Characterization of Security Notions for Probabilistic Private-Key Encryption

The development of precise definitions of security for encryption, as well as a detailed understanding of their relationships, has been a major area of research in modern cryptography. Here, we focus on the case of private-key encryption. Extending security notions from the public-key setting, we define security in the sense of both indistinguishability and non-malleability against chosen-plaintext and chosen-ciphertext attacks, considering both non-adaptive (i.e., ``lunchtime') and adaptive oracle access (adaptive here refers to an adversary's ability to interact with a given oracle even after viewing the challenge ciphertext). We then characterize the 18 resulting security notions in two ways. First, we construct a complete hierarchy of security notions; that is, for every pair of definitions we show whether one definition is stronger than the other, whether the definitions are equivalent, or whether they are incomparable. Second, we partition these notions of security into two classes (computational or information-theoretic) depending on whether one-way functions are necessary in order for encryption schemes satisfying the definition to exist. Perhaps our most surprising result is that security against adaptive chosen-plaintext attack is (polynomially) equivalent to security against non-adaptive chosen-plaintext attack. On the other hand, the ability of an adversary to mount a (non-adaptive) chosen-plaintext attack is the key feature distinguishing computational and information-theoretic notions of security. These results hold for all security notions considered here.     

A matrix key-distribution scheme

A new key-distribution scheme is presented. It is based on the distinctive idea that lets each node have a set of keys of which it shares a distinct subset with every other node. This has the advantage that the numbers of keys that must be generated is proportional to the number of nodes. Moreover, two nodes can start a session with virtually no delay. The scheme suits an environment where there is a certain level of trust among the insiders. The security property to an outsider remains identical to that of other existing schemes. Two versions of the scheme are given. Analysis of security and performance shows it is a practical solution to some key-distribution problems.     

一种密钥的设计和管理方法

文章以近几年公钥密码学研究的热点椭圆曲线密码体制为例。说明密钥数据的结构及其存储问题。所设计的公钥密码系统是一个开放式系统。在用户终端建立私钥库PrKD和公钥库PuKD，产生各种密钥。同时完成数据加解密、签名及验证功能；在密钥服务器上建立一个公钥库SevD，存放密码系统中所有用户的公钥信息。为用户提供公钥发布和交换功能。按照不同的安全性要求，PrKD中的数据要求完全保密。SevD的数据要求防止篡改。     

Rao-Nam私钥密码体制的修正

该文提出了一种非查表的错误图样生成算法。该算法通过将可纠正的错误矢量的部分信息嵌入到明文消息中,从而得到比原错误矢量具有更大汉明重量的错误图样。用该算法修正的Rao-Nam私钥密码体制高效实用,既无需存储错误图样,又增强了安全性。