Based on my understanding, when PFS is used, the session keys derived in ISAKMP phase 1 is not used for encryption rather another set of session keys is derived in ISAKMP phase 2 using the DH group defined for PFS. Even, if the attacker knows the session keys that was used in ISAKMP phase 1, he/she can't crack the IPSec session.
With regards Kings On Wed, May 18, 2011 at 9:32 AM, Vybhav Ramachandran <[email protected]>wrote: > Hello All, > > Damn! It feels good to be back :). So here goes. > > I was studying about PFS yesterday. I couldn't get hold of any good > documentation on this so , based on bits and pieces of information gathered > from various sites, here's how i think it works. Please let me know if my > understand is correct or flawed. > > > *Without* PFS, what happens is, after the IKE Phase 2 lifetime expires, if > there is any traffic which has to go through the VPN, then the IKE Phase 2 > SA is renegotiated. The IKE Phase 1 SAs which are derived from the first IKE > Phase 1 negotiation are kept as they are and they are not renegotiated. This > could lead to a possible case where the attacker, if he/she got hold of the > IKE Phase 1 keys, could derive and decrypt the information being passed > between the VPN peers. This attack would last untill the IKE Phase 1 > lifetime expired. > > *With *PFS, after the IKE Phase 2 lifetime expires, if there is any > traffic which has to go through the VPN, then BOTH the IKE Phase 1 and IKE > Phase 2 tunnels are renegotiated. This ensures better security. > > > Cheers, > TacACK > > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com > > Are you a CCNP or CCIE and looking for a job? Check out > www.PlatinumPlacement.com >
_______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com
