| 摘要 |
PROBLEM TO BE SOLVED: To provide a public key cryptograph which can certify that it is highly secret against the attack of an enhanced adaptively selected cryptography. SOLUTION: A cryptograph is created so that not only a message sentence but also partial information about an input value to a hash function may be difficult to calculate from the cryptograph. Thus, even if an attacker obtains any information attached to a random oracle from a third oracle, the information about the input value to the hash function cannot be calculated from the cryptograph, thereby this attack is invalidated.
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