TCP/IP Protocol Suite 1 Chapter 30 Security Credit: most slides from Forouzan, TCP/IP protocol suit.

TCP/IP Protocol Suite 1

Chapter 30Chapter 30

SecuritySecurity

Credit: most slides from Forouzan, TCP/IP protocol suit

Criminal Expoits and Attacks Phishing: Masquerading as a well-

known site to obtain a user’ personal info.

Denial of Service: Intentionally blocking a site to prevent business activities.

Loss of control: an intruder gains control of a system.

Loss of data: Steal or delete.

Attacks

Software Based Attackes Malware – Malicious software – damaging or

annoying software. Viruses or worms.

Hardware Based Attacks Bios, USB devices, NAS, Cell phones

Attacks on Virtualized Systems

Software based attacks: Viruses Attaches to a legitimate software (carrier, a

program or document) and then replicates through other programs, devices, emails, instant messaging, etc. Computer crashes, destruction of HD, fill up HD,

Reduce security settings allowing others to come in, reformat HD, etc.

File infecting virus attaches to executables (such as cascade virus), resident virus loaded into RAM (such as Randex, Meve, MrKlunky), Boot virus infects MBR (Polyboot.B , AntiEXE), companion virus adds program to OS replacing legitimate OS programs (Stator, Asimove.1539), Macro virus written in any macro scripting (Melissa.A, Bablas.Pc).

Polymorphic virus changes itself to avoid detection

Worms Stand alone programs Takes advantage of the OS/application

vulnerabilities. Worms uses networks to send copies of itself

slowing down networks. While virus requires user action to start an infected

program, worms do not (can start executing itself).

Worms as they travel through internet can leave a payload behind on each system which can delete files or allow remote controlling of the system.

Concealing malware

Trojan horses, rootkits, logic bombs and privilege escalation.

Trojan Horse

Installed with the knowledge of the user. A program advertised as a utility but actually does something else (screen saver, calendar, player, etc.). These programs may do a legitimate activity, but also might capture credit card info, etc and send it.

Rootkits Programs installed on computers that takes

control of certain aspects of the computer by replacing OS utilities. Sony installed a program on their CDs (2005) preventing copying of the CD by operating system routines. Others used this idea and created their own, or added features to Sony’s program. Rootkits do not spread themselves. Very difficult to remove from HD. Boot from another device and see if problems disappear.

Logic Bombs

Lies Dormant until triggered by an event such as a date, person fired, etc. Usually done by employees. Very difficult to discover before triggered. Embedded in large programs.

Privilege Escalation

Either change own privilege to higher level, or use another employees higher privilege. Done by exploiting vulnerabilities of OS.

Malware for profit

Spam, spyware and botnets Spam

Waste of time, checking and deleting. Email lists are sold by many ISPs, and other sites.

Spyware Tracking software installed without the knowledge of

the user. Advertises and Collects and distributes personal information. Harder to detect and remove than viruses. Causes the computer to slow down, freezes up, new browser toolbars or menus installed, hijacked homepage and increased popups.

Adware – a software that delivers advertising for gambling sites or pornography. Keeps track of browsing behavior and reports to give specific pop-ups for merchandize.

Keyloggers. A small hardware attached to the keyboard interface or a resident software that monitors and logs each keystroke.

Botnets

Programs that render your computer to be controlled remotely. The computer is called a zombie. Thousands of zombie computers under the control of a single attacker is called a botnet.

Attackers use internet relay chat (IRC) to remotely control the zombies.

Zombies are used for spamming, spreading malware, denying services, etc.

Hardware based attacks

BIOS BIOS can be flashed with viruses or rootkits.

Flashing the bios can render the computer useless until it is replaced. You can write protect BIOS to prevent this from happening.

USB devices NAS and SANs can get all malware

discussed. Cell phones – infected messages, launch

attacks, make calls, etc.

Attacks on Virtualized systems Operating system virtualization with virtual

machine Storage virtualization Multiple os on the same machine. However,

existing anti virus/spam software do not work. Additional concern – one existing virtual machine

may infect another. Protection approaches:

Hypervisor-runs on the physical machine and manages the virtual machines.

Run security software such as a firewall on the physical machine

Techniques used

Wiretapping Replay – sending packets captured from previous

session such as username and password. Buffer overflow: sending more data than receiver

expects, thereby storing values in memory buffer. Address spoofing. Faking IP source address Name spoofing. Misspelling of a well-known name

or poisoning name server. SYN flood – sending stream of TCP SYN Key breaking – guessing password Port Scanning – to find vulnerability Packet Interception – man in the middle attack.

Security Techniques

Hardening Operating system Encryption Digital Signatures Firewall Intrusion detection systems Packet inspection and content

scanning VPN

Hardening Operating System 3 pronged approach:

operating system updates, Protect against buffer overflows, configuring operating system

protections

Operating System updates

Security Patch: Covers discovered Vulnerabilities

Turn on automatic updates Hotfix – specific to a customer situation Service Pack – Cumulative security patches

and other software updates. Designate one server within your

organization as the patch update service

Buffer Overflow Protection

Corrupts system memory and causes freezing

May change the return address (from a routine) to a different one where the malware is residing.

Programmers should write defensive programming. Show the textbook to the students.◦ For windows based programming use: Data

execution prevention(DEP) and Address Space Layout Randomization (ASLR)

Defensive programming Microsoft environment Data Execution Prevention (DEP)

◦ DEP is available in VISTA and beyond◦ Designated memory only to hold data not

code (No eXecute NX bit associated with the memory). Buffer overflow redirection would not work within a NX memory.

◦ Programmers can turn on this feature. Address Space Randomization (ASLR).

◦ Each time Vista.. Is rebooted .EXE and .DLL are loaded randomly into 256 possible locations. Attackers find it difficult to work with unpredictable code locations.

Configuring Operating System Protection Security Policy

A document that clearly defines the defense mechanisms an organization will employ in order to keep information secure.

Configuration baseline – permissions on files, registry permissions, logins, authentications, etc. You may want to create a Security template to handle it.

Deployment – individually or by group policy

Preventing Attacks that Target Web Preventing Attacks that Target Web browserbrowser

Attacks through cookies, scripts, Java, Attacks through cookies, scripts, Java, ActiveX and cross-site scripting.ActiveX and cross-site scripting.

CookiesCookies

information about visits saved on user’s information about visits saved on user’s computer. First party cookie is created by computer. First party cookie is created by the site that the user is currently viewing. the site that the user is currently viewing. Third-party cookies are cookies created by Third-party cookies are cookies created by some one else is accessed in a current some one else is accessed in a current visit to a different site.visit to a different site.

Cookies do not present a security threat, Cookies do not present a security threat, but is a privacy risk. Track browsing but is a privacy risk. Track browsing habits, etc. Also provides IP address.habits, etc. Also provides IP address.

Scripts (Java, VB, etc.)Scripts (Java, VB, etc.)

Web pages containing scripts download Web pages containing scripts download the scripts to the computer and is the scripts to the computer and is executed. The program can send executed. The program can send information about the user to a host. information about the user to a host. Scripts can’t access files on the computer, Scripts can’t access files on the computer, so limited risk exists.so limited risk exists.

JavaJava

Java can create applets that run on local Java can create applets that run on local computers. Defense against hostile jave computers. Defense against hostile jave applets is a Sandbox (a fence). Unsigned applets is a Sandbox (a fence). Unsigned java applet does not come from a trusted java applet does not come from a trusted source and must be run within the sandbox source and must be run within the sandbox and gives warning to the users. If users do and gives warning to the users. If users do not read the message, or understand the not read the message, or understand the risk, it can cause serious trouble. Sandbox risk, it can cause serious trouble. Sandbox warnings are given at the bottom left. warnings are given at the bottom left. Signed java applets are from trusted sources Signed java applets are from trusted sources and have not been altered.and have not been altered.

ActiveX – Add-onsActiveX – Add-ons

framework for defining reusable software framework for defining reusable software components (known as controls) that perform components (known as controls) that perform a particular function or a set of functions in a particular function or a set of functions in Microsoft Windows in a way that is Microsoft Windows in a way that is independent of the programming language. A independent of the programming language. A software application can then be formed from software application can then be formed from one or more of these components in order to one or more of these components in order to provide its functionality. They do not run in a provide its functionality. They do not run in a sandbox. It can do anything on the computer sandbox. It can do anything on the computer such as creating, modifying and deleting such as creating, modifying and deleting files. A signed ActiveX control is generally files. A signed ActiveX control is generally safe. Unsigned is riskier.safe. Unsigned is riskier.

Cross Site Scripting (XSS)Cross Site Scripting (XSS)

Scripts that extract information from Scripts that extract information from victim and pass it to the attacker.victim and pass it to the attacker.

Changes contents of dynamic websites Changes contents of dynamic websites and injects a script into it that asks for and injects a script into it that asks for personal information through input personal information through input validation.validation.

A web site that displays bad login screens A web site that displays bad login screens with login name is a good one for these with login name is a good one for these types of attacks.types of attacks.

It could send a URL to clickIt could send a URL to click

SMTP Open RelaysSMTP Open Relays

A user can set up a email receiving A user can set up a email receiving address and a sending address. Usually address and a sending address. Usually they are the same like pop.dia.sbc.net and they are the same like pop.dia.sbc.net and smtp.dia.sbc.net. Some smpt servers are smtp.dia.sbc.net. Some smpt servers are configured to sned mail through other configured to sned mail through other domains (known as relays). An attacker domains (known as relays). An attacker can send spam through such relays can send spam through such relays without getting caught.without getting caught.

Instant MessagingInstant Messaging

Once a user signs up with the instan Once a user signs up with the instan message server, the client’s IP and port is message server, the client’s IP and port is sent to all buddies and communication can sent to all buddies and communication can take place directly. With direct connection take place directly. With direct connection virus and worms can be spread. Attacker virus and worms can be spread. Attacker can also view contents of messages.can also view contents of messages.

Peer-to peerPeer-to peer

All types of attacks can take place through All types of attacks can take place through P2P networks. BitTorrent is more secure P2P networks. BitTorrent is more secure than P2P. However, both can be used to than P2P. However, both can be used to download illegal software or music.download illegal software or music.

DefensesDefenses

Antivirus – always a step behind, update Antivirus – always a step behind, update with definition files.with definition files.

Pop-up blockers. Now incorporated into Pop-up blockers. Now incorporated into the browser.the browser.

Anti-spam. Spam filter with smtp server. Anti-spam. Spam filter with smtp server. Install spam filter with pop3Install spam filter with pop3

Personal firewals.Personal firewals. Host Intrusion Detection systems (HIDS) Host Intrusion Detection systems (HIDS)

monitoring files systems and logfiles.monitoring files systems and logfiles.

28.1 CRYPTOGRAPHY

The word cryptography in Greek means “secret writing.” The term today The word cryptography in Greek means “secret writing.” The term today refers to the science and art of transforming messages to make them refers to the science and art of transforming messages to make them secure and immune to attacks.secure and immune to attacks.

The topics discussed in this section include:The topics discussed in this section include:

Symmetric-Key Cryptography Symmetric-Key Cryptography Asymmetric-Key Cryptography Asymmetric-Key Cryptography Comparison Comparison

Figure 28.1 Cryptography components

In cryptography, the encryption/decryption algorithms are

public; the keys are secret.

Note:Note:

In symmetric-key cryptography, the same key is used by the sender (for encryption) and the receiver (for decryption). The key is shared.

Note:Note:

Figure 28.2 Symmetric-key cryptography

In symmetric-key cryptography, the same key is used in both directions.

Note:Note:

Figure 28.3 Caesar cipher

Figure 28.4 Transpositional cipher

Data encryption Standard (DES) Is a block cipher Takes 64-bit plaintext and creates a

64-bit ciphertext. The cipher key is a 56-bit key.

It uses 16 rounds, each round mixes and swapps (left half with right half)

Figure 28.5 DES (Data Encryption Standard)

The DES cipher uses the same concept as the Caesar cipher, but the

encryption/ decryption algorithm is much more complex.

Note:Note:

Asymmetric-key ciphers

The secret key is personal and unshared. Symmetric key scheme would require n(n-

1)/2 keys, for a million people it would require half a billion shared secret keys. Whereas, in asymmetric scheme we would only require a million secret keys.

Asymmetric ciphers use two keys, private and public.

Asymmetric is much slower. Both symmetric and asymmetric can be used if need to be. Think: if you want to send a secret symmetric key, you can use asymmetric.

Protocols IPSec (internet Security Protocol) operates in the

network layer. Used in VPN. IP sec supports Authentication Header (AH)

protocal and Encapsulation Security Payload (ESP) protocol

The SSL (Secure Socket Layer) protocol serves as a security for transferring encrypted data.

WEP (Wired Equivalent Privacy) standard. Data stream is encrypted with RC4 algorithm. RC4 is simple, it is not very secure.

WPA (Wi-Fi Protected Access) specification and AES (Advanced Encryption standard) I more secure for encrypting wireless data.

Figure 28.8 Public-key cryptography

Symmetric-key cryptography is often used for long messages.

Note:Note:

Asymmetric-key algorithms are more efficient for short messages.

Note:Note:

Digital signature can provide authentication, integrity, and

nonrepudiation for a message.

Note:Note:

28.3 DIGITAL SIGNATURE

Digital signature can provide authentication, integrity, and Digital signature can provide authentication, integrity, and nonrepudiation for a message. nonrepudiation for a message.

Signing the Whole Document Signing the Whole Document Signing the Digest Signing the Digest

Figure 28.12 Signing the whole document

Digital signature does not provide privacy. If there is a need for privacy, another layer of encryption/decryption

must be applied.

Note:Note:

Figure 28.13 Hash function

Figure 28.14 Sender site

Figure 28.15 Receiver site

The digest is much shorter than the message. The message itself may not lend itself to asymmetric cryptography because it is too long.

Hash functions

Message of arbitrary length is made into a fixed length message.

MD2, MD4, MD5 SHA (Secure Hash Algorithm)

developed by NIST.

Non-repudiation

If alice signs a message then denies it, the message can be verified. That means we have to keep the messages.

A trusted center can be created. Alice send the digitally signed message to the trusted center who verifies it, saves a copy of the message, recreates the message with its own signature and send to bob. Bob can verify the trusted center’s public key.

28.5 KEY MANAGEMENT

In this section we explain how symmetric keys are distributed and how In this section we explain how symmetric keys are distributed and how public keys are certified. public keys are certified.

Symmetric-Key Distribution Symmetric-Key Distribution Public-Key Certification Public-Key Certification Kerberos Kerberos

A symmetric key between two parties is useful if it is used only once; it must be created for one session and destroyed

when the session is over.

Note:Note:

Figure 28.19 Diffie-Hellman method

The symmetric (shared) key in the Diffie-Hellman protocol is

K = G xy mod N.

Note:Note:

Let us give an example to make the procedure clear. Our example uses small numbers, but note that in a real situation, the numbers are very large. Assume G = 7 and N = 23. The steps are as follows:

1. Alice chooses x = 3 and calculates R1 = 73 mod 23 = 21.

2. Alice sends the number 21 to Bob.

3. Bob chooses y = 6 and calculates R2 = 76 mod 23 = 4.

4. Bob sends the number 4 to Alice.

5. Alice calculates the symmetric key K = 43 mod 23 = 18.

6. Bob calculates the symmetric key K = 216 mod 23 = 18.

The value of K is the same for both Alice and Bob; G xy mod N = 718 mod 23 = 18.

Example 1

Figure 28.20 Man-in-the-middle attack

Figure 28.21 First approach using KDC

Figure 28.22 Needham-Schroeder protocol

Figure 28.23 Otway-Rees protocol

In public-key cryptography, everyone has access to everyone’s public key.

Note:Note:

Table 28.1 X.509 fieldsTable 28.1 X.509 fields

Figure 28.24 PKI hierarchy

Figure 28.25 Kerberos servers

Figure 28.26 Kerberos example

28.6 SECURITY IN THE INTERNET

In this section we discuss a security method for each of the top 3 layers In this section we discuss a security method for each of the top 3 layers of the Internet model. At the IP level we discuss a protocol called IPSec; of the Internet model. At the IP level we discuss a protocol called IPSec; at the transport layer we discuss a protocol that “glues” a new layer to at the transport layer we discuss a protocol that “glues” a new layer to the transport layer; at the application layer we discuss a security method the transport layer; at the application layer we discuss a security method called PGP.called PGP.

IP Level Security: IPSec IP Level Security: IPSec Transport Layer Security Transport Layer Security Application Layer Security: PGP Application Layer Security: PGP

Figure 28.27 Transport mode

Figure 28.28 Tunnel mode

Figure 28.29 AH

The AH protocol provides message authentication and integrity,

but not privacy.

Note:Note:

Figure 28.30 ESP

ESP provides message authentication, integrity, and privacy.

Note:Note:

Figure 28.31 Position of TLS

Figure 28.32 TLS layers

Figure 28.33 Handshake protocol

Figure 28.34 Record Protocol

Figure 28.35 PGP at the sender site

Figure 28.36 PGP at the receiver site

28.7 FIREWALLS

A firewall is a device (usually a router or a computer) installed between A firewall is a device (usually a router or a computer) installed between the internal network of an organization and the rest of the Internet. It is the internal network of an organization and the rest of the Internet. It is designed to forward some packets and filter (not forward) others.designed to forward some packets and filter (not forward) others.

Packet-Filter Firewall Packet-Filter Firewall Proxy Firewall Proxy Firewall

Figure 28.37 Firewall

Figure 28.38 Packet-filter firewall

A packet-filter firewall filters at the network or transport layer.

Note:Note:

Figure 28.39 Proxy firewall

A proxy firewall filters at the application layer.

Note:Note:

TCP/IP Protocol Suite 1 Chapter 30 Security Credit: most slides from Forouzan, TCP/IP protocol suit.

Documents

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