[Openswan Users]

[Brian Candler]

On Wed, May 10, 2006 at 03:01:33PM +0200, Paul Wouters wrote:
> On Wed, 10 May 2006, Brian Candler wrote:
> 
> > (*) Note that if you use aggressive mode, you can use a different pre-shared
> > key for each endpoint. That is, the IKE exchange also includes an identity
> > (which could be an FQDN or E-mail address), and you can use this to select
> > the appropriate secret. Many VPN solutions are built on this.
> 
> And can be ikecrack'ed

Same applies to many other systems, e.g. WPA-PSK for wireless. If you're
going to use a shared secret, make sure it's a strong shared secret.

A note for those talking about XAUTH: from the Cisco XAUTH implementations
I've seen, they use aggressive mode with a (group) shared secret, and then
the XAUTH exchange takes place thereafter.

Cisco have realised the weakness of this and subsequently designed an IKE
"hybrid" mode, where the VPN concentrator authenticates itself to the client
with a certificate, but the client authenticates itself back to the
concentrator with a username/password. However I don't know what open-source
implementations of this are available.

Regards,

Brian.