Method for embedding manipulation-secure digital fingerprints into electronic documents

A method for inserting manipulation-secure digital fingerprints for an electronic document, a first copy of the document being assigned to a first buyer and a second copy of the document being assigned to a second buyer, the method comprising:

• inserting a first fingerprint into the first copy at a first set of marking locations, the first fingerprint being unrecognizable by the first buyer;
• and
• inserting a second fingerprint into the second copy at a second set of marking locations, the second fingerprint being unrecognizable by the second buyer;
• the first and second set of marking locations being different, each marking location of the first and second set of marking locations being uniquely assigned to a respective corresponding point in a projective space PG (d, q) of hyperplanes using a secret function;
• at least two first hyperplanes of the projective space PG (d, q) being exclusively assigned to the first fingerprint, marking locations of the first set of marking locations corresponding to the at least two hyperplanes being flagged at first flagged positions;
• at least two second hyperplanes of the projective space PG (d, q) being exclusively assigned to the second fingerprint, marking locations of the second set of marking locations corresponding to the at least two hyperplanes being flagged at second flagged positions;
• the at least two first hyperplanes at least partially intersecting with the at least two second hyperplanes.