Chapter Objectives

After reading this chapter and completing the exercises, you will be able to do the following:

Identify the most common dangers to networks.

Understand basic networking.

Employ basic security terminology.

Find the best approach to network security for your organization.

Evaluate the legal issues that will affect your work as a network administrator.

Use resources available for network security.

More venues for training also exist now. Many universities offer Information Assurance degrees from the bachelor’s level up through the doctoral level. A plethora of industry certification training programs are available, including the CISSP, EC Council’s CEH, Mile2 Security, SANS, and CompTIA’s Security+. There are also now a number of universities offering degrees in cyber security, including distance learning degrees.

Despite this attention from the media and the opportunities to acquire security training, far too many computer professionals—including a surprising number of network administrators—do not have a clear understanding of the type of threats to which network systems are exposed, or which ones are most likely to actually occur. Mainstream media focuses attention on the most dramatic computer security breaches rather than giving an accurate picture of the most plausible threat scenarios.

This chapter looks at the threats posed to networks, defines basic security terminology, and lays the foundation for concepts covered in the chapters that follow. The steps required to ensure the integrity and security of your network are methodical and, for the most part, already outlined. By the time you complete this book, you will be able to identify the most common attacks, explain how they are perpetrated in order to prevent them, and understand how to secure your data transmissions.

A network is simply a way for machines/computers to communicate. At the physical level, it consists of all the machines you want to connect and the devices you use to connect them. Individual machines are connected either with a physical connection (a category 5 cable going into a network interface card, or NIC) or wirelessly. To connect multiple machines together, each machine must connect to a hub or switch, and then those hubs/switches must connect together. In larger networks, each subnetwork is connected to the others by a router. We look at many attacks in this book (including several in Chapter 2, “Types of Attacks”) that focus on the devices that connect machines together on a network (that is, routers, hubs, and switches). If you find this chapter is not enough, this resource might assist you: http://compnetworking.about.com/od/basicnetworkingconcepts/Networking_Basics_Key_Concepts_in_Computer_Networking.htm.

The real essence of networks is communication—allowing one machine to communicate with another. However, every avenue of communication is also an avenue of attack. The first step in understanding how to defend a network is having a detailed understanding of how computers communicate over a network.

The previously mentioned network interface cards, switches, routers, hubs, and firewalls are the fundamental physical pieces of a network. The way they are connected and the format they use for communication is the network architecture.

A packet can have multiple headers. In fact, most packets will have at least three headers. The IP header has information such as IP addresses for the source and destination, as well as what protocol the packet is. The TCP header has information such as port number. The Ethernet header has information such as the MAC address for the source and destination. If a packet is encrypted with Transport Layer Security (TLS), it will also have a TLS header.

An IP version 4 address is a series of four three-digit numbers separated by periods. (An example is 107.22.98.198.) Each of the three-digit numbers must be between 0 and 255. You can see that an address of 107.22.98.466 would not be a valid one. The reason for this rule is that these addresses are actually four binary numbers: The computer simply displays them to you in decimal format. Recall that 1 byte is 8 bits (1s and 0s), and an 8-bit binary number converted to decimal format will be between 0 and 255. The total of 32 bits means that approximately 4.2 billion possible IP version 4 addresses exist.

The IP address of a computer tells you a lot about that computer. The first byte (or the first decimal number) in an address tells you to what class of network that machine belongs. Table 1-1 summarizes the five network classes.

TABLE 1-1 Network Classes

Class	IP Range for the First Byte	Use
A	0–126	Extremely large networks. No Class A network IP addresses are left. All have been used.
B	128–191	Large corporate and government networks. All Class B IP addresses have been used.
C	192–223	The most common group of IP addresses. Your ISP probably has a Class C address.
D	224–247	These are reserved for multicasting (transmitting different data on the same channel).
E	248–255	Reserved for experimental use.

These five classes of networks will become more important later in this book (or should you decide to study networking on a deeper level). Observe Table 1-1 carefully, and you probably will discover that the IP range of 127 was not listed. This omission is because that range is reserved for testing. The IP address of 127.0.0.1 designates the machine you are on, regardless of that machine’s assigned IP address. This address is often referred to as the loopback address. That address will be used often in testing your machine and your NIC. We will examine its use a bit later in this chapter in the section on network utilities.

These particular classes are important as they tell you what part of the address represents the network and what part represents the node. For example, in a Class A address, the first octet represents the network, and the remaining three represent the node. In a Class B address, the first two octets represent the network, and the second two represent the node. And finally, in a Class C address, the first three octets represent the network, and the last represents the node.

There are also some very specific IP addresses and IP address ranges you should be aware of. The first, as previously mentioned, is 127.0.0.1, or the loopback address. It is another way of referring to the network interface card of the machine you are on.

Private IP addresses are another issue to be aware of. Certain ranges of IP addresses have been designated for use within networks. These cannot be used as public IP addresses but can be used for internal workstations and servers. Those IP addresses are

10.0.0.10 to 10.255.255.255

172.16.0.0 to 172.31.255.255

192.168.0.0 to 192.168.255.255

Sometimes people new to networking have some trouble understanding public and private IP addresses. A good analogy is an office building. Within a single office building, each office number must be unique. You can only have one 305. And within that building, if you discuss office 305 it is immediately clear what you are talking about. But there are other office buildings, many of which have their own office 305. You can think of private IP addresses as office numbers. They must be unique within their network, but there may be other networks with the same private IP.

Public IP addresses are more like traditional mailing addresses. Those must be unique worldwide. When communicating from office to office you can use the office number, but to get a letter to another building you have to use the complete mailing address. It is much the same with networking. You can communicate within your network using private IP addresses, but to communicate with any computer outside your network, you have to use public IP addresses.

One of the roles of a gateway router is to perform what is called network address translation (NAT). Using NAT, a router takes the private IP address on outgoing packets and replaces it with the public IP address of the gateway router so that the packet can be routed through the Internet.

We have already discussed IP version 4 network addresses; now let’s turn our attention to subnetting. If you are already familiar with this topic, feel free to skip this section. For some reason this topic tends to give networking students a great deal of trouble. So we will begin with a conceptual understanding. Subnetting is simply chopping up a network into smaller portions. For example, if you have a network using the IP address 192.168.1.X (X being whatever the address is for the specific computer), then you have allocated 255 possible IP addresses. What if you want to divide that into two separate subnetworks? Subnetting is how you do that.

More technically, the subnet mask is a 32-bit number that is assigned to each host to divide the 32-bit binary IP address into network and node portions. You also cannot just put in any number you want. The first value of a subnet mask must be 255; the remaining three values can be 255, 254, 252, 248, 240, 224, or 128. Your computer will take your network IP address and the subnet mask and use a binary AND operation to combine them.

It may surprise you to know that you already have a subnet mask even if you have not been subnetting. If you have a Class C IP address, then your network subnet mask is 255.255.255.0. If you have a Class B IP address, then your subnet mask is 255.255.0.0. And finally, if it is Class A, your subnet mask is 255.0.0.0.

Now think about these numbers in relationship to binary numbers. The decimal value 255 converts to 11111111 in binary. So you are literally “masking” the portion of the network address that is used to define the network, and the remaining portion is used to define individual nodes. Now if you want fewer than 255 nodes in your subnet, then you need something like 255.255.255.240 for your subnet. If you convert 240 to binary, it is 11110000. That means the first three octets and the first 4 bits of the last octet define the network. The last 4 bits of the last octet define the node. That means you could have as many as 1111 (in binary) or 15 (in decimal) nodes on this subnetwork. This is the basic essence of subnetting.

Subnetting only allows you to use certain, limited subnets. Another approach is CIDR, or classless interdomain routing. Rather than define a subnet mask, you have the IP address followed by a slash and a number. That number can be any number between 0 and 32, which results in IP addresses like these:

192.168.1.10/24 (basically a Class C IP address)

192.168.1.10/31 (much like a Class C IP address with a subnet mask)

When you use this, rather than having classes with subnets, you have variable-length subnet masking (VLSM) that provides classless IP addresses. This is the most common way to define network IP addresses today.

You should not be concerned that new IP addresses are likely to run out soon. The IP version 6 standard is already available, and methods are in place already to extend the use of IPv4 addresses. The IP addresses come in two groups: public and private. The public IP addresses are for computers connected to the Internet. No two public IP addresses can be the same. However, a private IP address, such as one on a private company network, has to be unique only in that network. It does not matter if other computers in the world have the same IP address, because this computer is never connected to those other worldwide computers. Network administrators often use private IP addresses that begin with a 10, such as 10.102.230.17. The other private IP addresses are 172.16.0.0–172.31.255.255 and 192.168.0.0–192.168.255.255.

Also note that an ISP often will buy a pool of public IP addresses and assign them to you when you log on. So, an ISP might own 1,000 public IP addresses and have 10,000 customers. Because all 10,000 customers will not be online at the same time, the ISP simply assigns an IP address to a customer when he or she logs on, and the ISP un-assigns the IP address when the customer logs off.

IPv6 utilizes a 128-bit address (instead of 32) and utilizes a hex numbering method in order to avoid long addresses such as 132.64.34.26.64.156.143.57.1.3.7.44.122.111.201.5. The hex address format appears in the form of 3FFE:B00:800:2::C, for example. This gives you 2¹²⁸ possible addresses (many trillions of addresses), so no chance exists of running out of IP addresses in the foreseeable future.

There is no subnetting in IPv6. Instead, it only uses CIDR. The network portion is indicated by a slash followed by the number of bits in the address that are assigned to the network portion, such as

/48

/64

There is a loopback address for IPv6, and it can be written as ::/128. Other differences between IPv4 and IPv6 are described here:

Link/machine-local.

IPv6 version of IPv4’s APIPA or Automatic Private IP Addressing. So if the machine is configured for dynamically assigned addresses and cannot communicate with a DHCP server, it assigns itself a generic IP address. DHCP, or Dynamic Host Configuration Protocol, is used to dynamically assign IP addresses within a network.

IPv6 link/machine-local IP addresses all start with fe80::. So if your computer has this address, that means it could not get to a DHCP server and therefore made up its own generic IP address.

Site/network-local.

IPv6 version of IPv4 private address. In other words, these are real IP addresses, but they only work on this local network. They are not routable on the Internet.

All site/network-local IP addresses begin with FE and have C to F for the third hexadecimal digit: FEC, FED, FEE, or FEF.

DHCPv6 uses the Managed Address Configuration Flag (M flag).

When set to 1, the device should use DHCPv6 to obtain a stateful IPv6 address.

Other stateful configuration flag (O flag).

When set to 1, the device should use DHCPv6 to obtain other TCP/IP configuration settings. In other words, it should use the DHCP server to set things like the IP address of the gateway and DNS servers.

E-mail works the same way as visiting websites. Your e-mail client will seek out the address of your e-mail server. Then your e-mail client will use either POP3 to retrieve your incoming e-mail, or SMTP to send your outgoing e-mail. Your e-mail server (probably at your ISP or your company) will then try to resolve the address you are sending to. If you send something to [email protected], your e-mail server will translate that e-mail address into an IP address for the e-mail server at yahoo.com, and then your server will send your e-mail there. Note that newer e-mail protocols are out there; however, POP3 is still the most commonly used.

IMAP is now widely used as well. Internet Message Access Protocol operates on port 143. The main advantage of IMAP over POP3 is it allows the client to download only the headers to the machine, and then the user can choose which messages to fully download. This is particularly useful for smart phones.

TABLE 1-2 Logical Ports and Protocols

Protocol	Purpose	Port
FTP (File Transfer Protocol)	For transferring files between computers.	20 & 21
SSH	Secure Shell. A secure/encrypted way to transfer files.	22
Telnet	Used to remotely log on to a system. You can then use a command prompt or shell to execute commands on that system. Popular with network administrators.	23
SMTP (Simple Mail Transfer Protocol)	Sends e-mail.	25
WhoIS	A command that queries a target IP address for information.	43
DNS (Domain Name Service)	Translates URLs into web addresses.	53
tFTP (Trivial File Transfer Protocol)	A quicker, but less reliable form of FTP.	69
HTTP (Hypertext Transfer Protocol)	Displays web pages.	80
POP3 (Post Office Protocol Version 3)	Retrieves e-mail.	110
NNTP (Network News Transfer Protocol)	Used for network news groups (Usenet newsgroups). You can access these groups over the web via www.google.com.	119
NetBIOS	An older Microsoft protocol for naming systems on a local network.	137, 138, 139
IRC (Internet Relay Chat)	Chat rooms.	194
HTTPS (Hypertext Transfer Protocol Secure)	HTTP encrypted with SSL or TLS.	443
SMB (Server Message Block)	Used by Microsoft Active Directory.	445
ICMP (Internet Control Message Protocol)	These are simply packets that contain error messages, informational messages, and control messages.	No specific port

You should note that this list is not complete. Hundreds of other protocols exist, but for now discussing these will suffice. All of these protocols are part of a suite of protocols referred to as TCP/IP (Transmission Control Protocol/Internet Protocol). The most important thing for you to realize is that the communication on networks takes place via packets, and those packets are transmitted according to certain protocols, depending on the type of communication that is occurring. You might be wondering what a port is. Don’t confuse this type of port with the connections on the back of your computer, such as a serial port or parallel port. A port in networking terms is a handle, a connection point. It is a numeric designation for a particular pathway of communications. All network communication, regardless of the port used, comes into your computer via the connection on your NIC. You might think of a port as a channel on your TV. You probably have one cable coming into your TV but you can view many channels. You have one cable coming into your computer, but you can communicate on many different ports.

So the picture we’ve drawn so far of networks is one of machines connected to each other via cables, and perhaps to hubs/switches/routers. Networks transmit binary information in packets using certain protocols and ports. This is an accurate picture of network communications, albeit a simple one.

This command gives you some information about your connection to a network (or to the Internet). Most importantly you find out your own IP address. The command also has the IP address for your default gateway, which is your connection to the outside world. Running the ipconfig command is a first step in determining your system’s network configuration. Most commands this text mentions, including ipconfig, have a number of parameters, or flags, that can be passed to the commands to make the computer behave in a certain way. You can find out what these commands are by typing in the command, followed by a space, and then typing in hyphen question mark: -?.

As you can see, you might use a number of options to find out different details about your computer’s configuration. The most commonly used method would probably be ipconfig/all, shown in Figure 1-2.

You can see that this option gives you much more information. For example, ipconfig/all gives the name of your computer, when your computer obtained its IP address, and more.

This figure tells you that a 32-byte echo packet was sent to the destination and returned. The ttl means “time to live.” That time unit is how many intermediary steps, or hops, the packet should take to the destination before giving up. Remember that the Internet is a vast conglomerate of interconnected networks. Your packet probably won’t go straight to its destination. It will have to take several hops to get there. As with ipconfig, you can type in ping -? to find out various ways you can refine your ping.

With tracert, you can see (in milliseconds) the time the IP addresses of each intermediate step listed, and how long it took to get to that step. Knowing the steps required to reach a destination can be very important. If you use Linux, it is traceroute rather than tracert.

Certainly, other utilities can be of use to you when working with network communications. However, the four we just examined are the core utilities. These four (ipconfig, ping, tracert, and netstat) are absolutely essential to any network administrator, and you can commit them to memory.

TABLE 1-3 The OSI Model

Layer	Description	Protocols
Application	This layer interfaces directly to applications and performs common application services for the application processes.	POP, SMTP, DNS, FTP, Telnet
Presentation	The presentation layer relieves the application layer of concern regarding syntactical differences in data representation within the end-user systems.	Telnet, Network Data Representation (NDR), Lightweight Presentation Protocol (LPP)
Session	The session layer provides the mechanism for managing the dialogue between end-user application processes.	NetBIOS
Transport	This layer provides end-to-end communication control.	TCP, UDP
Network	This layer routes the information in the network.	IP, ARP, ICMP
Data link	This layer describes the logical organization of data bits transmitted on a particular medium. The data link layer is divided into two sublayers: the Media Access Control layer (MAC) and the Logical Link Control layer (LLC).	SLIP, PPP
Physical	This layer describes the physical properties of the various communications media, as well as the electrical properties and interpretation of the exchanged signals. In other words, the physical layer is the actual NIC, Ethernet cable, and so forth.	IEEE 1394, DSL, ISDN

Many networking students memorize this model. At least memorizing the names of the seven layers and understanding basically what they each do is good. From a security perspective, the more you understand about network communications, the more sophisticated your defense can be. The most important thing for you to understand is that this model describes a hierarchy of communication. One layer communicates only with the layer directly above it or below it.

The data itself: After data leaves your network, the packets are vulnerable for interception and even alteration. Later in this book, during the discussion of encryption and virtual private networks, you will learn how to secure this data. Data can also be attacked at rest, when stored on a computer.

The network connection points: Whether it is the routers or the firewall, any place where one computer connects to another is a place that can be attacked, and one that must be defended. When looking at a system’s security, you should first look at the connectivity points.

The people: People always pose a security risk. Either through ignorance, malicious intent, or simple error, people on a system can compromise the system’s security.

As you proceed through this book, don’t lose sight of the basic purpose, which is to secure networks and the data they store and transmit.

In this regard, there seem to be two extreme attitudes toward computer security. The first viewpoint holds that little real danger or threat exists to computer systems and that much of the negative news is simply a reflection of unwarranted panic. People of this attitude often think that taking only minimal security precautions should ensure the safety of their systems. Unfortunately, some people in decision-making positions hold this point of view. The prevailing sentiment of these individuals is, “If our computer/organization has not been attacked so far, we must be secure.”

This viewpoint often leads to a reactive approach to computer security, meaning that people will wait until after an incident to decide to address security issues. Waiting to address security until an attack occurs might be too late. In the best of circumstances, the incident might have only a minor impact on the organization and serve as a much-needed wake-up call. In less fortunate cases, an organization might face serious, possibly catastrophic consequences. For example, some organizations did not have an effective network security system in place when the WannaCry virus attacked their systems. In fact, WannaCry would have been completely avoided, if systems had been patched. Avoiding this laissez faire approach to security is imperative.

Any organization that embraces this extreme—and erroneous—philosophy is likely to invest little time or resources in computer security. They might have a basic firewall and antivirus software, but most likely expend little effort ensuring that they are properly configured or routinely updated.

The second viewpoint is that every teenager with a laptop is a highly skilled hacker who can traverse your systems at will and bring your network to its knees. Think of hacking skill like military experience. Finding someone who was in the military is not too hard, but encountering a person who was in Delta Force or Seal Team 6 is rare. Although military experience is fairly common, high levels of special operations skills are not. The same is true with hacking skills. Finding individuals who know a few hacking tricks is easy. Finding truly skilled hackers is far less common.

At the other end of the spectrum, some executives overestimate security threats. They assume that very talented hackers exist in great numbers and that all of them are an imminent threat to their system. They might believe that virtually any teenager with a laptop can traverse highly secure systems at will. This viewpoint has, unfortunately, been fostered by a number of movies that depict computer hacking in a somewhat glamorous light. Such a worldview makes excellent movie plots, but is simply unrealistic. The reality is that many people who call themselves hackers are less knowledgeable than they think. Systems protected by even moderate security precautions have a low probability of being compromised by a hacker of this skill level.

This does not mean that skillful hackers do not exist. They most certainly do. However, people with the skill to compromise relatively secure systems must use rather time-consuming and tedious techniques to breach system security. These hackers must also weigh the costs and benefits of any hacking mission. Skilled hackers tend to target systems that have a high benefit, either financially or ideologically. If a system is not perceived as having sufficient benefit, a skilled hacker is less likely to expend the resources to compromise it. Burglars are one good analogy: Certainly, highly skilled burglars exist; however, they typically seek high-value targets. The thief who targets small businesses and homes usually has limited skills. The same is true of hackers.

Both extreme attitudes regarding the dangers to computer systems are inaccurate. It is certainly true that people exist who have both the comprehension of computer systems and the skills to compromise the security of many, if not most, systems. However, it is also true that many who call themselves hackers are not as skilled as they claim. They have ascertained a few buzzwords from the Internet and are convinced of their own digital supremacy, but they are not able to effect any real compromises to even a moderately secure system.

You might think that erring on the side of caution, or extreme diligence, would be the appropriate approach. In reality, you do not need to take either extreme view. You should take a realistic view of security and formulate practical strategies for defense. Every organization and IT department has finite resources: You only have so much time and money. If you squander part of those resources guarding against unrealistic threats, then you might not have adequate resources left for more practical projects. Therefore, a realistic approach to network security is the only practical approach.

You might be wondering why some people overestimate dangers to their networks. The answer, in part at least, lies with the nature of the hacking community and with the media. Media outlets have a tendency to sensationalize. You don’t get good ratings by downplaying danger; you get them by emphasizing, and perhaps outright exaggerating. Also, the Internet is replete with people claiming significant skill as hackers. As with any field of human endeavor, the majority is merely average. The truly talented hacker is no more common than the truly talented concert pianist. Consider how many people take piano lessons at some point in their lives, and then consider how many of those ever truly become virtuosos.

The same is true of computer hackers. Keep in mind that even those who do possess the requisite skill also need the motivation to expend the time and effort necessary to compromise your system. Keep this fact in mind when considering any claims of cyber prowess you might encounter.

The claim that many people who describe themselves as hackers lack real skill is not based on any study or survey. A reliable study on this topic would be impossible because hackers are unlikely to identify themselves and submit to skills tests. I came to this conclusion based on two considerations:

The first is simply years of experience traversing hacker discussion groups, chat rooms, and bulletin boards. In more than two decades of work in this field, I have encountered talented and highly skilled hackers, yet I encounter far more who claim to be hackers but clearly demonstrate a lack of sufficient skill. I have also been a frequent speaker at hacking conferences, including DEF CON, and have published in hacking magazines such as 2600. I have had the opportunity to interact extensively with the hacking community.

The second is that it is a fact of human nature that the vast majority of people in any field are, by definition, mediocre. Consider the millions of people who work out at a gym on a regular basis, and consider how few ever become competitive body builders. In any field, most participants will be mediocre. That is not meant as a derogatory statement, it is just a fact of life.

This statement is also not meant to minimize the dangers of hacking. That is not my intent at all. Even an unskilled novice attempting to intrude on a system will get in, in the absence of appropriate security precautions. Even if the would-be hacker does not successfully breach security, he can still be quite a nuisance. Additionally, some forms of attack don’t require much skill at all. We discuss these later in this book.

A more balanced view (and therefore, a better way to assess the threat level to any system) is to weigh the attractiveness of a system to potential intruders against the security measures in place. As you shall see, the greatest threat to any system is not actually hackers. Viruses and other attacks are far more prevalent. Threat assessment is a complex task with multiple facets.

Intrusion

Blocking

Malware

Figure 1-6 shows the three categories. The intrusion category includes attacks meant to breach security and gain unauthorized access to a system. This group of attacks includes any attempt to gain unauthorized access to a system. This is generally what hackers do. The second category of attack, blocking, includes attacks designed to prevent legitimate access to a system. Blocking attacks are often called denial of service attacks (or simply DoS). In these types of attacks the purpose is not to actually get into your system but simply to block legitimate users from gaining access.

The third category of threats is the installation of malware on a system. Malware is a generic term for software that has a malicious purpose. It includes virus attacks, Trojan horses, and spyware. Because this category of attack is perhaps the most prevalent danger to systems, we examine it first.

The most obvious example of malware is the computer virus. You probably have a general idea of what a virus is. If you consult different textbooks you will probably see the definition of a virus worded slightly differently. One definition for a virus is “a program that can ‘infect’ other programs by modifying them to include a possibly evolved copy of itself.” That is a very good definition, and one you will see throughout this book. A computer virus is analogous to a biological virus in that both replicate and spread. The most common method for spreading a virus is using the victim’s e-mail account to spread the virus to everyone in his address book. Some viruses do not actually harm the system itself, but all of them cause network slowdowns or shutdowns due to the heavy network traffic caused by the virus replication.

Another type of malware, often closely related to the virus, is the Trojan horse. The term is borrowed from the ancient tale. In this tale, the city of Troy was besieged for a long period of time, but the attackers could not gain entrance. They constructed a huge wooden horse and left it one night in front of the gates to Troy one night. The next morning, the residents of Troy saw the horse and assumed it to be a gift, consequently rolling the wooden horse into the city. Unbeknownst to them, several soldiers were hidden inside the horse. That evening, the soldiers left the horse, opened the city gates, and let their fellow attackers into the city. An electronic Trojan horse works in the same manner, appearing to be benign software but secretly downloading a virus or some other type of malware onto your computer from within. In short, you have an enticing gift that you install on your computer, and later find it has unleashed something quite different from what you expected. It is a fact that Trojan horses are more likely to be found in illicit software. There are many places on the Internet to get pirated copies of commercial software. Finding that such software is actually part of a Trojan horse is not at all uncommon.

Trojan horses and viruses are the two most widely encountered forms of malware. A third category of malware is spyware, which is increasing in frequency at a dramatic pace. Spyware is software that literally spies on what you do on your computer. This can be as simple as a cookie—a text file that your browser creates and stores on your hard drive. Cookies are downloaded onto your machine by websites you visit. This text file is then used to recognize you when you return to the same site. That file can enable you to access pages more quickly and save you from having to enter your information multiple times on pages you visit frequently. However, in order to do this, that file must be read by the website; this means it can also be read by other websites. Any data that the file saves can be retrieved by any website, so your entire Internet browsing history can be tracked.

Another form of spyware, called a key logger, records all of your keystrokes. Some also take periodic screen shots of your computer. Data is then either stored for retrieval later by the party who installed the key logger or is sent immediately back via e-mail. In either case, every single thing you do on your computer is recorded for the interested party.

Using security flaws is not the only method for intruding into a system. In fact, some methods can be technologically much easier to execute. For example, one completely not technologically based method for breaching a system’s security is called social engineering, which, as the name implies, relies more on human nature than technology. This was the type of attack that the famous hacker Kevin Mitnick most often used. Social engineering uses standard con artist techniques to get users to offer up the information needed to gain access to a target system. The way this method works is rather simple. The perpetrator obtains preliminary information about a target organization, such as the name of its system administrator, and leverages it to gain additional information from the system’s users. For example, he might call someone in accounting and claim to be one of the company’s technical support personnel. The intruder could use the system administrator’s name to validate that claim. He could then ask various questions to learn additional details about the system’s specifications. A savvy intruder might even get a person to provide a username and password. As you can see, this method is based on how well the intruder can manipulate people and actually has little to do with computer skills.

Social engineering and exploiting software flaws are not the only means of executing an intrusion attack. The growing popularity of wireless networks gives rise to new kinds of attacks. The most obvious and dangerous activity is war-driving. This type of attack is an offshoot of war-dialing. With war-dialing, a hacker sets up a computer to call phone numbers in sequence until another computer answers to try and gain entry to its system. War-driving, using much the same concept, is applied to locating vulnerable wireless networks. In this scenario, a hacker simply drives around trying to locate wireless networks. Many people forget that their wireless network signal often extends as much as 100 feet (thus, past walls). At DEF CON 2003, the annual hackers’ convention, contestants participated in a war-driving contest in which they drove around the city trying to locate as many vulnerable wireless networks as they could.

The most likely threat to any computer or network is the computer virus. For example, in just the month of October 2017, McAfee listed 31 active viruses (https://home.mcafee.com/virusinfo/virus-calendar). Each month, several new virus outbreaks are typically documented. New viruses are constantly being created, and old ones are still out there.

Note that many people do not update their antivirus software as often as they should. The evidence for this fact is that many of the viruses spreading around the Internet already have countermeasures released, but people are simply not applying them. Therefore, even when a virus is known and protection against it exists, it can continue to thrive because many people do not update their protection or clean their systems regularly. If all computer systems and networks had regularly updated security patches and employed virus-scanning software, a great many virus outbreaks would be avoided altogether, or their effects would at least be minimized.

Blocking has become the most common form of attack besides viruses. As you will learn later in this book, blocking attacks are easier to perpetrate than intrusions and therefore occur more often. A resourceful hacker can find tools on the Internet to help her launch a blocking attack. You will learn more about blocking attacks, as well as malware, in Chapter 2.

Regardless of the nature of the computer crime, the fact is that cyber crimes are prevalent. A 2016 survey of computer crime found that 32% of organizations have been affected by cyber crime, with some experiencing losses in excess of $5 million. Only 37% of respondents have a fully operational incident response plan.

The second risk factor is the nature of the information on the system. If the system has sensitive or critical information, then its security requirements are higher. Personal data such as Social Security numbers, credit card numbers, and medical records have a high security requirement. Systems with sensitive research data or classified information have even higher security needs.

A final consideration is traffic to the system. The more people who have some sort of remote access to the system, the more security dangers exist. For example, a number of people access e-commerce systems from outside the network. Each of these connections represents a danger. If, on the other hand, a system is self-contained with no external connections, its security vulnerabilities are reduced.

Considering the attractiveness of the system to hackers, the nature of the information the system stores, and the number of remote connections to your system together allows administrators to provide a complete assessment of security needs.

The following numerical scale can provide a basic overview of a system’s security requirements.

Three factors are considered (attractiveness, information content, and security devices present). Each of those factors is given a numeric designation between 1 and 10. The first two are added together, and then the third number is subtracted. The final score ranges from –8 (very low risk, high security) to 19 (very high risk, low security); the lower the number the less vulnerable the system, the higher the number the greater the risk. The best rating is for a system that

Receives a 1 in attractiveness to hackers (that is, a system that is virtually unknown, has no political or ideological significance, etc.).

Receives a 1 in informational content (that is, a system that contains no confidential or sensitive data).

Receives a 10 in security (that is, a system with an extensive layered, proactive security system complete with firewalls, ports blocked, antivirus software, IDS, antispyware, appropriate policies, all workstations and servers hardened, etc.).

Evaluating attractiveness is certainly quite subjective. However, evaluating the value of informational content or the level of security can be done with rather crude but simple metrics. This system will be reiterated and then further expanded in Chapter 12, “Assessing System Security.”

Obviously, this evaluation system is not an exact science and is contingent to some extent on a personal assessment of a system. This method does, however, provide a starting point for assessing a system’s security but is certainly not the final word in security metrics.

For example, someone well-versed in the Linux operating system who works to understand that system by learning its weaknesses and flaws would be a hacker. However, this does often mean seeing whether a flaw can be exploited to gain access to a system. This “exploiting” part of the process is where hackers differentiate themselves into three groups:

White hat hackers, upon finding vulnerability in a system, will report the vulnerability to the vendor of that system. For example, if they were to discover some flaw in Red Hat Linux, they would then e-mail the Red Hat company (probably anonymously) and explain what the flaw is and how it was exploited.

Black hat hackers are the people normally depicted in the media (e.g., movies and news). After they gain access to a system, their goal is to cause some type of harm. They might steal data, erase files, or deface websites. Black hat hackers are sometimes referred to as crackers.

Gray hat hackers are typically law-abiding citizens, but in some cases will venture into illegal activities. They might do so for a wide variety of reasons. Commonly, gray hat hackers conduct illegal activities for reasons they feel are ethical, such as hacking into a system belonging to a corporation that the hacker feels is engaged in unethical activities. Note that this term is not found in many textbooks, but is a commonly used term in the hacking community itself.

Regardless of how hackers view themselves, intruding on any system without permission is illegal. This means that, technically speaking, all hackers, regardless of the color of the metaphorical hat they wear, are in violation of the law. However, many people feel that white hat hackers actually perform a service by finding flaws and informing vendors before those flaws are exploited by less ethically inclined individuals.

The various shades of hackers are only the beginning of learning hacker terminology. Recall that a hacker is an expert in a given system. If so, what is the term for someone who calls herself a hacker but lacks expertise? The most common term for an inexperienced hacker is script kiddy. The name derives from the fact that the Internet is full of utilities and scripts that one can download to perform some hacking tasks. Someone who downloads these tools without really understanding the target system would be considered a script kiddy. A significant number of the people who call themselves hackers are, in reality, merely script kiddies.

This discussion brings us to some specific types of hackers. A cracker is someone whose goal is to compromise a system’s security for purposes other than to learn about the system. No difference exists between a black hat hacker and a cracker. Both terms refer to a person who breaks through a system’s security and intrudes on that system without permission from the appropriate parties, with some malicious intent.

When and why would someone give permission to another party to hack/crack a system? The most common reason is to assess the system’s vulnerabilities. This is yet another specialized type of hacker—the ethical hacker or sneaker (an older term, not often used these days), a person who legally hacks/cracks a system in order to assess security deficiencies. In 1992, Robert Redford, Dan Aykroyd, and Sydney Poitier starred in a movie about this very subject, named Sneakers. Consultants exist who perform work of this type, and you can even find firms that specialize in this activity as more and more companies solicit these services to assess their vulnerabilities. Today, these are usually called penetration testers (or simply pen testers). And the profession has matured since the first edition of this book.

A word of caution for readers either considering becoming or hiring a pen tester: Any person hired to assess the vulnerabilities of a system must be both technically proficient and morally sound. This means that a criminal background check should be done before engaging his/her services. You certainly would not hire a convicted burglar as your night watchman. Neither should you consider hiring someone with any criminal background, especially in computer crimes, as a penetration tester/ethical hacker. Some people might argue that a convicted hacker/cracker has the best qualifications to assess your system’s vulnerabilities. This is simply not the case, for several reasons:

You can find legitimate security professionals who know and understand hacker skills but have never committed any crime. You can get the skills required to assess your system without using a consultant with a demonstrated lack of integrity.

If you take the argument that hiring convicted hackers means hiring talented people to its logical conclusion, you could surmise that the person in question is not as good a hacker as he would like to think, because he was caught.

Most importantly, giving a person with a criminal background access to your systems is comparable to hiring a person with multiple DWI convictions as your driver. In both cases you are inviting problems and, perhaps, assuming significant civil and criminal liabilities.

A thorough review of a penetration tester’s qualifications is also recommended. Just as some people falsely claim to be highly skilled hackers, there are those who will falsely claim to be skilled pen testers. An unqualified pen tester might pronounce your system sound when in fact it was a lack of skill that prevented him from successfully breaching your security. Chapter 12 covers the basics of assessing a target system as well as the necessary qualifications of any consultant hired for this purpose.

Another specialized branch of hacking involves breaking into telephone systems. This sub-specialty of hacking is referred to as phreaking. The New Hackers Dictionary actually defines phreaking as “The action of using mischievous and mostly illegal ways in order to not pay for some sort of telecommunications bill, order, transfer, or other service” (Raymond, 2003). Phreaking requires a rather significant knowledge of telecommunications, and many phreakers have some professional experience working for a phone company or other telecommunications business. This type of activity is often dependent upon specific technology required to compromise phone systems more than simply knowing certain techniques. For example, certain devices are used to compromise phone systems. Phone systems are often dependent on frequencies. (If you have a touchtone phone, you will notice that, as you press the keys, each has a different frequency.) Machines that record and duplicate certain frequencies are often essential to phone phreaking.

The first and most basic security device is the firewall. A firewall is a barrier between a network and the outside world. Sometimes a firewall is a stand-alone server, sometimes a router, and sometimes software running on a machine. Whatever its physical form, the purpose is the same: to filter traffic entering and exiting a network. Firewalls are related to, and often used in conjunction with, a proxy server. A proxy server hides your internal network IP addresses and presents a single IP address (its own) to the outside world.

Firewalls and proxy servers are added to networks to provide basic perimeter security. They filter incoming and outgoing network traffic but do not affect traffic on the network. Sometimes these devices are augmented by an intrusion-detection system (IDS). An IDS monitors traffic looking for suspicious activity that might indicate an attempted intrusion.

Access control is another important computer security term that will be of particular interest to you in several of the later chapters. Access control is the aggregate of all measures taken to limit access to resources. This includes logon procedures, encryption, and any method that is designed to prevent unauthorized personnel from accessing a resource. Authentication is clearly a subset of access controls, perhaps the most basic security activity. Authentication is simply the process of determining whether the credentials given by a user or another system, such as a username and password, are authorized to access the network resource in question. When a user logs in with a username and password, the system attempts to authenticate that username and password. If they are authenticated, the user will be granted access.

Non-repudiation is another term you encounter frequently in computer security. It is any technique that is used to ensure that someone performing an action on a computer cannot falsely deny that they performed that action. Non-repudiation provides reliable records of what user took a particular action at a specific time. In short, it is methods to track what actions are taken by what user. Various system logs provide one method for non-repudiation. One of the most important security activities is auditing. Auditing is the process of reviewing logs, records, and procedures to determine whether they meet standards. This activity is discussed throughout this book and is the focus of Chapter 12. Auditing is essential to do because checking that systems have appropriate security in place is the only way to ensure system security.

Least privileges is a concept you should keep in mind when assigning privileges to any user or device. The concept is that you only assign the minimum privileges required for that person to do his job, no more. Keep this simple but critical concept in mind.

You should also keep in mind the CIA triangle, or Confidentiality, Integrity, and Availability. All security measures should affect one or more of these areas. For example, hard drive encryption and good passwords help protect confidentiality. Digital signatures help ensure integrity, and a good backup system, or network server redundancy, can support availability.

An entire book could be written on computer security terminology. These few terms you have been introduced to here are ubiquitous and being familiar with them is important. Some of the exercises at the end of this chapter will help you expand your knowledge of computer security terminology. You might also find these links helpful:

https://niccs.us-cert.gov/glossary (National Initiative for Cybersecurity Careers and Studies Glossary)

https://www.sans.org/security-resources/glossary-of-terms/ (SANS Institute Glossary of Security Terms)

http://nvlpubs.nist.gov/nistpubs/ir/2013/NIST.IR.7298r2.pdf (NIST Glossary of Key Information Security Terms)

This perimeter approach is clearly flawed. So why do some companies use it? A small organization might use the perimeter approach if they have budget constraints or inexperienced network administrators. This method might be adequate for small organizations that do not store sensitive data, but it rarely works in a larger corporate setting.

You should also measure your security approach by how proactive and/or reactive it is. You do this by gauging how much of the system’s security infrastructure and policies are dedicated to preventive measures as opposed to how much are devoted to simply responding to an attack after it has occurred.

A passive security approach takes few or no steps to prevent an attack. Conversely a dynamic security approach, or proactive defense, is one in which steps are taken to prevent attacks before they occur. One example of a proactive defense is the use of an IDS, which works to detect attempts to circumvent security measures. These systems can tell a system administrator that an attempt to breach security has been made, even if that attempt is not successful. An IDS can also be used to detect various techniques intruders use to assess a target system, thus alerting a network administrator to the potential for an attempted breach before the attempt is even initiated.

One of the oldest pieces of legislation in the United States affecting computer security is the Computer Security Act of 1987 (100th Congress, 1987). This act requires government agencies to identify sensitive systems, conduct computer security training, and develop computer security plans. This law is a vague mandate ordering federal agencies in the United States to establish security measures without specifying any standards.

This legislation established a legal mandate to enact specific standards, paving the way for future guidelines and regulations. It also helped define certain terms, such as what information is indeed “sensitive,” according to the following quote found in the legislation itself:

Keep this definition in mind, for it is not just Social Security information or medical history that must be secured. When considering what information needs to be secure, simply ask the question: Would the unauthorized access or modification of this information adversely affect my organization? If the answer is “yes,” then you must consider that information “sensitive” and in need of security precautions.

Another more specific federal law that applies to mandated security for government systems is OMB Circular A-130 (specifically, Appendix III). This document requires that federal agencies establish security programs containing specified elements. This document describes requirements for developing standards for computer systems and for records held by government agencies.

Most states have specific laws regarding computer security, such as legislation like the Computer Crimes Act of Florida, the Computer Crime Act of Alabama, and the Computer Crimes Act of Oklahoma. Any person responsible for network security might potentially be involved in a criminal investigation. This could be an investigation into a hacking incident or employee misuse of computer resources. Whatever the nature of the crime instigating the investigation, being aware of the computer crime laws in your state is invaluable. A list of computer crime laws by state is available at http://www.irongeek.com/i.php?page=computerlaws/state-hacking-laws. This government list is from the Advanced Laboratory Workstation (ALW), National Institutes for Health (NIH), and Center for Information Technology.

Keep in mind that any law that governs privacy (such as the Health Insurance Portability and Accountability Act [HIPAA], for medical records) also has a direct impact on computer security. If a system is compromised and data that is covered under any privacy statute is compromised, you might need to prove that you exercised due diligence to protect that data. A finding that you did not take proper precautions can result in civil liability.

A law that is probably even more pertinent to business network security is Sarbanes-Oxley, often called SOX (http://www.soxlaw.com/) This law governs how publicly traded companies store and report on financial data, and keeping that data secure is a vital part of this. Obviously, full coverage of this law is beyond the scope of this chapter, or even this book. It is mentioned to point out to you that in addition to network security being a technical discipline, you must also consider business and legal ramifications.

CERT (www.cert.org/). CERT stands for Computer Emergency Response Team, a group sponsored by Carnegie-Mellon University. CERT was the first computer incident-response team and is still one of the most respected in the industry. Anyone interested in network security should visit the site routinely. On the website is a wealth of documentation, including guidelines for security policies, cutting-edge security research, security alerts, and more.

Microsoft Security TechCenter (https://technet.microsoft.com/en-us/security). This site is particularly useful because so many computers run Microsoft operating systems. This site is a portal to all Microsoft security information, tools, and updates. Users of Microsoft software should visit this website regularly.

F-Secure Corporation (www.f-secure.com/). This site is, among other things, a repository for detailed information on virus outbreaks. Here you will find notifications and detailed information about specific viruses. This information includes how the virus spreads, ways to recognize the virus, and specific tools for cleaning an infected system of a particular virus.

F-Secure Labs (www.f-secure.com/en/web/labs_global/home).

SANS Institute (www.sans.org/). This site provides detailed documentation on virtually every aspect of computer security. The SANS Institute also sponsors a number of security research projects and publishes information about those projects on its website.

This chapter has introduced you to the basic concepts of network security, the general classes of danger, and basic security terminology. Subsequent chapters elaborate on this information.