According to Hanafi school [one of the major schools of thought among Muslims] corrupt contracts are permissible between Muslims and non-Muslims in non-Muslim countries. However, I would like to make it clear that dar al-kufr and dar al-harb are terms that were used in specific times. Dar al-harb refers to the nations that have been waging Muslim hostility, have been conquering Muslim territories and they have been displacing Muslim from their homes as in the Crusades. Dar al-kufr referred to nations where Muslim were barred from proselytizing or living. Nowdays, things are changed, so I prefer to call these countries non-Muslim countries.