DARPA Unshredding Challenge

In CACM:  Solved it says.   I encountered a related problem very early in my enterprise career.  Not involved with anything secret.   We partially solved the problem and got real value from it.  These additional learnings would have helped considerably.  It has been known for a long time that paper shredding is insecure.   We used a 'pulping' method that mixed paper with water and created a sludge.   The background of the challenge

" ... To seek "unexpected advances" that could be applied to such situations, the U.S. Defense Advanced Research Projects Agency (DARPA) issued its Shredder Challenge in October 2011, daring the public to unshred five documents and extract their hidden messages. The puzzles were designed to be progressively difficult on multiple axes, ranging from about 200 chads to more than 6,000 each. Text files accompanying the scanned chads provided questions, with points reflecting each question's difficulty. For example, puzzle #3 asked "What is the indicated location?" while the reassembled document showed a set of geographic coordinates and a drawing of Cuba. (Naming the country was worth two points; the city of Cienfuegos was worth an additional six.) Solvers needed to both answer the questions and show how their reconstruction of the document led to that answer. More than 9,000 teams applied for the challenge, but only 69 of them answered one or more questions correctly.... "