At operation 2004 {HEAD ~ the reader} retrieves {TAIL ~ a signing authority} public key , also known as a master public key, from a signing authority 
At operation 2004 { HEAD ~ the reader } retrieves { TAIL ~ a signing authority } public key , also known as a master public key , from a signing authority
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH