10,693 research outputs found
Safe Locking Policies for Dynamic Databases
AbstractYannakakis showed that a locking policy is not safe if and only if it allows a canonical nonserializable schedule of transactions in which all transactions except one are executed serially (Yannakakis, 1982). In the present paper, we study the generalization of this result to a dynamic database, that is, a database that may undergo insertions and deletions of entities. We illustrate the utility of this generalization by applying it to obtain correctness proofs of three locking policies that handle dynamic databases
Pre-analysis locking
Locking is considered as a means to achieve serializable schedules of concurrent transactions. Transactions are assumed to be predeclared such that a pre-analysis for locking becomes feasible to increase concurrency. A condition for safety is introduced which, based on a pre-analysis, allows the design of policies strictly dominating known policies such as 2-phase locking. The static case, in which the complete set of transactions is known in advance, and the online case, in which a transaction is known when it is started, are considered. It is shown that a policy strictly dominating 2-phase locking and some other interesting pre-analysis policies can also be applied in an online environment
On the complexity of concurrency control by locking in distributed database systems
Given a pair of locked transactions, accessing a distributed database, the problem is studied of whether this pair is safe, i.e., guaranteed to produce only serializable schedules. It is shown that an easy-to-test graph condition, which characterizes safety for a pair of locked transactions in a centralized database, also applies when the database has been distributed among at most three sites
ConXsense - Automated Context Classification for Context-Aware Access Control
We present ConXsense, the first framework for context-aware access control on
mobile devices based on context classification. Previous context-aware access
control systems often require users to laboriously specify detailed policies or
they rely on pre-defined policies not adequately reflecting the true
preferences of users. We present the design and implementation of a
context-aware framework that uses a probabilistic approach to overcome these
deficiencies. The framework utilizes context sensing and machine learning to
automatically classify contexts according to their security and privacy-related
properties. We apply the framework to two important smartphone-related use
cases: protection against device misuse using a dynamic device lock and
protection against sensory malware. We ground our analysis on a sociological
survey examining the perceptions and concerns of users related to contextual
smartphone security and analyze the effectiveness of our approach with
real-world context data. We also demonstrate the integration of our framework
with the FlaskDroid architecture for fine-grained access control enforcement on
the Android platform.Comment: Recipient of the Best Paper Awar
Middleware-based Database Replication: The Gaps between Theory and Practice
The need for high availability and performance in data management systems has
been fueling a long running interest in database replication from both academia
and industry. However, academic groups often attack replication problems in
isolation, overlooking the need for completeness in their solutions, while
commercial teams take a holistic approach that often misses opportunities for
fundamental innovation. This has created over time a gap between academic
research and industrial practice.
This paper aims to characterize the gap along three axes: performance,
availability, and administration. We build on our own experience developing and
deploying replication systems in commercial and academic settings, as well as
on a large body of prior related work. We sift through representative examples
from the last decade of open-source, academic, and commercial database
replication systems and combine this material with case studies from real
systems deployed at Fortune 500 customers. We propose two agendas, one for
academic research and one for industrial R&D, which we believe can bridge the
gap within 5-10 years. This way, we hope to both motivate and help researchers
in making the theory and practice of middleware-based database replication more
relevant to each other.Comment: 14 pages. Appears in Proc. ACM SIGMOD International Conference on
Management of Data, Vancouver, Canada, June 200
PALPAS - PAsswordLess PAssword Synchronization
Tools that synchronize passwords over several user devices typically store
the encrypted passwords in a central online database. For encryption, a
low-entropy, password-based key is used. Such a database may be subject to
unauthorized access which can lead to the disclosure of all passwords by an
offline brute-force attack. In this paper, we present PALPAS, a secure and
user-friendly tool that synchronizes passwords between user devices without
storing information about them centrally. The idea of PALPAS is to generate a
password from a high entropy secret shared by all devices and a random salt
value for each service. Only the salt values are stored on a server but not the
secret. The salt enables the user devices to generate the same password but is
statistically independent of the password. In order for PALPAS to generate
passwords according to different password policies, we also present a mechanism
that automatically retrieves and processes the password requirements of
services. PALPAS users need to only memorize a single password and the setup of
PALPAS on a further device demands only a one-time transfer of few static data.Comment: An extended abstract of this work appears in the proceedings of ARES
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