Question

Why is the Vigenere cipher hard to crack? (select 2)

A. One cannot solve using frequency analysis directly.
B. The key length is variable and potentially very long
C. The key is always secret to both the sender and receiver of the message.
D. A Vigenere cipher relies upon an "alphabet shift" algorithm.

Answer 1

The Vigenere cipher is hard to crack because each letter in a message could be encoded as any of the 26 letters in the alphabet