Coursera-Internet_History

Coursera: Internet History, Techornology and Security study notes

Coursera courses Internet History, Techornology and Security study notes

WEEK1

War Time Computing and Communication

• Brian Cheli Bletchley Park Manor: a top-secret code breaking effort by the British government during World War II the British government in order to decipher the "Enigma" encryption device telegram Germany established during World War II, gathered a large number of high-end cryptography. mathematical talent base. Finally, under the leadership of Alan Truing (Alan Turing) designed the first computer. (More comments from Chinese author views the movie "Imitation Game" got)
  • The author comments: Alan Turing in the strict sense at this time to participate in the development of the computer and common computer is now a little different. Called electronic analog computer on a computer academic Bletchley Park birth, its value is rotated by some pointers, represented by the length of the slide rule (this operation scenes in a video, for example, computer replica Alan Turing and Bletchley Park this course is also It can be proved, when its operations have a number of carousel in motion at the same time). Now commonly referred to as electronic computer is a digital computer, which value is the bitwise operation, and constantly beating.
• Bomba: Poles developed to crack the Enigma machine is aimed primarily at German repeating the message header (header information reuse)
• Bombe: to design team led by Alan Turing machine, aimed primarily at German sending stereotyped messages (modular information, that is, there are certain military instruction format).
• Colossus (giant): German encryption machine for an upgraded version of the machine, the first is called Mark 1. (Does Iron Man inspiration comes from the name of this?) The second stage is called Mark 2.Mark 2 directly involved in the Normandy landing. The computer giant has a feature of most modern computers, in addition to no memory. Read data strip,

Computing with Phone Lines

• This section describes the link between the early computer model: information transmission implemented by dialing a telephone line
  • local call to local computer
  • distance call to remote computer (somewhat similar to a remote computer)
  • computer to computer (leased lines): more expensive, common in the banking system

WEEK2

Supercomputers Justify a National Network

• This section describes the connection between the early and the evolution of the computer.
  • 1. The cable (wired connection, dedicated line) leased lines
    • Linked directly to the computer via a cable. It is really expensive.The cost base on distance. Linearly related to cost and distance.
    • Transmission speed
    • Information required by queuing
    • Save Money with More "Hops": by connecting more schools (because it was the only school with a computer) to build cost-sharing way cable way to reduce expenses has been reached.
  • 2.Bitnet bit network, the main form of campus network
    • Connection in order to save costs arising
    • As obvious disadvantages and advantages: Large files may take up a long line, affect the transmission of other smaller files, the transmission speed is very slow.
  • 3.ARPANET: The US military developed supply network used by the military
    • the primary motivation was to improve the use of their compution equipment.
    • The main difference between the ARPANET and Bitnet: "packet switching" (packet switched): sending data across the link and then keep sending it until it was done.
      • packet: breakinga big message into small parts, labeling each one of them individually to the data packet block becomes to the data transmission units of the packet
      • able to sneak and bypass the traffic jam can avoid traffic congestion (traffic jam here can be understood as being in busy line)
      • allowing simultaneously multible message to be in fight at the same time (to allow individuals to understand this sentence is the same transmit different messages, here it reflects the importance of different ARPANET and Bitnet)
      • Same set of data may be transmitted via different paths after being divided into data packets, but because of the different paths of packets may be transmitted at different times. I like to buy things on Taobao a hand to do (message), but this hand stores do break down into parts (packets), from the Beijing Zhongguancun sent to Fuzhou on street town, but probably each part from Beijing to Fuzhou For example there is a path not the same as taking part (Beijing -> Jinan -> Nanjing -> Hangzhou -> Fuzhou), while the other part is taking the (Beijing -> Taiyuan -> Xian -> Chongqing -> Guiyang -> Nanning -> Guangzhou -> Fuzhou), but no matter what path through, finally able to Fuzhou, and I need to do is follow the instructions to do hands put together.
  • 
    • between getway and getway have links and routers (routers, the main role is to forward the information): breaking messages into packets, packets can take different paths, and then they arrive and they are reassembled (reorganization)
• Larry Smarr
  • Astrophysicist, because the contact needs to issue a super super computing power, so spare no effort to promote the building of supercomputers. After continuous efforts, and later established the NSFNET

The time "Internet"

• This section focuses on some of the Internet in the development of the story twists and related interviews.
• Doug Van Houweiling
  • Because all aspects of the University of reasons difficult to have their own supercomputer, so another way to establish a computer network for the University of Michigan. The first budget is only enough to establish a transport speed of the line 56kb, and later after a series of fight, it will increase to 1.5mb. Since then, NSFNet become the world's fastest network, ARPANET replaced as the world's mainstream network.
• Leonard Kilenrock
• Katie Hafner (a reporter, once ready to write feature stories about the Internet)
• NSFNet: National Science Foundation, the National Science Foundation, referred to as the NSF

WEEK3

The Early World-Wide-Web

• This section describes the early world-wide-web (WWW)
• Robert Cailliau :one of the co-inventor of the world-wide-web
  • Physcists have need for spreeding documentation around .So they built something like centralized databases ((centralized database) to kept high energy physics articles (high energy physics article).
  • Robert will be divided into upper computer (browser browser) and lower (database database)
  • The first server was up end of 1990 in the USA.
  • Gopher: Early information retrieval tools, before the emergence of major WWW information retrieval tool.
  • Mosaic: Firefox browser predecessor, the famous browser history, running only one window, each window is automatically replaced by a new interface.
  • WWW features: every time that you clicked here, you had another window (with the Mosaic important difference: Each click will open a new page)
  • In 1994, the First International World Wide Web Conference,

A Search Engine for Physics Articles

• This section describes the physics of the article search engine
• use the database by the web. (database is stored here physics articles centralized databases previously mentioned)
• The first Web server in America can query a database on a mainframe. (America's first network server can query the data in the database)
• Paul kunz used a CREN server software ,which was written in C to creates the first Web server in America.
  • get the query that the user had made and turn it into a database query. (acquisition made by the user query and convert it to a database query)

Making the Web Available to All

• Gopher: gopher before the web became popular mainstream network resources Search Tools
• Mosaic: Another browser, invented by Joseph Hardin led the NCSA
  • At 1990s, NCSA at Urbana-Champaign, University of Illinois, built an open source web browser that worked on Mac, Windows, and Unix. (Support multiple multiple systems)
  • it is possible for people to share in real time images of their data, the spreadsheets of their data, and papers.
  • It is necessary to mention that most of the staff later Mosaic project created the famous Netscape (Netscape), the company launched the Firefox browser is now used by many people.

WEEK4

Explosive Growth of the Internet and Web

• 1994: Year of the Web (in 1994 an important year for the development of the Internet, the Internet is no longer a purely academic or technical, but brought a lot of capital investment, the establishment of many of it's, etc.)
  in a time when many of among the companies, Netscape and Microsoft is undoubtedly a strong competitor, but at the time the body mass compared to Netscape's and Microsoft is still relatively small, the acquisition of Netscape by Microsoft almost annexation.
• Mitchell Baker: one of the founders of Mozilla.
  • Microsoft acquired Netscape later both failed to enter the competition.
  • Netscape is a failure product，because of it ，Baker was be laying off in 2001. But it wasn’t really possible to take her place and she continued as a volunteer.
  • During this competition years, Netscape has created and still is the fire of the JavaScript language. Later price as the main battlefield of the war between the two business will not go, after all, I do not need to analyze the pros and cons as well as the historical significance of the market-competitive behavior. (Routine is nothing more than a vicious price competition, even free products, to achieve the purpose of occupying the market, but this time continued to focus on technology development, rather than to compete on price. If there were financing this kind of thing, then it and and some companies in recent years to compete in certain areas like a)
  • In 2003 the Mozilla foundation was formed
• Brendan Eich: JavaScript creator and principal architect
  • JavaScript and Java has little (I have long thought that Java JavaScript when the extension application or a customized version in one respect, this corrected my mindset this lesson)
  • JavaScript is a beginner and amateur programmers are more friendly language.

Commercialization of the Web

• This section focuses on the commercial network
• Microsoft give their browser away free, which made it impossible for Netscape to charge for the browser. (Microsoft in order to compete and offer free browser user)
• the World Wide Web Consortium (World Wide Web Consortium) was created in October of 1994.
  • Jeff Bezos: the founder of Amazon.com (Amazon founder Jeff Bezos, yes that is recently divorced)
    • books is the frist product to sell online.Music is the second. The earliest Amazon to buy books, and later extended to a class of CD music products.
    • When it comes to online shopping platform, suddenly remembered recently I saw a video about Ma, deep feelings, video from tiger flutter Street -> Portal

WEEK5

Link

• Hops:one portion of the path between source and destination. Data packets pass through bridges(网桥), routers and gateways（网关） as they travel between source and destination. Each time packets are passed to the next network device, a hop occurs.[插入图片Hop-count-trans.png]
• Packet-switching (packet switched): break message into packets (the information is divided into packets)
  • bridge, router, gateway is forwarding packets (bridges, routers, gateways are responsible for storage and transit packet), but not longs term storage of message.
• shared Network infratructure only focuses on packets, not reliability or anyting else. (shared network data packets rather than just focus on reliability or other)
• layered network model (layered network model): OSI model (Open System Interconnection model Open Systems Interconnection model): In order to simplify the solution, in order to solve the problem, the management, the network will be divided into several parts. In each layer need only consider the problem of the present layer, the other layers need not be of the impact.
• Layered Architecture (hierarchical architecture)

  • 

  • Link: some transmission medium, such as fiber optic cable, a data link is a hop, a router receiving data on the link and push the received data to the next link. Like to buy things on Taobao a hand to do (message), but this hand stores do break down into parts (packets), each of the packets will go through many transit station (rounter), and each transit on the way to Fuzhou use a variety of transport vehicles (link) between the stations, the transportation between the relay station is hop.

    • how to avoid the chaos when they’re sharing?
      • with a technique called, Carrier Sense Media Access with Collision Detection.
      • To aviod garbled messages,systems must observe “rules”(Protocols)
      • Ethernet rules are simple
    • common link technologies: Ethernet (Ethernet), WiFi, Cable modem (cable modem), DSL (Digital Subscriber Line [dial]), Satellite (satellite), Optical (fiber)

Internet Protocol (Internet Protocol)

• IP drop data if it go bad. If the packet data transmission error or failure, the packet may be discarded, to avoid erroneous packet being broken. the address is broken into two parts. There is the network number part which is the prefix (prefix), and then there is the computer number within network.As soon as the packets enter the network, it only looks at the prefix. Internet only care about IP address prefix, which is the only concern from the network.
• portable cpmputer: dynamic host configuration protocol: Dynamic Host Configuration Protocol, mainly for mobile computers such as IP address to resolve a laptop, iPad like no fixed allocation of local connection. I.e. assigned temporary local IP, the general format for the 192.168.xxx.xxx, but only the IP address belongs to the local network, the IP address can be understood as a branch. This method can also be used to solve the problem of insufficient number of IP addresses.
• network address translation (rewriting source IP address or destination IP address in the IP packets through a router or firewall)
• Time-to-live (TTL) is a value in an Internet Protocol (IP) packet that tells a network router whether or not the packet has been in the network too long and should be discarded. Tell router packet exists in the network for too long. When the number of hops a data packet exceeds 255 (32bit) is discarded. Principle is that if a packet through the 255hops have not served, can be considered the data into an infinite loop. To avoid the use of network caused by network congestion, it creates this diagnosis method.
  # WEEK6

Transport/Reliability

• TCP layer built on top of the IP layer, the role of the TCP layer IP layer to make up for some problems that may arise.
• TCP（Transmission Control Protocol 传输控制协议）layer:The purpose of the TCP layer is to compensate for the possible errors in the IP layer as well as make best use of available resources.
• the key idea in TCP / IP is that when we send some data, we break it into packets and then we send each one. And then we keep (delivery confirmation response) them until they get an acknowledgement from the other side and then and only then do we throw them away. and at some point, if a packet gets lost It can be sent again, until it finally is acknowledged in the destination system. (prevention of transmission errors mechanism provided until the sender to confirm the transmission complete before the end of the transmission, if a transmission error occurs again sent until completely successful transmission so far) It figures out which packets have or have not made it across the Internet layer.
• As a fan, it would be understood as TCP Modric (IP) around Casemiro (TCP), to help defend IP and IP collaboration while making the team (network) operating more smoothly and successfully. (This is the author's self-Hi, replaced by Gennaro Gattuso and Andrea Pirlo or similar and who, like the establishment do not understand please ignore ^ ^_ ^)
• the slow start algorithm at a high level。

  • As more and more computer access network, speed becomes very slow, a lot of packet loss. (Is it because too long not served, last week spoke of the Time-to-live mechanisms play a role?) Van Jacobson this response is: TCP congestion control.

  • 

  • 

  • This mechanism is a simple description, enter the number of the control packet network (somewhat similar to Beijing n ring restricting the number of travelers to ease traffic jams both visual sense), it is sent to the network when the packet is received acknowledgement of acknowledgment of service. But this mechanism is to have a difficult start when the sender does not know how the current network conditions (because the first packet is sent when there is no data on acknowledgement a package). So van Jacobson designed the Slow Start Algorithm (slow start algorithm), which is sent to slow in the early stages of data transmission. This makes it possible to prevent network congestion.

    • Added: next acknowledgement not only receive a packet before sending a packet (this is too slow, a loss), but at the time of start of transmission speed down the back and gradually increase transmission without affecting network speed speed.
• Domain Name System (DNS): the visible name that we could switch the mapping from the name of the IP address transparently (visible names can be switched from the IP address mapped name), a big distributed data base (distributed data system). [easier to use human memory naming instead of IP address, IP address, from left to right is descending, and domain name system contrast, for example www.si.umich.edu this domain, edu behalf of the domain name belongs to educational institutions, umich educational institutions on behalf of the University of Michigan inside, si is represented by the University of Michigan School of information, www server]
• the transport control protocol has a responsibility of compensating for the imperfections of the IP layer

WEEK7

Application

• client application (client application)

• server application (server application)

• client app make request, and server make response back. client sends a request, the server returns a response content.

• two basic problem

  • which application gets the data:
    • this is using a mechanism (mechanisms) called ports (ports) .ports allow a IP address or a single computer or a single server. IP port attached present, branch path similar to an IP address. Different ports correspond to different features and services.
    • The figure is part of my computer's port information
      

• application protocols (application protocol), the port rules for information exchange.

• 过程：click–>request–>response–>display

• browers(浏览器)：request the server application ,HTML comes back ,which discribe how this page document supposed to show.And show to user.

• HTTP: Hypertext Transfer Protocol, a widely used network protocol, a number of sites added in front of the "http: //", which means that the site follows the HTTP protocol

• If we know how to talk, if we know what port to talk to, and we know what protocol to talk to that port we can write a client that meets the needs of that server and extract the data. (If we know how to communicate, If we want to know which port to communicate with, if we know the protocol to communicate with the port, we can write a server to meet the needs of the client and extracted data.)

• Information that's sort of qualitatively the same as all naming or. Identity information, but it's spread randomly across the whole packet (information of the same name or identity of all information on the quality, but it is randomly spread throughout the packet)

WEEK8

Hiding Data from Others

• It is does not exist of absolute security.Security is a cost benefit analysis (cost-benefit analysis)
• security is naturally imperfect (safety are born imperfect), absolute security does not exist in the world, various activities will limit itself to excessive security, we should adopt a compromise.
• Confidentiality (confidentiality), encryption (encryption) and decryption (decryption)
  • plain text and ciphertext(纯文本和密文)：Encryption is the act of going from plain text to ciphertext.And returning the ciphertext back to the plain text is decryption.
  • secret key
    • symmetric key (symmetric key), which means that both parties have to be in possession of the same information, basically use the same key material to encrypt as you do to decrypt. (Both sides must have the same information, and decryption using substantially the same key material is encrypted)
    • the problem that secret key has, that led to the need to invent a public key, is the fact that you need to at some point have a secure communication. (issue key mechanism is the need to have a completely safe way to decrypt way transmission)
    • shift (shift cipher): text letters upward / downward movement of n bits (n = shift number, 1 <shift number <26)
      • The shift to decipher an encrypted way violence is very simple, is to shift number from 1 to 25, all the time (apparently shift number 0 or 26 does not make sense, shift number is greater than equal to 26 may be viewed as a variant of 0-25)
      • rot13: common displacement encryption, the same encryption and decryption mode, so once again encrypted decryption only.
  • public key
    • it has a way of distributing the key in a using insecure medium. (There is a way to distribute public keys over an insecure medium)

Insuring Data Intergrity

• Cryptographic Hashing(哈希):map from a message to the hash（散列） or the digest（摘要）
  • takes a large amount of text and reduces it down to some small set of numbers (reduced to a lot of text)
  • hashing passwords(哈希密码):when creating a password,run a cryptographic hash on it, store the cryptographic hash.when log in next,just input the plain text to the system,and the system will run the presented password through the same cryptographic hash.
    • hash can not go backward. (hash is one-way), you can go from the frame text to the hash, but you can not go from the hash to the plain text, which is very different than encryption and decryption. (Ha Greece and the biggest difference is that encryption and decryption of the hash is irreversible, not by hashing reduction text), you need to run the plain text through the hash again and then compare
    • the system doesn’t know what is the password, but it know what is not the password.
  • Hash and preservation methods widely used to identify and confirm the password, if the operator can send the password in clear text to the user, the password mechanism operator's certainly not safe, because hackers can get the password by intercepting mail. Operators should be stored hash value of the password, but because the hash irreversibility, operators themselves can not know how much is the real password, and user input after the next login password plaintext password hash is sent to the future operators, operators to confirm the identity by comparing the password hash stored.
  • Hashing may also be used to confirm whether the message is malicious tampering, method, after the piece of information plus a specific string, the entire text to be hashed, and then added to the text first few hash value Behind. Text behind the text to the recipient received hash after adding the specific character string, if the text had been tampered, the hash value will be different in the first few

WEEK 9

Securing Web Connections

• public key encryption(公钥加密)，it relies on two asymmetric keys(依赖于两个不对称的键).There is a public key, which is actually, does not need any protection whatsoever, and a private key(私钥).You generate the public key and the private key. You send out the public key, the public is used to do the encryption. And then private key is used to do the decryption. And they’re related mathematically(在数学上是相关的)
• if you're going to use public private key encryption, you have to generate a pair. (public and private key must exist in pairs)
• choose a random number really big–>look around for a nearby prime number and you choose two of those(选择两个附近的质数)–>multiply them–>through some calculations, you compute the public and the private keys from that large number.
• Resolve the public key cryptography is that it is difficult to calculate a large number of which are also two large prime numbers multiplied, and the receiver knows where the file because a prime number, the decryption is very simple.
• Message was encrypt by application protocols(such as HTTP).it stay encrypted all the way through the entire network.all of the sequencing and re-transmission that happens in the TCP layer(所有的排序和传输都发生在TCP层).The rest of the internet just move the data.
• Transport Layer Security(SSL、HTTPS):it’s between the TCP layer and the application layer.

Identity on the Web

• Secure Socket Layer, an public private key encryption.
• SSL layer between the application layer and the TCP layer is to provide a guarantee of safety for the part, the network connection to provide secure network interface. Using the Hypertext Transfer Protocol over SSL is HTTPS. SSL later evolved into TLS.
• the certificate authority which is a trusted, third-party that signs these certificates (trusted certificate authority, third-party signed certificate to confirm that the object of dialogue is not the real server)