Internet Protocol Security (IP Sec)

Securing Intranets and Extranets at all levels

Major Cryptographic Systems

Application

Layer

Transport

WAN e.g. Internet

Data Link

Physical

PPTP, L2TP (really only a tunneling system)

Not applicable. No messages are sent at thislayer—only individual bits

IPsec

SSL/TLS

Kerberos

Cryptographic System

Securing Network Communication: What Are the Challenges?

Challenges to securing network communication include:Challenges to securing network communication include:

Preventing data modification while in transit

Preventing data from being read and interpreted while in transit

Keeping data secure from unauthorized users

Keeping data from being captured and replayed

Preventing data modification while in transit

Preventing data from being read and interpreted while in transit

Keeping data secure from unauthorized users

Keeping data from being captured and replayed

What Is Internet Protocol Security?

IPSec provides the following benefits:IPSec provides the following benefits:

Transparent to users and applications

Provides restricted access to servers

Customizable security configuration

Centralized IPSec policy administration through Active Directory

Supports authentication and encryption of traffic.

Certifies the originator of the packet.

Protects the data from interception and tampering while in transit.

Transparent to users and applications

Provides restricted access to servers

Customizable security configuration

Centralized IPSec policy administration through Active Directory

Supports authentication and encryption of traffic.

Certifies the originator of the packet.

Protects the data from interception and tampering while in transit.

IPSec: A framework of open standards to ensure private, secure communications over IP networks through the use of cryptographic security services

Application of IPsec to protect data packets

IPsec

• IPSec consists of two Internet protocol extensions: the Authentication Header (AH) and the Encapsulating Security Payload (ESP) that support creation of secure networks.

• Access is controlled by a companion key management protocol called the Internet Key Exchange (IKE).

IPsec• Together, IPSec and IKE ensure that

authorized parties may exchange private IP packets securely over a public network.

• Packet content is kept confidential by applying encryption and protected against modification through digital signing. IPSec can be used to securely “tunnel” packets to routers or firewalls over a WAN, or to securely “transport” packets end to- end between desktops and servers.

IPsec Operation: Transport Modes

Secure Connection

Secure onthe WAN e.g. Internet

SiteNetwork

SiteNetwork

Securityin Site

Network

Securityin Site

Network

ExtraSoftwareRequired

ExtraSoftwareRequired

TunneledConnection

Secure onthe WAN e.g. Internet

SiteNetwork

SiteNetwork

NoSecurityin Site

Network

NoSecurityin Site

Network

NoExtra

Software

NoExtra

Software

IPsecServer

IPsecServer

IPsec Operation: Tunnel Modes

Tunnel vs. Transport Mode IPSec

Security Association (SA)

• One of the most important concepts in IPSec is called a Security Association (SA). Defined in RFC 1825.

• SAs are the combination of a given Security Parameter Index (SPI) and Destination Address.

• SAs are one way. A minimum of two SAs are required for a single IPSec connection.

Security Association (SA)

• SAs contain parameters including:– Authentication algorithm and algorithm mode – Encryption algorithm and algorithm mode – Key(s) used with the authentication/encryption

algorithm(s) – Lifetime of the key– Lifetime of the SA– Source Address(es) of the SA– Sensitivity level (ie Secret or Unclassified)

How IPSec works: Phase 1

• Internet Key Exchange (IKE) is used to setup IPSec.

• IKE Phase 1:– Establishes a secure, authenticated channel between

the two computers– Authenticates and protects the identities of the peers– Negotiates what SA policy to use– Performs an authenticated shared secret keys

exchange– Sets up a secure tunnel for phase 2– Main Mode or Aggressive mode

How IPSec works: Phase 1

• Main Mode IKE1.Negotiate algorithms & hashes. 2.Generate shared secret keys using a Diffie-Hillman

exchange.3.Verification of Identities.

• Aggressive Mode IKE– Squeezes all negotiation, key exchange, etc. into less

packets.– Advantage: Less network traffic & faster than main

mode.– Disadvantage: Information exchanged before a

secure channel is created. Vulnerable to sniffing.

Establishing IPsec Security Associations Using IKE

Internet Key ExchangeSecurity Association

UDP Port 500

Party A Party B

IPsec SAsFirst establish IKE association andprotected session

Then create IPsec SAs within theProtection of the IKE session.

How IPSec works: Phase 2

– An AH or ESP packet is then sent using the agreed upon “main” SA during the IKE phase 1.

– IKE Phase 2• Negotiates IPSec SA parameters• Establishes IPSec security associations for specific

connections (like FTP, telnet, etc)• Renegotiates IPSec SAs periodically• Optionally performs an additional Diffie-Hellman

exchange

How IPSec works: Communication

• Once Phase 2 has established an SA for a particular connection, all traffic on that connection is communicated using the SA.

• IKE Phase 1 exchange uses UDP Port 500.

• AH uses IP protocol 51.

• ESP uses IP protocol 50.

3-phase strategy in general terms that can be applied to many different enterprises

Phase One: A Simple, Generic Policy

3-phase strategy in general terms that can be applied to many different enterprises

Phase Two: Custom Workgroups

Phase Three: Adding Trust Infrastructure

• Replacing pre-shared keys with credentials enabling strong authentication.

• In homogenous Windows environments, Kerberos tickets might be used.

• In all other environments, including mixed Windows networks; a Public Key Infrastructure should be used.

• IPSec partners can be authenticated with “raw” public keys, but most enterprises will prefer X.509 digital certificates verified by a trusted CA.

• PKI combines strong access control with scalable administration through the use of CA hierarchies, cross-certification, and delegation.