复旦大学：《信息安全》教学课件_06 The Intro to Information Security

Information Security 06 The Intro to Information Security 迟到的序 Chapter1, 2, 3, 9, 11 復大软件学院

1 Information Security 06 The Intro to Information Security —迟到的序言 Chapter1, 2, 3, 9, 11

内容间的联系 密码学 安全协议 基本理论成熟 认证、PK、数字证书等 应用相当广泛 什么是 信息安全? 网络安全 讨论、总结、清晰 代码安全 復大软件学院

2 内容间的联系 密码学 基本理论-成熟 安全协议 认证、PKI、数字证书等 应用相当广泛 什么是 信息安全? 讨论、总结、清晰 代码安全 网络安全

Content What is "Information Security a brief history of Info sec · Threats、 Attacks and defenses 復大软件学院

3 Content • What is “Information Security” • A brief history of Info sec • Threats、Attacks and Defenses

Review Classic cipher Symmetric Modern block cipher one secret key Public Key cryptography- Asymmetric two keys ·MAC& Hash function 復大软件学院

4 Review • Classic cipher • Modern block cipher • Public Key cryptography • MAC & Hash function Symmetric one secret key Asymmetric two keys

What is“ Information”? 復大软件学院

5 What is “Information”?

What is“ Information”? Definition Source is an ordered pair p=(S, p), where S=X,,, Xn is a finite set, the source alphabet, and p is the probability distribution on s Denote the probability of xi by p, or p(xi) Amount of Uncertainty(before) Output lL Amount ofInformation(after according to probability Distribution · Shannon1945, Bell lab 復大软件学院

6 What is “Information”? • Definition: Source is an ordered pair , where S={x1 ,…,xn } is a finite set, the source alphabet, and P is the probability distribution on S. Denote the probability of xi by pi or p(xi ) • Amount of • Amount of • Shannon 1945, Bell lab   (S, P) Uncertainty (before) Output Information (after) Xi according to probability Distribution

cott Example for uncertainty 1)p(x=1,p(x)=0, i>1. The uncertainty is 0 2)p(xi)=-,i=l,,n. The uncertainty is Maxium 3Uncertainty = Information 復大软件学院

7 Example for uncertainty • 1) • 2) • 3) Uncertainty = Information p(x1 ) 1, p(xi )  0,i 1.The uncertainty is 0 , 1, , . The uncertainty is Maxium 1 p( ) i n n xi   

cott Example for uncertainty 1)p(x=1,p(x)=0, i>1. The uncertainty is 0 2)p(xi)=-,i=l,,n. The uncertainty is Maxium 3Uncertainty= Information )=∑ pi logb p,b>0 i=1 8 復大软件学院

8 Example for uncertainty • 1) • 2) • 3) Uncertainty = Information p(x1 ) 1, p(xi )  0,i 1.The uncertainty is 0 , 1, , . The uncertainty is Maxium 1 p( ) i n n xi        n i p pn pi b pi b 1 Hb ( 1 ,, ) log , 0

Units of Entropy Hh measures the number of b-ary units of information Example 1. S=X1, 2, X33, p =1/3, gives H2(,=,)=log23+log23+log23 33 =log23≈1.585bits EXample 2. p1-p2=1/4, p3=1/2 gives )==log, 4+=log, 4+log, 2 4424 1. 5 bits 復大软件学院

9 Units of Entropy • Hb measures the number of b-ary units of information. • Example 1. S={x1 ,x2 ,x3 }, pi=1/3, gives • Example 2. p1=p2=1/4, p3=1/2 gives log 3 1.585 bits log 3 3 1 log 3 3 1 log 3 3 1 ) 3 1 , 3 1 , 3 1 ( 2 2 2 2 2   H    1.5 bits log 2 2 1 log 4 4 1 log 4 4 1 ) 2 1 , 4 1 , 4 1 (2 2 2 2  H   

cott What is "Information System"? 復大软件学院

11 What is “Information System”?