Chapter 6 Network infrastructure security IPSec

Eavesdropping Modification of packets in transit Identity spoofing (forged source IP addresses) Denial of service Many solutions are application-specific TLS for Web, S/MIME for email, SSH for remote login IPsec aims to provide a framework of open standards for secure communications over IP Protect every protocol running on top of IPv4 and IPv6

IPsec Protocol Suite

o ESP, AH, IKE

Packet Encapsulation in IPsec

o Transport mode

o Tunnel mode

Internet Key Exchange (IKE)

 Eavesdropping

 Modification of packets in transit

 Identity spoofing (forged source IP addresses)

 Denial of service

 Many solutions are application-specific

 TLS for Web, S/MIME for email, SSH for remote login

 IPsec aims to provide a framework of open standards for

secure communications over IP

 Protect every protocol running on top of IPv4 and IPv6

• makes use of the HMAC message authentication code

• can be applied to the entire original IP packet (tunnel mode) or to all

of the packet except for the IP header (transport mode).

 IPsec provides the capability to secure communications across

a LAN, across private and public WANs, and across the

Internet

o Secure branch office connectivity over the Internet:

saving costs and network management overhead.

o Secure remote access over the Internet:

reduces the cost of toll charges for traveling employees and

telecommuters.

o Establishing extranet and intranet connectivity with partners:

ensuring authentication and confidentiality and providing a key

exchange mechanism.

o Enhancing electronic commerce security:

guarantees data is both encrypted and authenticate.

 In a firewall or router, it provides strong security that can be

applied to all traffic crossing the perimeter (edge).

 IPsec in a firewall is resistant to bypass if all traffic from the

outside must use IP and the firewall is the only means of

entrance from the Internet into the organization.

 IPsec is below the transport layer (TCP, UDP) and so is

transparent to applications.

 IPsec can be transparent to end users.

 IPsec can provide security for individual users

 IPsec provides security services at the IP layer by:

o enabling a system to select required security protocols,

o determining the algorithm(s) to use for the service(s), and

o putting in place any cryptographic keys required to provide the

requested services.

 RFC 4301 lists the following services:

o Access control

o Connectionless integrity

o Data origin authentication

o Rejection of replayed packets (a form of partial sequence

integrity)

o Confidentiality (encryption)

o Limited traffic flow confidentiality

Authentication Header (AH) protocol

o For authenticating and securing data

o IP protocol 51

Encapsulating Security Payload (ESP) protocol

o For encrypting, authenticating, and securing data

o IP protocol 50

Internet Key Exchange (IKE) protocol

o For negotiating security parameters and establishing

authenticated keys

o Uses UDP port 500 for ISAKMP

Authentication Header (AH) - RFC4302

o is an extension header

o Provide data origin authentication for IP datagrams

o provide connectionless integrityand

o provide protection against replays.

 Encapsulating Security Payload (ESP) RFC4303

o consists of an encapsulating header and trailer used to provide

encryption or combined encryption/authentication

o ESP can be used to provide:

• confidentiality,

• Data origin authentication,

• connectionless integrity,

• an anti-replay service (a form of partial sequence integrity),

• and (limited) traffic flow confidentiality.

o ESP can work with a variety of encryption and authentication

algorithms

 AH and ESP support 2 modes: transport and tunnel mode

 Transport mode:

o provides protection primarily for upper-layer protocols.

o extends to the payload of an IP packet.

o is used for end-to-end communication between

o to encrypt & optionally authenticate IP data

• can do traffic analysis but is efficient

• good for ESP host-to-host traffic

 Tunnel mode:

o provides protection to the entire IP packet.

o Packet travels through a tunnel from one point a IP network to another

o encrypts entire IP packet

o add new header for next hop

o no routers on way can examine inner IP header

o good for VPNs, gateway to gateway security

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 The two protocols AH and ESP can provide several

security services for packets at the network layer as

shown in the table below:

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 handles key generation & distribution

 typically need 2 pairs of keys

o 2 per direction for AH & ESP

 manual key management

o Sys admin manually configures every system

 automated key management

o automated system for on demand creation of keys for SA’s in

large systems

o has Oakley & ISAKMP elements

 key exchange algorithm: Diffie-Hellman:

o Secret keys are created only w hen needed There is no need to store secret

keys for a long period of time, exposing them to increased vulnerability.

o The exchange requires no pre-existing infrastructure other than an

agreement on the global parameters.

 IKE key determination is designed to retain the advantages of

DiffieHellman:

o 1 It employs a mechanism know n as cookies to thw art clogging attacks.

o 2 It enables the tw o parties to negotiate a group; this, in essence, specifies

the global

o parameters of the Diffie-Hellman key exchange.

o 3 It uses nonce to ensure against replay attacks.

o 4 It enables the exchange of Diffie-Hellman public key values.

o 5 It authenticates the Diffie-Hellman exchange to thw art man-in-the-middle

o attacks.

 Negotiates IPsec tunnel characteristics between two

IPsec peers

 Negotiates IPsec protocol parameters

 Exchanges public keys

 Authenticates both sides

 Manages keys after the exchange

 Automates entire key-exchange process

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 Identify interesting traffic by an IPsec peer that has been

configured to initiate an IPsec session for this traffic

 IPsec peers negotiate a secure authenticated

communication channel using main mode or aggressive

mode negotiation, resulting in creation of an IKE

Security Association (SA) between the two IPsec peers

(IKE phase I)

 Create two IPsec SAs between the two IPsec peers via

IKE quick mode negotiation (IKE phase II)

 Send data over encrypted tunnel using ESP and/or AH

encapsulation

 Agreeing on a set of parameters that are to be used to

authenticate the two peers

 Agreeing on parameters used to encrypt a portion of the

main mode and all of the quick mode messages

 None of the aggressive mode messages are encrypted

 Authenticate the two peers to each other

 Generate keys used to generate keying material for

subsequent encryption of data

 All of the parameters negotiated and the keys used to

generate keys for encryption are stored as IKE or ISAKMP

security association (SA)

Main mode using preshared key authentication

followed by quick mode negotiation

Main mode using digital signature authentication

followed by quick mode negotiation

Aggressive mode using preshared key

authentication followed by quick mode negotiation

Main mode using nonces authentication followed by

quick mode negotiation

Aggressive mode using digital signature

authentication followed by quick mode negotiation

 To have two peers agree on a set of attributes for

creating the IPsec security associations that could be

used by ESP to encrypt the data

 To redo Diffie-Hellman (DH) exchange so that new

keying material can be used to generate IPsec

encryption keys

 Preshared keys

 Digital signatures

 Encrypted nonces

 Data Encryption Standard (DES)

 Triple DES (3DES)

- Cipher block: DES encryption algorithm converting fixed -length

message into cipher text of same length

-block size of DES is 64 bits while key length is 56 bits

-Initialization vector is sent in ESP header

Overall key length is 168 bits

 a security policy applied to each IP packet that transits

from a source to a destination

 IPsec policy is determined primarily by the interaction of

two databases:

o the security association database (SAD) and

o the security policy database (SPD)

 Security Associations

 Security Association Database

 Security Policy Database

 IP Traffic Processing

 a one-way logical connection between sender & receiver that

affords security service to the traffic carried on it

 It is a mechanism that IPSec used to establish the security

parameters between a sender and a particular receiver the

first time they have communication

 Using SA, IPSec changes a connectionless protocol (IP) to a

connection- oriented protocol

 SA is identified by 3 parameters:

o Security Parameters Index (SPI): A bit string assigned to this SA

and having local significance only

o IP Destination Address : address of the destination endpoint

o Security Protocol Identifier : indicates whether the association is an

AH or ESP security association

 SAD defines the parameters associated with each SA

o Security Parameter Index

o Sequence Number Counter

o Sequence Counter Overflow

o Anti-Replay Window

o AH Information

o ESP Information

o Lifetime of this Security Association

o IPsec Protocol Mode

o Path MTU

SAD is needed to collect those of SAs

It is a two-dimensional table with each row defining a single SA

 defined by a set of IP and upper-layer protocol field

values, called selectors

 The following selectors determine an SPD entry:

o Remote IP Address: (e.g., behind a firewall)

o Local IP Address: (e.g., behind a firewall).

o Next Layer Protocol: The IP protocol header (IPv4, IPv6, or

IPv6 Extension)

o Name: A user identifier from the operating

o Local and Remote Ports: TCP or UDP port values

 This case illustrates simple VPN

 The tunnel could support AH, ESP,

or ESP with the authentication

option

 support for a remote host that uses

the Internet to reach an

organization’s firewall and

 then to gain access to some server or

workstation behind the firewall

 LAN-to-LAN or site-to-site

o Used to connect two private networks to form one combined

virtual private network

 Remote-access client IPsec

o Used to allow road warriors to be part of the trusted network

Applications of Ipsec

IPsec Architecture

IPsec Protocol Suite

o ESP, AH, IKE

Packet Encapsulation in IPsec

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and Practice, William Stallings, Prentice Hall,

Sixth Edition, 2013

o Chapter 19

o Others