{HEAD ~ The strongest attack} known against {TAIL ~ HMAC} is the birthday attack, based on the frequency of collisions for the hash function 
known against
{ HEAD ~ The strongest attack } known against { TAIL ~ HMAC } is the birthday attack , based on the frequency of collisions for the hash function
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH