I am learning about Hill Cipher and know that it is a block cipher where each block of n letters (considered as an $n$-component vector) is multiplied by an invertible $n \times n$ matrix, again modulus $26$.
The article did not touch on what happens if the the block of letters is less than length $n$.
Eg: Assume I am supposed to encrypt 100 letters – how do I encrypt the last 22 letters?
I was thinking of padding similar to MD5, or are there other methods to resolve this issue? If so, what are those methods?