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Configuring IKE
Overview
Built on a framework defined by the Internet Security Association and Key Management Protocol
(ISAKMP), Internet Key Exchange (IKE) provides automatic key negotiation and SA establishment
services for IPsec, simplifying the application, management, configuration and maintenance of IPsec
dramatically.
Instead of transmitting keys directly across a network, IKE peers transmit keying materials between
them, and calculate shared keys respectively. Even if a third party captures all exchanged data for
calculating the keys, it cannot calculate the keys.
NOTE:
Unless otherwise specified, IKE in this chapter refers to IKEv1.
IKE security mechanism
IKE has a series of self-protection mechanisms and supports secure identity authentication, key
distribution, and IPsec SA establishment on insecure networks.
Data authentication
Data authentication involves two concepts:
• Identity authentication—Mutual identity authentication between peers. Two authentication
methods are available: pre-shared key authentication and PKI-based digital signature
authentication (RSA signature).
• Identity protection—Encrypts the identity information with the generated keys before sending
the information.
DH
The DH algorithm is a public key algorithm. With this algorithm, two peers can exchange keying
material and then use the material to calculate the shared keys. Due to the decryption complexity, a
third party cannot decrypt the keys even after intercepting all keying materials.
PFS
The Perfect Forward Secrecy (PFS) feature is a security feature based on the DH algorithm. By
making sure keys have no derivative relations, it guarantees a broken key brings no threats to other
keys. For IPsec, PFS is implemented by adding an additional key exchange at IKE negotiation phase
2.
IKE operation
IKE negotiates keys and establishes SAs for IPsec in two phases:
1. Phase 1—The two peers establish an ISAKMP SA, a secure, authenticated channel for
communication. In this phase, two modes are available: main mode and aggressive mode.
2. Phase 2—Using the ISAKMP SA established in phase 1, the two peers negotiate to establish
IPsec SAs.
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