Oct / 25

A foreign navy has implemented a secure communications system in which submarine commanders transmit a single?

                        A foreign navy has implemented a secure communications system in which submarine commanders transmit a single?
A foreign navy has implemented a secure communications system in which submarine commanders transmit a single 5-letter message every day. The messages may only use capital (English) letters, and all messages are equally probable. A crypto device encrypts each message into 20 bits of ciphertext.
a. What is the entropy of the plaintext message?

b. What is the entropy of the ciphertext message?
c. Is this a good cryptosystem? Why or why not?

Please help after analysis of the question I came up with the followin answer: 
plain text message capacity of 26^5 = 11.88e6 distinct messages possible
encrypted message capacity of 2^20 = 1.048e6 distinct messages possible

I not sure if its correct, please show work so I can grasp the concept, thank you in advance.
Answer