$4$a$.[$Points $5]$ Design an access matrix with domains and objects to$$ illustrate the principle of least privilege for the following program$----$the program has four sequential $$logical phases, with phase $1$ reading file F$1$ and F$2,$ phase $2$ doing computation, phase $3$ writing file F$3,$ and phase $4$ writing file F$4.$

$4$b$.[$Points $5]$ Alice intends to send a secure message to Bob. $($i$)$ What are the threats that Alice should be concerned about in sending messages to Bob?$($ii$)$ What information does Alice need if symmetric key encryption is used? $($iii$)$ What is needed if asymmetric key encryption is used?$($iv$)$ Is encryption alone sufficient to defend against these threats?

$4$c$.[$Points $5]$ Using RSA public key generation scheme, with p$=5$ and q$=11,$ with e$=7,$ determine the public key and private key.

$4$d$.[$Points $5]$ Encrypt m$=2$ with RSA public key $(5,91).$ Show the cyphertext. Decrypt the cyphertext with the corresponding RSA private key $(29,91).$