KEY SHARING METHOD, KEY SHARING SYSTEM, AUTHENTICATING DEVICE, AUTHENTICATION TARGET DEVICE, RECORDING MEDIUM, AND AUTHENTICATION METHOD

A key sharing method between the authentication device and the authentication target device. The authentication device shares sharing information with the authentication target device in advance, one of the authentication device and the authentication target device shares a generation value generated by a predetermined method with the other of the authentication device and the authentication target device, and each of the authentication device and the authentication target device generates a plurality of pieces of first distribution information from the sharing information by using generation value with a predetermined encoding method capable of restoring data before distribution by arranging all or a part of a plurality of pieces of distribution data obtained by distributing the data before distribution, and shares one piece of first distribution information among the plurality of pieces of first distribution information or derivation information derived from the one piece of first distribution information as a common key.