392 research outputs found
Lazy updates in key assignment schemes for hierarchical access control
Hierarchical access control policies are used to restrict access to
objects by users based on their respective security labels. There are
many key assignment schemes in the literature for implementing
such policies using cryptographic mechanisms. Updating keys in such
schemes has always been problematic, not least because many objects
may be encrypted with the same key. We propose a number of techniques
by which this process can be improved, making use of the idea of
lazy key updates, which have been studied in the context of
cryptographic file systems. We demonstrate in passing that schemes
for lazy key updates can be regarded as simple instances of key
assignment schemes. Finally, we illustrate the utility of our
techniques by applying them to hierarchical file systems and to
temporal access control policies
Provably-Secure Time-Bound Hierarchical Key Assignment Schemes
A time-bound hierarchical key assignment scheme is a method to assign time-dependent encryption keys to a set of classes in a partially ordered hierarchy, in such a way that each class can compute the keys of all classes lower down in the hierarchy, according to temporal constraints.
In this paper we design and analyze time-bound hierarchical key assignment schemes which are provably-secure and efficient. We consider both the unconditionally secure and the computationally secure settings and distinguish between two different goals: security with respect to key indistinguishability and against key recovery. We first present definitions of security with respect to both goals in the unconditionally secure setting and we show tight lower bounds on the size of the private information distributed to each class. Then, we consider the computational setting and we further distinguish security against static and adaptive adversarial behaviors. We explore the relations between all possible combinations of security goals and adversarial behaviors and, in particular, we prove that security against adaptive adversaries is (polynomially) equivalent to security against static adversaries. Afterwards, we prove that a recently proposed scheme is insecure against key recovery. Finally, we propose two different constructions for time-bound key assignment schemes. The first one is based on symmetric encryption schemes, whereas, the second one makes use of bilinear maps. Both constructions support updates to the access hierarchy with local changes to the public information and without requiring any private information to be re-distributed. These appear to be the first constructions for time-bound hierarchical key assignment schemes which are simultaneously practical and provably-secure
Key Indistinguishability vs. Strong Key Indistinguishability for Hierarchical Key Assignment Schemes
A hierarchical key assignment scheme is a method to assign some private information and encryption keys to a set of classes in a partially ordered hierarchy, in such a way that the private information of a higher class can be used to derive the keys of all classes lower down in the hierarchy.
In this paper we analyze the security of hierarchical key assignment schemes according to different notions: security with respect to key indistinguishability and against key recovery, as well as the two recently proposed notions of security with respect to strong key indistinguishability and against strong key recovery. We first explore the relations between all security notions and, in particular, we prove that security with respect to strong key indistinguishability is not stronger than the one with respect to key indistinguishability. Afterwards, we propose a general construction yielding a hierarchical key assignment scheme offering security against strong key recovery, given any hierarchical key assignment scheme which guarantees security against key recovery
New Insights on cryptographic hierarchical access control: models, schemes and analysis
2014 - 2015Nowadays the current network-centric world has given rise to several
security concerns regarding the access control management, which en-
sures that only authorized users are given access to certain resources
or tasks. In particular, according to their respective roles and respon-
sibilities, users are typically organized into hierarchies composed of
several disjoint classes (security classes). A hierarchy is characterized
by the fact that some users may have more access rights than others,
according to a top-down inclusion paradigm following speci c hier-
archical dependencies. A user with access rights for a given class is
granted access to objects stored in that class, as well as to all the de-
scendant ones in the hierarchy. The problem of key management for
such hierarchies consists in assigning a key to each class of the hierar-
chy, so that the keys for descendant classes can be e ciently obtained
from users belonging to classes at a higher level in the hierarchy.
In this thesis we analyze the security of hierarchical key assignment
schemes according to di erent notions: security with respect to key
indistinguishability and against key recovery [4], as well as the two
recently proposed notions of security with respect to strong key in-
distinguishability and against strong key recovery [42]. More precisely,
we rst explore the relations between all security notions and, in par-
ticular, we prove that security with respect to strong key indistin-
guishability is not stronger than the one with respect to key indistin-
guishability. Afterwards, we propose a general construction yielding
a hierarchical key assignment scheme that ensures security against
strong key recovery, given any hierarchical key assignment scheme
which guarantees security against key recovery.
Moreover, we de ne the concept of hierarchical key assignment
schemes supporting dynamic updates, formalizing the relative secu-
rity model. In particular, we provide the notions of security with
respect to key indistinguishability and key recovery, by taking into ac-
count the dynamic changes to the hierarchy. Furthermore, we show
how to construct a hierarchical key assignment scheme supporting dy-
namic updates, by using as a building block a symmetric encryption
scheme. The proposed construction is provably secure with respect to
key indistinguishability, provides e cient key derivation and updat-
ing procedures, while requiring each user to store only a single private
key.
Finally, we propose a novel model that generalizes the conventional
hierarchical access control paradigm, by extending it to certain addi-
tional sets of quali ed users. Afterwards, we propose two construc-
tions for hierarchical key assignment schemes in this new model, which
are provably secure with respect to key indistinguishability. In par-
ticular, the former construction relies on both symmetric encryption
and perfect secret sharing, whereas, the latter is based on public-key
threshold broadcast encryption. [edited by author]XIV n.s
Handling Confidential Data on the Untrusted Cloud: An Agent-based Approach
Cloud computing allows shared computer and storage facilities to be used by a
multitude of clients. While cloud management is centralized, the information
resides in the cloud and information sharing can be implemented via
off-the-shelf techniques for multiuser databases. Users, however, are very
diffident for not having full control over their sensitive data. Untrusted
database-as-a-server techniques are neither readily extendable to the cloud
environment nor easily understandable by non-technical users. To solve this
problem, we present an approach where agents share reserved data in a secure
manner by the use of simple grant-and-revoke permissions on shared data.Comment: 7 pages, 9 figures, Cloud Computing 201
Arcula: A Secure Hierarchical Deterministic Wallet for Multi-asset Blockchains
This work presents Arcula, a new design for hierarchical deterministic
wallets that brings identity-based addresses to the blockchain. Arcula is built
on top of provably secure cryptographic primitives. It generates all its
cryptographic secrets from a user-provided seed and enables the derivation of
new public keys based on the identities of users, without requiring any secret
information. Unlike other wallets, it achieves all these properties while being
secure against privilege escalation. We formalize the security model of
hierarchical deterministic wallets and prove that an attacker compromising an
arbitrary number of users within an Arcula wallet cannot escalate his
privileges and compromise users higher in the access hierarchy. Our design
works out-of-the-box with any blockchain that enables the verification of
signatures on arbitrary messages. We evaluate its usage in a real-world
scenario on the Bitcoin Cash network
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