Although the Internet which has accomplished rapid progress in recent years is convenient and efficient , the negative sides , such as a threat of a virus and unauthorized access , are also actualized , In order that these threats may realize not an exception but safe and secure Internet environment also in scientific envtronment , construction of a public key infrastructure ( PKI) is desired, but the deployment is not sufficient . Generally it is said that PKI is high cost structure , and it

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... one of the reasons to PKI deployment. This paper clarifies cost structure in PKI quantitatively , and contributes