Control apparatus for enabling access to one or more information systems by one or more entities on a path across a supply network to be controlled, access to the or each information system being policed by means of an access-policer, the network comprising: at least one token-issuer operable to issue an access pre-authorisation token, said access pre-authorisation token having associated therewith an information identifier and a digital signature, and to forward said access pre-authorisation token towards one or more entities on a path across said network; and at least one receiver entity operable to receive an access pre-authorisation token issued by said at least one token-issuer; the control apparatus comprising: a key generator operable to generate, in respect of said at least one receiver entity: (i) a receiver entity public key / private key pair comprising a public key and a private key, the receiver entity public key enabling a digital signature guaranteeing the authenticity of a message created using the receiver entity private key to be verified; and (ii) a token translation key, said token translation key enabling translation of a digital signature created using a private key generated in respect of said at least one receiver entity into a digital signature associated with the token-issuer; the key generator being further operable to generate, in respect of said at least one token-issuer: (iii) a token-issuer public key / private key pair, said token-issuer public key enabling a digital signature guaranteeing the authenticity of a message created using said token-issuer private key to be verified; the control apparatus further comprising a key distributor operable to distribute: to said at least one token-issuer, the receiver entity private key generated in respect of said at least one receiver entity; to said at least one receiver entity, the token translation key generated in respect of said at least one receiver entity; and to said access-policer, said token-issuer public key. a key generator operable to generate, in respect of said at least one receiver entity: (i) a receiver entity public key / private key pair comprising a public key and a private key, the receiver entity public key enabling a digital signature guaranteeing the authenticity of a message created using the receiver entity private key to be verified; and (ii) a token translation key, said token translation key enabling translation of a digital signature created using a private key generated in respect of said at least one receiver entity into a digital signature associated with the token-issuer; (i) a receiver entity public key / private key pair comprising a public key and a private key, the receiver entity public key enabling a digital signature guaranteeing the authenticity of a message created using the receiver entity private key to be verified; and (ii) a token translation key, said token translation key enabling translation of a digital signature created using a private key generated in respect of said at least one receiver entity into a digital signature associated with the token-issuer; the key generator being further operable to generate, in respect of said at least one token-issuer: (iii) a token-issuer public key / private key pair, said token-issuer public key enabling a digital signature guaranteeing the authenticity of a message created using said token-issuer private key to be verified; (iii) a token-issuer public key / private key pair, said token-issuer public key enabling a digital signature guaranteeing the authenticity of a message created using said token-issuer private key to be verified; to said at least one token-issuer, the receiver entity private key generated in respect of said at least one receiver entity; to said at least one receiver entity, the token translation key generated in respect of said at least one receiver entity; and to said access-policer, said token-issuer public key.