Two people found the solution. They used the power of research, not cryptanalysis, finding clues amongst the Sanborn papers at the Smithsonian’s Archives of American Art. This comes as an awkward time, as Sanborn is auctioning off the solution. There were legal threats—I don’t understand their basis—and the solvers are not publishing their solution.

Well, this is interesting: > The auction, which will include other items related to cryptology, will be > held Nov. 20. RR Auction, the company arranging the sale, estimates a winning > bid between $300,000 and $500,000. > > Along with the original handwritten plain text of K4 and other papers related > to the coding, Mr. Sanborn will also be providing a 12-by-18-inch copper plate > that has three lines of alphabetic characters cut through with a jigsaw, which > he calls “my proof-of-concept piece” and which he kept on a table for > inspiration during the two years he and helpers hand-cut the letters for the > project. The process was grueling, exacting and nerve wracking. “You could not > make any mistake with 1,800 letters,” he said. “It could not be repaired.”...

Long article on the difficulty (impossibility?) of human spying in the age of ubiquitous digital surveillance.