## On the Subject of the Hill CM

Sometimes, you need to scale a mountain rather than a hill.

**All letter-number conversions are to be done with respect to the scheme A1Y25Z0. All rows and columns of the matrices are numbered from 1 going down or right respectively.**

Concatenate the letters on all numbered screens in order, and convert them into numbers. These numbers, in reading order, are entries in an N×N matrix, where N is the number of letters on a given numbered screen. This matrix will be labeled M.

If the Submit Button is white, use matrix M to decrypt the word. Otherwise, you will need to calculate the inverse matrix, I, to decrypt the word.

Concatenate the encrypted word with the letters on screen A (if any), then split this string into substrings of the same length as the width of the matrix. These will be the vectors to be used with the matrix.

Perform matrix-vector multiplication on each vector using correct matrix, M or I. To do this:

- For each row of the matrix, multiply the X
^{th}entry of the row with the X^{th}entry of the vector. - Take the sum of these numbers, this result will be the X
^{th}entry of the resulting vector. - Take each entry, modulo 26, and convert it to a letter. You should now have a decrypted set of letters

The instructions to calculate matrix I are written on the next pages.