Possible encryption method used for the K4 code

Encryption method principles

The encryption method used for the K4 code could be based on the successive application of two layers of Vigenère code.

The keys corresponding to each of these codes were defined using the two available clues provided by the creators of the sculpture : “FLRVQQPRNGKSS” means “EASTNORTHEAST” (position 21-33) and “VTTMZFPK” means “BERLINCLOCK” (position 63-74).

First encryption layer

The first layer would be Vigenère code based on a sentence from an American book “Two hundred miles on the Delaware River” published in 1867 by Hoff, J. Wallace (https://www.loc.gov/item/01021510/).

The specific sentence used would be : “[… ] clear cut against the dark blue sky, Luna's upper edge appeared, forming an enchanting background for the display of the feathery limbs and leafy tree tops on the brow of the rocky eminence.” (the first word “Then” is eluded).

Source: Library of Congress https://www.loc.gov/item/01021510/

Why this sentence?

I have not been able to determine whether this book, its subject matter, or its author have any particular connection to Langley or the creators of Kryptos. 

But, it can be noted that:

• This sentence could be a very suitable answer to the question concluding the K3 code: “Can you see anything?”.

• This sentence was discovered based on available clues located in the middle of the code; however, it fits perfectly the start of the K4 code, by removing the first word “Then” from the full sentence.

All of this data can be summarized as follows:

 Second encryption layer

The second layer would be a Vigenère using a key based on geometric sequences of letters, according to the Kryptos alphabet. These sequences are defined by:

• A first letter, corresponding to the starting letter of the sequence.

• A second letter, corresponding to the constant shift interval between two consecutive letters of the sequence.

For example, the sequence associated with the letters D and Y is as follows: 

, which gives the sequence DFHJM…

By convention, we can note this sequence DY: as we will see next, I think that these sequences are linked to the DY A HR anomaly located at the upper left corner of the second panel of the sculpture.

Finally, it should be noted that these sequences of letters are quite comparable to the operating principles of the famous Berlin Clock or Mengenlehreuhr, which appears in the solution given by Jim Sanborn and whose principles were widely thought to have inspired the coding method.

Application of this method to available clues

The application of these principles leads to the following results:

 

First Clue “EAST NORTHEAST” (Position 21-33)

• The TN sequence makes it possible to explain 10 of the 13 letters of this clue, which constitutes, in my opinion, a very good result (or at least a rather promising result).

• The sequences located at both ends of the clue (?R and V?) cannot be, at this stage, completely determined: for the sequence ?R, we do not know where its start is located in the code and so the first letter used. For the sequence V?, it is impossible to determine the shift used from a single letter.

Second Clue “BERLIN CLOCK” (Position 63-73)

• The sequences are shorter than for the first clue, between 3 and 4 characters: DH (4 characters), MT (3 or 4 characters), KK (3 or 4 characters): in fact, these last two sequences have the letter K in common at one end, which does not make it possible to determine their exact length.

• This method gives “CLOQK” as the solution instead of “CLOCK”, which does not necessarily seem insurmountable, especially since this error could recall the one appearing in the solution of the K1 code (“IQLUSION” instead of “ILLUSION”).

• The method also requires an inversion of two letters T and N, in the first Vigenère code (“ENCHATNING” instead of “ENCHANTING”). This point could be seen as a weakness of the proposed solution, but I do not have the impression that it is, in itself, a sufficient reason to definitively rule it out.