对称加密是密码学领域中最古老的分支，至今仍是最重要的一个分支。本文对现代对称加密算法进行了分析和设计。首先对不同类型的加密算法进行了概述，指出了它们的安全性要求以及它们在方法上的根本区别。然后我们将重点放在分组密码，并解释在现代密码分析中使用的基本策略和技术。为了说明这一点，我们提出了一些具体的攻击，这些攻击基于一些新的思想，但仍然是基本方法的很好的例子。最通用和强大的分析技术之一是线性密码分析，这就是为什么我们专门用一个单独的章节来讨论它。我们推导了一个新的理论框架，允许严格和准确地分析这种攻击的性能，同时将攻击扩展到同时利用多个线性近似。在本文的第二部分，我们集中讨论对称加密算法的设计。我们首先介绍了分析和分类替换盒的工具，替换盒是设计抵抗第一部分所讨论攻击的分组密码的重要组成部分。在此基础上提出了一种新的基于分组分析的密码增强策略。这最终导致了一个紧凑而优雅的新型流密码TRIVIUM规范。

Symmetric encryption is the oldest branch in the field of cryptology, and is still one of the most important ones today. This thesis covers several aspects of the analysis and design of modern symmetric encryption algorithms. The thesis starts with an overview of the different types of encryption algorithms, pointing out their security requirements and their fundamental differences in approach. We then focus on block ciphers and explain the basic strategies and techniques used in modern cryptanalysis. In order to illustrate this, we present some concrete attacks, which are based on a number of new ideas, but still serve as nice examples of the basic approach. One of the most generic and powerful analysis techniques is linear cryptanalysis, which is why we devote a separate chapter to it. We derive a new theoretical framework which allows to rigorously and accurately analyze the performance of this attack, and at the same time extend the attack to simultaneously exploit multiple linear approximations. In the second part of this thesis, we concentrate on design aspects of symmetric encryption algorithms. We first present tools to analyze and classify substitutions boxes, components which play an important role in the design of block ciphers which resist the attacks discussed in the first part. We then present a new design strategy for stream ciphers based on techniques similar to those used to strengthen block ciphers against linear cryptanalysis. This eventually leads to the specification of a compact and elegant new stream cipher called TRIVIUM.

1.  引言

2.  对称加密

3.  分组密码分析

4.  再论线性密码分析

5.  S-Box分类

6.  流密码设计

7.  结论与开放问题

附录A SHA-1中的微分特性

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