Ipsec

IPSec - IPSec - OverviewOverview

Mr. Rupesh Mishra St. Francis Institute of Tech

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OutlineOutline• Introduction

• IPSec Architecture

• Internet Key Exchange (IKE)

• IPSec Policy

• Discussion

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IP is not Secure!IP is not Secure!• IP protocol was designed in the late

70s to early 80s

o Part of DARPA Internet Project

o Very small network

• All hosts are known!

• So are the users!

• Therefore, security was not an issue

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Security Issues in IPSecurity Issues in IP

• source spoofing - DOS Attack

• replay packets - Replay Attack

• No data integrity - Modification

• No confidentiality - Spying

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What is IPSecWhat is IPSec

• A set of protocol and algorithm used to

secure IP data and network layer

• Open standard for VPN implementation

• Inbuilt in IPV6 and compatible with IPV4

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Goals of IPSecGoals of IPSec• to verify sources of IP packets

o authentication

• to prevent replaying of old packets

• to protect integrity and/or confidentiality of

packetso data Integrity/Data Encryption

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OutlineOutline• Why IPsec?

• IPSec Architecture


• IPsec Policy

• Discussion

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The IPSec Security The IPSec Security ModelModel

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Secure

Insecure

IPSec ArchitectureIPSec Architecture

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ESP AH

IKE

IPSec Security Policy

Encapsulating SecurityPayload

Authentication Header

The Internet Key Exchange

IPSec ArchitectureIPSec Architecture

• IPSec provides security in three

situations:o Host-to-host, host-to-gateway and gateway-to-gateway

• IPSec operates in two modes:o Transport mode (for end-to-end)

o Tunnel mode (for VPN)

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IPsec ArchitectureIPsec Architecture

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Tunnel ModeRouter Router

Transport Mode

Various PacketsVarious Packets

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IP header

IP header

IP header

TCP header

TCP header

TCP header

data

data

data

IPSec header

IPSec header IP header

Original

Transportmode

Tunnelmode

Security Association Security Association (SA)(SA)

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• Specification of security for the

communication

• Specification of key , algorithm , policy , etc

• Unidirectional

• SADB

ISAKMPISAKMP

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• Defines the procedure for security

association

• SA and Key Management

IPSecIPSec• A collection of protocols (RFC 2401)

o Authentication Header (AH)

• RFC 2402

o Encapsulating Security Payload (ESP)

• RFC 2406

o Internet Key Exchange (IKE)

• RFC 2409

o IP Payload Compression (IPcomp)

• RFC 3137

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Authentication Header Authentication Header (AH)(AH)

• Provides source authentication

o Protects against source spoofing

• Provides data integrity

• Protects against replay attacks

o Use monotonically increasing sequence

numbers

o Protects against denial of service attacks

• NO protection for confidentiality!16

AH DetailsAH Details• Use 32-bit monotonically increasing

sequence number to avoid replay attacks

• Use cryptographically strong hash

algorithms to protect data integrity (96-bit)

o Use symmetric key cryptography

o HMAC-SHA-96, HMAC-MD5-96

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AH Packet DetailsAH Packet Details

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Authentication Data

Sequence Number

Security Parameters Index (SPI)

Nextheader

Payloadlength Reserved

Old IP header (only in Tunnel mode)

TCP header

New IP header

Authenticated

Data

EncapsulatedTCP or IP packet

Hash of everythingelse

Encapsulating Encapsulating Security Payload Security Payload

(ESP)(ESP)• Provides all that AH offers, and

• in addition provides data confidentialityo Uses symmetric key encryption

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ESP DetailsESP Details• Same as AH:

o Use 32-bit sequence number to counter replaying attacks

o Use integrity check algorithms

• Only in ESP:o Data confidentiality:

• Uses symmetric key encryption algorithms to encrypt

packets

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ESP Packet DetailsESP Packet Details

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Authentication Data

Sequence Number

Security Parameters Index (SPI)

Nextheader

Payloadlength Reserved

TCP header

Authenticated

IP header

Initialization vector

Data

Pad Pad length Next

Encrypted TCP packet


• IPsec Architecture


• IPsec Policy

• Discussion

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Internet Key Exchange Internet Key Exchange (IKE)(IKE)

• Exchange and negotiate security policies

• Establish security sessionso Identified as Security Associations

• Key exchange

• Key management

• Can be used outside IPsec as well

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How It WorksHow It Works• IKE operates in two phases

o Phase 1: negotiate and establish an auxiliary end-to-end secure channel• Used by subsequent phase 2 negotiations• Only established once between two end points!

o Phase 2: negotiate and establish custom secure channels• Occurs multiple times

o Both phases use Diffie-Hellman key exchange to establish a shared key

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IKE Phase 1IKE Phase 1• Goal: to establish a secure channel between

two end points

o This channel provides basic security features:

• Source authentication

• Data integrity and data confidentiality

• Protection against replay attacks

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IKE Phase 1IKE Phase 1• Rationale: each application has different

security requirements

• But they all need to negotiate policies and

exchange keys!

• So, provide the basic security features and

allow application to establish custom

sessions

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ExamplesExamples• All packets sent to address mybank.com

must be encrypted using 3DES with HMAC-

MD5 integrity check

• All packets sent to address www.forum.com

must use integrity check with HMAC-SHA1

(no encryption is required)

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Phase 1 ExchangePhase 1 Exchange• Can operate in two modes:

o Main mode

• Six messages in three round trips

• More options

o Quick mode

• Four messages in two round trips

• Less options

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Phase 1 (Main Mode)Phase 1 (Main Mode)

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Initiator Responder

[Header, SA1]


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Initiator Responder

[Header, SA1]

[Header, SA2]

Establish vocabulary for further communication


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Initiator Responder

[Header, SA1]

[Header, SA2]

[Header, KE, Ni, {Cert_Reg} ]


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Initiator Responder

Header, SA1

[Header, SA1]

[Header, KE, Ni { , Cert_Req} ]

[Header, KE, Nr {, Cert_Req}]

Establish secret key using Diffie-Hellman key exchangeUse nonces to prevent replay attacks


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Initiator Responder

[Header, SA1]

[Header, SA1]

[Header, KE, Ni {,Cert_Req} ]

[Header, KE, Nr {,Cert_Req}]

[Header, IDi, {CERT} sig]


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Initiator Responder

[Header, SA1]

[Header, SA1]

[Header, KE, Ni {, Cert_req}]

[Header, KE, Nr {, Cert_req}]

[Header, IDi, {CERT} sig]

[Header, IDr, {CERT} sig]

Signed hash of IDi (without Cert_req , just send the hash)

Phase 1 (Quick Mode)Phase 1 (Quick Mode)

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Initiator Responder

[Header, SA1, KE, Ni, IDi]

Phase 1 (Quick Mode)Phase 1 (Quick Mode)

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Initiator Responder

[Header, SA1, KE, Ni, IDi]

[Header, SA2, KE, Nr, IDr, [Cert]sig]

[Header, [Cert]sig]

First two messages combined into one(combine Hello and DH key exchange)

IPSec (Phase 1)IPSec (Phase 1)• Four different way to authenticate

(either mode)o Digital signature

o Two forms of authentication with public key encryption

o Pre-shared key

• NOTE: IKE does use public-key based

cryptography for encryption

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IPSec (Phase 2)IPSec (Phase 2)• Goal: to establish custom secure

channels between two end pointso End points are identified by <IP, port>:

• e.g. <www.mybank.com, 8000>

o Or by packet:

• e.g. All packets going to 128.124.100.0/24

o Use the secure channel established in Phase 1 for

communication

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IPSec (Phase 2)IPSec (Phase 2)• Only one mode: Quick Mode

• Multiple quick mode exchanges can be

multiplexed

• Generate SAs for two end points

• Can use secure channel established in

phase 1

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IP Payload IP Payload CompressionCompression

• Used for compression

• Can be specified as part of the IPSec policy

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• IPSec Policy

• Discussion

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IPsec PolicyIPsec Policy• Phase 1 policies are defined in terms of

protection suites

• Each protection suite

o Must contain the following:

• Encryption algorithm

• Hash algorithm

• Authentication method

• Diffie-Hellman Group

o May optionally contain the following:

• Lifetime

• …

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IPSec PolicyIPSec Policy• Phase 2 policies are defined in terms of

proposals

• Each proposal:o May contain one or more of the following

• AH sub-proposals

• ESP sub-proposals

• IPComp sub-proposals

• Along with necessary attributes such as

o Key length, life time, etc

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IPSec Policy ExampleIPSec Policy Example• In English:

o All traffic to 128.104.120.0/24 must be:

• Use pre-hashed key authentication

• DH group is MODP with 1024-bit modulus

• Hash algorithm is HMAC-SHA (128 bit key)

• Encryption using 3DES

• In IPSec:

o [Auth=Pre-Hash;

DH=MODP(1024-bit);

HASH=HMAC-SHA;

ENC=3DES]

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IPsec Policy ExampleIPsec Policy Example• In English:

o All traffic to 128.104.120.0/24 must use one of the following:• AH with HMAC-SHA or,• ESP with 3DES as encryption algorithm and

(HMAC-MD5 or HMAC-SHA as hashing algorithm)

• In IPsec:o [AH: HMAC-SHA] or, o [ESP: (3DES and HMAC-MD5) or

(3DES and HMAC-SHA)]

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Virtual Private Virtual Private Networks (VPNs)Networks (VPNs)

• Protocolo Data Link Later – PPTP , L2F , L2TF

o Network Layer - IPSec

• Virtualo It is not a physically distinct network

• Privateo Tunnels are encrypted to provide confidentiality

• Computer dept might have a VPNo I can be on this VPN while traveling

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• IPsec Policy

• Discussion

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DiscussionDiscussion• IPSec is not the only solution!

o Security features can be added on top of IP!

• e.g. Kerberos, SSL

o IP, IPSec protocols are very complex!

• Two modes, three sub protocols

o Complexity is the biggest enemy of security

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DiscussionDiscussion• Has it been used?

o Yes—primarily used by some VPN vendors

• But not all routers support it

o No—it is not really an end-to-end solution

• Authentication is too coarse (host based)

• Default encryption algorithm too weak (DES)

• Too complex for applications to use

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ResourcesResources• IP, IPsec and related RFCs:

o http://www.ietf.org/html.charters/ipsec-charter.

html

o IPsec: RFC 2401, IKE: RFC 2409

o www.freeswan.org

• Google search

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Ipsec

Software

o data confidentiality

gateway ipsec

security policies

o host

security sessionso

symmetric key encryption19

data integrity modification

o main mode