The JavaFX MenuBar adds a top menu to a JavaFX application, just like you are used to from desktop applications.
The Java Certificate class represents a cryptographic identity certificate, possibly signed by a Certificate Authority (CA).
The Java KeyPair class represents a public key, private key pair used in asymmetric encryption (e.g. RSA).
The Java KeyPairGenerator can generate asymmetric encryption key pairs (public key, private key). This Java KeyPairGenerator tutorial explains how to use the KeyPairGenerator class.