函数加密体制（一） (13-12)

So far we defined the most general syntax for a functional encryption scheme. For th|e applications we have in mind it is convenient to define two sub-classes of functional encryption where the plaintext space Xhas additional structure.

Predicate encryption [BW07，KSW08]. In many applications a plaintext x ∈ X is itself a pair (ind，m) ∈ I × M where ind is called an index and m is called the payload message. For example, in an email system the index might be the sender's name while the payload is the email contents.

In this context, an FE scheme is defined in terms of a polvnomial-time predicate P：K × l → {0，1} where K is the key space. More precisely, the FE functionality over (K∪{ϵ}， (I × M)) is defined as

F(k E K， (ind，m) ∈ X)↓

m if P(k，ind)＝1，and

：＝{ ←

⊥ if P(k，ind)＝0

Consequently，let c be an encryption of (ind，m) and let skₖ be a secret key for k ∈ K. Then dec(skₖ，c) reveals the payload in c when P(k，ind)＝1 and roueals aothing new about m otherwise.

带有公开索引的谓词加密：谓词加密的一个子类是从密文中可以很容易的获得明文索引。特别地，在函数加密的这种类型中，空密钥 ϵ 明确显示了索引 ind ，即 F(ϵ，(ind m))＝(ind，len(m)) 。因此，解密过程 dec(ϵ，c) 让任何人都可以获得明文 m 的索引以及比特长度。

Predicate encryption with public index.A sub-class of predicate encryption makes the plaintext index easily readable from the ciphertext.In particular,in this type of FE the empty key ϵ explicitly reveals the index ind, namely

F(ϵ，(ind，m)) ＝ (ind， len(m) )

数学联邦政治世界观提示您：看后求收藏（同人小说网http://tongren.me），接着再看更方便。