A method of manufacturing an item of electronic equipment that includes a data processing device, the data processing device comprising a processor, an access control mechanism and a memory storing a device identifier, the data processing device being operable in secure and non-secure modes, the memory having secure and non-secure regions, the secure region containing cryptographic data, and the access control mechanism being operable to prevent the processor from reading the cryptographic data when the data processing device is operating in the non-secure mode, the method of manufacturing the item of electronic equipment comprising: receiving, by a second manufacturing party from a first manufacturing party, secure data processing hardware containing data to be stored on the data processing device and a value representative of a permitted number of devices on which the data are permitted to be stored, or means for obtaining access to the secure data processing hardware; the second manufacturing party requesting permission from the secure data processing hardware to store the data on the data processing device, thereby causing the secure data processing hardware to determine from the value representative of the permitted number of devices whether to permit the request and, if so, authenticate the data processing device by obtaining the device identifier from the data processing device; sending the device identifier to a trusted data store containing at least one device identifier; if the device identifier is recognised, obtaining the device certificate and a public key of the first asymmetric encryption key pair; and authenticating the data processing device by verifying the device certificate using the device identifier and the public key of the first asymmetric encryption key pair; if the authentication is successful, storing the data on the data processing device, and adjusting the value representative of the permitted number of devices. receiving, by a second manufacturing party from a first manufacturing party, secure data processing hardware containing data to be stored on the data processing device and a value representative of a permitted number of devices on which the data are permitted to be stored, or means for obtaining access to the secure data processing hardware; the second manufacturing party requesting permission from the secure data processing hardware to store the data on the data processing device, thereby causing the secure data processing hardware to determine from the value representative of the permitted number of devices whether to permit the request and, if so, authenticate the data processing device by obtaining the device identifier from the data processing device; sending the device identifier to a trusted data store containing at least one device identifier; if the device identifier is recognised, obtaining the device certificate and a public key of the first asymmetric encryption key pair; and authenticating the data processing device by verifying the device certificate using the device identifier and the public key of the first asymmetric encryption key pair; if the authentication is successful, storing the data on the data processing device, and adjusting the value representative of the permitted number of devices.