“The message as its own key, plus a repeating secret word on top”
Experiments 3 and 12 tested the autokey that feeds on the message itself, with no other key. The NSA's 1992 note named 'plain-text auto-key'. Here a repeating secret word is added on top, at every distance where two known letters can be compared and every word length, on the sculpture's table and on tables rebuilt from words.
In a plaintextthe message The 97 letters of English that Jim Sanborn wrote and enciphered.autokeyan autokey cipher A cipher that uses the message itself, or the scrambled text itself, as the secret word, each letter enciphered with the letter a fixed distance before it. cipher each letter is enciphered with the message letter a fixed distance backthe lag In an autokey cipher, how far back the key letter sits from the letter being enciphered., so the message is its own key. Experiments 3 and 12 showed that alone does not fit. Here we add a repeating secret wordthe secret word The word or string a cipher needs besides the method. on top. We can only test it where two known letters sit the right distance apart, but there are enough such pairs to get clear answers for many distances, and scrambled coppers show how many fits luck alone gives.
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 cipher
In a plaintext autokey each message letter is keyed by the message letter a fixed distance before it; here a short repeating word is added on top.
the check
At distance 3 with a 7-letter word, places 25 and 32 share a slot but need A and I: dead.
the bound
Every distance where two known letters pair, every word length, 161 word alphabets: 12 settings pass three checks against 0 to 6 on shuffled coppers, but they are four coincidences repeated at nested lengths and none passes four.
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.
Lag 3, a 7-letter word, the sculpture's alphabet KRYPTOSABCDEFGHIJLMNQUVWXZ from K = 0, Vigenere.
Place 25: carved V (22) minus known T (4) is 18; the message letter 3 back is E (11); the word's letter is 18 - 11 = 7, in slot
Place 32: carved K (0) minus known A (7) is -7, which is 19; 3 back is T (4); 19 - 4 = 15, also slot 3.
7 and 15 disagree: lag 3 with a 7-letter word is dead under this way of using the table.
Repeat for every lag with known pairs, every word length and every way of using the 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.
lag 3, 7-letter word, sculpture's alphabet throughout, Vigenere
place known carved 3 back word letter slot
25 T V E 7 3
32 A K T 15 3
26 N Q A 20 4
33 S S H 12 4
5
Hypothesis, for a cryptanalyst
Family, key space, the constraint under test, and the clues it reads.
Family 1, plaintext autokey as a component of a two-part key (C11a: NSA 1992 'plain-text auto-key', sources/nsa-foia-1992-2014-blackvault-compilation.txt; C5(b) 'key word/s'): T[i] = s*A(p[i-L]) + k[i mod P]. Only places where both p[i] and p[i-L] are known give equations: lags 1-12 inside EASTNORTHEAST, 1-10 inside BERLINCLOCK, 30-52 across them. Each such pair forces k at slot i mod P, and pairs sharing a slot must agree. Classes: plain, cipher and key alphabets standard or KRYPTOS, Vigenere or Beaufort, sign +1 or -1 (32 classes); plus one alphabet keyword-mixed from each vocabulary word, K1-K3 word and C13/C14 word (as in 0053) used on both sides, with the key read on it or on the standard alphabet (8 more per alphabet). Periods 1-96. Survivors tallied by redundant checks against ten shuffled coppers; no candidates (the key outside the pairs is unknown). Clue entries: C11a, C5(b).
6
Prediction
Written before the run; the result decides it.
No case with three or more redundant checks survives beyond the shuffled-copper range; the lags 7 and 21 named by the fingerprints and the NSA's 'interval 7' are no different. Zero candidates pass.
7
Method
For each lag, list the pairs of known places that far apart.
For each class, the pair forces the secret word's letter in slot i mod P: total key minus the earlier message letter's value.
For each period, check slots agree; tally survivors by redundant checks.
Repeat on ten shuffled coppers.
8
Result and bounds
The harness's record: candidates, gates, loss, and the negative result this experiment leaves behind.