Counter-password

All this is the cultural equivalent of spy movies in which the hero must look for a man wearing a green carnation, mumble, “The thrush flies at midnight,” and listen for the counter-password.

Source: wiktionary

He had rehearsed his own counter-password over and over again throughout that time, as he nervously looked at his watch and wondered what could have gone wrong.

Source: wiktionary

Give him the password 'Charlton Athletic for the Cup', and he will give the counter-password 'Tottenham Hotspurs for the League'.

Source: wiktionary

We had an angry dialogue for a couple of minutes and could not establish the password and counter-password.

Source: wiktionary