This paper demonstrates and confirms that a large-network-oriented key sharing method called the key predistribution system (KPS) is really practical and useful for supporting end-to-end cryptographic communication, by presenting a prototype implementation of KPS using special IC cards and its application to facsimile systems. This prototype can build a secure channel over any ordinary facsimile network using the following types of equipments: (1) an IC card implementing a linear scheme for KPS and the DES algorithm, (2) an adaptor-type interface device between the IC card and a facsimile terminal with no cryptographic function, and (3) a device for each managing center of KPS.