Mr. Kobek lives in California, so he asked a friend in the Washington area, Richard Byrne, a journalist and playwright, to request the Sanborn papers at the Smithsonian’s Archives of American Art.
Mr. Byrne spent hours photographing documents at the archives on Sept. 2. Mr. Kobek that evening, while reviewing the images his friend sent, saw scraps of paper, some held together by yellowed tape, and got a shock: “Hey — that says ‘BERLIN CLOCK’!”
Those two words were clues to K4 that Mr. Sanborn released in 2010 and 2014. Another scrap had more of what looked like the original, uncoded message, known in cryptography as the plaintext, including the words “EAST NORTHEAST” — two clues released in 2020. Together, there were 97 characters, the number of characters in K4, that he assembled into a readable passage.
“This is a problem everybody has been attacking as a STEM problem,” Mr. Kobek said in an interview, referring to the fields of science, technology, engineering and mathematics that underlie cryptography. Cryptographic science, he argued, could not solve Kryptos — “but library science could.”
Mr. Byrne compared their find to open-source intelligence.
On Sept. 3, the men sent their email to Mr. Sanborn, including an assurance that their “primary concern” was “moving forward without imperiling your forthcoming auction.” They had a half-hour telephone call in which Mr. Sanborn confirmed that they had the solution.