ISAKMP IKE Phase 1 Details

(1) ISAKMP and IKE Overview

ISAKMP and IKE background

• Manual keying presents many challenges and disadvantages
• November 1998, IETF specified a framework to address these issues
  • ISAKMP was officially standardised by IETF in RFC 2407, 2408
  • IKE was officially standardised by IETF in RFC 2409
  • The vast majority of IPsec leverage the scalability features provided by ISAKMP and IKE
• IKE/ISAKMP key functions
  • Dynamically and securely exchange keys
  • Negotiate security parameters

ISAKMP and IKE Overview

ISAKMP “Internet Security Association and Key Management Protocol”

• Protocol framework for establishing security context, defines the procedures for:
  • Payload formats of communication
  • The mechanics of implementing a key exchange protocol
  • The negotiation of a security association
• Protocol used for key exchange and SA negotiation: IKE, Oakley, SKEME
  • IKE protocol is being used for IPsec VPN
  • IKE is hybrid protocol, combines the strengths of Oakley and SKEME protocols

IKE “Internet Key Exchange”

• Protocol that is used by IPsec for establishing security context, and defines the actual mechanics for the process:
  • Authentication of the IPSec peers
  • Negotiates IPSec keys
  • Negotiates IPSec security associations

* ISAKMP/IKE occurs in 2 phases: Phase-1 and Phase-2.

(2) ISAKMP/IKE Phase 1:

Phase 1

• Authenticates and protects the identities of the IPSec peers (identities protection only available in Main mode)
• Negotiates a matching IKE SA policy between peers to protect the IKE exchange
• Performs an authenticated Diffie-Hellman exchange with the end result of having matching shared secret keys
• Establishes IKE SA
  • Sets up a bidirectional (2-ways) secure tunnel to negotiate IKE phase 2 parameters

*Phase-1 has 2 modes: Main mode, Aggressive mode.

Main Mode

• Main mode has three “two-way exchanges” (6 messages in total)
• Offers identity protection (through encryption)

• 1st exchange (negotiate policy)
  • Encryption algorithm (DES / 3DES / AES)
  • HMAC function (MD5 / SHA)
  • Crypto peer authentication type (PSK / RSA Certificate)
  • Diffie-Hellman key group
  • SA lifetime
• 2nd exchange (exchange DH public values and ancillary data)
  • Public keys, Nonces are sent for a Diffie-Hellman exchange
  • Nonces: random numbers each party must sign and return to prove their identities
• 3rd exchange (authenticate the DH Exchange)
  • Encrypted identity exchange
  • Identity verification confirmation (hash payload)

Aggressive Mode

• Aggresive mode has two exchanges (3 messages in total)
• Offers speed and lightweight (no identity protection)
  • It’s possible to “sniff” the wire and discover who formed the new SA. However, it is faster than main mode.

• 1st exchange
  • Encryption algorithm, HMAC function, Device authentication type
  • Diffie-Hellman key group, SA lifetime
  • Public key, nonces are sent for a Diffie-Hellman exchange
  • Identity exchange
• 2nd exchange
  • Identity verification confirmation (hash payload)