Wikipedia Says that Internet Protocol Security (IPsec) is a protocol suite for securing Internet Protocol (IP) communications by authenticating and encrypting each IP packet of a data stream. IPsec also includes protocols for establishing mutual authentication between agents at the beginning of the session and negotiation of cryptographic keys to be used during the session. IPsec can be used to protect data flows between a pair of hosts (e.g. computer users or servers), between a pair of security gateways (e.g. routers or firewalls), or between a security gateway and a host.  This chart will provide some of the major point to review for the CISSP.


IPSEC PROTOCOL STANDARD

IPSEC (IP Security)
Ø         To comply with the Internet Engineering Task Force (IETF) standard, IPSEC was designed to permit flexibility in choosing hashing, encryption, and key exchange mechanisms. Depending on the implementation, key exchange may be a manual process or an automated one.

Ø         Default Hashing protocols are HMAC-MD5 or HMAC-SHA-1.

Ø         Default Encryption protocol is Cipher Block Chaining mode DES, but other algorithms like ECC (Elliptic curve cryptosystem) can be used.

Ø         Supports two communication modes – Tunnel mode and Transport mode. Tunnel mode is required for communication with a Gateway at the receiving end (gateway-to-gateway or host-to-gateway). Tunnel encrypts everything and is better security than Transport mode.

Ø         The two main concepts of IPSec are Security Associations (SA) and tunneling. Security association is a simplex logical connection between two IPSec systems. For bi-directional communication to be established between two IPSec systems, two separate Security Associations, one in each direction, must be defined. The security protocols can either be AH or ESP, which can be used independently, or together. AH provides integrity and authentication and ESP provides integrity, authentication and encryption. ESP can be operated in either tunnel mode (where the original packet is encapsulated into a new one) or transport mode (where only the data payload of each packet is encrypted, leaving the header untouched).

Ø         IKE (IPSEC Key Exchange) is defined as an Internet, IPsec, key-establishment protocol (partly based on OAKLEY) that is intended for putting in place authenticated keying material for use with ISAKMP and for other security associations, such as in AH and ESP.

Ø         Does NOT use CHAP as an authentication mechanism, but can use

o          Pre shared key

o          Certificate based authentication

o          Public key authentication

Ø         The 3 components of IPSEC:

1. IKE (Internet Key Exchange), based on Diffie-Hellman encryption protocol. Optional, but usually used.

2. SA (Security Association).

3. SPI (Security Parameter Index), control channel for direction of traffic.

IKE (IPSEC Key Exchange)
Ø         Defined as an Internet, IPsec, key-establishment protocol (partly based on OAKLEY) that is intended for putting in place authenticated keying material for use with ISAKMP and for other security associations, such as in AH and ESP.

Ø         Used in conjunction with the IPSec standard; enhances IPSec by providing additional features, flexibility, and ease of configuration for the IPSec standard. IPSec can however, be configured without IKE by manually configuring the gateways communicating with each other for example.

Ø         A security association (SA) is a relationship between two or more entities that describes how the entities will use security services to communicate securely. In phase 1 of this process, IKE creates an authenticated, secure channel between the two IKE peers, called the IKE SA (security association). The Diffie-Hellman key agreement is always performed in this phase. In phase 2 IKE negotiates the IPSec SA’s and generates the required key material for IPSec. The sender offers one or more transform sets that are used to specify an allowed combination of transforms with their respective settings.

Ø         Diffie-Hellman is a widely-used key exchange algorithm used by IKE.

Ø         Eliminates the need to manually specify all the IPSec security parameters in the crypto maps at both peers.

Ø         Allows you to specify a lifetime for the IPSec SA.

Ø         Allows encryption keys to change during IPSec sessions.

Ø         Allows IPSec to provide anti-replay services.

Ø         Permits Certification Authority (CA) support for a manageable, scalable IPSec implementation.

Ø        Allows dynamic authentication of peers.

AH (Authentication Header)
Ø         Mechanism for providing strong integrity and authentication for IP datagrams. It might also provide non-repudiation, depending on which cryptographic algorithm is used and how keying is performed. For example, use of an asymmetric digital signature algorithm, such as RSA, could provide non-repudiation.

Ø         Does NOT provide confidentiality.

Ø         Integrity and authentication for IP datagrams are provided by AH.

Ø         Provides 3 services in IPSEC:

1. Authentication.

2. Anti-reply.

3. Data integrity services.

ESP (Encapsulating Security Protocol)
Ø         Mechanism for providing integrity and confidentiality (encryption) to IP datagrams. It may also provide authentication, depending on which algorithm and algorithm mode are used.

Ø         Does NOT provide Non-repudiation and protection from traffic analysis.

Ø         In transport mode, ESP only encrypts the data payload of each packet.

Ø         Provides 4 services in IPSEC:

1. Payload protocol encrypts information in IP datagrams.

2. Authentication.

3. Anti-replay.

4. Integrity.

ISAKMP (Internet Security Association Key Management Protocol)
Ø         Internet IPsec protocol to negotiate, establish, modify, and delete security associations, and to exchange key generation and authentication data, independent of the details of any specific key generation technique, key establishment protocol, encryption algorithm, or authentication mechanism.

Ø        Key management protocol typically used with IPsec, but intentionally excludes selection of any particular key exchange method.