A key managing system including information transmitting apparatus which
transmits a date and time when secrecy protection is ended to a key
controlling apparatus. The key controlling apparatus searches a key
control table for an encryption key associated with a decryption key and
the date and time. The key controlling apparatus transmits an encryption
key from the search to the information transmitting apparatus. The key
controlling apparatus discloses a decryption key for the present date and
time to an information receiving apparatus in response to a request for a
decryption key. The information transmitting apparatus, upon receipt of
the encryption key, encrypts information using the encryption key and
transmits the encrypted information to the information receiving
apparatus. The information receiving apparatus, for the present date and
time matching with the date and time, acquires a disclosed decryption key
and decrypts the encrypted information by using the decryption key.