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IPSec

IP Security (IPSec)

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IP Security (IPSec)• IPSec overview• Authentication Header (AH)• Encapsulating Security Payload (ESP)• Internet Key Exchange (IKE)• Main Mode negotiation• Quick Mode negotiation• Retransmit behavior

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Overall Architecture (RFC 1825)

• Framework for security protocols to provide:– Data integrity– Data authentication– Data confidentiality– Security association management– Key management

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Authentication Header (RFC 1826)

• Data integrity—no twiddling of bits• Origin authentication—definitely came from router• Uses keyed-hash mechanism• Does not provide confidentiality

IP Header plus Data

AH

AuthenticationData (00ABCDEF)

AuthenticationData (00ABCDEF)

IP Header plus Data

Router IP HDRIP HDR DataData Router

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Encapsulating Security Payload (RFC 1827)

• Confidentiality• Data origin authentication• Data integrity• Replay protection (optional)

All Data-EncryptedRouter Router

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Security Association (SA)

Router

Firewall

Insecure Channel

• Agreement between two entities on method to communicate securely

• Unidirectional—two way communication consists of two SAs

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IKE Policy Negotiation

Encryption Algorithm, Hash Algorithm, and Method of Authentication

3DES, MD5, and RSA Signatures, or

IDEA, SHA, and DSS Signatures,or

Blowfish, SHA, and RSA Encryption

3DES, MD5, and RSA Signatures, or

IDEA, SHA, and DSS Signatures,or

Blowfish, SHA, and RSA EncryptionIDEA, SHA, and DSS SignaturesIDEA, SHA, and DSS Signatures

ISAKMP Policy TunnelISAKMP Policy Tunnel

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IPSec Model

• Device authentication

– Crypto devices obtain digital certificates from CAs

• Authorization

– Packet selection via ACLs

– Security Association (SA) established via ISAKMP/OAKLAY

• Privacy and integrity

– IPSec-based encryption and digital signature

Certificate Authority

Digital CertificateDigital CertificateSASA

Authenticated Encrypted Tunnel

Encrypted

Clear TextInternal Network

Internal Network

Digital CertificateDigital Certificate

IKE S

ession

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IPsec Protocols and Formats

Headers

KeyExchange

Modes

Encryption Hashing

Headers

KeyExchange

Modes

Encryption Hashing

AuthenticationHeaderEncapsulatingSecurity Payload

ISAKMP/Oakley

Diffie-Hellman

Transport

Tunnel

AuthenticationHeaderEncapsulatingSecurity Payload

ISAKMP/Oakley

Diffie-Hellman

Transport

Tunnel

• Integrity, authentication

• Adds confidentiality

• Negotiates security parameters• Uses digital certificates

• Generates shared secret keys

• IP payload only, Layer 4 is obscured• Both end systems need IPsec

• Entire datagram• No changes to intermediate systems

• DES, 3DES, RC4, IDEA, AES ...

• HMAC MD5, HMAC SHA1

• Integrity, authentication

• Adds confidentiality

• Negotiates security parameters• Uses digital certificates

• Generates shared secret keys

• IP payload only, Layer 4 is obscured• Both end systems need IPsec

• Entire datagram• No changes to intermediate systems

• DES, 3DES, RC4, IDEA, AES ...

• HMAC MD5, HMAC SHA1

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IPSec Modes

IP HDRIP HDR

Encrypted

IP HDRIP HDR DATADATA

IPSec HDRIPSec HDR DATADATA

IP HDRIP HDR DATADATA

IPSec HDRIPSec HDR IP HDRIP HDRNew IP HDRNew IP HDR

Encrypted

DATADATA

Tunnel Mode

Transport Mode

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Tunnel and Transport Modes

• Transport mode for end-to-end session

• Tunnel mode for everything else

HR Server

Joe’s PC

Transport Mode

Tunnel ModeTunnel Mode

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Ipsec—Standards Based

Internet

CampusFirewall

VLANsIPsec

IPsec

IPsec

Dial

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IPSec Overview

Router to Router

Router to FirewallPC to Router

PC to Server

• Proposed Internet standard for IP-layer cryptography with IPv4 and IPv6

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IPSec Process• Initiating the IPSec session

– Phase one—exchanging keys– Phase two—setting up security

associations• Encrypting/decrypting packets• Rebuilding security associations• Timing out security associations

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Initiating the IPSec Session Phase One — ISAKMP

• Internet Security Association Key Management Protocol (ISAKMP)

• Both sides need to agree on the ISAKMP security parameters (ISAKMP SADB)– ISAKMP parameters

•Encryption algorithm•Hash algorithm•Authentication method•Diffie-Hellman modulus•Group lifetime

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Initiating the IPSec Session Phase Two

• Both sides need to agree on the IPSec security parameters (IPSec SADB)

• IPSec parameters– IPSec peer

•Endpoint of IPSec tunnel– IPSec proxy

•Traffic to be encrypted/decrypted– IPSec transform

•Encryption and hashing– IPSec lifetime

•Phase two SA regeneration time

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Encrypting and Decrypting Packets• Phase one and phase two completes• Security Associations (SA) are created at

both IPSec endpoints • Using the negotiated SADB information

– Outbound packets are encrypted– Inbound packets are decrypted

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Rebuilding Security Associations• To ensure that keys are not compromised

they are periodically refreshed• Security associations will be rebuilt when:

– The lifetime expires, or– Data volume has been exceeded, or– Another SA is attempted with identical

parameters

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Security Associations• Combination of mutually agreed security services,

protection mechanisms, and cryptographic keys• ISAKMP SA• IPSec SAs

– One for inbound traffic– One for outbound traffic

• Security Parameters Index (SPI)– Helps identify an SA

• Creating SAs– Main Mode for ISAKMP SA– Quick Mode for IPSec SAs

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IPSec Headers

• Authentication Header (AH)– Provides data origin authentication, data

integrity, and replay protection for the entire IP datagram

• Encapsulating Security Payload (ESP)– Provides data origin authentication, data

integrity, replay protection, and data confidentiality for the ESP-encapsulated portion of the packet

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IPSec Modes

• Transport mode– Typically used for IPSec peers doing end-to-

end security– Provides protection for upper-layer protocol

data units (PDUs)• Tunnel mode

– Typically used by network routers to protect IP datagrams

– Provides protection for entire IP datagrams

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AH Transport Mode

IP Upper layer PDU

IP AH

Authenticated

Upper layer PDU

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AH Tunnel Mode

AH

Authenticated

IP

IP

IP (new)

Upper layer PDU

Upper layer PDU

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ESP Transport Mode

IP ESP ESPAuthData

Encrypted

Authenticated

IP Upper layer PDU

Upper layer PDU

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ESP with AH Transport Mode

IP ESP ESPESPAuth

Encrypted

Authenticated with AH

IP

AH

Upper layer PDU

Upper layer PDU

Authenticated with ESP

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ESP Tunnel Mode

IP (new) ESP ESPAuthData

IP

Encrypted

Authenticated

IP Upper layer PDU

Upper layer PDU