To meet password selection criteria of a server, a user occasionally needs to provide multiple choices of password candidates to an on-line password meter, but such user-chosen candidates tend to be derived from the user’s previous passwords—the meter may have a high chance to acquire information about a user’s passwords employed for various purposes. A third party password metering service may worsen this threat. In this paper, we first explore a new on-line password meter concept that does not necessitate the exposure of user’s passwords for evaluating user-chosen password candidates in the server side. Our basic idea is straightforward; to adapt fully homomorphic encryption (FHE) schemes to build such a system but its performance achievement is greatly challenging. Optimization techniques are necessary for performance achievement in practice. We employ various performance enhancement techniques and implement the NIST (National Institute of Standards and Technology) metering method as seminal work in this field. Our experiment results demonstrate that the running time of the proposed meter is around 60 s in a conventional desktop server, expecting better performance in high-end hardware, with an FHE scheme in HElib library where parameters support at least 80-bit security. We believe the proposed method can be further explored and used for a password metering in case that password secrecy is very important—the user’s password candidates should not be exposed to the meter and also an internal mechanism of password metering should not be disclosed to users and any other third parties.

In digital identity authentication, credentials are typically stored in a digital wallet and authenticated through a single key-based signature and public key verification. However, ensuring compatibility between systems and credentials can be challenging and the existing architecture can create a single point of failure, which can hinder system stability and prevent data interchange. To address this problem, we propose a multiparty distributed signature structure using FROST, a Schnorr signature-based threshold signature algorithm, applied to the WACI protocol framework for credential interaction. This approach eliminates a single point of failure and secures the signer’s anonymity. Additionally, by following standard interoperability protocol procedures, we can ensure interoperability during the exchange of digital wallets and credentials. This paper presents a method that combines a multiparty distributed signature algorithm and an interoperability protocol, and discusses the implementation results.

This paper delves into the advantages of authentication algorithms employing self-sovereign identity, highlighting a reduced communication overhead and the elimination of single points of failure. However, it acknowledges the vulnerability of digital wallets to real-world issues like loss or theft. To address these challenges, we propose an efficient key backup and recovery protocol based on the FROST threshold signature algorithm. This protocol involves trusted third parties and backup devices, ensuring secure secret key sharing and rapid key recovery. Performance evaluations, including key recovery time, demonstrate the protocol’s efficiency and reliability, bolstering the overall robustness of self-sovereign identity systems.

The purpose of this study is to provide an efficient search function over a large amount of encrypted data, where the bit length of each item is several tens of bits. For this purpose, we have improved the existing hybrid homomorphic encryption by enabling the longer data items to be stored while using multiple encrypted databases and by suggesting an improved search method working on top of the multiple instances of the database. Further, we found the optimal number of databases to be needed when 40-bit information, such as social security number, is stored after encryption. Through experiments, we were able to check the existence of a given (Korean) social security number of 13 decimal digits in approximately 12 s from a database that has 10 million encrypted social security numbers over a typical personal computer environment. The outcome of this research can be used to build a large-scale, practical encrypted database in order to support the search operation. In addition, it is expected to be used as a method for providing both security and practicality to the industry dealing with credit information evaluation and personal data requiring privacy.