A method for providing a set of certificates encoding authorisations, the method comprising processing respective ones of multiple authorisation requests at a trusted signing authority apparatus to verify respective digital signatures applied to the requests, the multiple authorisation requests received over a first communication link between the trusted signing authority apparatus and an administration apparatus, validating one or more authorisation request parameters of respective ones of the authorisation requests, generating a certificate encoding an authorisation at the trusted signing authority apparatus and transmitting the generated certificate to the administration apparatus or a requesting apparatus over a second communication link.