Encryption is enabled by the exchange of at least one key and {HEAD ~ the generation} of additional keys by {TAIL ~ the access point} and the mobile computing unit to make the communications secure 
by
Encryption is enabled by the exchange of at least one key and { HEAD ~ the generation } of additional keys by { TAIL ~ the access point } and the mobile computing unit to make the communications secure
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH