session_09_vpn__ipsec__and_tls_101908

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

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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...
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