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I think this code is my masterpiece- let's see what you think:

159368358147349358267359259267348169367149159248348147168169147268349259149267168367147359358169257269347158269159257257358249259168358147349358

In all seriousness, though: I came up with this cipher recently to test a friend of mine who claimed he was good at cryptography, with the solemn promise that it had a solution. He still hasn't found the solution, even though he (as well as you, I bet) has already seen it before. It is one sentence, in English. I don't really know that it's my masterpiece, but I imagine it's good enough.

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    $\begingroup$ Have you seen Code Puzzles: What Not To Do? This seems to me to be the exact type of puzzle that those guidelines warn against. I've found a pattern, but I've now reached the "throw spaghetti at the wall until it comes up English" phase, and that's not particularly fun (or clever -- security by obscurity is easy). $\endgroup$
    – Deusovi
    Feb 24, 2020 at 23:02
  • $\begingroup$ I added a bit more information that should make it easier to solve. I still don't know if it's up to the standards in your document, but I think it's better. $\endgroup$ Feb 24, 2020 at 23:13
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    $\begingroup$ Knowing specific details about the solution doesn't help solve it -- the problem is that there's no real indication of what to do, so it ends up being "just try random things until English comes out". It's easy to make an impossible puzzle -- but "guess what I'm thinking" isn't a fun puzzle at all, and that's what this looks like it might boil down to. $\endgroup$
    – Deusovi
    Feb 25, 2020 at 0:03
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    $\begingroup$ I understand and respect your criticism, but it's not just that I gave a specific detail- I actually rot13(tnir gur fbyhgvba va gur dhrfgvba) with that detail. If you were to spot that hint, then the puzzle becomes more verifying the answer. $\endgroup$ Feb 25, 2020 at 0:08
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    $\begingroup$ Ah, I see -- yeah, that's a slight improvement. It makes it more solvable, at least. $\endgroup$
    – Deusovi
    Feb 25, 2020 at 0:18

1 Answer 1

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To decode this:

- Divide the numbers into blocks of 9.
- "Transpose" every block of 9: write it in rows in a 3x3 square, then read it in columns.
- Now, each triplet of digits is either all digits 1-3, all 4-6, or all 7-9; these three repeat in each block of 9. Subtract 3 or 6 from the groups of the latter two types. Then, replace all 3s with 0s. [This step can also be performed more simply by taking digits mod 3, but this version is invertible.]
- Read triplets as ternary, and take the corresponding letters of the alphabet to get the first sentence in the question: "I THINK THIS CODE IS MY MASTERPIECE LET'S SEE WHAT YOU THINK". (Spaces are not encoded.)

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