Ajay Banga has declared war on cash. As chief executive officer of MasterCard, he wants his troops to do whatever they can to persuade consumers to slap down the plastic and increase the 15% of global retail transactions made with credit and debit cards or other electronic means. New regulations bar debit-card processors from demanding exclusive agreements with merchants, which Banga says will let him sign up more retailers. The company has teamed up with Google to let consumers make retail payments with smartphones and is working with Intel to enhance security for online shopping.