A secure email system is expected to provide confidentiality, sender$\text{'}$s non$-$repudiation, and message integrity. Nicole uses three keys to achieve this goal. The three keys are Nicole's private key $($KN$-),$ Gary's public key $($KG$+),$ and a randomly generated symmetric key$(KS).$

The encryption procedure is shown below:

How can Gary $1)$ decrypt the data, $2)$ verify the message's integrity, and $3)$ verify the sender$\text{'}$s non$-$repudiation? Describe the detailed steps $($including the formulas$)$ and show your work.