A device includes a storage unit that stores generated challenges which are challenges previously generated, a determination unit that determines whether a newly generated challenge matches any of the generated challenges or not, an output unit that outputs the newly generated challenge as an unused challenge when the determination unit determines that the newly generated challenge does not match any of the generated challenges, and a registration unit that stores the newly generated challenge as a new generated challenge in the storage unit when the determination unit determines that the newly generated challenge does not match any of the generated challenges.