2,087 research outputs found
Lattice Forward-Secure Identity Based Encryption Scheme
Abstract Protecting secret keys is crucial for cryptography. There are some relatively insecure devices (smart cards, mobile phones etc.) which have threat of key exposure. The goal of the forward security is to protect security of past uses of key even if the current secret key is exposed. In this paper we propose lattice based forward-secure identity based encryption scheme based on LWE assumption in random oracle model. We also propose lattice based forward-secure identity based encryption scheme in the standard model
Server-Aided Revocable Predicate Encryption: Formalization and Lattice-Based Instantiation
Efficient user revocation is a necessary but challenging problem in many
multi-user cryptosystems. Among known approaches, server-aided revocation
yields a promising solution, because it allows to outsource the major workloads
of system users to a computationally powerful third party, called the server,
whose only requirement is to carry out the computations correctly. Such a
revocation mechanism was considered in the settings of identity-based
encryption and attribute-based encryption by Qin et al. (ESORICS 2015) and Cui
et al. (ESORICS 2016), respectively.
In this work, we consider the server-aided revocation mechanism in the more
elaborate setting of predicate encryption (PE). The latter, introduced by Katz,
Sahai, and Waters (EUROCRYPT 2008), provides fine-grained and role-based access
to encrypted data and can be viewed as a generalization of identity-based and
attribute-based encryption. Our contribution is two-fold. First, we formalize
the model of server-aided revocable predicate encryption (SR-PE), with rigorous
definitions and security notions. Our model can be seen as a non-trivial
adaptation of Cui et al.'s work into the PE context. Second, we put forward a
lattice-based instantiation of SR-PE. The scheme employs the PE scheme of
Agrawal, Freeman and Vaikuntanathan (ASIACRYPT 2011) and the complete subtree
method of Naor, Naor, and Lotspiech (CRYPTO 2001) as the two main ingredients,
which work smoothly together thanks to a few additional techniques. Our scheme
is proven secure in the standard model (in a selective manner), based on the
hardness of the Learning With Errors (LWE) problem.Comment: 24 page
The weak password problem: chaos, criticality, and encrypted p-CAPTCHAs
Vulnerabilities related to weak passwords are a pressing global economic and
security issue. We report a novel, simple, and effective approach to address
the weak password problem. Building upon chaotic dynamics, criticality at phase
transitions, CAPTCHA recognition, and computational round-off errors we design
an algorithm that strengthens security of passwords. The core idea of our
method is to split a long and secure password into two components. The first
component is memorized by the user. The second component is transformed into a
CAPTCHA image and then protected using evolution of a two-dimensional dynamical
system close to a phase transition, in such a way that standard brute-force
attacks become ineffective. We expect our approach to have wide applications
for authentication and encryption technologies.Comment: 5 pages, 6 figer
Lattice-Based Group Signatures: Achieving Full Dynamicity (and Deniability) with Ease
In this work, we provide the first lattice-based group signature that offers
full dynamicity (i.e., users have the flexibility in joining and leaving the
group), and thus, resolve a prominent open problem posed by previous works.
Moreover, we achieve this non-trivial feat in a relatively simple manner.
Starting with Libert et al.'s fully static construction (Eurocrypt 2016) -
which is arguably the most efficient lattice-based group signature to date, we
introduce simple-but-insightful tweaks that allow to upgrade it directly into
the fully dynamic setting. More startlingly, our scheme even produces slightly
shorter signatures than the former, thanks to an adaptation of a technique
proposed by Ling et al. (PKC 2013), allowing to prove inequalities in
zero-knowledge. Our design approach consists of upgrading Libert et al.'s
static construction (EUROCRYPT 2016) - which is arguably the most efficient
lattice-based group signature to date - into the fully dynamic setting.
Somewhat surprisingly, our scheme produces slightly shorter signatures than the
former, thanks to a new technique for proving inequality in zero-knowledge
without relying on any inequality check. The scheme satisfies the strong
security requirements of Bootle et al.'s model (ACNS 2016), under the Short
Integer Solution (SIS) and the Learning With Errors (LWE) assumptions.
Furthermore, we demonstrate how to equip the obtained group signature scheme
with the deniability functionality in a simple way. This attractive
functionality, put forward by Ishida et al. (CANS 2016), enables the tracing
authority to provide an evidence that a given user is not the owner of a
signature in question. In the process, we design a zero-knowledge protocol for
proving that a given LWE ciphertext does not decrypt to a particular message
Chosen-ciphertext security from subset sum
We construct a public-key encryption (PKE) scheme whose
security is polynomial-time equivalent to the hardness of the Subset Sum problem. Our scheme achieves the standard notion of indistinguishability against chosen-ciphertext attacks (IND-CCA) and can be used to encrypt messages of arbitrary polynomial length, improving upon a previous construction by Lyubashevsky, Palacio, and Segev (TCC 2010) which achieved only the weaker notion of semantic security (IND-CPA) and whose concrete security decreases with the length of the message being encrypted. At the core of our construction is a trapdoor technique which originates in the work of Micciancio and Peikert (Eurocrypt 2012
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