Patent ID: 7516321

Claim:
A method of delegating key-provision authority to a device from a trusted authority, the method comprising providing a yet-to-be completed chain of public/private cryptographic key pairs linked in a subversion-resistant manner and comprising: a starting key pair formed by a public/private key pair of the trusted authority, a penultimate key pair formed by public/private data, the private data being securely stored in the device for access only under circumstances that have been pre-authorised by the trusted authority and comprise a specific key-generation process running in a subversion-resistant operating environment, and a link between the penultimate key pair and an end key pair to be formed by an encryption/decryption key pair of an Identifier-Based Encryption, IBE, scheme; this link being said key-generation process arranged to execute in said subversion-resistant operating environment on the device to generate said decryption key using said private data and the IBE encryption key and to make the generated key available for use.