Databases Reference
In-Depth Information
in the system. Also, any user knows the private key of the vertex representing
herself in the hierarchy, and each resource is encrypted with the private key
associated with the vertex representing its
acl
. However, differently from other
proposals, key derivation goes from leaves to the root of the tree.
5.2 Overview of XML Document Outsourcing Solutions
Besides traditional databases, also XML documents can contain sensitive in-
formation, and their outsourcing may cause privacy breaches. As a conse-
quence, it is necessary to develop techniques for enforcing access control on
outsourced XML data as well. Although some of the approaches presented
for the relational database outsourcing scenario are suited for XML data out-
sourcing, they do not exploit the main characteristics of XML documents
(e.g., their tree structure) and different specific approaches have then been
proposed. The solutions presented exploit once again selective encryption as
a way for enforcing access control when publishing or outsourcing sensitive
data.
Miklau and Suciu [50] propose a way for differentiating the encryption
of different portions of an XML document, on the basis of users or groups
who can access them. The proposed access control mechanism is enriched by
adding metadata XML nodes, adopted to enforce access control rules with
conditions on the values contained in the document. Wang et al. [57] present
an access control system that both protects data stored in the XML document
and the associations among data by introducing association constraints that
need to be satisfied by the encryption model adopted.
6 Conclusions
This chapter discussed recent trends in the access control field. We described
the basic concepts of access control and investigated different issues concern-
ing the development of an access control system. In particular, we outlined
the needs for providing means to: support access control in open environ-
ments, where the identities of the involved parties may be unknown; combine
authorization specifications that may be independently stated; enforce ac-
cess control through the use of selective encryption. For these contexts, we
described recent proposals and ongoing work.
Acknowledgements
This work was supported in part by the European Union under contract IST-
2002-507591, and by the Italian Ministry of Research, within programs FIRB,
under project “RBNE05FKZ2”, and PRIN 2006, under project “Basi di dati
crittografate” (2006099978).
