{HEAD ~ The remote service} obtains {TAIL ~ a service authentication code} that has been generated, using a code generation algorithm, based on a first secret key 
obtains
{ HEAD ~ The remote service } obtains { TAIL ~ a service authentication code } that has been generated , using a code generation algorithm , based on a first secret key
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH