applying to each of the segments a threshold encryption scheme using a first key from {HEAD ~ the first set} of {TAIL ~ keys} and a second key from the second set of keys 
of
applying to each of the segments a threshold encryption scheme using a first key from { HEAD ~ the first set } of { TAIL ~ keys } and a second key from the second set of keys
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH