Question 1. Encryption of German messages in WWII could be boiled down to transformations of a
26\times 26
identity matrix (a row for each letter) that encoded a message, which could then be decoded with a 'key'. We will take a similar, yet less-sophisticated approach, which assigns each letter a vector with two components:
^(')=[[0],[0]],^(')a^(')=[[0],[1]],^(')b^(')=[[0],[2]],dots, 'z' =[[2],[6]].
The
2\times 2
matrix
A
encrypts this code by left multiplying each letter's associated vector by
A
. For example, if
A
is given by
A=[[3,1],[2,1]]
we could encrypt the letter 'a' with matrix-vector multiplication:
encrypted 'a' =[[3,1],[2,1]][[0],[1]]=[[1],[1]]
For us, the matrix
A
is the 'key' and an accompanying
2\times n
matrix is an encrypted message, where
n
is the number of characters in the message. Decipher the following message
[[2,16,10,0,4,17,18,8,14,10,0,18,19,0,11,4,2],[4,40,25,0,10,42,45,20,35,25,0,45,47,0,27,9,4]]
if the key is given as
A=[[1,2],[2,5]]