Except for server and client, we also need a Certificate Authority $($CA$)$ who

validates server$$s public key. We assume both server and client has CA$$s public

key stored in a file.

Do the following tasks locally $($without connecting server and client$).$

$1.$ Create a class CA$,$ which has its own RSA key pair.

$2.$ Implement a Sign function for CA$,$ which takes CA$$s secret key and

server$$s public key as input, and generates a certificate.

$3.$ Implement a Verify function, which takes the certificate $($and the list

of recognized CAs$)$ as input, and output the result $($True$/$False$).$ The

function is typically used by client, so you may also need to consider what

$1$