session_09_vpn__ipsec__and_tls_101908

# Initiator g 12 p 47 i secret i 3 nonce ni 11 g

This preview shows page 1. Sign up to view the full content.

This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: nents: a generator g, the modulo p, and a secret that in IKEv2 terminology is called i or r. During IKE_INIT, the Initiator and Responder exchange Diffie-Hellman information in KEi and KEr. That information includes gii and gr, as well as nonces Ni and Nr. • The shared key, SKEYSEED, is calculated by both the Initiator and Responder from the nonces exchanged and the Diffie-Hellman shared secret key generated, gi and gr, according to the following formula: SKEYSEED = prf ( Ni | Nr , g ir ) 29 VPN, IPSec and TLS IKE v2 DH Key Agreement In the security association, the initiator and responder agreed on the same group or pair of g and p. Initiator g =12 p = 47 I Secret = i = 3 Nonce = Ni = 11 g i = 12 3 (mod 47) = 36 g and p do not need to be secret 36, 11 14, 7 Responder g = 12 p = 47 R Secret = r =5 Nonce = Nr = 7 g r = 12 5 (mod 47) = 14 g i r = 36 5 (mod 47) = 18 g i r = 14 3 (mod 47) = 18 18 18 Both ends use 11, 7, and 18, as the secret and seed to calculate SKEYSEED SKEYSEED = prf ( Ni | Nr , g ir ) SKEYSEED = prf ( secret, seed ) VPN IPsec IKE v2 TLS M. Mogollon – 01/08 - 30 • This slide uses the same example used to describe Diffie-Hellman, the different is how the values are named in IKEv2. • Whenever a key exchange is established, the initiator and the responder agree on the corresponding p and g numbers by selecting a Diffie-Hellman group. • Then, they exchange not only their public keys, gi and gr, but also their nonces. • The nonces are not used to calculated the agreed key, in this case 18, but to calculate the SKEYSEED using a pseudo random function. 30 VPN, IPSec and TLS Diffie-Hellman Groups in IKE • Three distinct group representations can be used with IKE. — Modular Exponentiation Groups (named MODP) — Elliptic Curve Groups over the field GF [2n] (named EC2N) — Elliptic Curve Groups over GF [P] (named ECP). • Groups Identifiers supported in IKE — — — — — — — — — — Group 0: Group 1: Group 2: Group 4: Group 5: Group 14: Group 15 Group 16 Group 17 Group 18 VPN No group (used as a placeholder and for non-DH exchan...
View Full Document

## This note was uploaded on 05/26/2010 for the course TECH 6350 taught by Professor Mogollon during the Spring '10 term at University of Arkansas for Medical Sciences.

Ask a homework question - tutors are online