schema:             KEY-CERT-SCHEMA
ref:                dn42.key-cert
key:                key-cert     required  single    primary schema
key:                method       required  single    > {PGP|X509|MTN}
key:                owner        required  multiple
key:                fingerpr     required  single
key:                certif       required  multiple
key:                org          optional  multiple  lookup=dn42.organisation
key:                remarks      optional  multiple
key:                admin-c      optional  multiple  lookup=dn42.person,dn42.role
key:                tech-c       optional  multiple  lookup=dn42.person,dn42.role
key:                mnt-by       required  multiple  lookup=dn42.mntner
key:                source       required  single
mnt-by:             DN42-MNT
source:             DN42