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Chapter 6Chapter 6

IP Security

Henric Johnson

Blekinge Institute of Technology, Sweden

http://www.its.bth.se/staff/hjo/

henric.johnson@bth.se

Revised by Andrew Yang

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OutlineOutline

• Internetworking and Internet Protocols (Appendix 6A)

• IP Security Overview• IP Security Architecture• Authentication Header• Encapsulating Security Payload• Combinations of Security Associations• Key Management

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TCP/IP ExampleTCP/IP Example

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IPv4 HeaderIPv4 Header

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IPv6 HeaderIPv6 Header

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IP Security OverviewIP Security Overview

• IPSec is not a single protocol. • Instead, IPSec provides a set of

security algorithms plus a general framework that allows a pair of communicating entities to use whichever algorithms to provide security appropriate for the communication.

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IP Security OverviewIP Security Overview

• Applications of IPSec– Secure branch office connectivity over

the Internet– Secure remote access over the

Internet– Establsihing extranet and intranet

connectivity with partners– Enhancing electronic commerce

security

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IP Security ScenarioIP Security Scenario

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IP Security OverviewIP Security Overview

• Benefits of IPSec– Transparent to applications (below transport

layer (TCP, UDP)– Provide security for individual users

• IPSec for route/router security:– A router or neighbor advertisement comes

from an authorized router– A redirect message comes from the router

to which the initial packet was sent– A routing update is not forged

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IP Security ArchitectureIP Security Architecture• IPSec documents:

– RFC 2401: Security Architecture for the Internet Protocol. S. Kent, R. Atkinson. November 1998. (An overview of security architecture)

– RFC 2402: IP Authentication Header. S. Kent, R. Atkinson. November 1998. (Description of a packet encryption extension to IPv4 and IPv6)

– RFC 2406: IP Encapsulating Security Payload (ESP). S. Kent, R. Atkinson. November 1998. (Description of a packet emcryption extension to IPv4 and IPv6)

– RFC 2408: Internet Security Association and Key Management Protocol (ISAKMP). D. Maughan, M. Schertler, M. Schneider, J. Turner. November 1998. (Specification of key managament capabilities)

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IPSec Document OverviewIPSec Document Overview

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IPSec ServicesIPSec Services• Access Control• Integrity

– Connectionless integrity (aka. data integrity)– Rejection of replayed packets (a form of

partial sequence integrity)– Data origin authentication (aka. origin

integrity)

• Confidentiality – Data confidentiality (encryption)– Limited traffic flow confidentiallity (to prevent

traffic analysis)

• Refer to http://www.linuxexposed.com/Articles/General/The-longest-short-IP-Sec-

Paper.html

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Security Associations Security Associations (SA)(SA)

• A one way relationsship between a sender and a receiver.

• Identified by three parameters:– Security Parameter Index (SPI)– IP Destination address– Security Protocol Identifier

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Transport Mode SA

Tunnel Mode SA

AH Authenticates IP payload and selected portions of IP header and IPv6 extension headers

Authenticates entire inner IP packet plus selected portions of outer IP header

ESP Encrypts IP payload and any IPv6 extesion header

Encrypts inner IP packet

ESP with authentication

Encrypts IP payload and any IPv6 extesion header. Authenticates IP payload but no IP header

Encrypts inner IP packet. Authenticates inner IP packet.

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Before applying AHBefore applying AH

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Transport Mode (AH Transport Mode (AH Authentication)Authentication)

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Tunnel Mode (AH Tunnel Mode (AH Authentication)Authentication)

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Authentication HeaderAuthentication Header

• Provides support for data integrity and authentication (MAC code) of IP packets.

• Guards against replay attacks.

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End-to-end versus End-End-to-end versus End-to-Intermediate to-Intermediate AuthenticationAuthentication

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Encapsulating Security Encapsulating Security PayloadPayload

• ESP provides confidentiality services

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Encryption and Encryption and Authentication Authentication

AlgorithmsAlgorithms• Encryption:

– Three-key triple DES– RC5– IDEA– Three-key triple IDEA– CAST– Blowfish

• Authentication:– HMAC-MD5-96– HMAC-SHA-1-96

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ESP Encryption and ESP Encryption and AuthenticationAuthentication

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ESP Encryption and ESP Encryption and AuthenticationAuthentication

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Combinations of Combinations of Security AssociationsSecurity Associations

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Combinations of Combinations of Security AssociationsSecurity Associations

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Combinations of Combinations of Security AssociationsSecurity Associations

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Combinations of Combinations of Security AssociationsSecurity Associations

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Key ManagementKey Management• Two types:

– Manual– Automated

• Oakley Key Determination Protocol• Internet Security Association and Key

Management Protocol (ISAKMP)

• RFCs:– RFC2412 The OAKLEY Key Determination Protocol. H.

Orman. November 1998. (INFORMATIONAL)– RFC2409 The Internet Key Exchange (IKE). D. Harkins,

D. Carrel. November 1998 (PROPOSED STANDARD)– RFC2408 Internet Security Association and Key

Management Protocol (ISAKMP). D. Maughan, M. Schertler, M. Schneider, J. Turner. November 1998 (PROPOSED STANDARD)

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OakleyOakley

• Three authentication methods:– Digital signatures– Public-key encryption– Symmetric-key encryption

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ISAKMPISAKMP• All payloads All payloads bvegin with the bvegin with the same generic same generic payload header.payload header. The ‘Next The ‘Next Payload’ field has Payload’ field has a value of 0 if this a value of 0 if this is the last payload is the last payload in the mesg.in the mesg. Otherwise it Otherwise it contains the type contains the type of the next of the next payload.payload.

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ISAKMP Payload TypesISAKMP Payload Types

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ISAKMP Exchange ISAKMP Exchange TypesTypes

• ISAKMP provides a ISAKMP provides a fraework fo rmessage fraework fo rmessage exchange, with the payload exchange, with the payload types as the building blocks.types as the building blocks.Five default exchange types Five default exchange types should be supported.should be supported.

Note: SA in the table refers to Note: SA in the table refers to SA type of payload with SA type of payload with associated Protocol associated Protocol (Proposal?) and Transform (Proposal?) and Transform payloads.payloads.

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Recommended ReadingRecommended Reading

• Comer, D. Internetworking with TCP/IP, Volume I: Principles, Protocols and Architecture. Prentic Hall, 1995

• Stevens, W. TCP/IP Illustrated, Volume 1: The Protocols. Addison-Wesley, 1994