安全通信

VPN technology is an important method to protect confidential communication and maintain network security. This article describes the VPN technology based on IPSec, including its concept, characteristic and principle. At the base of these, in the campus network environment and linux OS, we realize the resource sharing for campus network which lies in separate location and solves the resource sharing problem in the enterprise effectively.

VPN技术是保障机密通信，维护网络安全的重要手段，本文介绍了基于IPSec的VPN技术，讨论了其基本概念、特点及工作原理，在此基础上，以具体的校园网络为应用环境，阐述了在linux平台下，利用VPN技术，实现大学校园异地校区共享校园网络内部资源的过程，有效解决了企业共享内部资源的实现途径问题。

Quantum cryptography is the combination of classical cryptography and quantum mechanics. The characteristics of quantum mechanics, such as no-cloning theorem and Heisenberg's uncertainty principle, provide the perfect secrecy for quantum cryptographic communication.

量子密码学是密码学与量子力学结合的产物，利用量子不可克隆定理和海森堡测不准原理等量子特性，量子密码通信理论上已经证明是绝对安全。

On the other hand, the more important thing is because the urban housing is a kind of heterogeneity products.

另一方面，更重要的是由于城市住房是一种异质性产品。

Climate histogram is the fall that collects place measure calm value, cent serves as cross axle for a few equal interval, the area that the frequency that the value appears according to place is accumulated and becomes will be determined inside each interval, discharge the graph that rise with post, also be called histogram.

气候直方图是将所收集的降水量测定值，分为几个相等的区间作为横轴，并将各区间内所测定值依所出现的次数累积而成的面积，用柱子排起来的图形，也叫做柱状图。