The authentication device then generates, using the same code generation algorithm, an expected code value based on a second secret key and compares {HEAD ~ the expected code value} to {TAIL ~ the service authentication code} 
to
The authentication device then generates , using the same code generation algorithm , an expected code value based on a second secret key and compares { HEAD ~ the expected code value } to { TAIL ~ the service authentication code }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL