Question

What is the basic difference between x.509 and pgp in terms of key hierarchy and key trust?

Answer 1

In terms of key hierarchy, you have to request to a Certification Authority in order for them to issue you an X.509 certificate. On the other hand, you can creat your own pgp.

In terms of key trust, X.509 supports only a sole key owner. It can support only one digital signature to confirm the key's validity. This does not work for pgp.