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