149 research outputs found
Hidden in the Cloud : Advanced Cryptographic Techniques for Untrusted Cloud Environments
In the contemporary digital age, the ability to search and perform operations on encrypted data has become increasingly important. This significance is primarily due to the exponential growth of data, often referred to as the "new oil," and the corresponding rise in data privacy concerns. As more and more data is stored in the cloud, the need for robust security measures to protect this data from unauthorized access and misuse has become paramount.
One of the key challenges in this context is the ability to perform meaningful operations on the data while it remains encrypted. Traditional encryption techniques, while providing a high level of security, render the data unusable for any practical purpose other than storage. This is where advanced cryptographic protocols like Symmetric Searchable Encryption (SSE), Functional Encryption (FE), Homomorphic Encryption (HE), and Hybrid Homomorphic Encryption (HHE) come into play. These protocols not only ensure the confidentiality of data but also allow computations on encrypted data, thereby offering a higher level of security and privacy.
The ability to search and perform operations on encrypted data has several practical implications. For instance, it enables efficient Boolean queries on encrypted databases, which is crucial for many "big data" applications. It also allows for the execution of phrase searches, which are important for many machine learning applications, such as intelligent medical data analytics. Moreover, these capabilities are particularly relevant in the context of sensitive data, such as health records or financial information, where the privacy and security of user data are of utmost importance.
Furthermore, these capabilities can help build trust in digital systems. Trust is a critical factor in the adoption and use of digital services. By ensuring the confidentiality, integrity, and availability of data, these protocols can help build user trust in cloud services. This trust, in turn, can drive the wider adoption of digital services, leading to a more inclusive digital society.
However, it is important to note that while these capabilities offer significant advantages, they also present certain challenges. For instance, the computational overhead of these protocols can be substantial, making them less suitable for scenarios where efficiency is a critical requirement. Moreover, these protocols often require sophisticated key management mechanisms, which can be challenging to implement in practice. Therefore, there is a need for ongoing research to address these challenges and make these protocols more efficient and practical for real-world applications.
The research publications included in this thesis offer a deep dive into the intricacies and advancements in the realm of cryptographic protocols, particularly in the context of the challenges and needs highlighted above.
Publication I presents a novel approach to hybrid encryption, combining the strengths of ABE and SSE. This fusion aims to overcome the inherent limitations of both techniques, offering a more secure and efficient solution for key sharing and access control in cloud-based systems. Publication II further expands on SSE, showcasing a dynamic scheme that emphasizes forward and backward privacy, crucial for ensuring data integrity and confidentiality. Publication III and Publication IV delve into the potential of MIFE, demonstrating its applicability in real-world scenarios, such as designing encrypted private databases and additive reputation systems. These publications highlight the transformative potential of MIFE in bridging the gap between theoretical cryptographic concepts and practical applications. Lastly, Publication V underscores the significance of HE and HHE as a foundational element for secure protocols, emphasizing its potential in devices with limited computational capabilities.
In essence, these publications not only validate the importance of searching and performing operations on encrypted data but also provide innovative solutions to the challenges mentioned. They collectively underscore the transformative potential of advanced cryptographic protocols in enhancing data security and privacy, paving the way for a more secure digital future
Breaking Parallel ROS: Implication for Isogeny and Lattice-based Blind Signatures
Many of the three-round blind signatures based on identification protocols are only proven to be -concurrently unforgeable for . It was only recently shown in a seminal work by Benhamouda et al. (EUROCRYPT\u2721) that this is not just a limitation of the proof technique. They proposed an elegant polynomial time attack against the -concurrently unforgeability of the classical blind Schnorr protocol for .
However, there are still many blind signatures following a similar recipe to blind Schnorr where the attack by Benhamouda et al. does not apply. This includes for instance the isogeny-based blind signature CSI-Otter by Katsumata et al (CRYPTO\u2723), the lattice-based blind signatures Blaze+ by Alkeilani et al. (ACISP\u2720) and BlindOR by Alkeilani et al. (CANS\u2720).
In this work, we provide a simple and novel attack on blind signatures based on identification protocols performing parallel repetition to reduce the soundness error. Our attack translates to a polynomial time break for the -concurrent unforgeability of CSI-Otter, Blaze+, and BlindOR for .
More formally, we define an intermediate problem called Parallel Random inhomogeneities in an Overdetermined Solvable system of linear equations (pROS) problem and show that an attack against pROS implies an attack to the above blind signatures.
One takeaway of our finding is that while parallel repetition allows to exponentially reduce the soundness error of an identification protocol, this has minimal effect on the resulting blind signature. Our attack is concretely very efficient and for instance breaks -concurrent unforgeability of CSI-Otter in time roughly hash computations
A Generic Construction of an Anonymous Reputation System and Instantiations from Lattices
With an anonymous reputation system one can realize the process of rating sellers anonymously in an online shop. While raters can stay anonymous, sellers still have the guarantee that they can be only be reviewed by raters who bought their product.We present the first generic construction of a reputation system from basic building blocks, namely digital signatures, encryption schemes, non-interactive zero-knowledge proofs, and linking indistinguishable tags. We then show the security of the reputation system in a strong security model. Among others, we instantiate the generic construction with building blocks based on lattice problems, leading to the first module lattice-based reputation system
On digital signatures based on isomorphism problems: QROM security, ring signatures, and applications
An isomorphism problem asks whether two combinatorial or algebraic structures are essentially the same. Based on the assumed hardness of an isomorphism problem, there is a well-known digital signature design based on the Goldreich-Micali-Widgerson (GMW) zero-knowledge protocol for graph isomorphism and the Fiat-Shamir (FS) transformation. Recently, there is a revival of activities on this design, as witnessed by the schemes SeaSign (Eurocrypt 2019), CSIFiSh (Asiacrypt 2019), LESS (Africacrypt 2020), ATFE (Eurocrypt 2022), and MEDS (Africacrypt 2023).
The contributions of this paper are two-folds: the first is about the GMW-FS design in general, and the second is on the ATFE-GMW-FS scheme.
First, we study the QROM security and ring signatures of the GMW-FS design in the group action framework. We distil properties of the underlying isomorphism problem for the GMW-FS design to be secure in the quantum random oracle model (QROM). We also show that this design supports a linkable ring signature construction following the work of Beullens, Katsumata and Pintore (Asiacrypt 2020).
Second, we apply the above results to prove the security of the ATFE-GMW-FS scheme in the QROM model. We then describe a linkable ring signature scheme based on it, and provide an implementation of the ring signature scheme. Preliminary experiments suggest that our scheme is competitive among existing post-quantum ring signatures. We also discuss the parameter choices of the ATFE-GMW-FS scheme based on the recent attack by Beullens (Cryptology ePrint Archive, Paper 2022/1528), and the MPC-in-the-head construction for general group actions by Joux (Cryptology ePrint Archive, Paper 2023/664)
SoK: Signatures With Randomizable Keys
Digital signature schemes with specific properties have recently seen various real-world applications with a strong emphasis on privacy-enhancing technologies. They have been extensively used to develop anonymous credentials schemes and to achieve an even more comprehensive range of functionalities in the decentralized web.
Substantial work has been done to formalize different types of signatures where an allowable set of transformations can be applied to message-signature pairs to obtain new related pairs. Most of the previous work focused on transformations with respect to the message being signed, but little has been done to study what happens when transformations apply to the signing keys. A first attempt to thoroughly formalize such aspects was carried by Derler and Slamanig (ePrint \u2716, Designs, Codes and Cryptography \u2719), followed by the more recent efforts by Backes et. al (ASIACRYPT \u2718) and Eaton et. al (ePrint \u2723). However, the literature on the topic is vast and different terminology is used across contributions, which makes it difficult to compare related works and understand the range of applications covered by a given construction.
In this work, we present a unified view of signatures with randomizable keys and revisit their security properties. We focus on state-of-the-art constructions and related applications, identifying existing challenges. Our systematization allows us to highlight gaps, open questions and directions for future research on signatures with randomizable keys
Critical Perspectives on Provable Security: Fifteen Years of Another Look Papers
We give an overview of our critiques of “proofs” of security and a guide to
our papers on the subject that have appeared over the past decade and a half. We also
provide numerous additional examples and a few updates and errata
A Framework for Practical Anonymous Credentials from Lattices
We present a framework for building practical anonymous credential schemes based on the hardness of lattice problems. The running time of the prover and verifier is independent of the number of users and linear in the number of attributes. The scheme is also compact in practice, with the proofs being as small as a few dozen kilobytes for arbitrarily large (say up to ) users with each user having several attributes. The security of our scheme is based on a new family of lattice assumptions which roughly states that given short pre-images of random elements in some set , it is hard to create a pre-image for a fresh element in such a set. We show that if the set admits efficient zero-knowledge proofs of knowledge of a commitment to a set element and its pre-image, then this yields practically-efficient privacy-preserving primitives such as blind signatures, anonymous credentials, and group signatures. We propose a candidate instantiation of a function from this family which allows for such proofs and thus yields practical lattice-based primitives
A comprehensive survey of V2X cybersecurity mechanisms and future research paths
Recent advancements in vehicle-to-everything (V2X) communication have notably improved existing transport systems by enabling increased connectivity and driving autonomy levels. The remarkable benefits of V2X connectivity come inadvertently with challenges which involve security vulnerabilities and breaches. Addressing security concerns is essential for seamless and safe operation of mission-critical V2X use cases. This paper surveys current literature on V2X security and provides a systematic and comprehensive review of the most relevant security enhancements to date. An in-depth classification of V2X attacks is first performed according to key security and privacy requirements. Our methodology resumes with a taxonomy of security mechanisms based on their proactive/reactive defensive approach, which helps identify strengths and limitations of state-of-the-art countermeasures for V2X attacks. In addition, this paper delves into the potential of emerging security approaches leveraging artificial intelligence tools to meet security objectives. Promising data-driven solutions tailored to tackle security, privacy and trust issues are thoroughly discussed along with new threat vectors introduced inevitably by these enablers. The lessons learned from the detailed review of existing works are also compiled and highlighted. We conclude this survey with a structured synthesis of open challenges and future research directions to foster contributions in this prominent field.This work is supported by the H2020-INSPIRE-5Gplus project (under Grant agreement No. 871808), the ”Ministerio de Asuntos Económicos y Transformacion Digital” and the European Union-NextGenerationEU in the frameworks of the ”Plan de Recuperación, Transformación y Resiliencia” and of the ”Mecanismo de Recuperación y Resiliencia” under references TSI-063000-2021-39/40/41, and the CHIST-ERA-17-BDSI-003 FIREMAN project funded by the Spanish National Foundation (Grant PCI2019-103780).Peer ReviewedPostprint (published version
Jornadas Nacionales de Investigación en Ciberseguridad: actas de las VIII Jornadas Nacionales de Investigación en ciberseguridad: Vigo, 21 a 23 de junio de 2023
Jornadas Nacionales de Investigación en Ciberseguridad (8ª. 2023. Vigo)atlanTTicAMTEGA: Axencia para a modernización tecnolóxica de GaliciaINCIBE: Instituto Nacional de Cibersegurida
Bringing data minimization to digital wallets at scale with general-purpose zero-knowledge proofs
Today, digital identity management for individuals is either inconvenient and
error-prone or creates undesirable lock-in effects and violates privacy and
security expectations. These shortcomings inhibit the digital transformation in
general and seem particularly concerning in the context of novel applications
such as access control for decentralized autonomous organizations and
identification in the Metaverse. Decentralized or self-sovereign identity (SSI)
aims to offer a solution to this dilemma by empowering individuals to manage
their digital identity through machine-verifiable attestations stored in a
"digital wallet" application on their edge devices. However, when presented to
a relying party, these attestations typically reveal more attributes than
required and allow tracking end users' activities. Several academic works and
practical solutions exist to reduce or avoid such excessive information
disclosure, from simple selective disclosure to data-minimizing anonymous
credentials based on zero-knowledge proofs (ZKPs). We first demonstrate that
the SSI solutions that are currently built with anonymous credentials still
lack essential features such as scalable revocation, certificate chaining, and
integration with secure elements. We then argue that general-purpose ZKPs in
the form of zk-SNARKs can appropriately address these pressing challenges. We
describe our implementation and conduct performance tests on different edge
devices to illustrate that the performance of zk-SNARK-based anonymous
credentials is already practical. We also discuss further advantages that
general-purpose ZKPs can easily provide for digital wallets, for instance, to
create "designated verifier presentations" that facilitate new design options
for digital identity infrastructures that previously were not accessible
because of the threat of man-in-the-middle attacks
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