[Cryptography] Holiday-themed decode contest

[Brad Klee]

Subtitle: Is that really what you call a Feistel cipher,
or are you being too loose with yr meta again?

A friend of mine from China sent me a calendar with
hexagrams and solar terms, so that I could have more
fun studying foreign languages and graphic design.

I then permuted the day frames and encrypted the data
to an online location, using a custom algorithm derived
from source code I read off etherscan. Data is here:

https://github.com/bradklee/CryptoAssets/tree/master/ExCrypt4

Then, I added a Feistel cipher to protect a more
vital secret, and encrypted this data into a prize box:

https://github.com/bradklee/CryptoAssets/tree/master/PrizeBox

The main rule for the contest is no peeping for the secret
keys! Win conditions are to obtain decodes, reorder the
calendar, and interpret what the secret means. Answers
will be given after two months or so.

I wanted to make part of the contest possible to win,
so here is a working implementation of the decryption:

https://www.wolframcloud.com/obj/bradklee/Published/ContestDecodes.nb

Considerably more notes are listed on the BB, with
pictures, animations, etc.

https://community.wolfram.com/groups/-/m/t/2425904

Since the 2D case is easy to crack without mixing,
maybe the 3D calendar data is also weak?

If no, perhaps we could spin this thread off into a
discussion of different mixing and padding schemes
in one dimension?

It's still a few months to Chinese lunisolar new year,
so we might have time to waste if the algorithm is
hard enough?

Thanks and Happy New Year!

--Brad
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