文章从消息层次上讨论了信息安全问题，重点介绍了信息理论密码学与复杂性理论密码学。

This paper discusses on the problem of information security from message level, and introduces emphatically information theory based cryptology and complexity theory based cryptology.

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密码学作为信息安全技术的核心领域，提供了多种密码算法与应用协议以满足人们实际应用的需要。

Cryptography is the core domain in the information security technique. It provides many algorithms and protocols to meet practical need.

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