Access control for digital content

摘要

A data storage arrangement is provided and is operable to apply access control processing to input data in dependence upon a public key of a public key / private key pair. The arrangement comprises an encrypting apparatus and a plurality of removable memory devices connectable to the encrypting apparatus via an interface. The encrypting apparatus stores a local copy of a user director which is identified by a local version identification tag and lists a user identifier and an associated public key for each of a plurality of authorised users. Each removable memory device securely stores an external copy of the user directory. The encryption apparatus also has encryption means for encrypting at least portions of the input data content in dependence on a public key derived from either the local or the external user directory. The encrypting apparatus has means for comparing the local version identification tag with the external version identification tag and when it is detected that these differ for updating, the plurality of user identifiers, respective public keys and version identification tag of the less recent version of the user directory to correspond to those of the more recent version of the user directory.