Using python write a program to encrypt plaintext into cipher using the Hill cipher.

Getting started:

1. Choose and use a 3 by 3 matrix representing the encryption key (Note: Make sure the matrix has an inverse.).

2. Iterate over each character of the plain text: 1. If the character is alphabet: 1. Calculate the position/index of the character in the 0-25 range.

2. Find the character at the new position.

3. Replace the current letter by this new character.

2. Else, If the character is not alphabet, ignore the character, and move to the next position in the plaintext. with no change.