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IPsec

IPsec. IT443 – Network Security Administration Instructor: Bo Sheng. Securing Networks. Applications Layer telnet/ftp: ssh , http: https , mail: PGP. ( SSL/TLS ) Transport Layer (TCP). Network Security Tools: Monitoring/Logging/Intrusion Detection. ( IPSec, IKE ) Network Layer (IP).

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IPsec

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  1. IPsec IT443 – Network Security Administration Instructor: Bo Sheng

  2. Securing Networks Applications Layer telnet/ftp: ssh, http: https, mail: PGP (SSL/TLS) Transport Layer (TCP) Network Security Tools: Monitoring/Logging/Intrusion Detection (IPSec, IKE) Network Layer (IP) Control/Management (configuration) Link Layer (IEEE802.1x/IEEE802.10) Physical Layer (spread-Spectrum, quantum crypto, etc.)

  3. IPsec Objectives • Why do we need IPsec? • IP V4 has no authentication • IP spoofing • Payload could be changed without detection. • IP V4 has no confidentiality mechanism • Eavesdropping • Denial of service (DoS) attacks • Cannot hold the attacker accountable due to the lack of authentication.

  4. IPsec Objectives • IP layer security mechanism for IPv4 and IPv6 • Not all applications need to be security aware • Can be transparent to users • Provide authentication and confidentiality mechanisms.

  5. IPsec Architecture IPsec module 1 IPsec module 2 SPD SPD IKE IKE IPsec SAD SAD IPsec SA SPD: Security Policy Database; IKE: Internet Key Exchange; SA: Security Association; SAD: Security Association Database.

  6. IPsec Architecture • Two Protocols (Mechanisms) • Authentication Header (AH) • Encapsulating Security Payload (ESP) • IKE Protocol • Internet Key Management

  7. IPsec Architecture • Can be implemented in • Host or gateway • Can work in two Modes • Tunnel mode • Transport mode • Hosts can implement IPsec to connect to: • Other hosts in transport or tunnel mode • Or Gateways in tunnel mode • Gateways to gateways • Tunnel mode

  8. Authentication Header (AH) • Data integrity • Entire packet has not been tampered with • Authentication • Can “trust” IP address source • Use MAC to authenticate • Anti-replay feature

  9. Encapsulated Security Protocol (ESP) • Confidentiality for upper layer protocol • Partial traffic flow confidentiality (Tunnel mode only) • Data origin authentication and connectionless integrity (optional)

  10. New IP Header AH or ESP Header Orig IP Header TCP Data Tunnel Mode Encrypted Tunnel Gateway Gateway Encrypted Unencrypted Unencrypted A B

  11. Tunnel Mode Outer IP header IPsec header Inner IP header Higher layer protocol ESP Real IP destination Destination IPsec entity AH • ESP applies only to the tunneled packet • AH can be applied to portions of the outer header

  12. New IP Header AH or ESP Header TCP Data Transport Mode Encrypted/Authenticated A B

  13. Transport Mode IP header IP options IPsec header Higher layer protocol ESP Real IP destination AH • ESP protects higher layer payload only • AH can protect IP headers as well as higher layer payload

  14. Security Association (SA) • An association between a sender and a receiver • Consists of a set of security related parameters • E.g., sequence number, encryption key • One way relationship • Determine IPsec processing for senders • Determine IPsec decoding for destination • SAs are not fixed! Generated and customized per traffic flows

  15. Security Parameters Index (SPI) • A 32-bits string assigned to an SA. • Carried in AH and ESP headers to enable the receiving system to select the SA under which the packet will be processed. • SPI + Dest IP address + IPsec Protocol • Uniquely identifies each SA in SA Database (SAD)

  16. SA Database (SAD) • Holds parameters for each SA • Sequence number counter • Lifetime of this SA • AH and ESP information • Tunnel or transport mode • Every host or gateway participating in IPsec has their own SA database

  17. SA Bundle • More than 1 SA can apply to a packet • Example: ESP does not authenticate new IP header. How to authenticate? • Use SA to apply ESP w/out authentication to original packet • Use 2nd SA to apply AH

  18. Security Policy Database (SPD) • Decide • What traffic to protect? • Has incoming traffic been properly secured? • Policy entries define which SA or SA Bundles to use on IP traffic • Each host or gateway has their own SPD • Index into SPD by Selector fields • Selectors: IP and upper-layer protocol field values. • Examples: Dest IP, Source IP, Transport Protocol, IPSec Protocol, Source & Dest Ports, …

  19. SPD(Policy) SA Database … … Outbound Processing Outbound packet (on A) A B IP Packet Is it for IPsec?If so, which policy entry to select? IPSec processing SPI & IPsec Packet Determine the SA and its SPI Send to B

  20. SPD(Policy) SA Database … … Inbound Processing Inbound packet (on B) A B From A SPI & Packet Use SPI to index the SAD Was packet properly secured? Original IP Packet “un-process”

  21. Issues • Firewalls • IPsec encrypts information used by firewalls to filter traffic (e.g., port number) • AH mutable/immutable/predictable fields: • Some fields get modified by the intermediate routers and can’t be protected by the AH • Mutable: type of service, flags, fragment offset, TTL, header checksum • Mutable but predictable fields are included in the AH computation using their expected value at the destination (e.g., destination address even when using source routing)

  22. Internet Key Exchange • Why do we need Internet key management • AH and ESP require encryption and authentication keys • Process to negotiate and establish IPsec SAs between two entities

  23. Security Principles • Basic security principle for session keys • Compromise of a session key • Doesn’t permit reuse of the compromised session key. • Doesn’t compromise future session keys and long-term keys. • Perfect forward secrecy (PFS) • Compromise of current keys (session key or long-term key) doesn’t compromise past session keys. • Concern for encryption keys but not for authentication keys.

  24. A Note about IKE • IKE v2 was introduced in RFC 4306 (December 2005) • IKE v2 does not interoperate with IKE v1 • Both version can unambiguously run over the same UDP port • IKE v2 combines the contents of previously separate documents • ISAKMP • IKE v1 • DOI • NAT • …

  25. IKE Overview • A separate RFC has been published for IKE • RFC 2409 • Request-response protocol • Initiator • Responder • Two phases • Phase 1: Establish an IKE (ISAKMP) SA • Essentially the ISAKMP phase 1 • Bi-directional • Phase 2: Use the IKE SA to establish IPsec SAs • Key exchange phase • Directional

  26. A Clarification About PFS • In RFC 2409: • When used in the memo Perfect Forward Secrecy (PFS) refers to the notion that compromise of a single key will permit access to only data protected by a single key. • The key used to protect transmission of data MUST NOT be used to derive any additional keys. • If the key used to protect transmission of data was derived from some other keying material, that material MUST NOT be used to derive any more keys.

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