The private key is a necessary part of Stripe's workflow and is used only in server side code to completed a transaction. Stripe EasyPay is a pure implementation of Stripe's checkout workflow for Joomla intended to be as flexible as possible. Customization is possible by Webmasters by using Joomla's template overrides feature and combined with the options available to the extension. Only the public and private key are required during configuration and these values are not stored anywhere except the configuration.