方案的前向安全性保证了签名密钥可定期更新，即使当前时间段的签名密钥被泄漏，敌手也不能伪造先前的签名。

Forward security of the scheme means that even if the secret key of current time period is compromised, some security remains. It is impossible to forge the signature relating to the past.

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然后它会使用可搜索的加密模式对索引进行加密，用基于属性的加密模式以恰当的手段对唯一密钥加密。

It then encrypts the index using a searchable encryption scheme and encrypts the unique key with an attribute-based encryption scheme under an appropriate policy.

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这些密钥为了安全目的被配置成可允许轻易地交替，或者它们有可能由于某种原因而泄露。

These keys are configured to allow for easy rotation for security purposes or if they are compromised for any reason.

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