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The problem is actually not to make sure that Alice cannot copy the document (i.e. preserve uniqueness as you asked) but to make sure that it is clear who owns this document currently. A solution to this problem might be if not only the documents are signed but the transactions (transfer of ownership) are signed too. In this case Alice might claim that she ...


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Voting to close this as it is not a question about security. It is a question about software engineering and architecture: The best place to handle the exception is as close as possible to where the exception occurs - the separation of functionality is all about abstraction - the remote higher levels are separate because they don't know about what is going ...


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