Combining Private Set-Intersection with Secure Two-Party Computation

Private Set-Intersection (PSI) is one of the most popular and practically relevant secure two-party computation (2PC) tasks. Therefore, designing special-purpose PSI protocols (which are more efficient than generic 2PC solutions) is a very active line of research. In particular, a recent line of work has proposed PSI protocols based on oblivious transfer (OT) which, thanks to recent advances in OT-extension techniques, is nowadays a very cheap cryptographic building block. Unfortunately, these protocols cannot be plugged into larger 2PC applications since in these protocols one party (by design) learns the output of the intersection. Therefore, it is not possible to perform secure post-processing of the output of the PSI protocol. In this paper we propose a novel and efficient OT-based PSI protocol that produces an encrypted output that can therefore be later used as an input to other 2PC protocols. In particular, the protocol can be used in combination with all common approaches to 2PC including garbled circuits, secret sharing and homomorphic encryption. Thus, our protocol can be combined with the right 2PC techniques to achieve more efficient protocols for computations of the form $z=f(X\cap Y)$ for arbitrary functions $f$

SoK: Privacy-Preserving Signatures

Modern security systems depend fundamentally on the ability of users to authenticate their communications to other parties in a network. Unfortunately, cryptographic authentication can substantially undermine the privacy of users. One possible solution to this problem is to use privacy-preserving cryptographic authentication. These protocols allow users to authenticate their communications without revealing their identity to the verifier. In the non-interactive setting, the most common protocols include blind, ring, and group signatures, each of which has been the subject of enormous research in the security and cryptography literature. These primitives are now being deployed at scale in major applications, including Intel\u27s SGX software attestation framework. The depth of the research literature and the prospect of large-scale deployment motivate us to systematize our understanding of the research in this area. This work provides an overview of these techniques, focusing on applications and efficiency

暗号要素技術の一般的構成を介した高い安全性・高度な機能を備えた暗号要素技術の構成

Recent years have witnessed an active research on cryptographic primitives with complex functionality beyond simple encryption or authentication. A cryptographic primitive is required to be proposed together with a formal model of its usage and a rigorous proof of security under that model.This approach has suffered from the two drawbacks: (1) security models are defined in a very specific manner for each primitive, which situation causes the relationship between these security models not to be very clear, and (2) no comprehensive ways to confirm that a formal model of security really captures every possible scenarios in practice.This research relaxes these two drawbacks by the following approach: (1) By observing the fact that a cryptographic primitive A should be crucial for constructing another primitive B, we identify an easy-to-understand approach for constructing various cryptographic primitives.(2) Consider a situation in which there are closely related cryptographic primitives A and B, and the primitive A has no known security requirement that corresponds to some wellknown security requirement (b) for the latter primitive B.We argue that this situation suggests that this unknown security requirement for A can capture some practical attack. This enables us to detect unknown threats for various cryptographic primitives that have been missed bythe current security models.Following this approach, we identify an overlooked security threat for a cryptographic primitive called group signature. Furthermore, we apply the methodology (2) to the “revocable”group signature and obtain a new extension of public-key encryption which allows to restrict a plaintext that can be securely encrypted.通常の暗号化や認証にとどまらず, 複雑な機能を備えた暗号要素技術の提案が活発になっている. 暗号要素技術の安全性は利用形態に応じて, セキュリティ上の脅威をモデル化して安全性要件を定め, 新方式はそれぞれ安全性定義を満たすことの証明と共に提案される.既存研究では, 次の問題があった: (1) 要素技術ごとに個別に安全性の定義を与えているため, 理論的な体系化が不十分であった. (2) 安全性定義が実用上の脅威を完全に捉えきれているかの検証が難しかった.本研究は上記の問題を次の考え方で解決する. (1) ある要素技術(A) を構成するには別の要素技術(B) を部品として用いることが不可欠であることに注目し, 各要素技術の安全性要件の関連を整理・体系化して, 新方式を見通し良く構成可能とする. (2) 要素技術(B)で考慮されていた安全性要件(b) に対応する要素技術(A) の安全性要件が未定義なら, それを(A) の新たな安全性要件(a) として定式化する. これにより未知の脅威の検出が容易になる.グループ署名と非対話開示機能付き公開鍵暗号という2 つの要素技術について上記の考え方を適用して, グループ署名について未知の脅威を指摘する.また, 証明書失効機能と呼ばれる拡張機能を持つグループ署名に上記の考え方を適用して, 公開鍵暗号についての新たな拡張機能である, 暗号化できる平文を制限できる公開鍵暗号の効率的な構成法を明らかにする.電気通信大学201

Simple and Efficient Single Round Almost Perfectly Secure Message Transmission Tolerating Generalized Adversary

Patra et al. gave a necessary and sufficient condition for the possibility of almost perfectly secure message transmission protocols tolerating general, non-threshold Q^2 adversary structure. However, their protocol requires at least three rounds and performs exponential (exponential in the size of the adversary structure) computation and communication. Moreover, they have left it as an open problem to design efficient protocol for almost perfectly secure message transmission, tolerating Q^2 adversary structure. In this paper, we show the first single round almost perfectly secure message transmission protocol tolerating Q^2 adversary structure. The computation and communication complexities of the protocol are both polynomial} in the size of underlying linear secret sharing scheme (LSSS) and adversary structure. This solves the open problem raised by Patra et al.. When we restrict our general protocol to threshold adversary with n=2t+1, we obtain a single round, communication optimal almost secure message transmission protocol tolerating threshold adversary, which is much more computationally efficient and relatively simpler than the previous communication optimal protocol of Srinathan et al

A Blockchain Framework for Patient-Centered Health Records and Exchange (HealthChain): Evaluation and Proof-of-Concept Study

Background: Blockchain has the potential to disrupt the current modes of patient data access, accumulation, contribution, exchange, and control. Using interoperability standards, smart contracts, and cryptographic identities, patients can securely exchange data with providers and regulate access. The resulting comprehensive, longitudinal medical records can significantly improve the cost and quality of patient care for individuals and populations alike. Objective: This work presents HealthChain, a novel patient-centered blockchain framework. The intent is to bolster patient engagement, data curation, and regulated dissemination of accumulated information in a secure, interoperable environment. A mixed-block blockchain is proposed to support immutable logging and redactable patient blocks. Patient data are generated and exchanged through Health Level-7 Fast Healthcare Interoperability Resources, allowing seamless transfer with compliant systems. In addition, patients receive cryptographic identities in the form of public and private key pairs. Public keys are stored in the blockchain and are suitable for securing and verifying transactions. Furthermore, the envisaged system uses proxy re-encryption (PRE) to share information through revocable, smart contracts, ensuring the preservation of privacy and confidentiality. Finally, several PRE improvements are offered to enhance performance and security. Methods: The framework was formulated to address key barriers to blockchain adoption in health care, namely, information security, interoperability, data integrity, identity validation, and scalability. It supports 16 configurations through the manipulation of 4 modes. An open-source, proof-of-concept tool was developed to evaluate the performance of the novel patient block components and system configurations. To demonstrate the utility of the proposed framework and evaluate resource consumption, extensive testing was performed on each of the 16 configurations over a variety of scenarios involving a variable number of existing and imported records. Results: The results indicate several clear high-performing, low-bandwidth configurations, although they are not the strongest cryptographically. Of the strongest models, one’s anticipated cumulative record size is shown to influence the selection. Although the most efficient algorithm is ultimately user specific, Advanced Encryption Standard–encrypted data with static keys, incremental server storage, and no additional server-side encryption are the fastest and least bandwidth intensive, whereas proxy re-encrypted data with dynamic keys, incremental server storage, and additional server-side encryption are the best performing of the strongest configurations. Conclusions: Blockchain is a potent and viable technology for patient-centered access to and exchange of health information. By integrating a structured, interoperable design with patient-accumulated and generated data shared through smart contracts into a universally accessible blockchain, HealthChain presents patients and providers with access to consistent and comprehensive medical records. Challenges addressed include data security, interoperability, block storage, and patient-administered data access, with several configurations emerging for further consideration regarding speed and security

How to backdoor LWE-like cryptosystems

We present a rather generic backdoor mechanism that can be applied to many LWE-like public-key cryptosystems. Our construction manipulates the key generation algorithm of such schemes in a way that allows a malicious adversary in possession of secret backdoor information to recover generated secret keys from corresponding public keys. To any user of the cryptosystem however, the output of our backdoored key generation is indistinguishable from output of the legitimate key generation algorithm. Our construction relies on elliptic-curve cryptography and draws on existing work on encoding of elliptic curve points as bit strings. Our backdoor mechanism can be applied to public-key cryptosystems where the secret key is generated from a secret seed and the public key includes a public seed of the same length. This holds - though not exclusively - for many cryptosystems based on LWE. In particular, we point out that our construction can be applied to backdoor HQC, FrodoKEM, Kyber and Dilithium. We also suggest a countermeasure that makes our backdoor detectable by users of the cryptosystem. To this end, we modify the key generation such that the public and secret key are pseudorandomly generated from a single seed which is included in the generated secret key. This allows any user of the key generation algorithm to regenerate keys using an independent implementation, making our backdooring attempt detectable

Faster Beta Weil Pairing on BLS Pairing Friendly Curves with Odd Embedding Degree

Since the advent of pairing-based cryptography, various optimization methods that increase the speed of pairing computations have been exploited, as well as new types of pairings. This paper extends the work of Kinoshita and Suzuki who proposed a new formula for the $\beta$-Weil pairing on curves with even embedding degree by eliminating denominators and exponents during the computation of the Weil pairing. We provide novel formulas suitable for the parallel computation for the $\beta$-Weil pairing on curves with odd embedding degree which involve vertical line functions useful for sparse multiplications. For computations we used Miller\u27s algorithm combined with storage and multifunction methods. Applying our framework to BLS-$27$, BLS-$15$ and BLS-$9$ curves at respectively the $256$ bit, the $192$ bit and the $128$ bit security level, we obtain faster $\beta$-Weil pairings than the previous state-of-the-art constructions. The correctness of all the formulas and bilinearity of pairings obtained in this work is verified by a SageMath code

Identity-as-a-Service: An Adaptive Security Infrastructure and Privacy-Preserving User Identity for the Cloud Environment

In recent years, enterprise applications have begun to migrate from a local hosting to a cloud provider and may have established a business-to-business relationship with each other manually. Adaptation of existing applications requires substantial implementation changes in individual architectural components. On the other hand, users may store their Personal Identifiable Information (PII) in the cloud environment so that cloud services may access and use it on demand. Even if cloud services specify their privacy policies, we cannot guarantee that they follow their policies and will not (accidentally) transfer PII to another party. In this paper, we present Identity-as-a-Service (IDaaS) as a trusted Identity and Access Management with two requirements: Firstly, IDaaS adapts trust between cloud services on demand. We move the trust relationship and identity propagation out of the application implementation and model them as a security topology. When the business comes up with a new e-commerce scenario, IDaaS uses the security topology to adapt a platform-specific security infrastructure for the given business scenario at runtime. Secondly, we protect the confidentiality of PII in federated security domains. We propose our Purpose-based Encryption to protect the disclosure of PII from intermediary entities in a business transaction and from untrusted hosts. Our solution is compliant with the General Data Protection Regulation and involves the least user interaction to prevent identity theft via the human link. The implementation can be easily adapted to existing Identity Management systems, and the performance is fast.</jats:p