Generation and verification of alternate data having specific format

The method for encoding a character string by a data processing device disclosed in the present specification comprises the steps of: acquiring input data; performing a one-way function to generate ciphertext based on the input data; and converting the ciphertext to output data. In the conversion step, the output characters constituting the output data are selected from the group of input characters constituting the input data, and the length of the output data becomes a specific length.