Re: Cracking preshared keys

[Gary Flynn <flynngn () jmu edu>]

Damir Rajnovic wrote:

> Please note that the same class of attack is possible even if 
> Xauth (Extended Authentication) is used. This is because Xauth is 
> performed after Phase 1 is completed and, for this attack, an adversary
> needs only a packet from Phase 1. Furthermore, after the pre-shared 
> key has been discovered, an adversary can mount an active MiTM attack
> on Xauth. The outcome depends on the exact authentication method used
> in Xauth.
May I ask how this applies to "IKE Shared Secret AAA"?
If a Radius backend authenticator is used, is the shared key
that is vulnerable one preconfigured in the VPN hosts or one
based on the Radius password? The reason I ask is that the
preconfigured shared key can easily be lengthened but the
backend password, if based on end user passwords, is not
as easy a solution. :)

Thank you.

Gary Flynn
Security Engineer - James Madison University