Abstract
Protection and secure exchange of Web documents is becoming a crucial need for many internetbased
applications. Securing Web documents entail addressing two main issues: confidentiality and
integrity. Ensuring document confidentiality means that document contents can only be disclosed
to subjects authorized according to specified security policies, whereas by document integrity we
mean that the document contents are correct with respect to a given application domain and that
the document contents are modified only by authorized subjects. Whereas the problem of document
confidentiality has been widely investigated in the literature, the problem of how to ensure that a
document, when moving among different parties, is modified only according to the stated policies
still lacks comprehensive solutions. In this paper we present a solution to this problem by proposing a
model for specifying update policies, and an infrastructure supporting the specification and enforcement
of these policies in a distributed and cooperative environment, in which subjects in different
organizational roles can modify possibly different portions of the same document. The key aspect
of our proposal is that, by using a combination of hash functions and digital signature techniques,
we create a distributed environment that enable subjects, in most cases, to verify, upon receiving
a document, whether the update operations performed on the document till that point are correct
with respect to the update policies, without interacting with the document server. Our approach
is particularly suited for environments, such as mobile systems, pervasive systems, decentralized
workflows, and peer-to-peer systems.
