Disclosed are a verifier used in a mobile node and a method of controlling plural states of the mobile node. The verifier comprises a secret key receiving part configured to listen and receive at least one secret key from at least one secret key transmitter in an area limited Ad-hoc network; a secret key stamp generating part configured to perform calculation on the at least one secret key according to a predetermined verification rule so as to generate a secret key stamp; and a secret key stamp verifying part configured to compare the secret key stamp and a predetermined standard value, wherein, if the secret key stamp is equal to the predetermined standard value, then the secret key is determined as valid, otherwise, the secret key is determined as invalid.