In distribution and sharing of a cipher key to be used when performing encrypted communication among a plurality of terminals, to share a cipher key without the need for each terminal to constantly hold and manage a large number of keys. Also, to shorten the time needed to start terminal-to-terminal encrypted communication. Also, to improve the portability of the terminal. A key management server 1 sends by broadcast communication a cipher key, which is specific to each set of terminals that perform encrypted communication, one-sidedly to the respective terminals. The key management server 1 sends, by broadcast communication, cipher key data obtained by encrypting the cipher key by using a device public key which is the public key of an addressed terminal. Each terminal acquires cipher key data addressed to itself and decrypts the acquired cipher key data, thus obtaining a cipher key.
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