Key management server, the terminal, the key sharing system, the key distribution program, the key receiving program, the key distribution method and the key receiving methods

In distribution and sharing of encryption key used when performing encrypted communication among a plurality of terminals, without constantly hold and manage a large number of keys in each terminal, and an object thereof is to share a key for encryption. Another object is to shorten the time until the start of encrypted communication among the terminals. In addition, an object of the present invention is to improve the portability of the terminal. The key management server 1, unilaterally broadcast to each terminal a unique encryption key for each set of terminals that perform encrypted communication. Here, the key management server 1, the device public key is a public key of the destination terminal, broadcasts the cipher key data obtained by encrypting the encryption key. Each terminal acquires cipher key data addressed to its own terminal, to obtain the encryption key by decrypting.