Chapter 12: Network Security

INTRODUCTION

Computer network security has reached a point at which it can be best be characterized by two seemingly conflicting statements: Never has network security been better than it is today, and never have computer networks been more vulnerable than they are today. The internet allows anyone in the world to access or attempt to access any computer system that is connected to the internet. It allows us to download web pages from anywhere in the world, but it also exposes all internet attached systems to invasion

COMMON SYSTEM ATTACKS

Some standard methods of system attacks are:

1. Socially engineered attacks: occurs in a form of a link in a web page that contains malicious code (malware) that could erase sensitive data, erase hard disk, or even make you pay for software to remove malware
2. Exploiting know vulnerabilities in operating systems and application software (unpatched software)

• Virus: a small program that alters the way a computer operates without knowledge of the users and often does various types of damage by deleting and corrupting data and program files, or by altering operating system components, so that computer operation os impaired or even halted
• Macro virus
• Boot sector virus
• Polymorphic virus
• File infector virus
• Botnes: malicious programs that take over operations on a compromised computer
• Worm: a program that copies itself from one system to another over a network, without the assistance of a human being
• User's computer is constantly vulnerable to malicious software programs on the internet that are scanning for unprotected computers and trying to exploit known operating system and application vulnerabilities
• Typically, a virus or a worm is transported as a Trojan horse
• hiding inside is a harmless looking piece of code such as an email or an application macro
• Other standard attacks
• Denial of service attacks, or distributed denial of service attacks
• Bombard computer site with so many messages that site is incapable of answering valid request
• E-mail bombing
• User sends an excessive amount of unwanted e-mail to someone
• Smurfing
• Nasty technique in which a program attacks a network by exploiting IP broadcast addressing operations
• Ping storm
• Condition in which the Internet ping program is used to send a flood of packets to a server
• Spoofing
• When a user creates a packet that appears to be something else or from someone else
• Trojan Horse
• Malicious piece of code hidden inside a seemingly harmless piece of code.
• Stealing, guessing, and intercepting passwords is also a tried and true form of attack
• Pharming
• Hacker redirects unknowing user to bogus look-alike website
• Phishing
• Hackers create emails which look as if they are coming from a legit source when in reality the hacker is trying to get the user to give up ID and password info
• Rootkit
• A program that has been installed deep within a user’s operating system; defies detection and takes over the user’s computer
• Keylogger
• A software system that secretly captures and records keystrokes made at a user’s keyboard

PHYSICAL PROTECTION

• Physical protection of a computer system consists of protecting the equipment from physical damage such as fire, floods, earthquakes, power surges, and vandalism
• Physical security such as locking rooms, locking down computers, keyboards and other devices
• To prevent electrical damage, high quality surge protectors should be used on all devices
• Noise protection from placing computers away from devices that generate electromagnetic interference
• Surveillance: a good deterrent of computer vandalism and theft
• Proper placement of security cameras can deter theft and vandalism
• Cameras can also provide a record of activities
• Intrusion detection is a field of study in which specialists try to prevent intrusion and try to determine if a computer system has been violated
• Honeypot is an indirect form of surveillance
• Network personnel create a trap, watching for unscrupulous activity

CONTROLLING ACCESS

• Involves deciding and then limiting who can use the system and when the system can be used
• Access right: defines the network resources that a user or set of users can acess

1. Password and ID Systems

• Password is the most common form of protection, however, it is the weakest form
• Because there are so many weakness to the password, other forms of identification emerged
• Biometric techniques: observe and record some aspect of the user such as voiceprints, fingerprints, eye prints and face prints

2. Access Rights

• Most access rights have two basic parameters: Who and How?
• The Who parameter lists who has access rights to the resource
• typically include the owner, a select group of users, and the entire user population
• The How parameter can specify how a user may access
• read, write, delete, print, copy or execute

3. Auditing

• Creating a computer or paper audit can help detect wrongdoing
• Auditing can also be used as a deterrent
• Many network operating systems allow the administrator to audit most types of transactions
• Many types of criminals have been caught because of computer-based audits

SECURING DATA

1. Basic encryption and decryption techniques

• Cryptography: the study of creating and using encryption and decryption techniques
• Plaintext: data before any encryption has been performed
• Encryption algorithm: the computer program that converts plaintext into an enciphered
• Ciphertext: data after encryption has been performed
• Key: the unique piece of information that is used to create ciphertext and decrypt the ciphertext back into plaintext

• Monoalphabetic Substitution - based ciphers: replace a character or characters with a different character or characters, based upon some key
• Replacing:  abcdefghijklmnopqrstuvwxyz
• with:  POIUYTREWQLKJHGFDSAMNBVCXZ
• The message: how about lunch at noon
• encodes into:    EGVPO GNMKN HIEPM HGGH
• Polyalphabetic Substitution - based Ciphers: similar to monoalphabetic ciphers except multiple alphabetic strings are used to encode the plaintext
• Example: Vigenere cipher - matrix of strings, 26 rows by 26 characters or columns can be used
• A key as COMPUTERSCIENCE is place repeatedly over the plaintext
• COMPUTERSCIENCECOMPUTERSCIENCECOMPUTER
• thisclassondatacommunicationsisthebest
• To encode the message, take the first letter of the plaintext, t, and the corresponding key character immediately above it, C
• Go to row C column t in the 26x26 matrix and retrieve the ciphertext character V
• Continue with the other characters in plaintext

• Transition-based ciphers: the order of the plaintext is not preserved
• Example: select a key such as COMPUTER
• Number the letters of the word COMPUTER in the order they appear in the alphabet
• 1 4 3 5 8 7 2 6
• C O M P U T E R
• Now take the plaintext message and write it under the key
• 1 4 3 5 8 7 2 6
  C O M P U T E R
  t h i s i s t he b e s t c l a
  s s i h a v e e
  v e r t a k e n
• Then read the ciphertext down the columns, starting with the column numbered 1, followed by column number 2
• TESVTLEEIEIRHBSESSHTHAENSCVKITAA
• Public Key Crytography
• Very powerful encryption technique in which two keys are used
• First key (the public key) encrypts the message
• Second key (the private key) decrypts the message
• Not possible to deduce one key from the other
• Not possible to break code given public key
• If you want someone to send you secure data, give them your public key, you keep the private key
• Secure Sockets Layer on the Internet is a common example of public key cryptography
• Data Encryption Standard and Advanced Encryption Standard
• Data encryption standard (DES) is a commonly employed encryption method used by business to send and receive secure transaction
• The standard came in effect in 1977 and was re-approved in 1983, 1988, and 1993 and took a 64-bit block of data and subjected it to 16 levels of encryption
• the choice of encryption performed at each of the 16 levels depends on the 56-bit key applied

• Triple-DES: data is encrypted using DES three times: first time by the first key, second time by a second key, third time by first key again
• While virtually unbreakable, triple-DES is CPU intensive
• Advanced Encryption standard (AES): was selected by the US government to replace DES
• Digital Signatures
• Document to be signed is sent through a complex mathematical computation that generates a hash
• Hash is encoded with owner’s private key then stored
• To prove future ownership, stored hash is decoded using the owner’s public key and that hash is compared with a current hash of the document
• f the two hashes agree, document belongs to the owner
• U.S. accepts digitally signed documents as legal proof (for some types of documents)
• Pretty Good Privacy (PGP): high quality encryption software that create secure email messages and encrypting other types of data files
• Kerberos: an authentication protocol designed to work on client/server networks that used secret or symmetric cryptography
• Employs both private key cryptography (one key both encrypts and decrypts) and public key cryptography (two separate keys)
• Another free software for use in the U.S.
• Many operating systems provide Kerberos for authentication of users and services
• Public Key Infrastructure: the combination of encryption techniques, software, and services that involves all the necessary pieces to support digital certificates, certificate authorities, and public key generation, storage, and management
• Certificate: is an electronic document, similar to a passport, that establishes your credentials when you are performing transactions
• A digital certificate contains your name, serial number, expiration dates, copy of your public key, and digital signature of certificate-issuing authority.
• Certificates are usually kept in a registry so other users may check them for authenticity
• Certificates are issued by a certificate authority (CA)
• A CA is either specialized software on a company network or a trusted third party 
• A certificate revocation list is used to “deactivate” a user’s certificate
• Applications that could benefit from PKI:
• Web transactions
• Virtual private networks
• Electronic mail
• Client-server applications
• Banking transactions
• Steganography: the art and science of hiding information inside other, seemingly ordinary message or documents
• examples include watermark over an image or taking random pixels from an image and replacing them with the hidden data

SECURING COMMUNICATIONS

1. Spread Spectrum Technology

• takes the date and rather transmitting it in a fixed bandwidth, spread it over a wider bandwidth
• two basic spread spectrum technologies:
• Frequency hopping spread spectrum: transmission is to bounce the signal around on random frequencies rather than transmit it on one fixed frequency
• direct sequence spread spectrum: spreads the transmission of a signal over a wide range of frequencies using mathematical values

2. Guarding Against Viruses

• Signature-based scanners look for particular virus patterns or signatures and alert the user
• Terminate-and-stay-resident programs run in the background constantly watching for viruses and their actions
• Multi-level generic scanning is a combination of antivirus techniques including intelligent checksum analysis and expert system analysis
• integrity checking: an antivirus technique that is used in conjunction with signature-based scanning and terminate-and-stay-resident monitoring

3. Firewalls

• a system or combination of systems that supports an access control policy between two networks
• Can limit users on the internet from accessing certain portions of a corporate network and various portions of the internet
• three types of basic firewalls
• Packet filter firewall: essentially a router that has been programmed to filter out or allow to pass certain IP addresses or TCP port numbers
• Proxy server:  more advanced firewall that acts as a doorman into a corporate network
• Any external transaction that requests something from the corporate network must enter through the proxy server
• Proxy servers are more advanced but make external accesses slower
• Application layer: inspects all packets coming into or leaving a connection using the application layer of the TCP/IP protocol suite
• Goes beyond IP addresses and TCP port numbers and inspects packet to see to which application it belongs

4. Wireless Security

• Wired Equivalency Protocol (WEP): first security protocol for wireless LANs
• It had weak 40-bit static and was too easy to break
• Wifi Protected Access (WPA): replace WEP
• Major improvement including dynamic key encryption and mutual authentication for wireless clients
• IEEE 802.11i (WPA2)
• Allows keys, encryption algorithms, and negotiation to be dynamically assigned
• AES encryption based on the Rijndael algorithm with 128-, 192- or 256- keys is incorporated

SECURITY POLICY DESIGN ISSUES

• What is the company’s desired level of security?
• How much money is the company willing to invest in security?
• If the company is serious about restricting access through an Internet link, what about restricting access through all other entry ways?
• The company must have a well-designed security policy