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Virtual Private Networks and IPSec

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  1. Virtual Private Networks and IPSec ECE 4112

  2. What is a VPN? • VPN Stands for Virtual Private Network • A method of ensuring private, secure communication between hosts over an insecure medium using tunneling • Usually between geographically separate locations, but doesn’t have to be • Via tunneling and software drivers, computer is logically directly connected to a network that it is not physically a part of ECE 4112 - Internetwork Security

  3. Sidebar: What is tunneling? • Putting one type of packet inside another • Both parties must be aware of tunnel for it to work • Example in next slide - AppleTalk over IP Tunnel ECE 4112 - Internetwork Security

  4. Example: AppleTalk over IP Tunnel ECE 4112 - Internetwork Security

  5. What is a VPN? (cont…) • Uses some means of encryption to secure communications • IPSec • SSH • Software could be written to support any type of encryption scheme • Two main types of VPNs – • Remote-Access • Site-to-Site ECE 4112 - Internetwork Security

  6. What is a VPN? (cont…) • Remote-Access • The typical example of this is a dial-up connection from home or for a mobile worker, who needs to connect to secure materials remotely • Site-to-Site • The typical example of this is a company that has offices in two different geographical locations, and wants to have a secure network connection between the two ECE 4112 - Internetwork Security

  7. Remote-Access Example ECE 4112 - Internetwork Security

  8. Site-to-Site Example ECE 4112 - Internetwork Security

  9. Why Use a VPN? • Originally designed as inexpensive alternative WAN over leased lines • Now mostly used to securely connect computers over the internet • Convenient • Lot’s of cheap and convenient protocols are insecure (IP, 802.11, etc) • Can now communicate securely over these insecure protocols ECE 4112 - Internetwork Security

  10. Why Use a VPN? (cont…) • Example – it can simplify security • (what is about to be proposed is not the most secure thing in the world – so don’t raise your hands and tell how you would make it more secure… it’s just an example) • Assume simple security policy with IP based access management – for example, an FTP server with site-licensed software on it for employees • Before VPN, complicated to allow access to FTP site for telecommuters or traveling employees • Train all employees to use SSH tunnel, etc… • After VPN, employees offsite can still connect using an internal IP address ECE 4112 - Internetwork Security

  11. VPN Advantages • Improved Security • Consolidation of Scattered Resources • Transparency to Users • If set up properly • Reduced Cost (vs. Leased Lines) ECE 4112 - Internetwork Security

  12. VPN Disadvantages • Time Consuming Setup • Possibly Frustrating Troubleshooting • Interoperability with other Networks/VPNs • Small performance overhead • Should be negligible on today’s hardware ECE 4112 - Internetwork Security

  13. VPN Security • In academic terms, VPN can provide Confidentiality, Integrity, and Authenticity • Security against determined hacker (read: academic attacks) depends largely upon underlying protocols used • Assuming security of SSH, IPSec, or other protocol used, should be secure ECE 4112 - Internetwork Security

  14. How are VPNs set up? • Many different types of setup • Vary in: • Amount of hardware used vs. amount of software used • All hardware based • All software based • Mixed • Amount of transparency to end-user • Does the user even realize that they are using a VPN? ECE 4112 - Internetwork Security

  15. How are VPNs set up? (cont…) • The following is not an exhaustive list • Gateway to gateway • Using two VPN aware Gateways • End host to gateway • End host uses VPN Software • End host to end host • Both hosts use software • End host to concentrator ECE 4112 - Internetwork Security

  16. How are VPNs set up? (cont…) • SSH over PPP • SSL over PPP • Concentrator using IPSec • Others (PPTP, L2TP, etc) ECE 4112 - Internetwork Security

  17. VPN via SSH & PPP • Point-to-Point Protocol over a Secure Shell connection • Establishing a Network Connection • Establish an SSH connection • VPN Client  VPN Server • Each have PPP daemons that will communicate through the SSH connection • Viola! A VPN CONNECTION! ECE 4112 - Internetwork Security

  18. VPN via SSL & PPP • Point-to-Point Protocol over a Secure Socket Layer connection • Secure Socket Layer • Built-in support for Host Authentication • Certificates ECE 4112 - Internetwork Security

  19. VPN via SSL & PPP (cont…) • Establishing a Network Connection • Initial Handshake for secure communication • “Hello” messages establish: • SSL Version, support for Cipher suites, and some random data • Key is determined separately from handshake • SSL Connection Complete! • Data transferred over the link ECE 4112 - Internetwork Security

  20. VPN via Concentrator • What is a Concentrator? • Concentrator is NOT a gateway or firewall • Specialized device that accepts connections from VPN peers • Authenticates clients • Enforces VPN security policies • Takes overhead of VPN management and encryption off of gateways and local hosts ECE 4112 - Internetwork Security

  21. VPN via Concentrator (cont…) • Steps to Establish VPN • Set up Concentrator (add users, specify authentication mechanisms, set IP address ranges, etc) • Install client software • Client runs software when wants to be on VPN ECE 4112 - Internetwork Security

  22. Other Methods • Point-to-Point Tunneling Protocol • Microsoft’s Implementation of VPN • Data is first encapsulated inside PPP packets • PPP packets are then encapsulated in GRE packets and sent over the link • PPTP uses two connections • One for the data being sent • Another for a control channel ECE 4112 - Internetwork Security

  23. Other Methods (cont…) • Any technology can be used • Must have hardware or software to support it • Another example: L2TP on Gateways • Layer 2 Tunneling Protocol • Supported by routers • If two routers support L2TP, and are properly configured, then VPN is set up between routers • Transparent to end user ECE 4112 - Internetwork Security

  24. Intro to IPSec • Created to add Authentication, Confidentiality, and Integrity to IP traffic • Designed to combat specific shortcomings in IP • IPSec is large and implementation is complicated • What follows is a high-level overview • As will see in lab, need not be used only as VPN technology – can be stand alone ECE 4112 - Internetwork Security

  25. Intro to IPSec (cont…) • IP Sec ≠ VPN • IP Sec is a protocol used in many VPNs • Two main modes • Transport • Tunnel • Two main services • AH (Authentication Header protocol) • ESP (Encapsulating Security Protocol) ECE 4112 - Internetwork Security

  26. Intro to IPSec (cont…) • Authentication Header protocol • Offers Authenticity and Integrity • Uses cryptographic hash • Covers entire packet, including static header fields • If any part of original message changes, it will be detected • Does not encrypt message • Can be used to authenticate – • Prevents IP Spoofing ECE 4112 - Internetwork Security

  27. Intro to IPSec (cont…) • Encapsulating Security Protocol • Provides Integrity and Confidentiality • Encrypts payload • If used in tunnel mode, encrypts original IP header ECE 4112 - Internetwork Security

  28. Real IP Header IP Options IPSec Header Payload (For example, TCP and Payload) Could be either ESP Header Encrypts Over Or AH Header Authenticates Over Intro to IPSec (cont…) • Transport Mode ECE 4112 - Internetwork Security

  29. GW IP Header IPSec Header Real IP Header Payload (For example, TCP and Payload) Could be either ESP Header Encrypts Over Or AH Header Authenticates Over Intro to IPSec (cont…) • Tunnel Mode ECE 4112 - Internetwork Security

  30. Intro to IPSec (cont…) • AH and ESP can be used together • Tunnel ESP through AH transport packets • Want to protect cryptographic keys • Internet Key Exchange protocol (IKE) • Secure way to exchange session keys based on shared secret • Can also use certificates (public key cryptography) ECE 4112 - Internetwork Security

  31. Resources • Books: • Building Linux Virtual Private Networks • Oleg Kolesnikov, Brian Hatch • Linux Server Hacks • Rob Flickenger • Network Security • Charlie Kaufman, Radia Perlman, Mike Speciner ECE 4112 - Internetwork Security

  32. Resources (cont…) • Lecture Slides by Wenke Lee (see below) • Websites: • http://vpn.shmoo.com/ • http://www.tldp.org/HOWTO/VPN-HOWTO/ • http://www.onlamp.com/lpt/a/3009 • http://www.cisco.com/warp/public/471/how_vpn_works.shtml • http://www.cc.gatech.edu/classes/AY2004/cs4803_fall/ipsec_1.ppt • http://www.cc.gatech.edu/classes/AY2004/cs4803_fall/ipsec_2.ppt ECE 4112 - Internetwork Security