计算机专业英语Unit-9--Security.ppt

,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,单击此处编辑母版标题样式,Computer English,Unit9 Security,Section A Understanding the 3 Main Types of Encryption,Background Knowledge,背景知识,网络安全是指网络系统的硬件、软件及其系统中的数据受到保护，不因偶然的或者恶意的原因而遭受到破坏、更改、泄露，系统连续可靠正常地运行，网络服务不中断。,数据加密技术是为提高信息系统及数据的安全性和保密性，防止秘密数据被外部破坏所采用的主要技术手段之一。,New Words and Useful Expressions,encryption/nkrpn/,编密码,;,加密,symmetric/smetrk(l)/,相称性的,;,均衡的,plaintext/plentekst/,明文，明码文本,parlance/prlns/,说法，术语,scramble/scrmbl/,使混杂,搅乱,prying/pra/,窥探的,;,爱打听的,random/rndm/,任意的,胡乱的,随便的,platform/pltfm/,平台；月台，站台；,compromise/kmprmaz/,泄露,behalf/bhf/,代表,;,利益,legitimately/ldtmtl/,正当地，合理地,asymmetric/smetrk(l)/,不均匀的,;,不对称的,cryptography/krptgrf/,密码学,;,密码方式,;,密码使用法,caveat/kvit/,警告，附加说明,dutifully/dju:tfl/,忠实地，忠贞地,certificate/stfkt/,证书,;,证明书,infeasible/nfi:zbl/,不可实行的,collision/kln/,碰撞,抵触,冲突,Contents,Symmetric Encryption,2,Hash,4,System Security,5,Asymmetric Encryption,3,Security Overview,1,Security Overview,Encryption protects your data,your interactions,and your access.,Security Threat,In a public network,there are opportunities for data to leak out,even if your software is standing guard effectively.-Even software developers dont necessarily understand this topic well enough to make good decisions on how to best use encryption to protect their users.,Symmetric Encryption Procedure,1.Take readable data(“plaintext”),2.Scramble it to make it unreadable(protecting it from prying eyes while its being stored on a disk or transmitted over a network),3.Unscramble it again when its needed.,Encryption Methods,There are lots of good encryption methods to choose from.,Examples of popular symmetric algorithms include Twofish,Serpent,AES(Rijndael),Blowfish,CAST5,RC4,3DES,Skipjack,Safer+/+(Bluetooth),and IDEA.,Symmetric Encryption Key Usage,The tricky part about using symmetric encryption is how to store the key and make it available only to the software that needs it.,The encrypter,and the decrypter need access to the same key.,Uses of Symmetric Encryption,In services that store encrypted data on behalf of a user(like cloud backup services)when those services leave the decryption key in the hands of the user.,To encrypt computer or device storage,To create a secure channel between two network endpoints provided theres a separate scheme for securely exchanging the key.,Contents,Symmetric Encryption,2,Hash,4,System Security,5,Asymmetric Encryption,3,Security Overview,1,Public Key and Private Key,The public key is public and it can and should be published.,The private key must be kept private,protected much like the key for symmetric encryption.-this is easier,since only one party ever needs access to it:the party that needs to decrypt the messages.,Digital Signature,In this system,the private key is used to make the signature,and the public key is used to verify it.,If you have data with a signature and the matching public key,You can thus prove it was signed with the private key.,Problems with Asymmetric Encryption,The biggest issue with public-key cryptography is making sure you can trust the public key you have.,A man-in-the-middle attack is a common way to compromise asymmetric encryption.,Protecting Solution,Making sure we always have the right public keys,1.by distributing them in trusted software,2.by having entities we already trust cryptographically sign new keys we need to use.-get a certificate for your HTTPS site from a certificate authorityweb browsers trust these authorities to sign keys,allowing websites to send signed public keys on to the browsers that they can then trust to secure the connection.,Asymmetric Encryption Usage,Used with TLS to secure connections between browser and website as well as other network services.,Used with SSH to secure login sessions to remote servers as well as authorize(through the use of signing)users without using passwords.,Used to sign software updates so that computers and devices can know that theyre getting code that originated from a trusted party.,Use asymmetric encryption for email with systems like OpenPGP or S/MIME.,Hash,Hashing is what is actually happening when you hear about passwords being“encrypted”.,Strictly speaking,hashing is not a form of encryption,though it does use cryptography.,Three Important Properties of Hash,The same data will always produce the same hash,Its impossible to reverse it back to the original data,Given knowledge of only the hash,its infeasible to create another string of data that will create the same hash(called a“collision”in crypto parlance),Usage of Hash,1.Check an incoming password by hashing that and seeing if the hashes match.,2.Authenticate otherwise clearly-transmitted data using a shared secret The hash is generated from the data and this secret,so that only the data and the hash are visible;the shared secret is not transmitted and it thus becomes infeasible to modify either the data or the hash without such modification being detected.,Ways to Deal with Weakness,Select a good password-hashing algorithm,Dont try to develop your own,even using a well-known hash algorithm,Research and use a proven,well-audited password-hashing function,such as bcrypt and scrypt.,Contents,Symmetric Encryption,2,Hash,4,System Security,5,Asymmetric Encryption,3,Security Overview,1,