Securing payment transactions with rotating application transaction counters

The invention relates to Securing payment transactions with rotating application transaction counters. An account management system creates a bundle of private application transaction counters (ATCs)and a bundle of corresponding public ATCs, and transmits them to a user device. The device receives a request for payment information from a merchant and processes the request without accessing a secure clement processor on the device. The device calculates a security code using one of the bundle of private ATCs and a transaction number received from the merchant. The device transmits proxy account information, the calculated security code, and the corresponding public ATCs to the merchant. The merchant transmits a payment request to the account management system as the issuer of the proxy account information. The account management system retrieves the private ATC using the public ATC, and determines the validity of the security code by re-computing it. The account management system retrieves the financial accoun