Is it permissible to purchase a house in installments, even though the National Savings and Provident Fund (CNEP), which deals with usury, is a party to the transaction, knowing that I am in dire need of the house and that the state takes the usury?

Financial transactions conducted through the state are either installment sales, which are permissible with their conditions, or lease-to-own agreements, which are impermissible, or interest-bearing loans, which are impermissible. There is no difference in the ruling on usurious transactions between the state and the private sector; indeed, it is a greater sin when dealing with the state. If the transaction is an installment sale through an interest-based institution, then it is not permissible to deal with it.