| 摘要 |
The control system has units that each have cards. Each card (2) has keyboard (6), screen (8), microprocessor (9), and public number (5). It may communicate with a server (15) via an interface (12) through a variety of channels for example an infra-red channel controlled by keys (7). Operation is initiated by the user entering the card public number and private identity number. Three variables are generated, two depending on time and access attempts and a third which is stored and updated and used as an encryption key to produce a password for transmission to server (15). The server uses the public number to produce the same variables and the same password.
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