So what makes this approach so special. Well, it is something that never happened before: Mr. Sanborn reacted to it. Indirectly, but he came up with a statement. You have to know that if you pay your $ 50 and submit your solution, Jim Sanborn will only give you a YES or NO. Never a reaction in any way. From the famous KRYPTOS FEES PDF: "PLEASE NOTE: THAT JIM SANBORN WILL NOT INTENTIONALLY REVEAL CLUES OR A SOLUTION TO THE REMAINING UNSOLVED K4 SECTION." So in my case:

After playing around with the described approach (different XOR keys and encoding CIAW etc.) I decided, at the end of February 2018, to pay my 50 Dollar and contacted Mr. Sanborn. I introduced myself, my ENIGMA message breaking background etc., and asked him to have a look at my first 10 letters of K4. (Like on the former cryptosclue website). This is the solution I sent to him:

OBKR (Part of the message key)


The answer was negative: "Sorry but these are not the first ten letters." That was all. So I thanked politely and briefly indicated how I came up with this solution. XOR combined with a modulo 5 addition. Not in detail. Convinced that this was the right approach, I continued to work on a solution.

In March 2019 Klaus Schmeh published his article "CNN documentary about Kryptos: A making-of report with many photographs". There you can read the following under the section "Notes from the meeting":

"When asked about the solutions that have been sent to him (Jim Sanborn), and whether any of them were close, Jim said he got one from Germany about a year ago that was “kind of scary”, that the first part had started to look right, but then the rest didn’t."

That was exactly 1 year after I submitted my proposed solution! This topic was discussed in the comments to this article and the term "GERMAN GUESSER" came up to describe the unknown solution.