关于窃听敌手不可区分与CPA安全的一个反例

摘要

In cryptography,the notions indistinguishable encryptions in the presence of an eavesdropper and CPA (chosen plaintext attack) security are not equivalent naturally.In symmetric key encryption,indistinguishable multiple encryptions in the presence of an eavesdropper is also a concept falling in between them,which is a significant difference between private key encryption and public key encryption.A concrete example is discussed which can explain the difference between indistinguishable multiple encryptions in the presence of an eavesdropper and CPA security using "reduction" and "hybrid reasoning" that are often used in cryptography so that we have a unambiguous cognition for those notions mentioned above.%在密码学中,窃听敌手不可区分与CPA(选择明文攻击)安全这两个概念有着“天然”的不等价性.对于私钥加密方案来说,窃听敌手不可区分的多次加密又是介于这两者之间的一个概念.这也是私钥加密方案与公钥加密方案非常重要的一个区别.针对一个具体构造的例子,通过运用“归约”和“混合论证”这两个密码学中最常用的方法详细论述了窃听敌手不可区分的多次加密与CPA安全之间的区别.从而,有助于人们对于前述三个概念进行区分.