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