Patent ID: 8688988

Claim:
A data security device ( 5 ) comprising memory ( 10 ) for storing user data, an interface ( 7 ) for transmission of data communications between the security device ( 5 ) and a terminal device ( 2 ) connectable to a data communications network ( 3 ), and a controller ( 8 ) for processing requests from the terminal device ( 2 ) for information about said user data, wherein the controller ( 8 ) is adapted to process said request by: generating a message comprising an indication of the information requested about the user data, the message being generated so as to permit verification, using secret data, that the message was generated by the controller ( 8 ); sending the message to the terminal device ( 2 ) for communication via said network ( 3 ) to a publication entity ( 4 ) for publication of the message in the network; receiving from the terminal device ( 2 ) a cryptographic construction, issued by the publication entity ( 4 ), encoding the message published by the publication entity ( 4 ); checking validity of the cryptographic construction for said message generated by the controller ( 8 ); and supplying the information requested about the user data to the terminal device ( 2 ) in dependence on said cryptographic construction, wherein the controller ( 8 ) is adapted to generate the message by encrypting said indication of the information requested about the user data to produce a ciphertext which is decryptable using a secret user key and the controller ( 8 ) is adapted to encrypt said indication in accordance with a key-anonymous encryption system.