Tracing the Source of a Shredded Document

Consider two ordinary, seemingly identical plain paper shredders labeled A and B. When each of the two shredders is fed a blank sheet of paper, the resulting remnants are sufficiently similar that they are indistinguishable upon visual inspection. Now suppose that one of the shredders has been modified to introduce imperceptible variations in the size of each remnant it cuts. One of the shredders is then selected at random to destroy a blank sheet. By examination of the resulting paper remnants, can one determine if the sheet was shredded by A or B? In this paper we show how information hidden in the size and shape of shredded page remnants can be used to reveal the identity of the device used for shredding. We describe means for modifying shredders to introduce this hidden information. Experimental results reveal that properly embedded information can survive the severe nonlinear distortions introduced by the mechanics of paper shredding. Finally, we consider the question of whether paper shreds could reveal shredder identity even in the absence of device modifications.