Lecture CCNA security partner - Chapter 13: IPsec Fundamentals

This chapter covers the role and operational impact of IPsec’s main components and its modes of operation in various scenarios. It provides a detailed description of the phases of IPsec connectivity. It also provides an overview of IPv6 VPNs.

Trang 1

Chapter 13 IPsec Fundamentals

Trang 2

This chapter addresses the protocols and algorithms that IPsec uses and the different security services that IPsec provides

• Analyzes the architecture of the IPsec protocol

• Details the role and operational impact of IPsec’s main components

• Describes IPsec modes of operation in various scenarios

• Describes the phases of IPsec connectivity

• Describes the role and component of IKE

• Provides an overview of the operations of IPv6 VPNs

Contents

Trang 3

• An IP Security (IPsec) virtual private network (VPN) is an essential tool for providing a secure network for business communication

• IPsec works at the network layer, protecting and authenticating IP

packets between participating IPsec devices (peers)

• IPsec is not bound to any specific encryption, authentication, or security algorithms or keying technology

• IPsec is a framework of open standards

IPsec Framework

Trang 4

Trang 5

• The following are some of the encryption algorithms and key lengths

that VPNs use:

– Date Encryption Standard (DES)

– Advanced Encryption Standard (AES)

– Rivest, Shamir, and Adleman (RSA)

– Software-Optimized Encryption Algorithm (SEAL) algorithm

Encryption Algorithms

Trang 6

• Encryption algorithms, such as DES and 3DES, require a symmetric

shared-secret key to perform encryption and decryption

• You can use email, courier, or overnight express to send the

shared-secret keys to the administrators of the devices

• But the easiest key-exchange method is a public-key exchange method between the encrypting and decrypting devices

The method has two variants:

• The Diffie-Hellman (DH) key agreement

• ECDH is a variant of the DH protocol using elliptic curve cryptography

(ECC) It is part of the Suite B standards

Key Exchange: Diffie-Hellman

Trang 7

• DH19: 256-bit ECDH key

Diffie-Hellman Group

Trang 8

• VPN data is typically transported over the public Internet Potentially,

this data could be intercepted and modified

• To guard against this problem, you can use a data-integrity algorithm

• Three common HMAC algorithms:

– HMAC-Message Digest 5 (HMAC-MD5)

– HMAC-Secure Hash Algorithm 1 (HMAC-SHA-1)

– HMAC-Secure Hash Algorithm 2 (HMAC-SHA-2)

Data Integrity

Trang 9

• When you are conducting business long distance, it is necessary to

know who is at the other end of the phone, email, or fax

• The same is true of VPN networks

• The device on the other end of the VPN tunnel must be authenticated

before the communication path is considered secure

– Preshared keys

– RSA signatures

– RSA encrypted nonces

– Elliptic Curve Digital Signature Algorithm (ECDSA)

Authentication

Trang 10

IPsec Framework Components

Trang 11

IPsec Protocol

Trang 12

AH Authentication and Integrity

Trang 13

• ESP provides confidentiality by encrypting the payload

• It supports a variety of symmetric encryption algorithms

• The lowest common algorithm for IPsec is 56-bit DES

• Cisco products also support the use of 3DES and especially AES for

stronger encryption

Encapsulating Security Payload

Trang 14

ESP Protocol

Trang 15

Encapsulation with Tunnel Mode and Transport

Mode

Trang 16

• IPsec implements a VPN solution using an encryption process that

involves the periodic changing of encryption keys

• IPsec uses the IKE protocol to authenticate a peer computer and to

generate encryption keys

• IKE negotiates a security association (SA), which is an agreement

between two peers engaging in an IPsec exchange and consists of all

the required parameters necessary to establish successful

communication

• An IPsec peer accepting incoming IKE requests listens on UDP port 500

IKE Protocol

Trang 17

IPsec uses the IKE protocol to provide these functions:

• Negotiation of SA characteristics

• Automatic key generation

• Automatic key refresh

• Manageable manual configuration

IKE Functions

Trang 18

• There are two versions of the IKE protocol: IKEv1 and IKEv2

• IKEv2 was created to overcome some of the limitations of IKEv1 IKEv2 provides the following enhancements:

• Simplicity, by requiring fewer transactions to establish security associations A simplified initial exchange of messages reduces latency and increases

connection establishment speed.

• Stronger security, through DoS protection and other functions.

• Reliability, by using sequence numbers, acknowledgements, and error

correction.

• Flexibility, through support for Extensible Authentication Protocol (EAP) as a

method for authenticating VPN endpoints.

• Mobility, by using the IKEv2 Mobility and Multihoming Protocol (MOBIKE)

extension This enhancement allows mobile users to roam and change IP

addresses without disconnecting their IPsec session.

IKE version

Trang 19

Visual Representation of IKEv1 and

IPsec Tunnels Being Built from the

Ground Up

Trang 20

• Main mode

• Aggressive mode

• Quick mode

IKEv1 Modes

Trang 21

• IKE Phase 1: Two IPsec peers perform the initial negotiation of SAs In

this phase, the SA negotiations are bidirectional; data may be sent and

received using the same encryption key

• IKE Phase 2: SAs are negotiated by the IKE process ISAKMP on behalf

of other services, such as IPsec, that need encryption key material for

operation Quick mode negotiates the IKE Phase 2 SAs In this phase, the SAs that IPsec uses are unidirectional; therefore, a separate key

exchange is required for each data flow

IKEv1 Phases

Trang 22

IKEv1 Phase 1

Trang 23

Main mode has three two-way exchanges between the initiator and

receiver:

• First exchange: Peers negotiate and agree on the algorithms and hashes that will be used to secure the IKE communications

• Second exchange: DH generates public and private values The peers

exchange their public values, and the result is a shared secret The

shared-secret key is used to generate all the other encryption and

authentication keys

• Third exchange: The identity of the other side is verified The main

outcome of main mode is a secure communications path for subsequent exchanges between the peers

Main Mode

Trang 24

• Aggressive mode, as explained earlier, compresses the IKE SA

negotiation phases into a total of three messages

• Negotiation is quicker, and the initiator and responder IDs pass in

plaintext

Aggressive Mode

Trang 25

IKEv1 Phase 1, First Exchange: Policy Is Negotiated

Trang 26

IKEv1 Phase 1, Second Exchange: DH Key

Exchange

Trang 27

As mentioned earlier, there are four data origin authentication methods

of a message encrypted with its private key as proof of its identity

• RSA encrypted nonces: Nonces are random numbers that are generated

by each peer and then encrypted and exchanged between peers The two nonces are used during the peer-authentication process

• ECDSA signatures: Exchange of certificates ECDSA certificates are

smaller than RSA signatures of similar cryptographic strength, resulting in improved communications efficiency ECDSA is available with Suite B

IKEv1 Phase 1, Third Exchange: Authenticate Peer

Identity

Trang 28

• Negotiates IPsec security parameters, known as IPsec transform sets

• Establishes IPsec SAs

• Periodically renegotiates IPsec SAs to ensure security

• Optionally, performs an additional DH exchange to generate IPsec SA

keys that have no relation to the IKE keys Generating IPsec keys from

scratch for the purpose of IPsec SAs is referred to as Perfect Forward

Secrecy (PFS), which is described after IKEv2 quick mode

IKEv1 Phase 2

Trang 29

• In IKEv2, there is a simplified initial exchange of messages that,

compared to IKEv1, reduces latency and increases the connection

establishment speed

• The IKEv2 base specification includes all the functionality of IKEv1 as

well as additional functionality

• It preserves most of the features of version 1, including the two

negotiation phases

IKE Version 2

Trang 30

IKEv2: A Simplified Approach

Trang 31

IKEv1 Versus IKEv2

Trang 32

• IPsec is mandatory for IPv6

• IPsec is native to IPv6

• Includes built-in confidentiality, integrity, authentication, and antireplay

• Offers flexibility and low overhead through extension headers

• The IPsec framework and behavior are the same as IPsec for IPv4

• Strong encryption (Suite B) and mobility enhancements (IKEv2) are key

in IPv6

• Only site-to-site tunnel mode VPNs are supported in Cisco IOS as of

version 15.1

IPv6 VPNs

Trang 33

IPsec Services for Transitioning to IPv6

Trang 34

Định dạng
Số trang	34
Dung lượng	608,73 KB