Open Research Questions

Prioritized unknowns driving the investigation. Each question represents a gap in our understanding of K4. Resolving any Tier 1 question would significantly narrow down possible solutions.

Tier 1: Maximum Leverage

RQ-1: What is the cipher TYPE?

Why it matters: Entire attack methodology changes. This is the single most valuable question.

Where it stands: (updated 2026-09-29) Unknown. In the standard letter-for-letter reading, no repeating key of any length from 1 to 26 fits the known letters, with either the standard alphabet or the KRYPTOS alphabet, and the key is not produced by any of the simple step-by-step formulas we tested (linear recurrences of order 1 to 8) on those alphabets. With one keyword-scrambled alphabet used on both sides (the way K1 and K2 used theirs), repeating keys of length 1 to 22, 24 and 25 are also ruled out, whatever that alphabet is; lengths 23 and 26 are not. Versions that use two different scrambled alphabets, or a Gromark cipher with keyed alphabets, are not yet ruled out in our published record. The 2026 program extended the negatives beyond the letter-for-letter reading: campaigns that first undo a rearrangement, or let the known words land anywhere (millions of configurations, each campaign checked against a chance baseline built the same way), found nothing. For the simple substitution + rearrangement + running-key family, the strongest detector we built could not tell real text from shuffled text at 97 letters (0 of 6 planted test cases detected), so that family stays open as a limit on what can be detected. It may be position-dependent (not state-dependent) based on the K5 shared-positions inference, but this inference is unproven.

20 candidate approaches catalogued for this question in the idea-triage ledger. (Completed experiments are recorded in the elimination database, not in this counter.)

RQ-2: What is the key source / generation method?

Why it matters: Directly produces the plaintext.

Where it stands: In the letter-for-letter reading, the key letters at the 24 known positions follow directly from the clues. Under Vigenere with the standard alphabet they are BLZCDCYYGCKAZ (positions 21-33) and MUYKLGKORNA (positions 63-73). They are not readable English, show no simple pattern, and do not follow a linear recurrence of order 1 to 8.

81 candidate approaches catalogued for this question in the idea-triage ledger. (Completed experiments are recorded in the elimination database, not in this counter.)

RQ-3: Is there a transposition layer, and what type?

Why it matters: Reduces problem from "find transposition AND substitution" to "find substitution."

Where it stands: (updated 2026-09-29) Rearrangements based on two Berlin clocks (480 from the Mengenlehreuhr set-theory clock, plus orderings from the Weltzeituhr world clock) were tested with thematic keyword alphabets and found nothing. In 2026 we scored candidates after undoing 52 route rearrangements, including routes combined with a Vigenere-style cipher using six keyword alphabets (KRYPTOS among them) and 27 thematic keywords (25,272 configurations, 2026-06-10), and found nothing. In August 2026 an older proof that ruled out repeating keys at most key lengths under any rearrangement was withdrawn, and the searches that relied on it were reopened. Columnar rearrangements were then re-run without the faulty check: for every grid width from 4 to 9 and every column order (substitution first, then rearrangement), no repeating key of length 1 to 24 on the standard alphabet fits the known letters. If a rearrangement layer exists, it is not one of the families whose searches still stand, at the depths tested.

29 candidate approaches catalogued for this question in the idea-triage ledger. (Completed experiments are recorded in the elimination database, not in this counter.)

Tier 2: High Leverage

RQ-4: What is the role of "the point"?

Why it matters: May reveal a key parameter or structural element.

22 candidate approaches catalogued for this question in the idea-triage ledger. (Completed experiments are recorded in the elimination database, not in this counter.)

RQ-5: How do Sanborn's 1986 Egypt trip and the 1989 fall of the Berlin Wall figure in the solution?

Why it matters: Constrains plaintext content, may reveal key parameters.

64 candidate approaches catalogued for this question in the idea-triage ledger. (Completed experiments are recorded in the elimination database, not in this counter.)

RQ-6: What does "delivering a message" mean?

Why it matters: Constrains the expected plaintext format.

3 candidate approaches catalogued for this question in the idea-triage ledger. (Completed experiments are recorded in the elimination database, not in this counter.)

RQ-7: What do the first 21 letters (positions 0-20, before EASTNORTHEAST) encode?

Why it matters: May reveal a "key indicator group" or separate cipher for the header.

5 candidate approaches catalogued for this question in the idea-triage ledger. (Completed experiments are recorded in the elimination database, not in this counter.)

Tier 3: Moderate Leverage

RQ-8: Is the "change in methodology" from K3→K4 a specific technique?

5 candidate approaches catalogued for this question in the idea-triage ledger. (Completed experiments are recorded in the elimination database, not in this counter.)

RQ-10: Is there a connection to the sculpture's physical properties?

15 candidate approaches catalogued for this question in the idea-triage ledger. (Completed experiments are recorded in the elimination database, not in this counter.)

Tier 4: Background

RQ-9: What is K5 and how does it relate to K4?

Why it matters: Additional cribs, constraints on the cipher.

RQ-11: Is there meaningful structure in the known keystream?

8 candidate approaches catalogued for this question in the idea-triage ledger. (Completed experiments are recorded in the elimination database, not in this counter.)

RQ-12: Could the cipher use a non-standard alphabet (keyword-mixed, reversed, etc.)?

5 candidate approaches catalogued for this question in the idea-triage ledger. (Completed experiments are recorded in the elimination database, not in this counter.)

RQ-13: Is the reading direction standard (left-to-right, top-to-bottom)?

16 candidate approaches catalogued for this question in the idea-triage ledger. (Completed experiments are recorded in the elimination database, not in this counter.)