Question: Encrypting/Decrypting with Maple

I'm working on a project in my Linear Algebra class dealing with Encrypting and Decrypting text. I have been trying for hours to find the right commands to do this the way my professor wants. Here's the question:

(a) Encrypt the following (choosing your own 3x3 key matrix):

"This class is starting to get boring" (Not including the quotation marks. There are 36 characters in this phrase.)

Use blocks of size 3 (ie a 3x12 matrix with all the characters) and the alphabet:

"a, b, c,..., x, y, z, " ", ".", "?"" (There are 29 different characters including the 26 letters of the alphabet, the space, the period, and the question mark.)

(b) Decrypt the text you just encrypted.

Thank you so much for any info you can give me about Encrypting and Decrypting text in Maple! Have a nice day.