Org.BouncyCastle.Bcpg.PublicKeyPacket
Non-Standard LibrePGP introduced v5, which is only supported by a subset of vendors.
OpenPGP v3 keys are deprecated. They can only be used with RSA.
OpenPGP v4 keys are (at the time of writing) widely used, but are subject to some attacks.
OpenPGP v6 keys are newly introduced.
Construct a version 4 public key packet.