关于混合加密方案匿名性质的几个一般性结果

Some General Results on Anonymity in Hybrid Encryption Schemes

公钥加密方案的匿名性(亦称公钥隐密性)与数据保密性同样都具有重要应用价值.文中首先建立关于公钥加密方案的两个通用的新概念,即相对匿名性和相对保密性.通过这些较弱的安全性概念,证明了关于公钥加密方案匿名性质的两类一般性结果.第一类结果建立了公钥加密方案的保密性与匿名性之间两个对偶式的普遍关系,即相对匿名性(相对保密性)连同保密性(匿名性)蕴涵匿名性(保密性);第二类结果给出两个典型的混合加密构造(即Fujisaki-Okamoto构造和Okamoto-Pointcheval构造(REACT))选择密文匿名的充分条件,这些条件仅包括特定意义上的相对匿名性质和其它一些自然的弱保密性要求.文中不仅用多个具体实例表明这些条件都是非常实用的判定准则,而且还进一步应用这些普遍结果,给出对某些具体公钥加密方案匿名性质的简化证明,并证明了著名的NESSIE方案PSEC-1/2/3的选择密文匿名性质.

Anonymity（key-privacy） as well as data-privacy are all important features in publickey encryption applications. In this paper two new and general concepts, named ＂relevant anonymity＂ and ＂relevant security＂, are defined. Based-upon these weak security concepts some general results on anonymity in public-key encryption are proved, which fall in two categories. The first results are two general conjugate relations between anonymity and data-privacy, i.e., relevant anonymity （relevant data-privacy） together with data-privacy （anonymity） imply anonymity（data-privacy） ; the second are sufficient conditions for chosen-ciphertext anonymity in Fujisaki-Okamoto and Okamoto-Pointcheval （REACT） hybrid constructions respectively, only containing specific relevant anonymity and some naturally, weak data-privacy requirements. As examples show, all these conditions are easy-to-check criterion in practice. These general consequences are applied to some specific schemes and, as a result, anonymity of some well-known schemes are re-established but in a simpler way. Furthermore, NESSIE scheme PSEC-/1/2/3′s chosen-ciphertext anonymity is proved as applications of these general results.