軟工專業(yè)英語PPTchapter4

1、我們畢業(yè)啦其實是答辯的標題地方Taiyuan University of Technology軟件工程專業(yè)英語計算機科學與技術(shù)學院 計算機軟件學院SOFTWARE ENGINEERING ESSENTIALS2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院24.1 LOCAL AREA NETWORK 4.2 TCP/IP4.3 SECURITYSUMMARYCHPTER 4 NETWORKING AND SECURITYCOMPETENCIESAfter reading this chapter, you should be able to:1Explain the Int

2、ernet.2Discuss the two kinds of LAN: Ethernet LAN, and Wi-Fi.3Describe how the data are transferred.4Describe how to send one packet through Ethernet.5Explain TCP/IP.6Describe the Ethernet design process and how to deal with collision.7Discuss security.2022/8/6太原理工大學.計算機軟件學院3In this chapter, we will

3、 first elaborate on how the computer network works. The basic principles of how the computer network works are surprisingly simple although the details arefairly complicated. Well start from the small-scale, Local Area Network, or shortly a LAN.And then in the next section well explain how the Inter

4、net covers the entire earth. Finally in this chapter, we will discuss computer security.2022/8/6太原理工大學.計算機軟件學院42022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院54.1 LOCAL NETWORK AREA4.1 LOCAL AREA NETWORK The details of networking can be quite complicated. But the basic ideas of how it all works are surprisingly s

5、imple, and thats what were going to study. The Internet is like a global phone system for computers: a computer can call another computer on the internet to get or send a little information. Suppose your laptop is connected to the internet, and you type into your browser - what happens? Your compute

6、r contacts the computer - placing a call in effect - and sends a request for the main web page. The machine sends back a large response which is the web page and ends the call. Your browser gets back all this data and formats it for your screen so you can read the text, click links etc. Well look at

7、 this fetch-webexample a few different ways to see how the internet works.2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院4.1 LAN It stands for a Local Area Network. These are very common. A LAN is a network that would be used to cover maybe one floor of a building or maybe just within a house or something like th

8、at. Two very common examples of LAN technology are Ethernet. which is wired, uses wires, its wired LAN technology, and Wi-Fi, which is the wireless radio sort of analog to Ethernet. Those are incredibly common.2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院4.1 LAN4.1.1 Ethernet LAN4.1.2 Packets - Data Transmissio

9、n4.1.3 Ethernet - Sending One Packet4.1.4 Wi-Fi - Same Strategy4.1.5 Ethernet Design Summary2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院4.1.1 Ethernet LANWires about as thick as a drinking straw100 meter max wire length, so its localWires often yellow or blueRJ-45 plug, like a big phone plug2022/8/6太原理工大學.計算機科

10、學與技術(shù)學院.計算機軟件學院Figure 4-1 Ethernet RJ-45 plug2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院Figure 4-3 data from computer 1 to computer 22022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院4.1.2 Packets - Data Transmission4.1.3 Ethernet - Sending One Packet2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院Figure 4-4 Sending one packet on EthernetREA

11、DING 1 NETWORKINGPacket Errors - Checksum Re-Send2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院Figure 4-9 checksumREADING 1 NETWORKINGMultiple Computers - Ethernet Design2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院Figure 4-10 Ethernet DesignREADING 1 NETWORKINGEthernet Collision2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院Figure 4-11

12、Ethernet Collision4.1.4 Wi-Fi - Same Strategy2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院4.1.5 Ethernet Design Summary1. Shared: theres just one wire shared by everyone, so its cheap; 2.Distributed and Collaborative: there is no central control, depending on each computer following the collaborative protocol i

13、n good faith; 3. Insecure: its not too hard to listen to or pick up packets not intended for the receiver; 4.Performance degrades:its performance does not break as more computers use the shared medium2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院184.2 TCP/IP4.2 TCP/IP The previou

14、s LAN examples are about connecting computers on the same LAN. Now we will scale the problem up to send packets between any two computers on the earth. The worldwide Internet is built on the TCP/IP family of standards (Transmission Control Protocol / Internet Protocol) which solves the problem of se

15、nding packets between computers across the whole internet. These are free and open, vendor-neutral standards which is probably the reason they have been so incredibly successful.2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院4.2 TCP/IP The worldwide Internet is based actually on some Government-funded research in

16、 the 70s from the United States, and some standards called TCP/IP are created. The TCP/IP is a family of standards (Transmission Control Protocol/Internet Protocol) which solves the problem of sending packets between computers across the whole internet. These are free and open, vendor-neutral standa

17、rds which is probably the reason they have been so incredibly successful.2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院4.2 TCP/IP4.2.1 IP Address4.2.2 Domain Names4.2.3 Router4.2.4 What Does it Mean to Be On the Internet?4.2.5 Ping2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院4.2.1 IP Address2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院

18、Figure 4-6 IP address4.2.2 Domain NameDomain names are essentially alternate names for IP addresses. We have domain names such as , . Domain names are easy for people to remember and type. Domain system can look up an IP address from a domain name. So when you use a domain name, it is looked up to g

19、et an IP address for the actual packets2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院4.2.3 Router2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院Figure 4-7 Router4.2.4 What Does it Mean to Be On the Internet?On the Internete.g. connect to a Wi-Fi router1. computer connects to an upstream router to handle traffic. Most Wi-Fi ac

20、cess points combine Wi-Fi- radios and a router.2. The router typically gives the computer an IP address to useThe computer cannot pick an arbitrary IP address, since the left part of the address depends on the location on the Internetdetail known by the router3. DHCP “Dynamic Host Configuration Prot

21、ocol”automatically configure network settings to work locally. Computers very often use this feature to get needed network configuration from the router automatically.2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院4.2.5 Pingping is an old and very simple internet utility. Your computer sends a ping packet to any

22、computer on the internet, and the computer responds with a ping reply (not all computers respond to ping). In this way, you can check if the other computer is functioning and if the network path between you and it works. As a verb, ping has now entered regular English usage, meaning a quick check-in

23、 with someone.Experiment:Most computers have a ping utility, or you can try ping on the command line. Try pinging .2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院Traceroute Traceroute is a program that will attempt to identify all the routers in between you and some other computer out on the internet - demonstrat

24、ing the hop-hop-hop quality of the internet. Most computers have some sort of traceroute utility available if you want to try it yourself (not required). Some routers are visible to traceroute and some not, so it does not provide completely reliable output. However, it is a neat reflection of the ho

25、p-hop-hop quality of the Internet. 2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院READING 2 TCP/IPHow Does a Packet Get Across the Internet?2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院Figure 4-12: a Packet Get Across the InternetREADING 2 TCP/IPRouter Analysis? Each router knows enough to figure the next hop, not the whole

26、route. The original computer does not typically know much, delegating to routers“Core” routers, towards the middle Routers measure connection functionality/breakage all the time. Route aroundRouters are another distributed, collaborative system2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院READING 2 TCP/IPSpecial

27、 Local IP AddressesNote that 10.x.x.x and 192.168.x.x addresses are special local IP addressesThese addresses are not valid out on the internet at largeThese are translated to a real IP address as a packet makes its wayFrequently given out by Wi-Fi routers 2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院2022/8/6太原

28、理工大學.計算機科學與技術(shù)學院.計算機軟件學院314.3 SECURITY4.3 SECURITY Computer security is a big and kind of dramatic area, and it can look scary. But it doesnt need to be. We going to talk about some of the most important cases. And in particular, staying safe is not that hard. It doesnt need to be that complicated. W

29、ell talk about the most important and interesting ideas. Keeping safe is not that hard.2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院4.3 Security Now, computer security is a scary topic and a dramatic area. We are going to talk about some of the most important cases and interesting ideas. In fact, staying safe i

30、s not that hard and complicated.2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院4.3 Security4.3.1 Computer - The Castle4.3.2 Password Attacks4.3.3 Phishing Attacks4.3.4 Malware Attacks4.3.5 Safety Recap2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院4.3.1 Computer - The Castle2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院Figure 4-8 Bad guy o

31、utside a computer4.3.2 Password AttacksThe bad guy could try to guess your password on a siteTry to log in again and againWorks if the password is commonAlso known as “dictionary attach”. Try all the words in a dictionaryThis fail mostly, but success here and there with an account with a poor passwo

32、rd is good enough for the bad guysTherefore: avoid having an obvious or commonly used password2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院Bad PasswordsDo not need to be super elaborate (some sites go crazy with this). Here we list some common passwords - do not use these!Common passwords: password，password1, 1

33、23456789, 12345678, 1234567890, abc123, computer, tigger, 1234, qwertyBesides, avoid a password that thousands of others out there have also chosen2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院Good PasswordsWhat I do for secure passwords, for example for a bank site, start with a word, add misspelling, then add

34、some random letters. Could add some digits and/or punctuation and maybe some upper case letters. mottens,erx - fine Mottens,9erx - better MotenX,97erx - probably more complex than necessary2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院Here we list some suggestions:The list of common passwords contains passwords

35、that are just a word or a word plus a tiny variation, like jane , secret1, mittens123, or two words like catmittens, so its vital that your password does not look like that.Its ok to have a word fragment, but it should also include significant nonsense letters. Personally, I like starting with a wor

36、d, since it is easy to remember and fast to type, but then random junk needs to be added in and around it.Some sites go crazy, requiring many upper case letters, digits, and punctuation letters. I think thats not necessary. Its security theater: adding more complexity and the appearance of action bu

37、t without actually adding to security.2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院4.3.3 Phishing Attacks“Phishing”, i.e. the bad guy is “fishing” for youBad guy tricks you into exposing your password or whateverNo doubt you have received many phishing emailsNote: not related to an actual transaction or account

38、, bad guys just spew these out, hoping to fool someoneAlternately could have a phishing web site that imitates the real eBay siteBad guys emails out or in some other way distributes the url to phishing siteBad guys want passwords for sites that have something to do with money2022/8/6太原理工大學.計算機科學與技術(shù)學

39、院.計算機軟件學院Here are some suggestions about how to avoid Phishing:Dont trust URLs in emails or random sites, especially when leading to a login pageScrutinize the URL as shown in your browser or email program. Bad guy URL will try to look legit, likewww.ebay.bad-guy.rumore secure) Type the URL in yours

40、elf. If it claims to be from eBay, type in yourself in your browser. Its a simple rule.Firefox etc. can do extra green highlighting of real site. e.g. Look forhttpsin the URL2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院4.3.4 Malware AttacksMalware is the general term for a program written by the bad guy to do b

41、ad things to your machine - break into the machine, steal passwords, send spam, etc. How can the bad guy get their program on a computer and get it to run? Here we will discuss two kinds of Malware: Trojan and Vulnerability, and their intrusion techniques.2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院Malware 1 T

42、rojanA Trojan is a malware disguised as something else, like awesome-cursors.exe or fun-game.exe or JustinBeiber.JPEG.exe“So the user downloads it or accesses it, not aware that it will do something bad. E.g. SuperAntivirus.exethis is actually a common Trojan ruse!Try to make it like harmless conten

43、t, not a programClaim to be a program that does something many people want, but really its malwareTherefore:Dont run programs from random sources(google it first, see what people say)If something is from a well known domain and has lots of download, someone would have flagged it if it was malware202

44、2/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院Malware 2-VulnerabilitySuppose there is a bug in the Flash animation display programWhen fed certain pathologic animation bytes, the program breaks and gives access to the machineSo the bad guy put a malicious Flash animation, and then sends links to it in spamJust visi

45、ting the page with the bad content is enough to compromise the machine if it is vulnerable. This is probably the most scary case, as the user does very little.2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院Malware 2-VulnerabilitySolution:Keep web-facing software up to dateAll browsers now have strong auto-update

46、channels, so by default the right thing tends to happenAside: this is also why having a proprietary format like Flash be a key part of the internet is maybe not a good architecture. People were very dependent on Adobe to fix the software very quickly, and Adobes record was very uneven.2022/8/6太原理工大學

47、.計算機科學與技術(shù)學院.計算機軟件學院4.3.5 Safety Recap1. Password attacksDont use a bad password for an important site (e.g. bank)Dont re-use passwords across important sites2. Phishing AttacksProceed carefully with content from email, or with provocative titlesLook at the browser URL-area when typing in passwordOr

48、just type in web address yourself in the browser instead of clicking in the email3. Malware AttacksTo avoid Trojan, be very wary of downloading and running code (Google the name or source).To avoid Vulnerability, keep internet-facing software on auto-update to stay at the latest.2022/8/6太原理工大學.計算機科學

49、與技術(shù)學院.計算機軟件學院2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院474.1 LANLANethernetpacketdigital transmissionNo central controlMAC addressTEXT4.2 TCP/IP4.3 SECURITY7. TCP/IP Standards8. domain names9. router10. DHCP 11. ping12. traceroute13. password Attacks14. Phishing Attacks15. HTTPS16. malware attacks17. Trojan1

50、8. vulnerabilityTermss2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院48CONCEPTS1. What is LAN?2. What is Ethernet?3. How the data are sent from one computer to another?4. What is the pattern of sending one packet on Ethernet?5. What is Wi-Fi?6. What is the difference between Ethernet LAN and Wi-Fi?2022/8/6太原理工大學.

51、計算機科學與技術(shù)學院.計算機軟件學院49CONCEPTS7. What are the features of the Ethernet Design?8. What is IP address?9. What is domain name?10. What is router?11. What does it mean for a computer to be on the internet?12. What is “ping”?13. What is “traceroute”?2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院50CONCEPTS14. What does

52、a computer like from outside?15. What is the suggestions of a good password?16. What is Phishing?17. What is Malware Attack? How to avoid it?18. What is Trojan? How to avoid it?19. What is Vulnerability? How to avoid it?Multiple Choice1. Suppose a computer wants to send a packet on Ethernet. what do

53、es the computer first wait for?a. Waits for its scheduled time in the predetermined transmission schedule.b. Waits for the central Ethernet controller to signal that transmission is now permitted.c. Waits for the recipient computer to signal that it is ready.d. Waits for the Ethernet wire to be quie

54、t.2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院2. Which one is not the feature of Ethernet?a. Sharedb. Distributed and Collaborative.c. Secure.d. Performance degrades .2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院3. Which one of the following is not a valid IP address?a. b. c. 00d. 42.257.99.112022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機

55、軟件學院4 Which of the following is generally not true about routers?a. Routers check the central internet-map which shows routes for all packets.b. Routers get packets from computers, forward them on.c. Routers continuously monitor the status of their connections.d. Routers forward each packet one hop

56、closer to its final destination.2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院5. What does ping do?a. Notifies the local router that the computer wants more packets.b. Sends a “are you there” packet to a computer, getting back a “yes” packet.c. Notifies the local router that the computer does not want any more p

57、ackets.d. Sends a “who is there” packet, getting back a description of the recipient.2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院6.Which one of the following is the worst password?a. snyrk34b. XXagflib1c. Xxagflibd. password2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院7. Again, which one of the following is the worst pass

58、word?a. hygyslb. ipludtc. secretd. ahtygx2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院8. Which of the following best describes a phishing attack?a. Try to obtain the password by tricking the victim into logging in to a fake but realistic looking web site.b. Try to figure out the password by continuously attempt

59、ing to login with password guesses.c. Try to figure out the password by intercepting the packets of the login network transaction.d. Try to obtain the password by breaking into the victims house and looking for it written down somewhere.2022/8/6太原理工大學.計算機科學與技術(shù)學院.計算機軟件學院9. Which one of the following E-Mails looks like a Trojan attack?a. Please visit www.scwhab.bad-guy.ru and log in with your regular passwordthe standard log-in page is broken today.b. We have detected a virus on your computer. Please download and run this program to check: SuperVirusChecker.exec. I have 27 million dollar