| 摘要 |
A key (such as a public key) used for encryption of information is easily obtained. A public key of A used for encryption when information is transmitted to a first communication terminal 100a is transmitted, a second communication terminal 100b receives the public key of A, a public key of B used for encryption when information is transmitted to the second communication terminal 100b in response to the reception of the public key of A, and the first communication terminal 100a receives the public key of B. As a result, the public keys are exchanged between the first communication terminal 100a and the second communication terminal 100b, and consequently the public key is easily obtained.
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