Discussed are a cross certification method and a certifying device to perform the method. The certifying device can include a certification communication unit; a certification storage unit; and a certification control unit, wherein when a first certification is approved, the certification control unit encrypts a second identification information with a unidirectional encryption algorithm to generate a certification cryptogram, and transmits the certification cryptogram to an electronic device to request a second certification, when receiving a first random number in response to the request for the second certification, the certification control unit inputs the second identification information and an initial vector to a random number generating algorithm to generate a second random number, and the certification control unit compares the first random number and the second random number to verify the first random number, and determines whether to approve the second certification according to a result of the verification.