14,162 research outputs found
A General Approach for Securely Querying and Updating XML Data
Over the past years several works have proposed access control models for XML
data where only read-access rights over non-recursive DTDs are considered. A
few amount of works have studied the access rights for updates. In this paper,
we present a general model for specifying access control on XML data in the
presence of update operations of W3C XQuery Update Facility. Our approach for
enforcing such updates specifications is based on the notion of query rewriting
where each update operation defined over arbitrary DTD (recursive or not) is
rewritten to a safe one in order to be evaluated only over XML data which can
be updated by the user. We investigate in the second part of this report the
secure of XML updating in the presence of read-access rights specified by a
security views. For an XML document, a security view represents for each class
of users all and only the parts of the document these users are able to see. We
show that an update operation defined over a security view can cause disclosure
of sensitive data hidden by this view if it is not thoroughly rewritten with
respect to both read and update access rights. Finally, we propose a security
view based approach for securely updating XML in order to preserve the
confidentiality and integrity of XML data.Comment: No. RR-7870 (2012
Access Control Synthesis for Physical Spaces
Access-control requirements for physical spaces, like office buildings and
airports, are best formulated from a global viewpoint in terms of system-wide
requirements. For example, "there is an authorized path to exit the building
from every room." In contrast, individual access-control components, such as
doors and turnstiles, can only enforce local policies, specifying when the
component may open. In practice, the gap between the system-wide, global
requirements and the many local policies is bridged manually, which is tedious,
error-prone, and scales poorly.
We propose a framework to automatically synthesize local access control
policies from a set of global requirements for physical spaces. Our framework
consists of an expressive language to specify both global requirements and
physical spaces, and an algorithm for synthesizing local, attribute-based
policies from the global specification. We empirically demonstrate the
framework's effectiveness on three substantial case studies. The studies
demonstrate that access control synthesis is practical even for complex
physical spaces, such as airports, with many interrelated security
requirements
Secure Querying of Recursive XML Views: A Standard XPath-based Technique
Most state-of-the art approaches for securing XML documents allow users to
access data only through authorized views defined by annotating an XML grammar
(e.g. DTD) with a collection of XPath expressions. To prevent improper
disclosure of confidential information, user queries posed on these views need
to be rewritten into equivalent queries on the underlying documents. This
rewriting enables us to avoid the overhead of view materialization and
maintenance. A major concern here is that query rewriting for recursive XML
views is still an open problem. To overcome this problem, some works have been
proposed to translate XPath queries into non-standard ones, called Regular
XPath queries. However, query rewriting under Regular XPath can be of
exponential size as it relies on automaton model. Most importantly, Regular
XPath remains a theoretical achievement. Indeed, it is not commonly used in
practice as translation and evaluation tools are not available. In this paper,
we show that query rewriting is always possible for recursive XML views using
only the expressive power of the standard XPath. We investigate the extension
of the downward class of XPath, composed only by child and descendant axes,
with some axes and operators and we propose a general approach to rewrite
queries under recursive XML views. Unlike Regular XPath-based works, we provide
a rewriting algorithm which processes the query only over the annotated DTD
grammar and which can run in linear time in the size of the query. An
experimental evaluation demonstrates that our algorithm is efficient and scales
well.Comment: (2011
Automated Certification of Authorisation Policy Resistance
Attribute-based Access Control (ABAC) extends traditional Access Control by
considering an access request as a set of pairs attribute name-value, making it
particularly useful in the context of open and distributed systems, where
security relevant information can be collected from different sources. However,
ABAC enables attribute hiding attacks, allowing an attacker to gain some access
by withholding information. In this paper, we first introduce the notion of
policy resistance to attribute hiding attacks. We then propose the tool ATRAP
(Automatic Term Rewriting for Authorisation Policies), based on the recent
formal ABAC language PTaCL, which first automatically searches for resistance
counter-examples using Maude, and then automatically searches for an Isabelle
proof of resistance. We illustrate our approach with two simple examples of
policies and propose an evaluation of ATRAP performances.Comment: 20 pages, 4 figures, version including proofs of the paper that will
be presented at ESORICS 201
SMOQE: A System for Providing Secure Access to XML
XML views have been widely used to enforce access control, support data integration, and speed up query answering. In many applications, e.g., XML security enforcement, it is prohibitively expensive to materialize and maintain a large number of views. Therefore, views are necessarily virtual. An immediate question then is how to answer queries on XML virtual views. A common approach is to rewrite a query on the view to an equivalent one on the underlying document, and evaluate the rewritten query. This is the approach used in the Secure MOdular Query Engine (SMOQE). The demo presents SMOQE, the first system to provide efficient support for answering queries over virtual and possibly recursively defined XML views. We demonstrate a set of novel techniques for the specification of views, the rewriting, evaluation and optimization of XML queries. Moreover, we provide insights into the internals of the engine by a set of visual tools. 1
Policy based roles for distributed systems security
Distributed systems are increasingly being used in commercial environments necessitating the development of trustworthy and reliable security mechanisms. There is often no clear informal or formal specification of enterprise authorisation policies and no tools to translate policy specifications to access control implementation mechanisms such as capabilities or Access Control Lists. It is thus difficult to analyse the policy to detect conflicts or flaws and it is difficult to verify that the implementation corresponds to the policy specification. We present in this paper a framework for the specification of management policies. We are concerned with two types of policies: obligations which specify what activities a manager or agent must or must not perform on a set of target objects and authorisations which specify what activities a subject (manager or agent) can or can not perform on the set of target objects. Management policies are then grouped into roles reflecting the organisation..
Rewrite based Verification of XML Updates
We consider problems of access control for update of XML documents. In the
context of XML programming, types can be viewed as hedge automata, and static
type checking amounts to verify that a program always converts valid source
documents into also valid output documents. Given a set of update operations we
are particularly interested by checking safety properties such as preservation
of document types along any sequence of updates. We are also interested by the
related policy consistency problem, that is detecting whether a sequence of
authorized operations can simulate a forbidden one. We reduce these questions
to type checking problems, solved by computing variants of hedge automata
characterizing the set of ancestors and descendants of the initial document
type for the closure of parameterized rewrite rules
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