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