“Sanborn's own letters as the key: his 1989 note to CIA staff, the 1991 dedication pages, and his 2025 open letter”
Running keys have been tried from K1-K3, Carter's book and the sculpture's own texts. Never from the things Sanborn himself wrote around the sculpture: his December 1989 letter to Agency employees about the work in progress, the 1991 Cryptogram pages with Webster's dedication remarks, and his August 2025 open letter. Each is slid along the copper at every offset, both directions, on the standard, KRYPTOS and vocabulary tables.
A running keya running key A secret word as long as the message, taken from a book or another text. is a long text, such as a page of a book, written under the messagethe message The 97 letters of English that Jim Sanborn wrote and enciphered. one letter per place. We have tried the solved messages and Carter's book. Here we try the texts Sanborn himself wrote about the sculpture: his 1989 letter telling CIA staff what he was building, the 1991 pages with the dedication speech, and his 2025 open letter with its 'clue'. Each is slid along the copper at every starting place, forwards and backwardsa mirror Reading or writing the text from the end to the start., and the 24 known lettersthe known letters Sanborn has confirmed that positions 22 to 34 of the message read EASTNORTHEAST and positions 64 to 74 read BERLINCLOCK. say how close each fits.
Words in the margin are defined on the glossary page.
1.1
The method at work
The carved letters go in at the top; the reading comes out at the bottom.
the idea
A running key is a long text written under the message. Sanborn might have used something he wrote himself: his 1989 letter to CIA staff, the 1991 dedication pages, or his 2025 open letter.
the check
Drawn for the 1989 letter at its first offset on the sculpture's table: 2 of the 24 known places come out right.
the bound
All three texts, every offset, both directions, 390 tables: never fewer than 15 misses of 24, the same as shuffled coppers searched the same way.
2
Best candidate against the known letters
This experiment produced no candidate: the search ruled everything out before a full text was built. Its product is the bounded negative in section 7.
3
Walkthrough, by hand
Redo the method on a few letters with pencil and paper.
Write the 1989 letter's letters, DEARAGENCYEMPLOYEESIAMWRITING..., under the copper so that its first letter sits under place 1.
Place 22 then has key letter M, the 22nd letter of DEARAGENCYEMPLOYEESIAM.
On the sculpture's table with Vigenere, counted from K = 0: known E (11) plus M (18) is 29, which is 3, P; the carved letter is F, so this place misses.
Count how many of the 24 known places come out right.
Slide the letter one place and repeat, for every offset, both directions and every table.
the worksheet: the first steps by hand, on squared paper
4
Worked example, generated
The same steps run by the code on the real letters.
1989 letter from its first letter under place 1; sculpture's alphabet, Vigenere
place known key would carve carved
22 E M P F
23 A W T L
24 S R A R
64 B U P N
5
Hypothesis, for a cryptanalyst
Family, key space, the constraint under test, and the clues it reads.
Family 1, running key from a new source (C6(a) 'the keys were concealed', C7 'instructions in the earlier text', C27: Sanborn's own documents). Texts, letters only, OCR '|' read as I: (1) Sanborn's 15 December 1989 letter to Agency employees ('Dear Agency Employees ... Sincerely, Jim Sanborn'), (2) the 1991 Cryptogram pages carrying Webster's 5 November 1990 dedication remarks and the Cryptolog story (both in sources/sanborn-1989-letter-and-webster-1990-cryptogram.txt), (3) the August 2025 open letter (sources/openletter-2025.txt). Key letter at place i: source[(o + i) mod len], every offset o, source forwards and reversed. Setups: the 24 standard/KRYPTOS conventions, plus each vocabulary word's keyword alphabet on both sides with the key read on it or on the standard alphabet, three modes. Statistic: mismatches among the 24 known letters; survivors are within 3; controls are ten shuffled coppers through the same sweep. OCR errors cost at most a few mismatches near the cribs.
6
Prediction
Written before the run; the result decides it.
No source, offset, direction and setup comes within three mismatches of the 24 known letters, beyond what the ten shuffled coppers reach; the best is about as close as the best on the shuffles. Zero candidates pass.
7
Method
Extract the three texts as letters.
For each source, direction and offset, read the key letter under each known place.
For each setup, count the known places where the carved letter would not come out; keep the fewest and all within three.
Repeat on ten shuffled coppers.
8
Result and bounds
The harness's record: candidates, gates, loss, and the negative result this experiment leaves behind.