https://scholar.dgist.ac.kr/handle/20.500.11750/46477 2026-04-04T17:17:31Z 2026-04-04T17:17:31Z Hong, Deokhwa Choi, Youngjin Lee, Yongwoo Kim, Young-Sik https://scholar.dgist.ac.kr/handle/20.500.11750/59965 2026-02-09T06:40:13Z 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.

2025-04-14T15:00:00Z Seo, Yujin Kim, Young-Sik https://scholar.dgist.ac.kr/handle/20.500.11750/59143 2025-11-06T01:40:10Z 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. © 2025 Elsevier B.V., All rights reserved.

2025-07-07T15:00:00Z Lee, Eunsang Lee, Joon-Woo Lee, Junghyun Kim, Young-Sik Kim, Yongjune No, Jong-Seon Choi, Woosuk https://scholar.dgist.ac.kr/handle/20.500.11750/58941 2025-08-22T10:10:11Z 2022-07-18T15:00:00Z

Title: Low-Complexity Deep Convolutional Neural Networks on Fully Homomorphic Encryption Using Multiplexed Parallel Convolutions Author(s): Lee, Eunsang; Lee, Joon-Woo; Lee, Junghyun; Kim, Young-Sik; Kim, Yongjune; No, Jong-Seon; Choi, Woosuk Abstract: Recently, the standard ResNet-20 network was successfully implemented on the fully homomorphic encryption scheme, residue number system variant Cheon-Kim-Kim-Song (RNS-CKKS) scheme using bootstrapping, but the implementation lacks practicality due to high latency and low security level. To improve the performance, we first minimize total bootstrapping runtime using multiplexed parallel convolution that collects sparse output data for multiple channels compactly. We also propose the imaginary-removing bootstrapping to prevent the deep neural networks from catastrophic divergence during approximate ReLU operations. In addition, we optimize level consumptions and use lighter and tighter parameters. Simulation results show that we have 4.67x lower inference latency and 134x less amortized runtime (runtime per image) for ResNet-20 compared to the state-of-the-art previous work, and we achieve standard 128-bit security. Furthermore, we successfully implement ResNet-110 with high accuracy on the RNS-CKKS scheme for the first time.

2022-07-18T15:00:00Z Lee, Joon-Woo Lee, Eunsang Kim, Young-Sik No, Jong-Seon https://scholar.dgist.ac.kr/handle/20.500.11750/47782 2025-07-25T03:38:15Z 2023-12-05T15:00:00Z

Title: Rotation Key Reduction forClient-Server Systems ofDeep Neural Network onFully Homomorphic Encryption Author(s): Lee, Joon-Woo; Lee, Eunsang; Kim, Young-Sik; No, Jong-Seon Abstract: In this paper, we propose a new concept of hierarchical rotation key for homomorphic encryption to reduce the burdens of the clients and the server running on the fully homomorphic encryption schemes such as Cheon-Kim-Kim-Song (CKKS) and Brakerski/Fan-Vercauteran (BFV) schemes. Using this concept, after the client generates and transmits only a small set of rotation keys to the server, the server can generate any required rotation keys from the public key and the smaller set of rotation keys that the client sent. This proposed method significantly reduces the communication cost of the client and the server, and the computation cost of the client. For example, if we implement the standard ResNet-18 network for the ImageNet dataset with the CKKS scheme, the server requires 617 rotation keys. It takes 145.1s for the client with a personal computer to generate whole rotation keys and the total size is 115.7GB. If we use the proposed two-level hierarchical rotation key system, the size of the rotation key set generated and transmitted by the client can be reduced from 115.7GB to 2.91GB (× 1/39.8), and the client-side rotation key generation runtime is reduced from 145.1s to 3.74s (× 38.8 faster) without any changes in any homomorphic operations to the ciphertexts. If we use the three-level hierarchical rotation key system, the size of the rotation key set generated and transmitted by the client can be further reduced from 1.54GB (× 1/75.1), and the client-side rotation key generation runtime is further reduced to 1.93s (× 75.2 faster) with a slight increase in the key-switching operation to the ciphertexts and further computation in the offline phase. © 2023, International Association for Cryptologic Research.

2023-12-05T15:00:00Z