In order to achieve perfect forward and perfect backward secrecy, and to counteract cryptoanalysis, the group session keys should be rekeyed.

为达到完美向前和完美向后保密以及对付密码分析，需要更新组会话密钥。

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This can happen to messages being transmitted in the clear, transmitted encrypted but stored in the clear, or decryption of messages due to stolen key or cryptoanalysis.

以明文方式传输消息、传输加密的但以明文方式存储的消息、或者由于密钥被窃取或通过密码分析获取后对消息进行解密，在以上几种情况下都可能发生这种攻击。

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