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