A method for use in a distribution system having a key management center, a distribution station and a reception terminal. The method updates a pair of distribution keys unique to the reception terminal, where the distribution public key is used to encrypt distribution data, and the distribution secret key is used to decrypt encrypted data. In the key updating method, the reception terminal acquires an update secret key prior to data distribution, and the key management center acquires an update public key making a pair with the update secret key, generates a new pair of distribution keys, encrypts a new distribution secret key by using the update public key, transmits an encrypted secret key to the reception terminal and updates to the new distribution public key. The reception terminal receives the encrypted secret key and restores the new distribution secret key by decrypting it using the update secret key and updates to the new distribution secret key.