Published papers

This study aimed to identify which message emphases in short-form notifications are most strongly associated with users’ intention to register a passkey in a switching context. Passkeys are increasingly being introduced as a phishing-resistant alternative to passwords, but existing account holders may continue using password-based sign-in. We compared eight smartphone-style stimuli: a service-based baseline approximating a current real-service notification, a guideline-based baseline based on the FIDO Alliance UX Guidelines, and six variants that added different concise messages to the guideline-based notification. We also examined whether reported password-autofill and two-factor authentication (2FA) use were associated with registration intention. An online experiment using a hypothetical sign-in situation was conducted with 800 participants in Japan who used Amazon Shopping on a smartphone, reported using password-based sign-in as their usual sign-in method, and recalled seeing an Amazon passkey-registration notification. The dependent variable was self-reported registration intention rather than observed registration behavior. Ordinal logistic regression and Holm-adjusted pairwise comparisons showed that several guideline-based conditions, which differed from the service-based baseline in both format and content, were associated with higher intention. Within the common guideline-based structure, the perceived-threat-focused variant showed the clearest and most consistent association with higher intention. Reported password-autofill use was positively associated with intention, whereas evidence for an association with 2FA use was inconclusive given the limited number of 2FA users. These findings suggest that brief message changes may inform candidate designs for passkey-registration notifications, while highlighting the need for behavioral validation in real-service settings. (Note: Contributed as the 3rd author (co-author) in a 3-member collaboration. The 1st author serves as the corresponding author.)

This paper proposes a technique for constructing programming languages under object-oriented operating systems. Such operating systems consist of independent modules, so one can build flexible systems and applications. However, traditional object-oriented operating systems provide users with system's object model (system object), so that programming language designers have to map their object model (language object) onto the system object model. In our proposed technique, called LO/SO amalgamation, language objects and system objects can be treated in a uniform fashion. So, it is now possible to specify system objects by using the rich programming environment supported by programming languages. Furthermore, message passing between two types of objects can be implemented efficiently by using our technique. In this paper, we present the concept of LO/SO amalgamation, and an evaluation of our prototype language, Apertos ConcurrentSmalltalk (ACST), which incorporates LO/SO amalgamation.

本稿では，FIDO（ファイド）アライアンスがW3C（World Wide Web Consortium）と共に推進するFIDO認証について解説する．近年，フィッシング攻撃などによる不正アクセスへの対策が急がれる中，FIDO認証はその対策の大きな決め手の一つとなる．FIDO認証は，リモートからの悪意者による攻撃を防ぐため，利用者による認証器の所持を基本とし，公開鍵暗号に基づく署名検証を利活用する．利用者にとって使い勝手が良く，フィッシング攻撃への耐性をもつ「シンプルで堅牢な」認証方式である． 　FIDO認証は，2014年12月に公開されたFIDO 1.0仕様を皮切りに本格的な商用利用が開始され，現在はW3Cが策定するWeb認証（Web Authentication，WebAuthn）の勧告仕様を含めて総称するFIDO2が議論の中心となっている．そして，普及に向けて長い間課題となっていたいわゆるアカウントリカバリーについても一定の方向性が確立し，いま「パスキー」としてさらなる広がりが期待されている．その一方，FIDO認証のために必要な認証資格情報（クレデンシャル）を認証器から取り出すことを認めた結果，新たに取り組むべき課題も認識されつつあり，業界を挙げての取り組みが必要である． FIDOアライアンスは，FIDO2とパスキーに加えて，バイオメトリック部品認定，IoTデバイスと認証にまつわる課題を解決するFDO（FIDO Device Onboard）仕様なども展開し，パスワード課題の解決に向けてさまざまな観点から取り組んでいる．FIDO認証とWeb認証に対しては国内からの貢献も顕著で，引き続くグローバルとしての取り組みで，社会課題の解決に向けてさらに貢献できる．

This article describes the idea of utilizing Attested Execution Secure Processors (AESPs) that fit into building a secure Self-Sovereign Identity (SSI) system satisfying Sybil-resistance under permissionless blockchains. Today's circumstances requiring people to be more online have encouraged us to address digital identity preserving privacy. There is a momentum of research addressing SSI, and many researchers approach blockchain technology as a foundation. SSI brings natural persons various benefits such as owning controls; on the other side, digital identity systems in the real world require Sybil-resistance to comply with Anti-Money-Laundering (AML) and other needs. The main idea in our proposal is to utilize AESPs for three reasons: first is the use of attested execution capability along with tamper-resistance, which is a strong assumption; second is powerfulness and flexibility, allowing various open-source programs to be executed within a secure enclave, and the third is that equipping hardware-assisted security in mobile devices has become a norm. Rafael Pass et al.'s formal abstraction of AESPs and the ideal functionality Gatt enable us to formulate how hardware-assisted security works for secure digital identity systems preserving privacy under permissionless blockchains mathematically. Our proposal of the AESP-based SSI architecture and system protocols, ΠGatt, demonstrates the advantages of building a proper SSI system that satisfies the Sybil-resistant requirement. The protocols may eliminate the online distributed committee assumed in other research, such as CanDID, because of assuming AESPs; thus, ΠGatt allows not to rely on multi-party computation (MPC), bringing drastic flexibility and efficiency compared with the existing SSI systems.

Increasing attention to digital identity and self-sovereign identity (SSI) is gaining momentum. SSI brings various benefits to natural persons, such as owning controls; conversely, digital identity systems in the real world require Sybil-resistance to comply with anti-money laundering (AML) and other needs. CanDID by Maram et al. proposed that decentralized digital identity systems may achieve Sybil-resistance and preserve privacy by utilizing multi-party computation (MPC), assuming a distributed committee of trusted nodes. Pass et al. proposed the formal abstraction of attested execution secure processors (AESPs) while equipping hardware-assisted security in mobile devices has become the norm. We first describe our proposal to utilize AESPs for building secure Sybil-resistant SSI systems, the architecture with a set of system protocols ΠGatt , which brings drastic flexibility and efficiency compared to existing systems. In addition, we propose a novel scheme that enables users (holders) to request verifiers to verify their credentials without AESPs, and it further achieves unlinkability among credentials created for public verification. Our scheme introduces a simplified format for computed claims and commitment-based anonymous identifiers. We also describe a technique to utilize zero-knowledge membership proofs, in particular, “One-Out-of-Many Proofs” Σ -protocol by Groth and Kohlweiss, which can prove the existence of an expected credential without identifying it. Along with other techniques, such as utilizing the BBS+ signature scheme, we demonstrate how our scheme can achieve its goals with the extended anonymous and Sybil-resistant SSI system protocols ΠGatt+ . Entitling unlinkability among derived credentials in the anonymous Sybil-resistant SSI results in proper privacy preservation.