Importance

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Abstract

A scanner (12) derives a digital image of a document that it scans optically, an image-processing circuitry (14) extracts a representation of a non-planner graph. A small-processor 'smart card' derives from the first graph a second graph that is isomorphic to it and related to it in accordance with a secret permutation matrix. The image processor 14 then embeds a representation of that graph into the image and sends the results to a printer (16) to generate a copy. A second scanner (30) generates a digital image of the copy, and processing circuitry (31) extracts the two isomorphic graphs, which it conveys to a verifier circuit (36) as well as the smart card (22). By repeatedly generating and submitting to the verifier (36) test graphs that are isomorphic to the extracted graphs, the smart card (22) can demonstrate, without revealing the secret permutation matrix, that it is in possession of that permutation matrix. It does so by sending the verifier a permutation matrix that relates the test graph to the extracted graph of the verifier's choice.

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First Claim