(Courtesy of Wikipedia)
In the history of cryptography, a grille cipher was a technique for encrypting a plaintext by writing it onto a sheet of paper through a pierced sheet (of paper or cardboard or similar). The earliest known description is due to the polymath Girolamo Cardano in 1550. His proposal was for a rectangular stencil allowing single letters, syllables, or words to be written, then later read, through its various apertures. The written fragments of the plaintext could be further disguised by filling the gaps between the fragments with anodyne words or letters. This variant is also an example of steganography, as are many of the grille ciphers.
It has made me curious that the location of the typos is what is important, the word palimpsest is used and the apparent non-usefulness of the other half of the copperplate. Once I got the idea in my head, it was hard to get out. After some gridding efforts and a little thought, I realized that a 28×31 grid fits both halves of the copperplate (866 letters on the vigenere side and 868 on the cipher side if you leave out the X that was left out for “aesthetic” reasons by Sanborn.
So you are left with three grids. One is the vigenere side padded out with two missing corners which may be intentional or a typo or of some unknown significance. One is the ciphertext as it is carved, written to fit the grid (I tried using his line lengths but then switched when I found they would fit). The last is the answer text and the ciphered K4. I like the idea of using the answer text because it allows for ease of planning if they were going to attempt a grille cipher. Trying to use the enciphered text would become challenging because they would have to mold the plaintext to fit through the cipher methods to then reveal some message and that sounds like a ridiculous amount of planning that would leave quite a bit of room for error. It also explains why the vigenere table is built the way it is, they used the extra a-z alphabets to fill out the letter count for Sanborn to use and allowed for an adjustment of where the message would read.
My guess is that the two men worked out the plaintext, decided one encryption method would be too easy and switched to 4 in view of the 4 separate messages combined into one larger message. This would change nothing for the grille cipher and was executed easily. There would need to be some agreement on what the grille message should be and then the plaintext on the cipher side adjusted accordingly. This be a likely explanation of the typos and the why K3 is not a direct quote.
I then needed to know the keyword to cut out of the vigenere side. I went with the simplest, KRYPTOS. I then cut out every piece of Kryptos I could find and overlayed this grille onto the text (I did try both but due to the logic of the preceding paragraph, focused my attention on the plaintext and not the ciphered text).
This is what I made:
This is in the direct or regular overlay of texts. I contemplated the nature of the panels on the actual Copperplate and decided that it was possible I would need the reverse orientation of what is shown here.
Here is another picture showing the separate layers (ref: palimpsest and “layer two”).
It’s possible that I don’t have the correct “holes” as no exceeedingly enlightening message was revealed. It’s possible that we’re given a clue in K4 or have already uncovered a clue that will refine the process but for now, this is the best I’ve got. I tried some anagrams (of course) and on the regular overlay, the first row can read Helios fugio or Fleeing Sun (Sunset). This made me initially excited and I attempted to anagram the rest of the rows. At this point, I can’t tell if there’s something really there. It’s a good idea and has worked to an extent but I’m suspicious that I don’t have the right grille to find an answer if it’s there. I’ll spend a little time on the rows and may post my results another time but to save you the hassle of making your own to find the letters, I’ll include them here:
It’s very likely this is an “after you’ve solved all of the plaintext” situation, so it may not be possible to know the real message if there is one until K4 is solved. Until then though, it is a diverting pastime to attempt to fit an answer to what we have now. I don’t know that I’ll put much more effort in at this time but I do think this is a tangible lead on what is left to be done after the plaintext is known completely.