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163 results on '"Emura, Keita"'

1. An Anonymous yet Accountable Contract Wallet System using Account Abstraction

Author

Chin, Kota, Emura, Keita, and Omote, Kazumasa

Subjects
Computer Science - Cryptography and Security
Abstract

Account abstraction allows a contract wallet to initiate transaction execution. Thus, account abstraction is useful for preserving the privacy of externally owned accounts (EOAs) because it can remove a transaction issued from an EOA to the contract wallet and hides who issued the transaction by additionally employing anonymous authentication procedures such as ring signatures. However, unconditional anonymity is undesirable in practice because it prevents to reveal who is accountable for a problem when it arises. Thus, maintaining a balancing between anonymity and accountability is important. In this paper, we propose an anonymous yet accountable contract wallet system. In addition to account abstraction, the proposed system also utilizes accountable ring signatures (Bootle et al., ESORICS 2015). The proposed system provides (1) anonymity of a transaction issuer that hides who agreed with running the contract wallet, and (2) accountability of the issuer, which allows the issuer to prove they agreed with running the contract wallet. Moreover, due to a security requirement of accountable ring signatures, the transaction issuer cannot claim that someone else issued the transaction. This functionality allows us to clarify the accountability involved in issuing a transaction. In addition, the proposed system allows an issuer to employ a typical signature scheme, e.g., ECDSA, together with the ring signature scheme. This functionality can be considered an extension of the common multi-signatures that require a certain number of ECDSA signatures to run a contract wallet. The proposed system was implemented using zkSync (Solidity). We discuss several potential applications of the proposed system, i.e., medical information sharing and asset management., Comment: 8 pages, 4 figures

Published
2023

2. An End-To-End Encrypted Cache System with Time-Dependent Access Control

Author

Emura, Keita and Yoshimi, Masato

Subjects
Computer Science - Cryptography and Security
Abstract

Due to the increasing use of encrypted communication, such as Transport Layer Security (TLS), encrypted cache systems are a promising approach for providing communication efficiency and privacy. Cache-22 is an encrypted cache system (Emura et al. ISITA 2020) that makes it possible to significantly reduce communication between a cache server and a service provider. In the final procedure of Cache-22, the service provider sends the corresponding decryption key to the user via TLS and this procedure allows the service provider to control which users can access the contents. For example, if a user has downloaded ciphertexts of several episodes of a show, the service provider can decide to provide some of the contents (e.g., the first episode) available for free while requiring a fee for the remaining contents. However, no concrete access control method has been implemented in the original Cache-22 system. In this paper, we add a scalable access control protocol to Cache-22. Specifically, we propose a time-dependent access control that requires a communication cost of $O(\log T_{\sf max})$ where $T_{\sf max}$ is the maximum time period. Although the protocol is stateful, we can provide time-dependent access control with scalability at the expense of this key management. We present experimental results and demonstrate that the modified system is effective for controlling access rights. We also observe a relationship between cache capacity and network traffic because the number of duplicated contents is higher than that in the original Cache-22 system, due to time-dependent access control.

Published
2023

3. Attribute-Based Keyed Fully Homomorphic Encryption

Author

Emura, Keita, Sato, Shingo, Takayasu, Atsushi, Goos, Gerhard, Series Editor, Hartmanis, Juris, Founding Editor, Bertino, Elisa, Editorial Board Member, Gao, Wen, Editorial Board Member, Steffen, Bernhard, Editorial Board Member, Yung, Moti, Editorial Board Member, Galdi, Clemente, editor, and Phan, Duong Hieu, editor

Published
2024
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6. A Sealed-bid Auction with Fund Binding: Preventing Maximum Bidding Price Leakage

Author

Chin, Kota, Emura, Keita, Omote, Kazumasa, and Sato, Shingo

Subjects
Computer Science - Cryptography and Security, Computer Science - Computer Science and Game Theory
Abstract

In an open-bid auction, a bidder can know the budgets of other bidders. Thus, a sealed-bid auction that hides bidding prices is desirable. However, in previous sealed-bid auction protocols, it has been difficult to provide a ``fund binding'' property, which would guarantee that a bidder has funds more than or equal to the bidding price and that the funds are forcibly withdrawn when the bidder wins. Thus, such protocols are vulnerable to false bidding. As a solution, many protocols employ a simple deposit method in which each bidder sends a deposit to a smart contract, which is greater than or equal to the bidding price, before the bidding phase. However, this deposit reveals the maximum bidding price, and it is preferable to hide this information. In this paper, we propose a sealed-bid auction protocol that provides a fund binding property. Our protocol not only hides the bidding price and a maximum bidding price, but also provides fund binding, simultaneously. For hiding the maximum bidding price, we pay attention to the fact that usual Ethereum transactions and transactions for sending funds to a one-time address have the same transaction structure, and it seems that they are indistinguishable. We discuss how much bidding transactions are hidden. We also employ DECO (Zhang et al,. CCS 2020) that proves the validity of the data to a verifier in which the data are taken from a source without showing the data itself. Finally, we give our implementation which shows transaction fees required and compare it to a sealed-bid auction protocol employing the simple deposit method.

Published
2022

8. Membership Privacy for Asynchronous Group Messaging

Author

Emura, Keita, Kajita, Kaisei, Nojima, Ryo, Ogawa, Kazuto, Ohtake, Go, Goos, Gerhard, Founding Editor, Hartmanis, Juris, Founding Editor, Bertino, Elisa, Editorial Board Member, Gao, Wen, Editorial Board Member, Steffen, Bernhard, Editorial Board Member, Yung, Moti, Editorial Board Member, You, Ilsun, editor, and Youn, Taek-Young, editor

Published
2023
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9. An Anonymous Trust-Marking Scheme on Blockchain Systems

Author

Sato, Teppei, Emura, Keita, Fujitani, Tomoki, and Omote, Kazumasa

Subjects
Computer Science - Cryptography and Security
Abstract

During the Coincheck incident, which recorded the largest damages in cryptocurrency history in 2018, it was demonstrated that using Mosaic token can have a certain effect. Although it seems attractive to employ tokens as countermeasures for cryptocurrency leakage, Mosaic is a specific token for the New Economy Movement (NEM) cryptocurrency and is not employed for other blockchain systems or cryptocurrencies. Moreover, although some volunteers tracked leaked NEM using Mosaic in the CoinCheck incident, it would be better to verify that the volunteers can be trusted. Simultaneously, if someone (e.g., who stole cryptocurrencies) can identify the volunteers, then that person or organization may be targets of them. In this paper, we propose an anonymous trust-marking scheme on blockchain systems that is universally applicable to any cryptocurrency. In our scheme, entities called token admitters are allowed to generate tokens adding trustworthiness or untrustworthiness to addresses. Anyone can anonymously verify whether these tokens were issued by a token admitter. Simultaneously, only the designated auditor and no one else, including nondesignated auditors, can identify the token admitters. Our scheme is based on accountable ring signatures and commitment, and is implemented on an elliptic curve called Curve25519, and we confirm that both cryptographic tools are efficient. Moreover, we also confirm that our scheme is applicable to Bitcoin, Ethereum, and NEM., Comment: An extended abstract appeared at the 3rd IEEE International Conference on Blockchain and Cryptocurrency, ICBC 2021. This is the full version

Published
2020

11. More Efficient Adaptively Secure Lattice-Based IBE with Equality Test in the Standard Model

Author

Asano, Kyoichi, Emura, Keita, Takayasu, Atsushi, Goos, Gerhard, Founding Editor, Hartmanis, Juris, Founding Editor, Bertino, Elisa, Editorial Board Member, Gao, Wen, Editorial Board Member, Steffen, Bernhard, Editorial Board Member, Yung, Moti, Editorial Board Member, Susilo, Willy, editor, Chen, Xiaofeng, editor, Guo, Fuchun, editor, Zhang, Yudi, editor, and Intan, Rolly, editor

Published
2022
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13. Output Prediction Attacks on Block Ciphers Using Deep Learning

Author

Kimura, Hayato, Emura, Keita, Isobe, Takanori, Ito, Ryoma, Ogawa, Kazuto, Ohigashi, Toshihiro, Goos, Gerhard, Founding Editor, Hartmanis, Juris, Founding Editor, Bertino, Elisa, Editorial Board Member, Gao, Wen, Editorial Board Member, Steffen, Bernhard, Editorial Board Member, Yung, Moti, Editorial Board Member, Zhou, Jianying, editor, Adepu, Sridhar, editor, Alcaraz, Cristina, editor, Batina, Lejla, editor, Casalicchio, Emiliano, editor, Chattopadhyay, Sudipta, editor, Jin, Chenglu, editor, Lin, Jingqiang, editor, Losiouk, Eleonora, editor, Majumdar, Suryadipta, editor, Meng, Weizhi, editor, Picek, Stjepan, editor, Shao, Jun, editor, Su, Chunhua, editor, Wang, Cong, editor, Zhauniarovich, Yury, editor, and Zonouz, Saman, editor

Published
2022
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16. Verifiable Functional Encryption Using Intel SGX

Author

Suzuki, Tatsuya, Emura, Keita, Ohigashi, Toshihiro, Omote, Kazumasa, Goos, Gerhard, Founding Editor, Hartmanis, Juris, Founding Editor, Bertino, Elisa, Editorial Board Member, Gao, Wen, Editorial Board Member, Steffen, Bernhard, Editorial Board Member, Woeginger, Gerhard, Editorial Board Member, Yung, Moti, Editorial Board Member, Huang, Qiong, editor, and Yu, Yu, editor

Published
2021
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23. Identity-Based Encryption with Security Against the KGC: A Formal Model and Its Instantiation from Lattices

Author

Emura, Keita, Katsumata, Shuichi, Watanabe, Yohei, Goos, Gerhard, Founding Editor, Hartmanis, Juris, Founding Editor, Bertino, Elisa, Editorial Board Member, Gao, Wen, Editorial Board Member, Steffen, Bernhard, Editorial Board Member, Woeginger, Gerhard, Editorial Board Member, Yung, Moti, Editorial Board Member, Sako, Kazue, editor, Schneider, Steve, editor, and Ryan, Peter Y. A., editor

Published
2019
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25. A Generic Construction of Integrated Secure-Channel Free PEKS and PKE

Author

Suzuki, Tatsuya, Emura, Keita, Ohigashi, Toshihiro, Hutchison, David, Series Editor, Kanade, Takeo, Series Editor, Kittler, Josef, Series Editor, Kleinberg, Jon M., Series Editor, Mattern, Friedemann, Series Editor, Mitchell, John C., Series Editor, Naor, Moni, Series Editor, Pandu Rangan, C., Series Editor, Steffen, Bernhard, Series Editor, Terzopoulos, Demetri, Series Editor, Tygar, Doug, Series Editor, Weikum, Gerhard, Series Editor, Su, Chunhua, editor, and Kikuchi, Hiroaki, editor

Published
2018
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26. A Revocable Group Signature Scheme with Scalability from Simple Assumptions and Its Implementation

Author

Emura, Keita, Hayashi, Takuya, Hutchison, David, Series Editor, Kanade, Takeo, Series Editor, Kittler, Josef, Series Editor, Kleinberg, Jon M., Series Editor, Mattern, Friedemann, Series Editor, Mitchell, John C., Series Editor, Naor, Moni, Series Editor, Pandu Rangan, C., Series Editor, Steffen, Bernhard, Series Editor, Terzopoulos, Demetri, Series Editor, Tygar, Doug, Series Editor, Weikum, Gerhard, Series Editor, Chen, Liqun, editor, Manulis, Mark, editor, and Schneider, Steve, editor

Published
2018
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27. Fully Anonymous Group Signature with Verifier-Local Revocation

Author

Ishida, Ai, Sakai, Yusuke, Emura, Keita, Hanaoka, Goichiro, Tanaka, Keisuke, Hutchison, David, Series Editor, Kanade, Takeo, Series Editor, Kittler, Josef, Series Editor, Kleinberg, Jon M., Series Editor, Mattern, Friedemann, Series Editor, Mitchell, John C., Series Editor, Naor, Moni, Series Editor, Pandu Rangan, C., Series Editor, Steffen, Bernhard, Series Editor, Terzopoulos, Demetri, Series Editor, Tygar, Doug, Series Editor, Weikum, Gerhard, Series Editor, Catalano, Dario, editor, and De Prisco, Roberto, editor

Published
2018
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30. Generic Constructions for Fully Secure Revocable Attribute-Based Encryption

Author

Yamada, Kotoko, Attrapadung, Nuttapong, Emura, Keita, Hanaoka, Goichiro, Tanaka, Keisuke, Hutchison, David, Series Editor, Kanade, Takeo, Series Editor, Kittler, Josef, Series Editor, Kleinberg, Jon M., Series Editor, Mattern, Friedemann, Series Editor, Mitchell, John C., Series Editor, Naor, Moni, Series Editor, Pandu Rangan, C., Series Editor, Steffen, Bernhard, Series Editor, Terzopoulos, Demetri, Series Editor, Tygar, Doug, Series Editor, Weikum, Gerhard, Series Editor, Foley, Simon N., editor, Gollmann, Dieter, editor, and Snekkenes, Einar, editor

Published
2017
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31. A Generic Construction of Secure-Channel Free Searchable Encryption with Multiple Keywords

Author

Emura, Keita, Hutchison, David, Series editor, Kanade, Takeo, Series editor, Kittler, Josef, Series editor, Kleinberg, Jon M., Series editor, Mattern, Friedemann, Series editor, Mitchell, John C., Series editor, Naor, Moni, Series editor, Pandu Rangan, C., Series editor, Steffen, Bernhard, Series editor, Terzopoulos, Demetri, Series editor, Tygar, Doug, Series editor, Weikum, Gerhard, Series editor, Yan, Zheng, editor, Molva, Refik, editor, Mazurczyk, Wojciech, editor, and Kantola, Raimo, editor

Published
2017
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32. Privacy-Preserving Aggregation of Time-Series Data with Public Verifiability from Simple Assumptions

Author

Emura, Keita, Hutchison, David, Series editor, Kanade, Takeo, Series editor, Kittler, Josef, Series editor, Kleinberg, Jon M., Series editor, Mattern, Friedemann, Series editor, Mitchell, John C., Series editor, Naor, Moni, Series editor, Pandu Rangan, C., Series editor, Steffen, Bernhard, Series editor, Terzopoulos, Demetri, Series editor, Tygar, Doug, Series editor, Weikum, Gerhard, Series editor, Pieprzyk, Josef, editor, and Suriadi, Suriadi, editor

Published
2017
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33. New Revocable IBE in Prime-Order Groups: Adaptively Secure, Decryption Key Exposure Resistant, and with Short Public Parameters

Author

Watanabe, Yohei, Emura, Keita, Seo, Jae Hong, Hutchison, David, Series editor, Kanade, Takeo, Series editor, Kittler, Josef, Series editor, Kleinberg, Jon M., Series editor, Mattern, Friedemann, Series editor, Mitchell, John C., Series editor, Naor, Moni, Series editor, Pandu Rangan, C., Series editor, Steffen, Bernhard, Series editor, Terzopoulos, Demetri, Series editor, Tygar, Doug, Series editor, Weikum, Gerhard, Series editor, and Handschuh, Helena, editor

Published
2017
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34. A Light-Weight Group Signature Scheme with Time-Token Dependent Linking

Author

Emura, Keita, Hayashi, Takuya, Hutchison, David, Series editor, Kanade, Takeo, Series editor, Kittler, Josef, Series editor, Kleinberg, Jon M., Series editor, Mattern, Friedemann, Series editor, Mitchell, John C., Series editor, Naor, Moni, Series editor, Pandu Rangan, C., Series editor, Steffen, Bernhard, Series editor, Terzopoulos, Demetri, Series editor, Tygar, Doug, Series editor, Weikum, Gerhard, Series editor, Güneysu, Tim, editor, Leander, Gregor, editor, and Moradi, Amir, editor

Published
2016
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35. Group Signature with Deniability: How to Disavow a Signature

Author

Ishida, Ai, Emura, Keita, Hanaoka, Goichiro, Sakai, Yusuke, Tanaka, Keisuke, Hutchison, David, Series editor, Kanade, Takeo, Series editor, Kittler, Josef, Series editor, Kleinberg, Jon M., Series editor, Mattern, Friedemann, Series editor, Mitchell, John C., Series editor, Naor, Moni, Series editor, Pandu Rangan, C., Series editor, Steffen, Bernhard, Series editor, Terzopoulos, Demetri, Series editor, Tygar, Doug, Series editor, Weikum, Gerhard, Series editor, Foresti, Sara, editor, and Persiano, Giuseppe, editor

Published
2016
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37. Accumulable Optimistic Fair Exchange from Verifiably Encrypted Homomorphic Signatures

Author

Seo, Jae Hong, Emura, Keita, Xagawa, Keita, Yoneyama, Kazuki, Hutchison, David, Series editor, Kanade, Takeo, Series editor, Kittler, Josef, Series editor, Kleinberg, Jon M., Series editor, Mattern, Friedemann, Series editor, Mitchell, John C., Series editor, Naor, Moni, Series editor, Pandu Rangan, C., Series editor, Steffen, Bernhard, Series editor, Terzopoulos, Demetri, Series editor, Tygar, Doug, Series editor, Weikum, Gerhard, Series editor, Malkin, Tal, editor, Kolesnikov, Vladimir, editor, Lewko, Allison Bishop, editor, and Polychronakis, Michalis, editor

Published
2015
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38. Adaptive-ID Secure Revocable Hierarchical Identity-Based Encryption

Author

Seo, Jae Hong, Emura, Keita, Hutchison, David, Series editor, Kanade, Takeo, Series editor, Kittler, Josef, Series editor, Kleinberg, Jon M., Series editor, Mattern, Friedemann, Series editor, Mitchell, John C., Series editor, Naor, Moni, Series editor, Pandu Rangan, C., Series editor, Steffen, Bernhard, Series editor, Terzopoulos, Demetri, Series editor, Tygar, Doug, Series editor, Weikum, Gerhard, Series editor, Tanaka, Keisuke, editor, and Suga, Yuji, editor

Published
2015
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39. Anonymous Data Collection System with Mediators

Author

Arai, Hiromi, Emura, Keita, Matsuda, Takahiro, Hutchison, David, Series editor, Kanade, Takeo, Series editor, Kittler, Josef, Series editor, Kleinberg, Jon M., Series editor, Mattern, Friedemann, Series editor, Mitchell, John C., Series editor, Naor, Moni, Series editor, Pandu Rangan, C., Series editor, Steffen, Bernhard, Series editor, Terzopoulos, Demetri, Series editor, Tygar, Doug, Series editor, Weikum, Gerhard, Series editor, Ors, Berna, editor, and Preneel, Bart, editor

Published
2015
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40. Dynamic Threshold Public-Key Encryption with Decryption Consistency from Static Assumptions

Author

Sakai, Yusuke, Emura, Keita, Schuldt, Jacob C.N., Hanaoka, Goichiro, Ohta, Kazuo, Hutchison, David, Series editor, Kanade, Takeo, Series editor, Kittler, Josef, Series editor, Kleinberg, Jon M., Series editor, Mattern, Friedemann, Series editor, Mitchell, John C., Series editor, Naor, Moni, Series editor, Pandu Rangan, C., Series editor, Steffen, Bernhard, Series editor, Terzopoulos, Demetri, Series editor, Tygar, Doug, Series editor, Weikum, Gerhard, Series editor, Foo, Ernest, editor, and Stebila, Douglas, editor

Published
2015
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41. Revocable Hierarchical Identity-Based Encryption: History-Free Update, Security Against Insiders, and Short Ciphertexts

Author

Seo, Jae Hong, Emura, Keita, Hutchison, David, Series editor, Kanade, Takeo, Series editor, Kittler, Josef, Series editor, Kleinberg, Jon M., Series editor, Mattern, Friedemann, Series editor, Mitchell, John C., Series editor, Naor, Moni, Series editor, Pandu Rangan, C., Series editor, Steffen, Bernhard, Series editor, Terzopoulos, Demetri, Series editor, Tygar, Doug, Series editor, Weikum, Gerhard, Series editor, and Nyberg, Kaisa, editor

Published
2015
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