Virtual Private Networks

CS-480b

Dick Steflik

Virtual Private Networks (VPNs)

• Used to connect two private networks together via the Internet

• Used to connect remote users to a private network via the Internet

• This could be done by opening your firewall to the LAN networking protocols (NETBIOS, NFS NetWare, AppleTalk))• But… it would also make those protocols available to any one on the

Internet and they could come into your LAN at will

• Effectively make the whole Internet your LAN• Exposes all of your data

• Anyone can easily take advantage of vulnerabilities in your internal hosts

• No privacy

• Better solution is to use a VPN in conjunction with your firewall

VPNs

• Since we all understand that IP is used to transport information between LANs if we add some security stuff to IP then this transport can be made more secure

• Can be done two ways:• At the network level using IPSec

• Currently the most widely used method– But requires special client installation on each workstation (more IT $)

• At the Transport level using SSL• Quickly gaining popularity because there are no special software installation

requirements for end user workstations– All that’s required is a browser with SSL support

• Mozilla• Internet Explorer• Netscape• Opera

IP Based VPNs

• Fundamental Components• IP Encapsulation

• Cryptographic based authentication• Secret Key Encryption

– Single shared secret key for encrypt and decrypt

• Public Key Encryption– Unidirectional keys

• Encrypt or decrypt (not both)

• Data Payload Encryption• Encrypt payload but not header (method depends on OEM/Vendor solution)

• IP/IP Encapsulation• Makes remotely located LANs appear to be adjacent

• Makes non-routable addresses (10.a.b.c a,d 192.168.c.d) routable

VPN Characteristics• Cheaper than WANs

• dedicated leased lines are very expensive

• Easier to establish than WANs• ISPs will usually help make the initial IP connection

• hours for VPNs vs. weeks for WANs

• slower than LANs• encryption/dectyption takes time

• typical LANS are 10-100 Mbps• endpoints connected by VPM may go through many router hops

– minimize by using same ISP for everything

• dial in users are going to be typically 56Kbps

• less reliable than WANs• with WANs routers are under your control and performance is negotiated

with provider, not so with VPN you only control initial IP connection

• less secure than isolated LANs or WANs• because Internet is used hackers can find you

• VPN protocol is one more thing to be attacked

Types of VPNs

• Server based

• Firewall based

• Router based (including VPN appliances

Server based• Windows

• Routing and Remote Access Service• NT supports only PPTP, W/2000 supports PPTP, L2TP and IPSec

• comes with everything needed to establish a VPN

• Linux • Blowfish, Free S/WAN, PPP over SSL, PPTP, L2TP

• with IP masquerading/IP Chains and additional open source software can be used to create a very robust VPN

• UNIX• many incorporating IPSec into their TCP/IP stacks

• Be aware that VPN traffic leaving your LAN traverses the LAN twice• once to the RRAS service as regular LAN traffic, once encapsulated to the

firewall

Firewall based VPNs

• Since firewalls already do all kinds of packet analysis, adding IP tunneling is relatively easy

• Rapid acceptance of IPSec and IKE are making VPNing at the firewall more common• not all vendors versions of IPSec+IKE work together

• make sure that remote clients software works with your firewall VPN

•

Router based VPNs

• Typically used on big networks• specialized devices for to isolate internal LAN traffic and quickly convey

inter-LAN traffic

• IBM 2210

• CISCO Routers running IOS

• Ascend’s MAX switches

VPN Architectures

• Mesh• each participant has a direct security relationship with every other user

• Hub and spoke• each participant has a single security association with a single VPN router

that has a security association with every VPN device

• Hybrid• combination of both

• mesh of hubs

• star of hubs

Implementations

• IPSec Tunnel Mode• RFC 2401

• Point-to-Point Tunneling Protocol (PPTP)• RFC 2637

• Layer 2 Tunneling Protocol (L2TP)• RFC 2661

• Point-to-Point Protocol over Secure Sockets Layer (PPP/SSL) or Point-to-Point Protocol over Secure Shell (PPP/SSL)• considered to be hacks not standards

VPN Best Practices• Use a real firewall

• Secure the base operating system

• Use a single ISP• minimize routing hops and insure cooperation

• Use packet filtering to reject unknown hosts

• Use public-key encryption and secure Authentication

• Compress before you encrypt• stream compression will help overall performance

• Secure remote hosts

NIAP

• National Information Assurance Partnership (NIAP) • U.S. Government initiative originated to meet the security testing

needs of both information technology (IT) consumers and producers.

• NIAP is a collaboration between the National Institute of Standards and Technology (NIST) and the National Security Agency (NSA)

• in fulfilling their respective responsibilities under PL 100-235 (Computer Security Act of 1987).

• combines the extensive IT security experience of both agencies to promote the development of technically sound security requirements for IT products and systems and appropriate measures for evaluating those products and systems.

NIAP Goals

• The long-term goal of NIAP is to help increase the level of trust consumers have in their information systems and networks through the use of cost-effective security testing, evaluation, and validation programs. In meeting this goal, NIAP seeks to:• Promote the development and use of evaluated IT products and

systems;• Champion the development and use of national and international

standards for IT security;• Foster research and development in IT security requirements

definition, test methods, tools, techniques, and assurance metrics;• Support a framework for international recognition and acceptance of

IT security testing and evaluation results; and• Facilitate the development and growth of a commercial security

testing industry within the U.S.

CCEVS

• Common Criteria Evaluation and Validation Scheme• jointly managed activity of NIST and NSA (NIAP)• the validation body• focus of the CCEVS is to establish a national program for the

evaluation of information technology products for conformance to the International Common Criteria for Information Technology Security Evaluation.

• Common Criteria Testing Laboratory (CCTL)• an approved testing laboratory

• Validation body reviews products tested by CCTL • awards certification (or not) • maintains a list of validated products (VPL)

Evaluation Assurance Levels

• EAL1 – Functionally tested

• EAL2 – Structurally tested

• EAL3 – Methodically tested and checked

• EAL4 – Methodically designed, tested and reviewed

• EAL5 – Semi formally designed and tested

• EAL6 – Semi formally verified design and tested

• EAL7 – Formally verified design and tested

SSL Based VPNs• Browser based

• PositivePRO – Positive Networks ; Connectra – Checkpoint Software

• No special client needed– can be used on any device that is web enabled that

supports SSL (PDA, Cell phones...)– OS independent

• Can’t access desktop applications

• Netifice• Browser based• Java Agent Based• SSL Windows client for desktop access

• SSL-Explorer – Open Source

SSL Based VPNs

• Non-browser based• OpenVPN

• requires client software be installed for each user• Open Source (free)• very good track record (Since 2002)• Runs on most OSs• compatible with with:

– SSL/TLS – RSA Certificates – X509 PKI– NAT– DHCP– TUN/TAP virtual devices