cipher doesn’t have to use letters. It easily could use numbers instead. A simple encryption scheme that many people already know is: a=1, b=2, etc. Numbers also can work in Atbash, Caesar, and mixed alphabets. Below is a numeric version of Atbash.
Plain: a b c d e f g h i j k l m n o p q r s t u v w x y z
Cipher: 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
Converting the ciphertext “24-26-13-26-23-26” yields the plaintext “canada.”
