Yes, but there may be more!

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All of the above

Eroding the trust and confidence that the general public has in their online privacy and secure online transactions.

Attacking electrical systems that control the energy grid.

A physical attack that involves cutting fiber-optic cables.

Which of the following are existing vulnerabilities of the Internet, according to experts?

Don't use iffy software. If the advertising says that the program will get you money, or free stuff, or pornography, or cheats for video games, it's very likely to be malware. A particularly sneaky category is fake antivirus software! Check the reviews in magazines to make sure you're getting what you really want.

Don't click links on web sites or (especially) in email, without first double-checking that the actual URL in the link is the same as the one that's shown in the message. (Where does this link to http://google.com really send you?) Two paragraphs up we said to keep your software up-to-date, and often the way you know there's an update is that a window pops up on your screen. Don't click the "update" button — or even the "close" button — unless you're sure it's really a legitimate update.

There are no perfect solutions you as an individual person can use to be sure you will never be victimized. But there are things you can do that will help a lot:

What Can You Do?

There are millions of such DNS requests every second, and if all of those requests had to begin at the same few root domain servers, those servers would be flooded with too many requests. Instead, DNS servers remember (cache) the results of host name queries, and they provide these remembered (non-authoritative) answers for most requests. However, if the IP address of the site you are requesting changes before before the non-authoritative answer is updated, you may be sent to the wrong site. More critically, a fraudulent DNS server may provide deliberately wrong non-authoritative answers. DNS was not designed to be perfectly secure.

The hierarchy of the DNS makes the system more efficient. When you visit snap.berkeley.edu, your computer only has to know where to find an edu name server. That server only has to know where to find the berkeley.edu server. And that server directs your computer to snap.berkeley.edu.

The Lack of DNS Security

A variant is the Distributed Denial of Service (DDoS) attack, in which the attacker first uses viruses and other malware to take control of many (sometimes hundreds of thousands of) computers around the world. This network of infected computers is called a botnet. The attacker then launches a DoS attack from all of the victims' computers at the same time. Besides increasing the number of simultaneous server requests, DDoS makes it harder to determine who is at fault, since the attack seems to come from many innocent people.

A Denial of Service (DoS) attack consists of sending a lot of requests to a server at the same time (for instance, requests for a web page or some data). This can overload the server's network bandwidth. A DoS attack doesn't destroy data or collect passwords; it just causes a temporary inability to reach the targeted server so other users of that server are denied service.

Distributed Denial of Service (DDoS) Attack

Phishing is a common security attack in which the victim is tricked into giving up personal information or downloading malware.

A firewall is a security system that controls the kinds of connections that can be made between a computer or network and the outside world.

Malware is software that was designed to harm your computer.

A virus is a type of malware that spreads and infects other computers.

Antivirus software is software designed to scan the files on your computer and delete or "quarantine" files that are infected with a virus.

Another common attack strategy is called phishing: an attacker sends you an email that appears to be from some official organization (such as your bank) and tricks you into giving information to the attackers (such as your bank password).

The general name for programs that try to affect your computer badly is malware. One kind of malware is called a virus. Computer viruses make copies of themselves (just as biological viruses do) and try to spread themselves over the network to other computers. People use antivirus software to help prevent these attacks. People also use firewalls to limit connections into or out of their computer. (Both your computer and your router probably run firewall software.)

That was before computer systems on the Internet became important to people other than their owners. Today, people give their credit card numbers to online shopping sites, and computers controlling infrastructure (such as power plants, telephone switching systems, traffic lights, and hospital equipment) can be attacked by other countries' military. (The United States has been both the attacker and the attacked in this sort of incident.) There are still teenagers having fun by attacking computers, but today such cases are far outnumbered by serious criminals and cyber-warriors.

Common Security Issues for Users

In the early days of the Internet, most attacks came from teenagers, who wanted to learn about the insides of computer software, feel smart, and show off to their friends. Most of the time, they didn't intend to do any harm, but often they did anyway, partly by making mistakes, and partly by convincing computer system managers that the early open-access network policies were dangerous.

Who Wants to Attack Other People's Computers?

Originally, network security was a relatively minor consideration because the Arpanet was a small computer network of military personnel and university users. The real need for security arose once businesses were allowed on the Internet in 1995.

you will learn about threats to online security.

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We hebben het aantal graden dat wordt gedraaid tussen de takken aangepast.

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Read Blown to Bits pages 312-316.

How Did the US End Up In Charge?

The issue of US control has become much more heated since 2013 when Edward Snowden (shown right, source: Wikipedia) exposed the US National Security Agency (NSA) for spying on Internet traffic worldwide. It's too soon to know how these concerns will eventually be resolved.

For example until 2009, all DNS domain names had to use the English alphabet, despite constant requests to accommodate other languages.

If you think it's strange for one country to control a worldwide network, you're not alone. Other countries have never been happy about the US control of the Internet, which was officially under US control until 2009 and is still, according to many critics, unofficially dominated by the US government.

The Issue of US Control

Learn more about these organizations.

The protocols for the Internet change over time. The Internet Engineering Task Force (IETF) are the experts in charge of developing and approving these protocols. ICANN controls the DNS hierarchy and the allocation of IP addresses.

Examples of open protocols: Standards for sharing information and communicating between browsers and servers on the Web include HTTP, Simple Mail Transfer Protocol (SMTP) and secure sockets layer/transport layer security (SSL/TLS) Standards for packets and routing include transmission control protocol/Internet protocol (TCP/IP).

The growth of the Internet has been fueled by open protocols, standards that are not owned by a company.

The Power of Open Protocols

In 2009 the US Department of Commerce signed a new agreement with ICANN recognizing it as an independent, multinational organization, although it is still under contract with the Department of Commerce to maintain certain principles. International critics are still not satisfied that ICANN is truly independent of the United States.

Some people think that nobody's in charge of the Internet—that everyone just cooperates freely with no central organization. It's true that free cooperation plays an important role, but people can't just pick any IP address or host name they want, or else there would be conflicts. For example, we can't start a server named bjc.org, because that name is already in use (by a health care provider in St. Louis, Missouri). Until 2009, the Internet domain name hierarchy was entirely controlled by the United States government, with the details delegated to ICANN (the Internet Corporation for Assigned Names and Numbers).

you will learn about the communities of people who control how the Internet works.

Who's In Charge of the Internet?

You might have used a substitution cipher to encode your message, substituting each letter of the alphabet with some other letter. You could substitute letters in any order, like this:

When you specify an IP address, you are using an abstraction. Why? What is the more detailed thing that you are abstracting away? Write out your explanation.

Write an explanation of the DNS and IP address hierarchy.

Pick one:

What's an undecillion? One undecillion is 103610^{36}10​36​​, a billion billion billion billion, a 1 with 36 zeros after it, 109⋅109⋅109⋅10910^9 \cdot 10^9 \cdot 10^9 \cdot 10^910​9​​⋅10​9​​⋅10​9​​⋅10​9​​.

watch the video here.

If your connection blocks YouTube,

This image is a simplified model of IP address hierarchy.

When we type in a domain name, the browser queries the domain name system to find the Internet Protocol (IP) address of the server we want to visit. IP addresses are unique numerical addresses assigned to every device on the Internet. Both the domain name syntax and IP addresses are hierarchical; however unlike domain names, with IP addresses, the individual site is on the right and the top-level groupings are on the left (see image at right).

IP Address Hierarchy

bicycles.com.org is not a typical address format because it has both the .com and .org category codes.

bicycles.org is a completely different domain name that would be on a .org (not .com) name server.

bicycles.co.uk would be used for a commercial site in the United Kingdom.

Correct! about.bicycles.com could be a subdomain on the bicycles.com domain.

Which of the following could be a subdomain of the domain bicycles.com?

This question is similar to those you will see on the AP CSP exam.

This image at is a simplified model of domain name hierarchy.

is a subdomain of

is a subdomain of

Just as the path in a URL locates a specific file in a hierarchy of folders on the server, domain names locate a specific website within a hierarchical domain name system (DNS). The hierarchy of the domain name system simplifies the process of finding the computer with the desired domain name because the DNS servers that help locate domains don't need enormous lists with every host name in the world. Instead, any user's computer only has to know where to find a root domain server (the one that knows where to find the top-level domains such as .org and .edu), and that server knows where to find the domain (like berkeley.edu), and that server knows where its subdomains are (like snap.berkeley.edu), and so on. The root domain may be a country code (such as .mx for Mexico) or a category code (like .gov for government). The last two segments of a domain name (like berkeley.edu) make up the primary domain, the main address for a site. Subdomains are subsections of primary domains or of other subdomains. For example:

:

Recall the structure of a

Domain Name Hierarchy

A domain name is a human-readable way of locating an Internet site. An IP address is a machine-readable way of locating an Internet site. A hierarchy is an arrangement with the biggest category at the top and subcategories below, like a triangle. The domain name system (DNS) is an Internet protocol for translating domain names to IP addresses

There are two hierarchical addressing systems on the Internet: domain names and IP addresses. People use domain names (like snap.berkeley.edu) to visit websites. Computers that are part of the domain name system translate those domain names to IP addresses (like 128.32.189.18) to locate and send data behind the scenes.

Before the Internet, there were only small networks of computers (like the Arpanet, which peaked at around 200 computers), and every computer knew the name of all the other computers on the network. That worked for small networks, but it's not realistic for the 3 billion computers on the Internet now. So now, a hierarchy allows the system to distribute requests for IP addresses to domain name servers across the growing network.

For example, in a school, the principal is at the top, the department chairs oversee the teachers, and the teachers lead the students. In biology, we use a taxonomic hierarchy: kingdom, phylum, class, order, family, genus, species. And on computers, we store files in a hierarchy of folders within folders.

you will learn how to interpret the pieces of a domain name or an IP address.

A hierarchy is an arrangement of things with the biggest or highest category at the top and things ranked into subcategories below. A hierarchy is often depicted as a triangle.

In the same model network, what is the maximum number of nodes that can fail and still let Sender and Receiver communicate?

In this model of a network, what is the minimum number of nodes (connection points) that can stop working before the sender and the receiver can't communicate? (Other than the sender or the receiver themselves, of course.)

Describe what's going on in this animation.

Internet scalability is the ability of the net to keep working even as the size of the network and the amount of traffic over the network increase. The page Internet 2012 in numbers has some astonishing numbers about Internet traffic from a few years ago.

Try to find a higher number of nodes that can stop working and still ensure communication.

Try to find a higher number of nodes that can stop working and still ensure communication.

If all 10 nodes fail, the sender and receiver can't communicate.

If 9 nodes fail, the sender and receiver can't communicate.

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Try to find a smaller number of nodes that can stop working and still break communication.

Try to find a smaller number of nodes that can stop working and still break communication.

Try to find a smaller number of nodes that can stop working and still break communication.

Correct! If the node with 6 connections goes down and also either of the two to its left, the sender and receiver can't communicate.

There are no nodes that are vital to the system. Pick any node to stop working, and you can still find another path.

Work through the following questions.

you will learn how the layout of the Internet is redundant (more than one path from here to there) in order to ensure reliability.

Given the enormous amount of data traveling around, the Internet needs to be reliable. We have achieved this by building many redundant connections into the physical systems of the Internet. Wherever information is going, there is more than one way to get there, so that if part of the Internet fails, the rest remains connected even if the failed part is in the usual path from one place to another. This increases the Internet's fault tolerance (ability to work around problems). And it also helps the Internet scale (expand) to more devices and people.

Improved security and privacy over storing data on a personal computer.

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Run-length encoding is a lossless compression format; it doesn't lose any information. The original picture can be reconstructed with every pixel exactly correct. But run-length encoding doesn't do well if the picture is a photograph where every pixel may be (at least slightly) different in color from its neighbors. If the length of each color run is just one pixel, both run length and color will take twice as much space as just storing the color of each pixel. Another lossless image format you may have heard of is PNG (Portable Network Graphics, pronounced "ping").

Use the Color Mixer at RGB colors and hexadecimal notation to check the result of the hex code E5A84A.

These days, the size of one picture isn't so significant, but think about every frame of a movie, and think about the time required to send the information over the Internet. Compression makes it easier to stream that movie to you.

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Instead of storing all 158 pixels individually, we could compress them with run-length encoding and just store six values (three numbers and three colors):

That is an inefficient way to store the information. Think about the 158 pixels in the top row. The first 60 or so are white. Then come five pixels of yellowish orange (the top slice of the "b"). And the rest of that row is white.

Lossless Compression

This picture of the BJC logo (shown right) is 158 pixels wide and 186 pixels tall, for a total of 29,388 pixels. The BMP (bitmap) format includes each of those pixels in the picture file, at four bytes per pixel, so the file size is about 120kB.

you learn about different data compression algorithms, such as the ones used in common picture file formats.

Data Compression

The original line is replaced by two other lines; together the three would form a right triangle, with the original line being the hypotenuse. If the original line's length is held by the variable size, what length must be passed to the recursive call? That is, what are the lengths of the legs? You can use the Pythagorean formula: a2+b2=c2a^2 + b^2 = c^2a​2​​+b​2​​=c​2​​.

At each level, the algorithm replaces a straight line with a bent line, following this rule: turn 45° left, do the previous level at a reduced size, turn 90° right, do the previous level again, and finally turn 45° left to return to the starting direction. You'll have to figure out how much smaller the size input should be in the recursive calls to make the new level exactly fit the level before.

Another well-known recursive shape is the Lévy C-curve. As in the snowflake algorithm, the base case is a single line segment.