counter-password
  
    
      vastuparool
olemus
parooli vastuseks antav parool inimestevahelisel autentimisel 
pretensioon-vastus-protseduuriga 
Wiktionary:
the response to a password, which identities the person to whom the password is given as the correct contact
näiteid
in the opening days of the Battle of Normandy, paratroopers of the U.S. 101st Airborne Division used a password — flash — which was presented as a challenge, and answered with the correct response — thunder