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Network Security Chapter 7


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Network Security Chapter 7

  2. 2. INTRODUCTION  Network is two devices connected across some medium by hardware and software that complete the communications (simple definition of network). User (Client) Host Server Communication medium Simple View of Network
  3. 3. Introduction  A network is normally not just single client to a single server; typically many clients interact with many servers. User (Client) Host Server User (Client) User (Client) User (Client) Host Server User (Client) User (Client) User (Client) System A System B
  4. 4. Network Security Issues Network have security problems for the following reasons:  Sharing – resources and workload sharing  Complexity of system  Unknown parameter – expandability of a network also implies uncertainty about the network boundary  Many points of attack – file may past through many host before reaching the destination  Anonymity – attacker can mount an attack with touching the system  Unknown path – there may be many path from one host to another.
  5. 5. Possible Network Security Threats  Wiretapping  Impersonation  Message confidence violations  Message integrity violations  Hacking  Denial of Service (DoS)
  6. 6. Possible Network Security Threats Wiretapping  Wiretap means to intercept communications.  Passive / Active Wiretapping  Packet sniffer can retrieve all packets on the net.  “Inductance” is a process where an intruder can tap a wire without making physical contact with the cable.  Microwave and satellite – higher possibility of interception due to wider broadcasting.
  7. 7. Possible Network Security Threats Wiretapping  Optical fiber offers two significant security advantages:  The entire optical network must be tuned carefully each time a new connection is made. Therefore, no one can tap an optical system without detection.  Optical fiber carries light energy, not electricity. Light does not emanate a magnetic field as electricity does. Therefore an inductive tap is impossible on an optical fiber cable.
  8. 8. Possible Network Security Threats Wiretapping  However, optical fiber also has weaknesses where wiretappers will try to tap at the repeaters, splices and other equipments that connects to the fiber optic and thus creates vulnerabilities.
  9. 9. Possible Network Security Threats Impersonation  Pretend to be someone (personnel) or something (process).  In an impersonation, the attacker has several choices:  Guess the identity and authentication details of the target  Pick up the identity and authentication details of the target from a previous communication  Circumvent or disable the authentication mechanism at the target computer  Use a target that will not be authenticated  Use a target whose authentication data is known
  10. 10. Possible Network Security Threats Message Confidentiality Violations  Misdelivery  Exposure  Traffic Flow Analysis
  11. 11. Possible Network Security Threats Message Integrity Violations  Falsification of Messages  Change the content of a message  Change any part of the content of a message  Replace a message entirely  Redirect a message  Destroy or delete the message  Noise – unintentional interference
  12. 12. Possible Network Security Threats Hacking  A source of threat to security in computer communication.  Hacker is considered as a separate threat because a hacker can develop tools to search widely and quickly for particular weaknesses and move swiftly to exploit weaknesses.  In this way, hacker has unlimited time to analyze, plan, code, simulate and test for future attack.  In reviewing the effects of this attack ; if it succeeds, what additional capability would that give the hacker for future attacks?
  13. 13. Possible Network Security Threats Denial of Service  Result of any action or series of actions that prevents any part of a telecommunications system from functioning.  Connectivity  Flooding  Routing problems  Disruption of Service
  14. 14. Network Security Control  Encryption – link encryption, end-to-end encryption  Link Encryption:  Data is encrypted just before the system places it on the physical communication links.  Decryption occurs just as the communication enters the receiving computer.
  15. 15. Application Presentation Session Transport Network Data Link Physical Sender ReceiverMessage Intermediate Host Message (Plaintext) Exposed Message Encrypted Message in Plaintext: Exposed Link Encryption
  16. 16. Network Security Control  End-to-end encryption:  Provides security from one end of a transmission through the other.
  17. 17. Application Presentation Session Transport Network Data Link Physical Sender Message Intermediate Host Message Encrypted Message in Plaintext: Exposed Receiver End-to-End Encryption
  18. 18. Network Security Control Link Encryption versus End-to-end Encryption: Link Encryption End-to-end Encryption Security Within Hosts Message exposed in the sending host Message expose in intermediate nodes Security Within Hosts Message encrypted in sending host Message encrypted in intermediate nodes Role of User Applied by sending host Invisible to user Host maintains encryption Can be done in hardware All or no messages encrypted Role of User Applied by sending process User applies encryption User must find algorithm Software implementation User chooses to encrypt or not, for each message
  19. 19. Authentication Issues in Distributed System There are two main concern regarding authentication issue in distributed system which are: (1) How to ensure the authenticity of the communicating hosts? (2) How to ensure authenticity of users who are using the hosts?
  20. 20. Authentication Issues in Distributed System That is by using:  Digital Distributed Authentication  DCE (Distributed Computer Environment)  Kerberos  SESAME  CORBA
  21. 21. Authentication Issues in Distributed System Kerberos  Is a system that supports authentication in distributed systems.  Was designed at Massachusetts Institute of technology.  The basis of kerberos is a central server that provides authenticated tokens called tickets to requesting applications.
  22. 22. Authentication Issues in Distributed System KERBEROS Initiating a Kerberos Session:
  23. 23. Authentication Issues in Distributed System KERBEROS Obtaining a Ticket to Access a File:
  24. 24. KERBEROS: Access to Services and Servers in Kerberos
  25. 25. Authentication Issues in Distributed System Kerberos was carefully designed to withstand attacks in distributed environments:  No password communicated on the network  Cryptographic protection against spoofing  Limited period of validity  Time stamps to prevent replay attacks  Mutual authentication
  26. 26. Authentication Issues in Distributed System  Kerberos is not a perfect answer to security problems in distributed systems because:  Kerberos requires continuous availability of a trusted ticket granting server.  Authenticity of servers requires a trusted relationship between the ticket granting server and every server  Kerberos requires timely transactions  A subverted workstation can save and later replay user passwords
  27. 27. Authentication Issues in Distributed System  Kerberos is not a perfect answer to security problems in distributed systems because:  Password guessing works  Kerberos does not scale well  Kerberos is not a complete solution
  28. 28. Privacy Enhanced Electronic Mail (PEM)  The basis of PEM is encryption.  In order to send a PEM message the sender must have a certificate for the receiver.
  29. 29. Message header + Body Message Encryption key Receiver’s public key New header Encrypted data Encrypted key Encrypted Message Header + Body Public key encryption Symmetric key encryption
  30. 30. Compose message PEM processing requested ? PEM Send message Receive message Privacy enhanced ? PEM View message Yes No Yes No PEM processing in Message Transmission
  31. 31. Privacy Enhanced Electronic Mail (PEM)  The major problem with PEM is key management.  Therefore PGP was designed to overcome this problem.
  32. 32. Pretty Good Privacy (PGP)  Was designed by Phil Zimmerman to offer a reasonable degree of privacy for email.  It uses a message structuring scheme similar to PEM.  The key management for PGP is ad hoc.  Each user has a set of people he or she knows and trusts.  The user exchanges public keys with those friends, exactly as one might swap business card at meeting.  Some people accept not just the friends’ public key but also all public keys their friends have.
  33. 33. Pretty Good privacy (PGP)  The assumption here is that any friend of yours is a friend of mine.  A PGP user builds a key ring which is the set of all public keys that person possesses.  In that way, when an encrypted messages arrives, the person can decrypt it if the key is on that person’s key ring.
  34. 34. Firewalls  A firewall is a process that filters all traffic between a protected or “inside” network and a less trustworthy or “outside” network.  There are three types of firewall:  Screening Routers  Proxy gateways  Guards
  35. 35. Firewalls Screening Router  Is the simplest and in some situations the most effective type of firewall.  Hosts tend not to be connected directly to a wide area network; more often hosts are connected to a router.
  36. 36. Firewalls Router joining LAN to two WANs
  37. 37. Firewalls Screening Router  Router will only see the header of the message.  Header will contain information on:  The sender/receiver address  Protocol  Port  Length of a packet  It can also control the traffic based on application – by using port numbers (eg: 21 for FTP and 25 for SMTP)  It can also decide which application is acceptable and not acceptable.  It can also determine the authentication of an inside address.
  38. 38. Firewalls Proxy Gateway  Is also called a bastion host.  Is a firewall that simulates the (proper) effects of an application so that the application will receive only requests to act properly.
  39. 39. Firewalls Proxy Gateway  To understand the real purpose of a proxy gateway, we consider some examples:  A company wants to set up an online lists so that outsiders can see the products and prices offered. It wants to be sure that no outsider can change the prices or product list and that outsiders can access only the price list not any of the more sensitive files stored inside.
  40. 40. Firewalls Guard  A guard is a sophisticated proxy firewall.  The guard decides what services to perform on the user’s behalf based on its available knowledge such as whether it can reliably know of the (outside) user’s identity, previous interactions and so forth.
  41. 41. Firewalls Guard  Here are some more sophisticated examples of guard activities:  A university wants to allow its students to use email up to a limit of so many messages or so many characters of email in the last so many days. Although this result could be achieved by modifying email handlers it is more easily done by monitoring the common point through which all email flows (the mail transfer protocol).  A school wants its students to be able to access the WWW but because of the slow speed of its connection to the Web it will allow only so many characters per download image.
  42. 42. Firewalls Firewalls are not complete solutions to all computer security problems.  Firewalls can protect an environment only if the firewalls control the entire perimeter.  Firewall do not protect data outside the perimeter.  Firewall are the most visible part of an installation to the outside and therefore is the most attractive point of attack.  Firewalls are targets of penetrators.  Firewalls must be correctly configured.  Firewalls exercise only minor control over the content admitted to the inside – inaccurate data or malicious code must be controlled inside the perimeter.