Answer the following questions for the mono-alphabetic substitution cipher. a) Describe the key space K. b) Describe the largest message space M {a, b, ..., z}" =U{a, b, ..., z}' for which the mono- i=1 alphabetic substitution cipher provides perfect secrecy. (Note: a message is simply a string of letters; it doesn't have to be a dictionary word. For example, abcxyz can be a valid message.)