学術論文誌

KeyUpdatable PublicKey Encryption with Keyword Search (Or: How to Realize PEKS with Efficient Key Updates for IoT Environments)
 著者
 H. Anada, A. Kanaoka, N. Matsuzaki, and Y. Watanabe
 雑誌名
 International Journal of Information Security
 巻
 19
 ページ
 15–38
 出版社
 Springer
 発行年
 2020
Abstract
Security and privacy are the key issues for the Internet of Things (IoT) systems. Especially, secure search is an important functionality for cooperation among users’ devices and nontrusted servers. Publickey encryption with keyword search (PEKS) enables us to search encrypted data and is expected to be used between a cloud server and users’ mobile devices or IoT devices. However, those mobile devices might be lost or stolen. For IoT devices, it might be difficult to store keys in a tamperproof manner due to prohibitive costs. In this paper, we deal with such a keyexposure problem on PEKS and introduce the concept of PEKS with keyupdating functionality, which we call keyupdatable PEKS (KUPEKS). Specifically, we propose two models of KUPEKS: the keyevolution model and the keyinsulation model. In the keyevolution model, a pair of public and secret keys can be updated if needed (e.g., the secret key is exposed). In the keyinsulation model, the public key remains fixed while the secret key can be updated if needed. The former model makes a construction simple and more efficient than the latter. On the other hand, the latter model is preferable for practical use since a user never updates their public key. We show constructions in each model in a blackbox manner. We also give implementation results on Raspberry Pi 3, which can be regarded as a reasonable platform of IoT devices.

MultiParty Computation for Modular Exponentiation Based on Replicated Secret Sharing
 著者
 K. Ohara, Y. Watanabe, M. Iwamoto, and K. Ohta
 雑誌名
 IEICE Transactions
 巻
 102A
 号
 9
 ページ
 1079–1090
 出版社
 IEICE
 発行年
 2019
Abstract
In recent years, multiparty computation (MPC) frameworks based on replicated secret sharing schemes (RSSS) have attracted the attention as a method to achieve high efficiency among known MPCs. However, the RSSSbased MPCs are still inefficient for several heavy computations like algebraic operations, as they require a large amount and number of communication proportional to the number of multiplications in the operations (which is not the case with other secret sharingbased MPCs). In this paper, we propose RSSSbased threeparty computation protocols for modular exponentiation, which is one of the most popular algebraic operations, on the case where the base is public and the exponent is private. Our proposed schemes are simple and efficient in both of the asymptotic and practical sense. On the asymptotic efficiency, the proposed schemes require O(n)bit communication and O(1) rounds,where n is the secretvalue size, in the best setting, whereas the previous scheme requires O(n2)bit communication and O(n) rounds. On the practical efficiency, we show the performance of our protocol by experiments on the scenario for distributed signatures, which is useful for secure key management on the distributed environment (e.g., distributed ledgers). As one of the cases, our implementation performs a modular exponentiation on a 3,072bit discretelog group and 256bit exponent with roughly 300ms, which is an acceptable parameter for 128bit security, even in the WAN setting.