1. An authentication method for verifying password input to an authentication device by a user, comprising the following steps: (a) defining a candidate character set including a plurality of characters, a subset of the candidate character set being a known character set contained in a predefined password; (b) randomly distributing all of the characters of the candidate character set into a plurality of candidate character subsets such that each candidate character subset includes two or more characters, and displaying all of the characters of the plurality of candidate character subsets in a plurality of interactive regions, respectively, all of the characters of each candidate character subset being randomly generated and distributed; and (c) receiving from the user a series of selections of specific ones of the plurality of interactive regions, checking whether each selected interactive region displayed a character of the known character set contained in the predefined password, and confirming successful authentication and outputting a signal indicating successful authentication when each of the interactive regions containing the characters of the known character set contained in the predefined password were directly selected by the user, wherein step (b) is repeated before each user selection of a specific one of the plurality of interactive regions, such that the characters in the plurality of candidate character subsets are randomly generated and distributed before each user selection.