Patent ID: 7557941

Claim:
A first entity including: a first bit-pattern; a non-volatile memory storing resource data; a first base key for use with at least a first variant key; and a second variant key for use with a second base key, the second variant key being the result of a one way function applied to: the second base key; and the first bit-pattern or a modified bit-pattern based on the first bit-pattern, wherein the first entity is configured to receive a request from any of a plurality of second entities, the request being indicative of at least one operation to be performed on the resource data, each of the second entities having an associated bit-pattern and one of the first variant keys, the first variant key in each of second entities being based on the result of applying a one way function to the first base key and the associated bit-pattern of that second entity, the first entity being configured to: (a) receive the request from one of the second entities; (b) perform the at least one operation in the request, thereby to generate a response; (c) use the first base key to digitally sign at least part of the response, thereby to generate a digital signaturel; and (d) send the response and the digital signature to the second entity from which the request was received, such that the second entity can verify the at least part of the response using its variant key.