A data communications system is described in which messages are processed using public key cryptography with a private key unique to one or more users (150) under the control of a portable security device (120), such as a smart card, held by each user, the system comprising: a server (130) for performing...http://www.google.se/patents/US5604801?utm_source=gb-gplus-sharePatent US5604801 - Public key data communications system under control of a portable security device
