World Puzzling Competition #2: bobby's transformation

Previously: This year, you were invited to attend the WPC, otherwise known as the World Puzzling Competition. The organizers also seem to suggest that there will be a 50 reputation bounty for every question (subject to change for future questions) for the "most contributive person".

Puzzle #1 and this puzzle (#2) are independent.

To remind you, here are the assumptions you can make about the puzzles. For the full version, refer to puzzle #1.

• Everything is self-contained.

• Any information contained in italics does not include any information required for the puzzle, though they may be clues that consider as contributions.

• Only the question itself can be used as a resource.

• Specific rules overwrite general rules.

• The puzzle never lies.

Relaxed from the last victory, you go for a stroll at your favourite local beach. As you walk across multiple stands, you see a fisher selling a stock of fish. "Sure seems fishy," you said, unaware of what is to happen next. Suddenly, the fisher transforms into none other than Sny Smartie, presenting you what you suspect is the second puzzle.

Handing you the puzzle, Sny Smartie suggests that participants win as fast as possible.

Sny Smartie then says: "by the way, my favorite number is 64, so make sure you base your decryption off of that!"

Suddenly, Sny Smartie disappears. In his place lies a piece of paper (the puzzle):

a3BwcDJCQi
9wcHAyQkIx
L3BwMkJCMi
9wMkJCMy8y
QkIybjEvMU
JCNS9CQjJu
My9CNksUW4
0blEvbjZuL
zdrLzgvOC9
LNy9uNm4vU
W40blEMW5i
MWtibjEvOC
84LzgvOC8z
Uk5QMi8zTj
FQMi8yQlFL
QjITheAnsw
erWillBeAT
hreeLetter
Abbreviati
onXXXXXSny


For whatever reason, you mind wanders off to space. Then you decide that you don't need it to solve your puzzle, so you quickly think back to the puzzle, trying to solve with all your might.

There are 6 clues to solving the puzzle, excluding the solution itself. A clue may be a part of the question that hints at the solution or the deduction of the solution, a connection between the solution and the question. A solution counts as 2 clues.

• Note the change that italic flavor texts may contain clues so as not to make clues glaringly obvious. This change was previously migrated to #1, but many may not notice.
– Sny
Feb 2 at 16:28
• Alas! If rot13(gur svefg jrer fvk engure guna sbhe naq gur guveq jrer sbhegrra engure guna gra), I would have a pretty confident answer, but that doesn't seem to be the case. Feb 2 at 18:53
• Ah, no, maybe rot13(gur svefg vf fvk nsgre nyy). Is it possible that rot13(lbhe qrcgu jnf gbb ybj)? Feb 2 at 18:57

(Unless I am confused, this answer can only be right if there is an error in the puzzle. So it's probably wrong.)

The given text is

three separate chunks of base64 (hinted at, of course, by the "64" and "base" in Sny's advice, with 64 doing double duty as the number of squares on a chessboard) glommed together (along with the plaintext bit about getting a TLA at the end). The line breaks will be ignored by typical decoding tools, as suggested by "space ... you don't need it". Decoding the first chunk yields kppp2BB/ppp2BB1/pp2BB2/p2BB3/2BB2n1/1BB5/BB2n3/B6K or ; decoding the second yields Qn4nQ/n6n/7k/8/8/K7/n6n/Qn4nQ or ; decoding the third yields 1nb1kbn1/8/8/8/8/3RNP2/3N1P2/2BQKB2 or

Since

we are told to "win as fast as possible", let's see what we can do. The first position is illegal, which means that e.g. Stockfish refuses to analyse it, so I'll skip it for a moment. In the second position white has several ways to mate in 5, including 1. Kxa2 and 1. Qxb1. In the third position it looks like the best white can do is mate in 10, starting with Qb3 or Qa4. BUT at lower depth Stockfish thinks white mates in 14, and I think this may be significant. As for the first, illegal, position, it looks to me as if it's a mate in 6 starting with Bxc8 (it's "morally" a mate in 4 but black has a couple of spite-checks). And the numbers 6, 5, 14 would translate via A1Z26 to FEN, short for the Forsyth-Edwards Notation we found by decoding the base64 text.

So

if it's possible that the puzzle-setter did the same thing as I did at first and put the third position into Lichess's engine with its default settings and didn't allow it to think more deeply than default, then the answer could be FEN. (Which, in case I didn't make it explicit enough before, is not just three random letters, it's the name of the notation used for the chess positions.)

Oh, of course

Bobby is Bobby Fischer, hence all the stuff about things being fishy. And -- I didn't notice this until OP directed me to the relevant paragraph, because I am an idiot -- of course the fisher has a stock of fish in reference to Stockfish.

• Yep, you're right. I used the default engine for chess.com, and I kept it running for a while (5 minutes), and I didn't really think depth would be a problem, yet the engine persisted with M14.
– Sny
Feb 3 at 1:09
• There's 3 more clues. One of them is the obvious indication of the first decryption step, another is a less obvious indication of another decryption (step?), and finally there's a subtle clue connecting with chess.
– Sny
Feb 3 at 1:11
• Oh, sorry, I hadn't realised you wanted us to be explicit about every hint we spotted. I've updated my answer to do more of that. If the "subtle clue connecting with chess" is none of {Fisher, 64, name of notation} then perhaps it was too subtle for me to notice. Feb 3 at 2:49
• It was something else, hidden in the first paragraph of flavor text.
– Sny
Feb 3 at 2:51
• The fact that space isn't needed also hints at the fact that the three b64 encodings are concatenated as well. I have previously decided to accept both reasonings.
– Sny
Feb 3 at 2:52