Show that the mono-alphabetic substitution cipher is trivial to break when the attacker launches a chosen-plaintext attack. How much chosen plaintext is needed to recover the entire secret key? What is the shortest chosen single-message plaintext that you can find, which is a valid English message and would successfully recover the key? Finally, under which conditions, and why, is the mono-alphabetic substitution cipher perfectly secure (against a ciphertext-only attacker)?