WooCommerce makes it easy to sell all kinds of physical and digital products. Thanks to the WooCommerce License Manager plugin, you will be able to sell license keys, pin codes, and gift cards. It lets you add them manually or bulk import licenses. It stores your codes in your database encrypted.
The plugin comes with a simple license key generator. Want to deliver license keys in image format? No problem. You can also define expiration date, validity (# of days) and # of deliveries for each license key.
firassaidi is the developer behind this plugin. You can find it on CodeCanyon.