A method of authenticating a data processing device includes receiving a request to authenticate the data processing device. In response, an authentication key is accessed an authenticated at an authentication module. The authentication key is stored at a storage module that is located within the same integrated circuit package as the authentication module, so that the authentication key can be communicated to the module without exposing the key to unauthorized probing. The integrated circuit package also includes a tamper detection module to determine whether a memory of the data processing device has been accessed. In response to determining the memory has been accessed, the tamper detection module instructs the authentication module to not authenticate the data processing device.