Implementation of smart-card access control with threshold scheme

We describe an electronic implementation of a security scheme to control ac cess to a building. Access to the building by a person alone is not possibl e but access by a group of authorized people whose number satisfies a presc ribed threshold is permissible. The scheme makes use of the shared-secret s ymmetry cryptography together with smart-card technology. The access key of a person is carefully encoded and stored on a smart card which can also be used for many other purposes. Access records are kept on these smart cards in a distributive fashion and with duplication. Innocent people are able t o present information regarding their recent accesses to the building and y et practically cannot be accused of fabricating these records. The scheme p ermits the use of a standalone controller and eliminates the need for expen sive wiring to a remote central database of authorized users.