The second computer system receives {HEAD ~ an encrypted message} from {TAIL ~ the first computer system} and processes the encrypted message to generate a response message 
from
The second computer system receives { HEAD ~ an encrypted message } from { TAIL ~ the first computer system } and processes the encrypted message to generate a response message
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH