Solution: Key Changes
Answer: MAC TAYLOR

Written by Jonah Ostroff

The “key changes” to perform are each common(-ish) puzzle hunt codes. Each one can be decoded to give the name of another encoding, so solvers can use this to identify the ones they’re missing. The encoded terms are in alphabetical order, but we can arrange the list to form one long loop, where each encoding decodes to the next one in the list: Maritime flags, Gold Bug, Pigpen, Ternary, Binary, NATO, Tap Code, Phone spelling, ASCII, Semaphore, A1Z26, Braille, Roman numerals, Elements, Morse code, and then back to Maritime flags again.

Below the key changes are a list of ways to “perform” these key changes. Each one can be interpreted as a way to transform one of these encodings. In a few of them, it also seems like the output is an encoded letter in another one of the fifteen codes.

With this in mind, solvers might guess that the output of “Replace the middle digit with ., increment the last digit, then write the name of that MacOS” is Sierra, a NATO alphabet letter. Sierra is version 10.12, which means the input is 10[something]11. Interpreted as 5-bit binary, this could be an S or W.

At this point solvers should notice that each instruction can be interpreted to send a letter in one encoding to the next encoding in loop order. Given this, it’s easy to deduce the pairs for some transformations (e.g. “Make the background yellow, then cut the image in half” goes from Morse code to maritime signal flags). Others can be deduced by process of elimination.

Once the encodings are known for the instructions, solvers can then notice that for each instruction, there is exactly one letter which is mapped to the same letter in the new encoding. For example, if you count the number of yellow regions in The maritime signal flag for G: a square colored in alternating vertical stripes: yellow, blue, yellow, blue, yellow, blue. (“G” in maritime signal flags), you get 3, which is the symbol for G in the gold bug cipher. No other letter has this property.

Here’s a table of all the letters that map to themselves:

Encoding 1 Encoding 2 Letter Instruction From To
Maritime flags Gold Bug G Write the number of yellow regions. The maritime signal flag for G: a square colored in alternating vertical stripes: yellow, blue, yellow, blue, yellow, blue. 3
Gold Bug Pigpen A Delete any curves, then rotate 180°. 5 The pigpen shape for A: the right and bottom sides of a square.
Pigpen Ternary R Let A, B, and C be the numbers of all lines, dots, and diagonal lines. Write A×B, A×C, and B×C. The pigpen shape for R: the top and left sides of a square, with a dot in between. 200
Ternary Binary Y Write 1 [first digit] times, then 0 [second digit] times, then 1 [third digit] times. 221 11001
Binary NATO S Replace the middle digit with ., increment the last digit, then write the name of that MacOS. 10011 SIERRA
NATO Prison Tap Code I Write the number of occurrences of the most frequent letter, then the number of distinct letters. INDIA 24
Prison Tap Code Phone spelling N Multiply by two. 33 66
Phone spelling ASCII I Write the largest prime factor, but backwards. 444 73
ASCII Sempahore S Hold flags in the positions of the digits, where 1=south, 2=southwest, ..., 8=southeast. 83 West-Southeast
Semaphore A1Z26 E Count the vowels in the names of the directions of the flags. South-Northeast 5
A1Z26 Braille O Fill in every dot that's a proper divisor of the number (using the standard numbering). 15 ⠕
Braille Roman numerals N Replace each row as follows: ⚬•s becomes Is, •⚬s becomes Vs, ••s becomes Xs. Delete ⚬⚬s. ⠝ XIV
Roman numerals Elements C Replace the first two letters with L and make the rest lowercase. III Li
Elements Morse code S Write a dot for each straight line, then a dash for each curve. K ...
Morse code Maritime flags I Make the background yellow, then cut the image in half. .. The maritime signal flag for I: a yellow square with a dot in the middle.

The letters that are fixed by the transformations spell GARY SINISE ON CSI, which clues the answer MAC TAYLOR.

Author’s Notes

This puzzle was inspired by the observation that semaphore for F, N, and U kind of look like their letters, that Braille and Morse I both consist of two dots (but oriented differently), and that semaphore I and U are both rotations of their pigpen analogues. None of these observations made it into the puzzle.

There are a number of interesting transformations that have two fixed points. For example, “count the dots from in each row from bottom to top” works for both A and N from braille to ternary, and “alphabetize all possible colors, and write 1 for each one that appears and 0 for each one that doesn’t” works for both F and J from maritime flags to binary.