receivers that includes first and second timing elements and first and second key storage units containing multiple keys in a predetermined order for selection depending on respective key times where the key times occur periodically according to the first and second timing elements respectively a data encryptor obtains a new key from the first key storage unit at each occurrence of the key time of the first key storage unit and uses the key to encrypt an inputted data and at least one data decryptor obtains a new key from the second key storage unit at each occurrence of the key time of the second key storage unit time synchronization of the participants 39 equipment provides the method of selecting compatible keys for the encryption and decryption process this approach not only selects the compatible keys at the sending and receiving ends but also serves to change keys on a regular basis to enhance the overall security of the system application_number US 51054000 A description fig1 is a block diagram of a cryptographic apparatus including three parallel data decryptors according to a preferred embodiment of the present invention referring to fig1 a reference time is input to the time input unit 101 and 121 of the crypto hardware that is supplied to the authorized user community the reference time is preferably universal coordinated time utc which is available worldwide from various sources the present invention functions equally well with other u201c world time u201d references or with u201c relative time u201d a time reference can be obtained from one or more of the following sources but is not limited to those described below 1 internet network time u2014 time extracted from the communication internet network using the network timing protocol ntp which works in conjunction with.