99,469 research outputs found
A Lattice-based Ring Signature Scheme Secure against Key Exposure
A ring signature scheme allows a group member to generate a signature on behalf of the whole group, while the verifier can not tell who computed this signature. However, most predecessors do not guarantee security from the secret key leakage of signers. In 2002, Anderson proposed the forward security mechanism to reduce the effect of such leakage. In this paper, we construct the first lattice-based ring signature scheme with forward security. Our scheme combines the binary tree and lattice basis delegation technique to realize a key evolution mechanism, where secret keys are ephemeral and updated with generating nodes in the binary tree. Thus, the adversary cannot forge the past signature even if the users\u27 present secret keys are revealed. Moreover, our scheme can offer unforgeability under standard models. Furthermore, our proposed scheme is expected to realize post-quantum security due to the underlying Short Integer Solution (SIS) problem in lattice-based cryptography
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
Accountable Tracing Signatures from Lattices
Group signatures allow users of a group to sign messages anonymously in the
name of the group, while incorporating a tracing mechanism to revoke anonymity
and identify the signer of any message. Since its introduction by Chaum and van
Heyst (EUROCRYPT 1991), numerous proposals have been put forward, yielding
various improvements on security, efficiency and functionality. However, a
drawback of traditional group signatures is that the opening authority is given
too much power, i.e., he can indiscriminately revoke anonymity and there is no
mechanism to keep him accountable. To overcome this problem, Kohlweiss and
Miers (PoPET 2015) introduced the notion of accountable tracing signatures
(ATS) - an enhanced group signature variant in which the opening authority is
kept accountable for his actions. Kohlweiss and Miers demonstrated a generic
construction of ATS and put forward a concrete instantiation based on
number-theoretic assumptions. To the best of our knowledge, no other ATS scheme
has been known, and the problem of instantiating ATS under post-quantum
assumptions, e.g., lattices, remains open to date.
In this work, we provide the first lattice-based accountable tracing
signature scheme. The scheme satisfies the security requirements suggested by
Kohlweiss and Miers, assuming the hardness of the Ring Short Integer Solution
(RSIS) and the Ring Learning With Errors (RLWE) problems. At the heart of our
construction are a lattice-based key-oblivious encryption scheme and a
zero-knowledge argument system allowing to prove that a given ciphertext is a
valid RLWE encryption under some hidden yet certified key. These technical
building blocks may be of independent interest, e.g., they can be useful for
the design of other lattice-based privacy-preserving protocols.Comment: CT-RSA 201
Efficient Fully-Leakage Resilient One-More Signature Schemes
In a recent paper Faonio, Nielsen and Venturi (ICALP 2015) gave new constructions of leakage-resilient signature schemes. The signature schemes proposed remain unforgeable against an adversary leaking arbitrary information on the entire state of the signer, including the random coins of the signing algorithm. The main feature of their signature schemes is that they offer a graceful degradation of security in situations where standard existential unforgeability is impossible.
The notion, put forward by Nielsen, Venturi, and Zottarel (PKC 2014), defines a slack parameter which, roughly speaking, describes how gracefully the security degrades. Unfortunately, the standard-model signature scheme of Faonio,Nielsen and Venturi has a slack parameter that depends on the number of signatures queried by the adversary.
In this paper we show two new constructions in the standard model where the above limitation is avoided. Specifically, the first scheme achieves slack parameter where is the security parameter and it is based on standard number theoretic assumptions, the second scheme achieves optimal slack parameter (i.e. ) and it is based on knowledge of the exponent assumptions.
Our constructions are efficient and have leakage rate , most notably our second construction has signature size of only 8 group elements which makes it the leakage-resilient signature scheme with the shortest signature size known to the best of our knowledge
One Round Group Key Exchange with Forward Security in the Standard Model
Constructing a one round group key exchange (GKE) protocol that provides forward secrecy is an open problem in the literature. In this paper, we investigate whether or not the security of one round GKE protocols can be enhanced with any form of forward secrecy without increasing the number of rounds. We apply the {\em key evolving} approach used for forward secure encryption/signature schemes and then model the notion of forward security for the first time for key exchange protocols. This notion is slightly weaker than forward secrecy, considered traditionally for key exchange protocols. We then revise an existing one round GKE protocol to propose a GKE protocol with forward security. In the security proof of the revised protocol we completely avoid reliance on the random oracle assumption that was needed for the proof of the base protocol. Our security proof can be directly applied to the base protocol, making it the most efficient one round GKE protocol secure in the standard model. Our one round GKE protocol is generically constructed from the primitive of forward secure encryption. We also propose a concrete forward secure encryption scheme with constant size ciphertext that can be used to efficiently instantiate our protocol
hinTS: Threshold Signatures with Silent Setup
We propose hinTS --- a new threshold signature scheme built on top of the widely used BLS signatures. Our scheme enjoys the following attractive features:
\begin{itemize}
\item A {\em silent setup} process where the joint public key of the parties is computed as a deterministic function of their locally computed public keys.
\item Support for {\em dynamic} choice of thresholds and signers, after the silent setup, without further interaction.
\item Support for {\em general} access policies; in particular, native support for {\em weighted} thresholds with zero additional overhead over standard threshold setting.
\item Strong security guarantees, including proactive security and forward security.
\end{itemize}We prove the security of our scheme in the algebraic group model and provide implementation and extensive evaluation. Our scheme outperforms all prior proposals that aim to avoid distributed key generation in terms of aggregation time, signature size, and verification time. As an example, the aggregation time for 1000 signers is under 0.5 seconds, while both signing and verification are constant time algorithms, taking roundly 1 ms and 17.5 ms respectively.
The key technical contribution of our work involves the design of special-purpose succinct proofs to {\em efficiently} prove the well-formedness of aggregated public keys. Our solution uses public ``hints\u27\u27 released by the signers as part of their public keys (hence the name hinTS)
Key management in mobile ad hoc networks.
Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2005.Mobile ad hoc networks (MANETs) eliminate the need for pre-existing infrastructure by relying on the nodes to perform all network services. The connectivity between the nodes is sporadic due to the shared, error-prone wireless medium and frequent route failures caused by node mobility. Fully self-organized MANETs are created solely by the end-users for a common purpose in an ad hoc fashion. Forming peer-to-peer security associations in MANETs is more challenging than in conventional networks due to the lack of central authority. This thesis is mainly concerned with peer- t o-peer key management in fully self-organized M ANETs. A key management protocol’s primary function is to bootstrap and maintain the security associations in the network, hence to create, distribute and revocate (symmetric or asymmetric) keying material as needed by the network security services. The fully self-organized feature means that t he key management protocol cannot rely on any form of off-line or on-line trusted third party (TTP). The first part of the thesis gives an introduction to MANETs and highlights MANETs' main characteristics and applications. The thesis follows with an overall perspective on the security issues in MANETs and motivates the importance of solving the key management problem in MANETs. The second part gives a comprehensive survey on the existing key management protocols in MANETs. The protocols are subdivided into groups based on their main characteristic or design strategy. Discussion and comments are provided on the strategy of each group. The discussions give insight into the state of the art and show researchers the way forward. The third part of the thesis proposes a novel peer- to-peer key management scheme for fully self-organized MANETs, called Self-Organized Peer-to-Peer Key Management (SelfOrgPKM). The scheme has low implementation complexity and provides self-organized mechanisms for certificate dissemination and key renewal without the need for any form of off-line or on-line authority. The fully distributed scheme is superior in communication and computational overhead with respect to its counterparts. All nodes send and receive the same number of messages and complete the same amount of computation. ScifOrgPKM therefore preserves the symmetric relationship between the nodes. Each node is its own authority domain which provides an adversary with no convenient point of attack. SelfOrgPKM solves t he classical routing-security interdependency problem and mitigates impersonation attacks by providing a strong one-to-one binding between a user’s certificate information and public key. The proposed scheme uses a novel certificate exchange mechanism t hat exploits user mobility but does not rely on mobility in anyway. The proposed certificate exchange mechanism is ideally suited for bootstraping the routing security. It enables nodes to setup security associations on the network layer in a localized fashion without any noticeable time delay. The thesis also introduces two generic cryptographic building blocks as the basis of SelfOrgPKM: 1) A variant on the ElGamal type signature scheme developed from the generalized ElGamal signature scheme introduced by Horster et al. The modified scheme is one of the most efficient ElGamal variants, outperforming most other variant s; and 2) A subordinate public key generation scheme. The thesis introduces t he novel notion of subordinate public keys, which allows the users of SelfOrgPKM to perform self-organized, self-certificate revocation without changing their network identifiers / addresses. Subordinate public keys therefore eliminate the main weakness of previous efforts to solve the address ownership problem in Mobile IPv6. Furthermore, the main weakness of previous efforts to break t he routing-security interdependence cycle in MANETs is also eliminated by a subordinate public key mechanism. The presented EIGamal signature variant is proved secure in t he Random Oracle and Generic Security Model (ROM+ GM ) without making any unrealistic assumptions . It is shown how the strong security of the signature scheme supports t he security of t he proposed subordinate key generation scheme. Based on the secure signature scheme a security argument for SelfOrgPKM is provided with respect to a genera l, active insider adversary model. The only operation of SelfOrgPKM affecting the network is the pairwise exchange of certificates. The cryptographic correctness, low implementation complexity and effectiveness of SelfOrgPKM were verified though extensive simulations using ns-2 and OpenSSL. Thorough analysis of the simulation results shows t hat t he localized certificate exchange mechanism on the network layer has negligible impact on network performance. The simulation results also correlate with efficiency analysis of SelfOrgPKM in an ideal network setting, hence assuming guaranteed connectivity. The simulation results furthermore demonstrate that network layer certificate exchanges can be triggered without extending routing protocol control packet
An Elliptic Curve-based Signcryption Scheme with Forward Secrecy
An elliptic curve-based signcryption scheme is introduced in this paper that
effectively combines the functionalities of digital signature and encryption,
and decreases the computational costs and communication overheads in comparison
with the traditional signature-then-encryption schemes. It simultaneously
provides the attributes of message confidentiality, authentication, integrity,
unforgeability, non-repudiation, public verifiability, and forward secrecy of
message confidentiality. Since it is based on elliptic curves and can use any
fast and secure symmetric algorithm for encrypting messages, it has great
advantages to be used for security establishments in store-and-forward
applications and when dealing with resource-constrained devices.Comment: 13 Pages, 5 Figures, 2 Table
- …