4 research outputs found
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A practical mandatory access control model for XML databases
A practical mandatory access control (MAC) model for XML databases is presented in this paper. The
label type and label access policy can be defined according to the requirements of different applications. In order to
preserve the integrity of data in XML databases, a constraint between a read-access rule and a write-access rule in
label access policy is introduced. Rules for label assignment and propagation are presented to alleviate the workload
of label assignments. Furthermore, a solution for resolving conflicts in label assignments is proposed. Rules for
update-related operations, rules for exceptional privileges of ordinary users and the administrator are also proposed
to preserve the security of operations in XML databases. The MAC model, we proposed in this study, has been
implemented in an XML database. Test results demonstrated that our approach provides rational and scalable
performance
Access Control Administration with Adjustable Decentralization
Access control is a key function of enterprises that preserve and propagate massive data. Access control enforcement and administration are two major components of the system. On one hand, enterprises are responsible for data security; thus, consistent and reliable access control enforcement is necessary although the data may be distributed. On the other hand, data often belongs to several organizational units with various access control policies and many users; therefore, decentralized administration is needed to accommodate diverse access control needs and to avoid the central bottleneck. Yet, the required degree of decentralization varies within different organizations: some organizations may require a powerful administrator in the system; whereas, some others may prefer a self-governing setting in which no central administrator exists, but users fully manage their own data. Hence, a single system with adjustable decentralization will be useful for supporting various (de)centralized models within the spectrum of access control administration.
Giving individual users the ability to delegate or grant privileges is a means of decentralizing access control administration. Revocation of arbitrary privileges is a means of retaining control over data. To provide flexible administration, the ability to delegate a specific privilege and the ability to revoke it should be held independently of each other and independently of the privilege itself. Moreover, supporting arbitrary user and data hierarchies, fine-grained access control, and protection of both data (end objects) and metadata (access control data) with a single uniform model will provide the most widely deployable access control system.
Conflict resolution is a major aspect of access control administration in systems. Resolving access conflicts when deriving effective privileges from explicit ones is a challenging problem in the presence of both positive and negative privileges, sophisticated data hierarchies, and diversity of conflict resolution strategies.
This thesis presents a uniform access control administration model with adjustable decentralization, to protect both data and metadata. There are several contributions in this work. First, we present a novel mechanism to constrain access control administration for each object type at object creation time, as a means of adjusting the degree of decentralization for the object when the system is configured. Second, by controlling the access control metadata with the same mechanism that controls the users’ data, privileges can be granted and revoked to the extent that these actions conform to the corporation’s access control policy. Thus, this model supports a whole spectrum of access control administration, in which each model is characterized as a network of access control states, similar to a finite state automaton. The model depends on a hierarchy of access banks of authorizations which is supported by a formal semantics. Within this framework, we also introduce the self-governance property in the context of access control, and show how the model facilitates it. In particular, using this model, we introduce a conflict-free and decentralized access control administration model in which all users are able to retain complete control over their own data while they are also able to delegate any subset of their privileges to other users or user groups. We also introduce two measures to compare any two access control models in terms of the degrees of decentralization and interpretation. Finally, as the conflict resolution component of access control models, we incorporate a unified algorithm to resolve access conflicts by simultaneously supporting several combined strategies
Query Evaluation in the Presence of Fine-grained Access Control
Access controls are mechanisms to enhance security by protecting
data from unauthorized accesses. In contrast to traditional access
controls that grant access rights at the granularity of the whole
tables or views, fine-grained access controls specify access
controls at finer granularity, e.g., individual nodes in XML
databases and individual tuples in relational databases.
While there is a voluminous literature on specifying and modeling
fine-grained access controls, less work has been done to address
the performance issues of database systems with fine-grained
access controls. This thesis addresses the performance issues of
fine-grained access controls and proposes corresponding solutions.
In particular, the following issues are addressed: effective
storage of massive access controls, efficient query planning for
secure query evaluation, and accurate cardinality estimation for
access controlled data.
Because fine-grained access controls specify access rights from
each user to each piece of data in the system, they are
effectively a massive matrix of the size as the product of the
number of users and the size of data. Therefore, fine-grained
access controls require a very compact encoding to be feasible.
The proposed storage system in this thesis achieves an
unprecedented level of compactness by leveraging the high
correlation of access controls found in real system data. This
correlation comes from two sides: the structural similarity of
access rights between data, and the similarity of access patterns
from different users. This encoding can be embedded into a
linearized representation of XML data such that a query evaluation
framework is able to compute the answer to the access controlled
query with minimal disk I/O to the access controls.
Query optimization is a crucial component for database systems.
This thesis proposes an intelligent query plan caching mechanism
that has lower amortized cost for query planning in the presence
of fine-grained access controls. The rationale behind this query
plan caching mechanism is that the queries, customized by
different access controls from different users, may share common
upper-level join trees in their optimal query plans. Since join
plan generation is an expensive step in query optimization,
reusing the upper-level join trees will reduce query optimization
significantly. The proposed caching mechanism is able to match
efficient query plans to access controlled query plans with
minimal runtime cost.
In case of a query plan cache miss, the optimizer needs to
optimize an access controlled query from scratch. This depends on
accurate cardinality estimation on the size of the intermediate
query results. This thesis proposes a novel sampling scheme that
has better accuracy than traditional cardinality estimation
techniques