| 摘要 |
According to the invention there is provided a computer system comprising a protection mechanism for protecting the contents of a file, the protection mechanism comprising at least one Viewer program, at least one challenge means associated with said Viewer program and said file, and at least one response means with private keying material that it can access, wherein: a) the challenge means has no access to the private keying material, b) the response means comprises means for proving that it has access to the private keying material by interacting with the challenge means using an asymmetric cryptographic scheme, c) the challenge means comprises means for instructing the Viewer program to avoid using some or all said file's content unless said proof is successful.
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