securelecture.tex

Secure Lecture Source

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\hypersetup{pdftitle={An introduction to email security},
  pdfsubject={An introduction to email security},
  pdfauthor={Zhou Mo,CC,PKU,<[e-mail]>},
  pdfkeywords={},
  pdfpagemode={FullScreen},
  colorlinks={true},
  linkcolor={red}
  }

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\begin{document}
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\newpage\pageTransitionDissolve
\begin{slide}
\vspace{-30mm}
\vspace{-2mm}\hspace{-2mm}\fs\raisebox{4mm}\\
\vspace{0.5cm}

\centering
\Large\color{blue} \textbf{An Introduction to Email Security}\\[-3mm]

\normalsize\vspace{1.75cm}\centering\textsc{\textbf{\textcolor[rgb]{0.00,0.00,0.50}{Zhou Mo}}}\\
\vspace{1.75cm}
\centering\color{black}\textsl{Computer Center, Peking University}\\\emph{Beijing, China}\\
\vspace{1.0cm}
\href{mailto:[e-mail]}{\color{section1}\textsf{zac\[e-mail]}}
\end{slide}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% the second slide

\linespread{1.3}
\newpage\pageTransitionGlitter{0}
\begin{slide}
\begin{center}
\Large{为什么要使用加密邮件？}
\end{center}

\begin{itemize}
\item 明文电子邮件安全性低于传统邮政邮件

\item 传统邮政邮件的信封可避免一般的窥视

\item 电子邮件传递中经过的任何节点可以随意查看其内容

\end{itemize}

\end{slide}

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\newpage\pageTransitionGlitter{90}
\begin{slide}

\begin{center}
\Large{我没有做任何非法的事情，为什么要加密电子邮件？}
\end{center}

\begin{itemize}
\item 在传统邮件中，并不是所有的通信都写在明信片背面。

\item 保护自己的隐私并等于自己在干什么非法的活动。

\item 未加密的电子邮件相当于写在明信片后面的信息，加密过的电子邮件相当于使用了信封的邮件，仅此而已。

\end{itemize}

\end{slide}

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\newpage\pageTransitionGlitter{180}
\begin{slide}

\begin{center}
\Large{信息安全的定义}
\end{center}

\begin{itemize}
\item \textcolor[rgb]{0.00,0.00,1.00}{机密性：}即信息在传输的过程中，不能被有恶意的第三方获取，因此要对信息进行一定的加密，使窃听者即使从通讯线路中获取到通讯双方传输的信息，也无法得知其确切含义。

\item \textcolor[rgb]{0.00,0.00,1.00}{完整性：}即保证信息能够不被恶意的篡改，要做到这一点需要对信息有一个完整性验证的机制，使得接收方可以检查信息是否被篡改。

\item \textcolor[rgb]{0.00,0.00,1.00}{有效性：}即不可否认性，发送方在发送完信息后无法抵赖，声称自己从来没有发送过这些信息，要做到这一点需要对发送过的信息进行数字签名，这种签名必须是可靠的，并且是容易被验证的。

\end{itemize}

\end{slide}

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\newpage\pageTransitionGlitter{270}
\begin{slide}

\begin{center}
\Large{密码学中的若干定义}
\end{center}

消息被称为明文。用某种方法伪装消息以隐藏它的内容的过程称为加密，被加密的消息称为密文，而把密文转变为明文的过程称为解密。
密码算法是用于加密和解密的数学函数。

\includegraphics{Crypt.pdf}

\end{slide}

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\newpage\pageTransitionWipe{0}
\begin{slide}

\begin{center}
\Large{密码算法的分类}
\end{center}

\begin{itemize}
\item \textcolor[rgb]{0.00,0.00,1.00}{对称密码算法: }Symmetric

\begin{itemize}

\item 古典密码

\item 现代对称分组密码:  DES  AES

\end{itemize}

\item \textcolor[rgb]{0.00,0.00,1.00}{非对称（公钥）算法：}Public-key

RSA、背包密码、椭圆曲线ECC

\end{itemize}

\end{slide}

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\newpage\pageTransitionWipe{90}
\begin{slide}

\begin{center}
\Large{对称密钥加密体系：}
\end{center}

$\star$加密和解密使用同一密钥

$$E(k,P)=C$$

$$D(k,C)=P$$

对称加密算法通常有算法速度快，软硬件实现的代价小的特点，但是密钥的分发问题是对称加密算法中一个难以解决的问题

\end{slide}

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\newpage\pageTransitionWipe{180}
\begin{slide}

\begin{center}
\Large{对称密钥加密体系：（续）}
\end{center}

\includegraphics[width=600pt]{Symmetric.pdf}

\end{slide}

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\newpage\pageTransitionWipe{270}
\begin{slide}

\begin{center}
\Large{非对称密钥加密体系：}
\end{center}

$\star$加密和解密使用不同密钥

$$E(k_{pub},P)=C$$

$$D(k_{pri},C)=P$$

非对称密钥加密算法解决了密钥分发的问题，也使得数字签名成为了可能，但是在保持同样加密强度的情况下，速度通常都较对称密钥加密算法要慢。

\end{slide}

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\newpage\pageTransitionBoxI
\begin{slide}

\begin{center}
\Large{非对称密钥加密体系：（续）}
\end{center}

\includegraphics[width=600pt]{Asymmetric.pdf}

\end{slide}

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\newpage\pageTransitionSplitVI
\begin{slide}

\begin{center}
\Large{经典公开密钥加密算法RSA介绍(实现原理)}
\end{center}

\begin{itemize}
\item 用户产生两个大素数$p$和$q$，满足$p\not=q$。

\item 用户计算出$n=pq$，$n$的欧拉数$\phi(n)=(p-1)(q-1)$

\item 用户选择随机数$e$，$(0<e<\phi(n))$，使得$gcd(e,\phi(n))=1$，这里gcd代表最大公约数。

\item 用户计算出$d \equiv e^{-1}mod\phi(n)$

\item 公钥：$K_u=\{e,n\}$，私钥：$K_r=\{d,p,q\}$

\item 假设明文为$P$，则加密过程为：$C=P^emod(n)$

\item 对应的解密过程为：$P=C^dmod(n)$

\end{itemize}

\end{slide}

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\newpage\pageTransitionSplitVI
\begin{slide}

\begin{center}
\Large{经典公开密钥加密算法RSA介绍(举例)}
\end{center}

\begin{itemize}
\item 产生素数，$p=5,q=7$

\item 计算出$n=35$，$n$的欧拉数$\phi(n)=(p-1)(q-1)=24$

\item 用户选择随机数$e=5$，$gcd(e,\phi(n))=1$。

\item 由于$d \equiv e^{-1}mod\phi(n)$，经计算$d=5$

\item 公钥：$K_u=\{5,35\}$，私钥：$K_r=\{5,5,7\}$

\item 现在假设明文为$P=11$，则密文$C=11^5(mod35)=16$

\item 解密：明文$P=16^5(mod35)=11$

\end{itemize}

\end{slide}

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\newpage\pageTransitionSplitVI
\begin{slide}

\begin{center}
\Large{散列函数(Hash函数)}
\end{center}

\begin{itemize}
\item \textcolor[rgb]{0.00,0.00,1.00}{特点：}一个散列函数以一个变长的报文作为输入，并产生一个固定长度的散列码，有时也称消息摘要，作为输出。

\item \textcolor[rgb]{0.00,0.00,1.00}{作用：}消息鉴别，即消息完整性的验证，数字签名

\end{itemize}

\end{slide}

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\newpage\pageTransitionSplitVI
\begin{slide}

\begin{center}
\Large{散列函数$H=h(m)$的要求}
\end{center}

\begin{itemize}
\item $h$可以作用于一个任意长度的数据块

\item $h$产生一个固定长度的输出

\item 对任意给定的$x$，$h(x)$计算相对容易，无论是软件还是硬件实现

\item 对任意给定码$H$，找到$x$满足$h(x)=H$具有计算不可行性（单向性）

\item 对任意给定的数据块$x$，找到满足$h(y)=h(x)$的$y\not=x$具有计算不可行性

\item 找到任意数据对$(x,y)$，满足$h(x)=h(y)$是计算不可行的

\end{itemize}

\end{slide}

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\newpage\pageTransitionSplitVI
\begin{slide}

\begin{center}
\Large{常用的散列函数}
\end{center}

\begin{itemize}
\item MD5

\item SHA-1

\item RIPEMD-160

\end{itemize}

\end{slide}

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\newpage\pageTransitionBoxO
\begin{slide}

\begin{center}
\Large{数字签名的需求}
\end{center}

消息鉴别只能保重通信双方的消息没有被第三方所篡改，无法保证双方互相的欺骗。
如：1.B伪造一份消息，声称是从A处发送的。
2.A发送一份消息，但是事后否认是自己发送的。

\end{slide}

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\newpage\pageTransitionBoxI
\begin{slide}

\begin{center}
\Large{数字签名的作用}
\end{center}

\begin{itemize}

\item 签名者事后不能否认自己的签名

\item 接收者能验证签名，而任何其他人都不能伪造签名

\item 在有争议时，可由第三方进行验证

\item 对签名的作者、日期和时间、签名时刻消息的内容提供验证

\end{itemize}

\end{slide}

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\newpage\pageTransitionSplitVI
\begin{slide}

\begin{center}
\Large{数字签名的过程}
\end{center}

\begin{itemize}

\item 签名过程：使用私钥对明文进行加密

\item 验证过程：使用公钥对加密后的信息(签名)进行解密，查看其是否与原始明文相同

\end{itemize}

在实际的数字签名过程中，通常不用私钥直接对明文进行加密来完成数字签名，而是首先使用散列函数生成消息摘要，然后使用私钥加密消息摘要

\end{slide}

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\newpage\pageTransitionSplitVO
\begin{slide}

\begin{center}
\Large{数字签名的过程(续)}
\end{center}

\includegraphics[width=600pt]{Digitalsignature.pdf}

\end{slide}

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\newpage\pageTransitionSplitHI
\begin{slide}

\begin{center}
\Large{实际应用中所面临的问题}
\end{center}

\begin{itemize}

\item 公钥的发放问题，即如何让其它人得到我的公钥？

\item 身份的认证问题，即网络另外一端的人声称自己是某人，并且告诉你这是他的公钥，是否该相信这一点？

\end{itemize}

\end{slide}

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\newpage\pageTransitionSplitHO
\begin{slide}

\begin{center}
\Large{常用的信任管理模型}
\end{center}

\begin{itemize}

\item PGP密钥管理模型：公钥环、私钥环，简单的信任模型，相当于把一个朋友介绍另一个朋友

\item X509：基于数字证书的信任模型，进行安全通讯的实体都需要信任数字证书认证中心(CA)

\end{itemize}

\end{slide}
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\begin{slide}

\begin{center}
\Large{PGP - Pretty Good Privacy}
\end{center}

\begin{flushleft}
\Huge
\emph{如果隐私权被判定为非法，那么世界上就将只有歹徒才能拥有隐私权。}
\newline
\emph{If privacy is outlawed, only outlaws will have privacy.}
\end{flushleft}

\begin{flushright}
\Huge
\emph{--Phil Zimmermann}
\end{flushright}
\vspace{20mm}

\end{slide}

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