Which of the following answers are correct about PKC$?$

$1.$ To use PKC securely$,$ each public key must associate with a public$-$key certificate.

$2.$ Public$-$key certificates are created and managed by PKI.

$3.$ PKC is the only way to authenticate data, even when two parties possess a shared secret.

$4.$ PKC has to be encryption.

$5.$ PKC is the method to distribute secretly data encryption keys between communication parties without sharing prior secrets$.$

$6.$ PKC encryption is typically used to encrypt long text messages.