Implementation of smart-card access control with threshold scheme

We describe an electronic implementation of a security scheme to control access to a building. Access to the building by a person alone is not possible but access by a group of authorized people whose number satisfies a prescribed threshold is permissible. The scheme makes use of the shared-secret symmetry 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 to present information regarding their recent accesses to the building and yet practically cannot be accused of fabricating these records. The scheme permits the use of a standalone controller and eliminates the need for expensive wiring to a remote central database of authorized users.