Abstract: Sequence Key（SK） which is a significant cryptography has attracted a lot of attention.Sequence Key specifications，Context Randomicity（CR）and Sequence Randomicity（SR），etc，are proposed to define stochastic property of sequence key，after the principle of sequence encryption being researched，and evaluation architecture is referred and proved.Weak context encryption relationship is required for sequence encryption according to CR，and CR is the intrinsic property of one time pad.SR requires weak relationship between keys from the same sequence to keep an enough huge key space.In the end，the paper concludes with an evaluation and comparison between two algorithms based on chaos and used to produce sequence key.

Key words: Sequence Key（SK）, sequence key specifications, Context Randomicity（CR）, Sequence Randomicity（SR）

摘要： 序列密码作为一种重要的加密体制受到关注。研究了序列密码的作用原理，提出了上下文随机性和序列随机性等概念来刻画密钥流的随机性属性，推导并证明了密钥流评价体系。上下文随机性要求密钥流具有弱加密上下文关系，是一次一密加密体制的本质属性。序列随机性要求构成密钥流的各密钥间具有弱相关性，以保证较大的密钥空间。最后，根据提出的评价体系，通过实验分析和理论证明对两个基于混沌的密钥流生成算法进行了评价。

关键词: 序列密码, 密钥流的指标, 上下文随机性, 序列随机性