You can't secure Mifare Classic directly, it's totally broken. The best solution is to assume that a card's encryption is or will be broken, and build a system

You can't secure Mifare Classic directly, it's totally broken. The best solution is to assume that a card's encryption is or will be broken, and build a system around it. That is to say, store encrypted or signed data on the MIFARE card. VIGIK is a French system that uses RSA signed data in MIFARE cards which has not been cracked to date.