Alice and Bob are communicating using a shift cipher with the capital letters in English, but with a twist. They use two keys instead of one, and the keys alternate. So the first letter would be encrypted using the key k₁ = 9, the second using the key k₂ = 14, the third with k₁, the fourth with k₂ and so on as needed. Their hope is that this will prevent frequency analysis by Oscar.

Do you think this approach is secure? Why? Explain using Kerckhoffs principle and the effort that it may take Oscar to use brute force.

Decrypt the following ciphertext exchanged by Alice and Bob (show steps): JWAVXDYSA