Do as many of the following as you can in the time given. Order of completion does not matter.
Implement a Caesar cipher, both encoding and decoding. The key is
an integer from 1 to 25. This cipher rotates the letters of the alphabet (A to
Z). The encoding replaces each letter with the 1st to 25th next letter in the
alphabet (wrapping Z to A). So key 2 encrypts "HI" to "JK", but key 20 encrypts
"HI" to "BC". This simple "monoalphabetic substitution cipher" provides almost
no security, because an attacker who has the encoded message can either use
frequency analysis to guess the key, or just try all 25 keys.