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