A hierarchical tree structure is used to facilitate the communication of encrypted keys to particular users having access to the tree. All users are in communication with a root node, but the information content of the material at the root node is decipherable only by the intended users of this information. Protected data is encrypted using a variety of data-keys specific to the data. These data-keys are encrypted using a combination of node- keys that are specific to particular users or groups of users. Users having access to the node-key associated with a particular encrypted data-key are able to decipher the data associated with the data-key; users without access to the particular node-key are unable to decrypt the data-key, and thus unable to decipher the data. The hierarchical tree is preferably structured based on a similarity of access rights among users, to minimize the overhead associated with providing user-specific access rights.
