$.$ E$-$mail is a critical Internet application. However, as more people join the Internet, concerns over privacy are mounting. PGP $($Pretty Good Privacy$)$ tries to combat

these concerns.

$1.$ Explain how PGP can achieve the confidentiality, integrity and authenticity of

an e$-$mail message.

$2.$ Discuss why trust management is essential to PGP public$-$key rings, and what

relationships exist among the four fields of a public$-$key ring: Owner Trust, Key

Legitimacy, Signature$($s$),$ and Signature Trust$($s$).$