Methods, apparatus and computer software are provided for authorizing an EMV transaction between a user device and a point of sale terminal, particularly, but not exclusively, in situations where a secure element is not made available for the deployment of a payment application on the user device. The payment application is instead deployed to a processing environment that is outside of any secure element on the user device. An ICC Master Key corresponding to the payment application is held by a trusted authority, such as the issuing bank. The trusted authority is adapted generate time-limited session keys on the basis of the ICC Master Key and distribute session keys to the payment application. Receipt of a session key by the payment application enables the payment application to conduct an EMV payment transaction. The session key is used to authorize a single EMV payment transaction.