Disclosed is a method of loading data into a data processing device. The method comprises receiving a payload data item by the data processing device; performing a cryptographic authentication process to ensure the authenticity of the payload data item; storing the authenticated received payload data item in the data processing device; and integrity protecting the stored payload data item. The cryptographic authentication process comprises calculating an audit hash value of at least the received data item. Integrity protecting further comprises calculating a reference message authentication code value of at least the audit hash value using a secret key stored in the data processing device as an input.