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The decision to outsource databases is strategic in many organizations due to the increasing costs of internally managing large volumes of information. The sensitive nature of this information raises the need for powerful mechanisms to protect it against unauthorized disclosure. Centralized encryption to access control at the data owner level has been proposed as one way of handling this issue. However, its prohibitive costs renders it impractical and inflexible. A distributed cryptographic approach has been suggested as a promising alternative, where keys are distributed to users on the basis of their assigned privileges. But in this case, key management becomes problematic in the face of frequent database updates and remains an open issue. In this paper, we present a novel approach based on binary tries. By exploiting the intrinsic properties of these data structures, key management complexity, and thus its cost, is significantly reduced. Changes to the binary trie structure remain limited in the face of frequent updates. Preliminary experimental analysis demonstrates the validity and the effectiveness of our approach.