An attacker must instead search for {HEAD ~ a collision message} that hashes to {TAIL ~ the same value}  
hashes to
An attacker must instead search for { HEAD ~ a collision message } that hashes to { TAIL ~ the same value }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH