Vigenere Cipher Key Security

Question

Example

Key 1: EEEE

Key 2: ERTY

What are the advantages of using key 2 over key 1 and why?

Answer 1

If you used the key EEEE, the cipher would not be a Vigenère. It would degenerate into an extremely weak Caesar cipher. With the key ERTY, you would get a genuine Vigenère cipher of period 4. While this is still very weak, breaking it nevertheless does require a little more work than a Caesar cipher does.