Since {HEAD ~ the Authentication Chip} must respond with H, but has {TAIL ~ no control} over the input value R, the birthday attack is not possible 
has
Since { HEAD ~ the Authentication Chip } must respond with H , but has { TAIL ~ no control } over the input value R , the birthday attack is not possible
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH