## On the Subject of 3×3 Yellow Ciphers

This yellow is not mellow, as it will try to give you 2 threes and X you.

This module contains 3 screens, a keyboard, 2 arrows, and a submit button that displays the current page you’re on.

Pressing the left or right arrow takes the defuser to the previous or next page, wrapping around the last page. There are 3 pages.

To disarm the module, decrypt a word using the following steps. Once you have the decrypted word, type it in using the keyboard. When you start typing, the screens go blank and the bottom screen will show what you are typing.

To clear your input, click one of the arrows.

Once you are satisfied with your input, press the button labeled “SUB” to submit your answer. An incorrect submission will cause a strike but NOT reset the module.

When the instructions say to modulo a value by N, repeatedly add or subtract N to that value to keep the value within the range of 0 to (N - 1).

### Step 1: 3×3 Matrix Inverse Calculation

Depending on what screen(s) are shown in white, you will need to calculate the inverse of exactly one of the matrices.
In the order of top to bottom on pages 2 and 3, the displayed numbers correspond to 2 separate matrices, with elements labeled a-i in reading order.
On page 1, the middle and bottom screens display the determinants of the matrices from pages 2 and 3 respectively.

**You do NOT need to calculate the determinant of a 3×3 matrix.**

If on page 2, all the screens are white, or the middle screen of page 1 is white, the inverse of the second matrix MUST be calculated. Otherwise, the inverse of the first matrix MUST be calculated.

Using the determinant of the matrix needed to be inversed, modulo 26, as E, calculate for D. *Instructions to calculate for D can be found on page 4.*

Then calculate the following 9 values in THIS order:

- (e * i) - (f * h)
- (f * g) - (d * i)
- (d * h) - (e * g)
- (c * h) - (b * i)
- (a * i) - (c * g)
- (b * g) - (a * h)
- (b * f) - (c * e)
- (c * d) - (a * f)
- (a * e) - (b * d)