs) in the quantum random-oracle model (QROM) incur non-tight loss terms that grow with an adversary's oracle access and the number of simultaneously attacked targets. While these losses are well characterized theoretically, their practical impact at deployment scale-where thousands of public keys may coexist under a single administrative domain-has not been systematically quantified. We present Q-AMT (QROM-motivated Amplified Multi-Target), a scheme-agnostic measurement framework that makes these losses operational for engineering decisions. Q-AMT formalizes a multi-target adversary model, derives practical surrogates for multi-target advantage, and defines a tightness gap metric Gamma that compares measured multi-target advantage to single-target baselines. The framework provides a round-based scheduler that allocates oracle budgets across targets, controls post-selection, and toggles oracle-hygiene configurations (domain separation and binding of KDF inputs to public-key-ciphertext context). We explicitly frame our classical proxy parameter q(G) as a concavity-sharing diagnostic-a tool for traversing the concavity regime of the single-target advantage function-rather than a simulation of quantum superposition queries. We prove that the resulting Gamma metric is invariant to the choice of concavity model and to the absolute security level, so that relative results at reduced lambda(eff) transfer to production-scale \lambda = 128 . We instantiate Q-AMT across representative lattice KEM families-MLWE/MLWR (ML-KEM/Kyber, SABER), NTRU-style (NTRU+), and FO-variant profiles-under constant-time, implicitly rejecting implementations and evaluate 1,056 configurations, including 192 lambda(eff) -invariance configurations, spanning fan-out N-t is an element of( ){1,...,32} , hash budgets q(H) up to 2(20) , five lambda(eff) values, and three post-selection rates. Under strict oracle hygiene, the measured tightness gap concentrates at Gamma = 1.022 +/- 0.310 across all configurations; disabling separation and/or binding raises the mean to Gamma = 1.127 with peaks near 2.0, confirming super-linear multi-target amplification from cross-target coupling, consistent with the formal multi-user QROM analysis of Duman et al. (2021). From the measured surfaces we extract operator-facing guidance: safe per-key query caps for given fan-out and acceptance rates, a worked 10,000-key enterprise deployment example, and an overhead-risk frontier showing that redundant FO/FO {}<^>{\perp } validation incurs 2-4% overhead across five hardware platforms (Cortex-M4/M7, ARMv8-A, x86-64, RISC-V) while substantially reducing the effective success probability of validation bypasses-even under targeted structural faults. Q-AMT does not directly compromise lattice KEMs; rather, it quantifies residual risk from multi-user accumulation and turns it into concrete engineering guidance.

Post-Quantum Cryptography Migration on V2X Certificate using KpqC Algorithms

2025-07-07T15:00:00Z

Title: Post-Quantum Cryptography Migration on V2X Certificate using KpqC Algorithms Author(s): Seo, Yujin; Kim, Young-Sik Abstract: Connected vehicles utilizing Vehicle-to-Everything (V2X) communication enhance road safety and transportation efficiency, supporting cooperative autonomous driving through real-time interactions. However, increased connectivity raises cyber-attack risks, endangering driver and pedestrian safety. This highlights the urgent need to integrate Post-Quantum Cryptography (PQC) into vehicular communications [6]. In this paper, we implement the Korean PQC digital signature algorithm HAETAE for V2X environments and compare its performance with the NIST PQC signature scheme, ML-DSA which is derived from CRYSTALS-DILITHIUM, and traditional signatures, RSA, and ECC under TLS 1.3 environments. Results indicate that PQC algorithms introduce substantial overhead, whereas traditional algorithms produce smaller certificates. Specifically, HAETAE provides more efficient certificates than ML-DSA [3], minimizing latency impacts in TLS operations. These findings inform the critical balance between enhanced security and certificate size, guiding future post-quantum TLS designs.

Overlapped Bootstrapping for FHEW/TFHE and Its Application to SHA3

2025-04-14T15:00:00Z

Title: Overlapped Bootstrapping for FHEW/TFHE and Its Application to SHA3 Author(s): Hong, Deokhwa; Choi, Youngjin; Lee, Yongwoo; Kim, Young-Sik Abstract: Homomorphic Encryption (HE) enables operations on encrypted data without requiring decryption, thus allowing secure handling of confidential data within smart contracts. Among the known HE schemes, FHEW and TFHE are particularly notable for use in smart contracts due to their lightweight nature and support for arbitrary logical gates. In contrast, other HE schemes often require several gigabytes of keys and are limited to supporting only addition and multiplication. As a result, many studies have been conducted on implementing smart contract functionalities over HE, broadening the potential applications of blockchain technology. However, a significant drawback of the FHEW/TFHE schemes is the need for bootstrapping after the execution of each binary gate. While bootstrapping reduces noise in the ciphertext, it also becomes a performance bottleneck due to its computational complexity. In this work, we propose an efficient new bootstrapping method for FHEW/TFHE that takes advantage of the flexible scaling factors of encrypted data. The proposed method is particularly beneficial in circuits with consecutive XOR gates. Moreover, we implement Keccak using FHEW/TFHE, as it is one of the most important functions in smart contracts. Our experimental results demonstrate that the proposed method reduces the runtime of Keccak over HE by 42%. Additionally, the proposed method does not require additional keys or parameter sets from the key-generating party and can be adopted by the computing party without the need for any extra information. © International Financial Cryptography Association 2026.

CKKS 동형암호를 이용한 ARX 연산 효율화 및 LEA 블록암호 키 마이그레이션 프레임워크

Title: CKKS 동형암호를 이용한 ARX 연산 효율화 및 LEA 블록암호 키 마이그레이션 프레임워크 Author(s): 이재연; 정세훈; 김영식; 조승현