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This paper introduces a distributed and fine grained access control mechanism based on encryption for XML document centric collaborative applications. This mechanism also makes it possible to simultaneously protect the confidentiality of a document and to verify its authenticity and integrity, as well to trace its updates. The enforcement of access control is distributed to participants and does not rely on a central authority. Novel aspects of the proposed framework include the adoption of a decentralized key management scheme to support the client-based enforcement of the access control policy. This scheme is driven by the expression of access patterns of interest of the participants over document parts to determine the keys required. A lazy rekeying protocol is also defined to accommodate the delegation of access control decisions that in particular reduces rekeying latency when faced with the addition and removal of participants.