Privacy plays a crucial role in the internet era, where many applications allow people to communicate and use their services through the internet. Privacy-preserving Identity Management (PPIdM) system is a scheme that helps manage users’ identities and protects users’ privacy by enabling users to authenticate themselves without disclosing their real identities. The PPIdM system also allows users to reveal some minor identity attributes while others remain secret selectively. However, anonymity also encourages malicious users to break the system’s policy and commit crimes since their real identities are anonymous. Existing PPIdM systems use the identity provider (IP) as a medium to verify users’ identity attributes, record all users’ real identities, and ensure that malicious users’ identities are traceable. Therefore, users’ identities are hidden from all entities but the IP. However, the user’s privacy is vulnerable because there is nothing to guarantee that the IP is always honest and not curious about their users’ activities and private information. This paper proposes a PPIdM system on the blockchain that helps users manage their identity attributes and keeps their real identities secret from all entities, including the IP. Still, the system’s consensus can trace malicious users’ real identities if they violate the system’s policy. The PPIdM’s security requirements are analyzed and proved informally using the game-based proof scheme. The main idea of this study is to combine zk-SNARK, a type of zero-knowledge proof (ZKP), Shamir’s secret sharing (SSS), and several other cryptography techniques.

Privacy is playing a crucial role in the smart health industry, where health service providers and their customers use the internet of things (IoT) to provide and consume health services. Preserving privacy for legitimate users and preventing illegitimate users from accessing services are difficult to implement simultaneously. In this study, we addressed this issue by proposing a new healthcare system for IoT based on the blockchain and zero-knowledge succinct noninteractive argument of knowledge (zk-SNARK). We employ the anonymity property of the public blockchain to protect users’ privacy. The zk-SNARK scheme works as an anonymous authenticator to prevent unauthorized users from using services. We also analyze the security of the proposed system by showing that it can resist various types of attacks, such as impersonation, collusion, and man-in-the-middle attacks. Finally, we evaluate the performance of the zk-SNARK scheme with respect to computational costs and the interactions with the Ethereum blockchain smart contract with respect to transaction fees.

NTRU was the first practical public key encryption scheme constructed on a lattice over a polynomial-based ring and has been considered secure against significant cryptanalytic attacks over the past few decades. However, NTRU and its variants suffer from several drawbacks, including difficulties in achieving worst-case correctness error in a moderate modulus, inconvenient sampling distributions for messages, and relatively slower algorithms compared to other lattice-based schemes. In this work, we propose a new NTRU-based key encapsulation mechanism (KEM), called NTRU+, which overcomes nearly all existing drawbacks. NTRU+ is constructed based on two new generic transformations: ACWC ₂ and FO ^⊥ (a variant of the Fujisaki-Okamoto transform). ACWC ₂ is used to easily achieve worst-case correctness error, while FO ^⊥ is used to achieve chosen-ciphertext security without re-encryption. Both ACWC ₂ and FO ^⊥ are defined using a randomness-recovery algorithm and an encoding method. In particular, our simple encoding method, the semi-generalized one-time pad (SOTP), allows us to sample a message from a natural bit-string space with an arbitrary distribution. We provide four parameter sets for NTRU+ and present implementation results using NTT-friendly rings over cyclotomic trinomials.