All Identity objects have a name and a public key.
Names are immutable.
Identities may also be scoped. That is, if an Identity is specified to have a particular scope, then the name and public key of the Identity are unique within that scope. The Principal names specified in these certificates need not be the same, only the key. An Identity can be subclassed, to include postal and email addresses, telephone numbers, images of faces and logos, and so on. Constructor for serialization only.