25. The viewer of claim 23 wherein the means for calculating the document identifier computes the document identifier from the encrypted document content and a text string embedded in code that implements the viewer.
23. A viewer for a secure digital content distribution system that distributes digital content from a content server over a network to a browser program in a workstation connected to the network, the viewer running in the browser program and comprising: means for generating in the browser a user interface that does not utilize the functions of the browser user interface, including a display area that is controlled exclusively by the viewer; means for requesting a document containing content from the content server; means for receiving an encrypted version of the requested document from the content server; means for calculating a document identifier as a result of a numerical computation using as one input encrypted content in the encrypted version of the requested document and as another input information that is downloaded with the viewer program, which document identifier cannot be derived solely from the encrypted version of the requested document and sending the document identifier to the content server; means for receiving a decryption key from the content server and decrypting the encrypted version of the document; and means for presenting the document content to the user in the viewer display area.