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Chapter 7 –Security in Networks

Chapter 7 –Security in Networks. Introduction to networks Threats against network applications Controls against network applications Firewalls Intrusion detection systems Private e-mail. Terminal-Host Systems. Created in the 1960s Central host computer does all the processing

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Chapter 7 –Security in Networks

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  1. Chapter 7 –Security in Networks • Introduction to networks • Threats against network applications • Controls against network applications • Firewalls • Intrusion detection systems • Private e-mail

  2. Terminal-Host Systems • Created in the 1960s • Central host computer does all the processing • Terminal is dumb--only a remote screen and keyboard • Created in the 1960s, when microprocessors for terminal intelligence did not exist Terminals Host

  3. PC Networks • The Most Common Platform in Organizations • Allows PCs to share resources • Both Wintel (Windows/Intel) PCs and Macintoshes Network

  4. Network • A Network is an Any-to-Any Communication System • Can connect any station to any other Network

  5. Network • Each Station has a Unique Network Address • To connect, only need to know the receiver’s address • Like telephone number GHI DEF “Connect to GHI” ABC MNO JKL

  6. LANs and WANs • Networks Have Different Geographical Scopes • Local Area Networks (LANs) • Small Office • Office Building • Industrial Park / University Campus • Wide Area Networks (WANs) • Connect corporate sites or • Connect corporate sites with sites of customers and suppliers

  7. Elements of a Simple LAN Hub or Switch connects all stations Wiring is standard business telephone wiring (4 pairs in a bundle) Hub or Switch Wiring

  8. Elements of a Simple LAN Client PC Client PCs are used by ordinary managers and professionals; receive service Servers provide services to client PCs Server Server Server Client PC

  9. Elements of a Simple LAN • Client PC • Begin with stand-alone PC • Add a network interface card (NIC) todeal with the network • Networks have many client PCs • Server • Most PC nets have multiple servers

  10. Wide Area Networks • WANs Link Sites (Locations) • Usually sites of the same organization • Sometimes, sites of different organizations Site B Site A Site C WAN

  11. Client/Server Processing • Two Programs • Client program on client machine • Server program on server machine • Work together to do the required processing Server Program Client Program Client Machine Server

  12. Client/Server Processing • Cooperation Through Message Exchange • Client program sends Request message, such as a database retrieval request • Server program sends a Responsemessage to deliver the requested information or an explanation for failure Server Program Client Program Request Client Machine Response Server

  13. Client/Server Processing • Widely Used on the Internet • For instance, webservice • Client program (browser) sends an HTTP request asking for a webserver file • Server program (webserver application program) sends an HTTP response message with the requested webpage HTTP Request Message HTTP Response Message

  14. Client/Server Processing • On the Internet, a Single Client Program--the Browser (also known as the client suite)--Works with Many Kinds of C/S server applications • WWW, some E-mail, etc. E-mail Server Browser Webserver

  15. Standards Organizations and Architectures • TCP/IP Standards • Created by the Internet Engineering Task Force (IETF) • Named after its two most widely known standards, TCP and IP • TCP/IP is the architecture, while TCP and IP are individual standards • However, these are not its only standards, even at the transport and internet layers • IETF standards dominate in corporations at the application, transport, and internet layers • However, application, transport, and internet standards from other architectures are still used

  16. Standards Organizations and Architectures • OSI Standards • Reference Model of Open Systems Interconnection • Created by the International Telecommunications Union-Telecommunications Standards Sector (ITU-T) • And the International Organization for Standardization (ISO) • OSI standards dominate the data link and physical layers • Other architectures specify the use of OSI standards at these layers

  17. OSI Reference Model

  18. TCP/IP versus OSI • Lowest Four Layers are Comparable in Functionality

  19. Internet Standards • Accessing the WWW from Home App HTTP App Trans TCP Trans Int IP Int IP Int DL PPP DL ? DL Phy Modem Phy ? Phy User PC Router Webserver

  20. IndirectCommunication • Application programs on different machines cannot communicate directly • They are on different machines! HTTP Request Browser Web App Trans Trans Int Int DL DL Phy Phy User PC Webserver

  21. Layer Cooperation on the Source Host • Application layer process passes HTTP-request to transport layer process Application HTTP Request Transport Internet Data Link User PC Physical

  22. Layer Cooperation on the Source Host • Transport layer makes TCP segments • HTTP message is the data field • Adds TCP header fields shown earlier • Transport process “encapsulates” HTTP request within a TCP segment TCP Segment HTTP Request TCP-H Data Field TCP Header

  23. Layer Cooperation on the Source Host • Transport layer process passes the TCP segment down to the internet layer process Application Transport TCP segment Internet Data Link User PC Physical

  24. Layer Cooperation on the Source Host • The internet layer process passes the IP packet to the data link layer process • Internet layer messages are called packets Application Transport Internet IP packet Data Link User PC Physical

  25. Layer Cooperation on the Source Host • The data link layer process passes the PPP frame to the physical layer process, which delivers it to the physical layer process on the first router, one bit at a time (no message at the physical layer) Application Transport Internet To first router Data Link PPP frame User PC Physical (10110 …)

  26. Layer Cooperation on the Source Host • Recap: Adding Headers and Trailers: Application HTTP msg Transport HTTP msg TCP-H Internet HTTP msg TCP-H IP-H Data Link PPP-T HTTP msg TCP-H IP-H PPP-H User PC Physical

  27. Protocols • A protocol is a standard for communication between peer processes, that is, processes at the same layer, but on different machines • TCP, IP, and PPP all have “protocol” as their final “P;” they are all protocols • TCP (Transmission Control Protocol) is the protocol governing communication between transport layer processes on two hosts Message Trans TCP Trans

  28. Domain Name System (DNS) • Only IP addresses are official • e.g., 128.171.17.13 • These are 32-bit binary numbers • Only they fit into the 32-bit destination and source address fields of the IP headers IP Packet 32-bit Source and Destination Addresses (110011...)

  29. Domain Name System (DNS) • Users typically only know host names • e.g., voyager.cba.hawaii.edu • More easily remembered, but • Will not fit into the address fields of an IP packet IP Packet NO voyager.cba.hawaii.edu

  30. Internet and Data Link Layer Addresses • Each host and router on a subnet needs a data link layer address to specify its address on the subnet • This address appears in the data link layer frame sent on a subnet • For instance, 48-bit 802.3 MAC layer frame addresses for LANs Subnet DA DL Frame for Subnet

  31. Addresses • Each host and router also needs an IP address at the internet layer to designate its position in the overall Internet 128.171.17.13 Subnet Subnet Subnet

  32. IPv6 • Current version of the Internet Protocol is Version 4 (v4) • Earlier versions were not implemented • The next version will be Version 6 (v6) • No v5 was implemented • Informally called IPng (Next Generation) • IPv6 is Already Defined • Continuing improvements in v4 may delay its adoption

  33. IPv6 • IPv6 will raise the size of the internet address from 32 bits to 128 bits • Now running out of IP addresses • Will solve the problem • But current work-arounds are delaying the need for IPv6 addresses

  34. What Makes a Network Vulnerable? • Anonymity • Many points of attack (targets & origins) • Sharing • Complexity of system • Unknown perimeter • Unknown path

  35. Who Attacks Networks Hackers break into organizations from the outside Challenge Fame Money & Espionage Ideology However, most security breaches are internal, by employees and ex-employees

  36. Threat Precursors • Port Scan • Social Engineering • Reconnaissance • Bulletin Board / Chat • Docs • Packet Sniffers (telnet/ftp in cleartext)

  37. Network Security Threats • Interception • If interceptor cannot read, have confidentiality (privacy) • If cannot modify without detection, have message integrity

  38. Network Security Threats • Impostors (Spoofing/ Masquerade) • Claim to be someone else • Need to authenticate the sender--prove that they are who they claim to be Impostor True Person

  39. Network Security Threats • Remotely Log in as Root User • Requires cracking the root login password • Then control the machine • Read and/or steal information • Damage data (erase hard disk) • Create backdoor user account that will let them in easily later Root Login Command

  40. Security Threats • Content Threats • Application layer content may cause problems • Viruses • In many ways, most severe security problem in corporations today • Must examine application messages

  41. Replay Attack • First, attacker intercepts a message • Not difficult to do

  42. Replay Attack • Later, attacker retransmits (replays) the message to the original destination host • Does not have to be able to read a message to replay it

  43. Replay Attack • Why replay attacks? • To gain access to resources by replaying an authentication message • In a denial-of-service attack, to confuse the destination host

  44. Thwarting Replay Attacks • Put a time stamp in each message to ensure that the message is “fresh” • Do not accept a message that is too old • Place a sequence number in each message • Do not accept a duplicated message Message Time Stamp Sequence Number

  45. Thwarting Replay Attacks • In request-response applications, • Sender of request generates a nonce (random number) • Places the nonce in the request • Server places the nonce in the response • Neither party accepts duplicate nonces Request Response Nonce Nonce

  46. Network Security Threats • Denial of Service (DOS) Attacks • Overload system with a flood of messages • Or, send a single message that crashes the machine

  47. Denial of Service (DOS) Attacks • Transmission Failure • Connection Flooding • Echo-Chargen • Ping of Death • Smurf • Syn Flood • Traffic Redirection • DNS Attacks • Distributed Denial of Service

  48. VPNs • IETF developing IPsec security standards • IP security • At the internet layer • Protects all messages at the transport and application layers E-Mail, WWW, Database, etc. TCP UDP IPsec

  49. VPNs • IPsec Transport Mode • End-to-end security for hosts Local Network Internet Local Network Secure Communication

  50. VPNs • IPsec Tunnel Mode • IPsec server at each site • Secure communication between sites Local Network Internet Local Network IPsec Server Secure Communication

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