To provide an authentication device or the like making a password symbol string hard to be unauthorisedly used even if the symbol string input by a user leaks when the user is authenticated by the symbol string allocated to the user.

In this authentication device 201, an input reception part 202 receives the input of the symbol string from the user, and an authentication part 203 makes the authentication of the user succeed when the symbol string whose input is received (hereinafter referred to as an "input symbol string") includes the password symbol string and when the input symbol string is longer than the password symbol string.

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