1.$1.$ The Caesar Cipher is our first historical cryptosystem and has numerous flaws.

($($a)$)$ Decrypt the Caesar Cipher ciphertext: IT STY ZXJ RJ YT JSHWDUY DTZW UFXXBTWI

($($b)$)$ The Caesar Cipher has an inadequate keyspace. What other problems does it have that make it insecure?

($($c)$)$ The Caesar Cipher is often described as having a fixed shift of three positions. Explain why in this case, the Caesar Cipher is not really a cryptosystem at all.

($($d)$)$ Is ROT13$13$ a cryptosystem?

2.$2.$ Describe Playfair Cipher ($($limit your answer to 50$50$ words).$).$

3.$3.$ Describe Vigen$$re Cipher ($($limit your answer to 50$50$ words).$).$

4.$4.$ R and Q appear as one−$-$letter words in a cryptogram. R has frequency 7,$7,$ and Q has frequency 3.$3.$ Which ciphertext letter is likely to be the substitute for a,$,$ and which is likely to be the substitute for i?$?$ Explain your reasoning.

5.$5.$ The two−$-$letter word KC appears in a cryptogram. K has frequency 5,$5,$ and C has frequency 2.$2.$ One of K and C is a consonant, and the other is a vowel. Which is likely to be which? Explain your reasoning.

6.$6.$ BKKL appears in a cryptogram. What are some possible plaintext words for this four−$-$letter encrypted word?