[strongSwan] Android VPN

[Martin Willi]

David,

> IKEv2 using PSK and MSCHAPv2 example
> 
> SEgw.xxx.yyy.net FQDN
> SEGWID  segw at xxx.xxx.net<mailto:segw at xxx.xxx.net>
> SEGW PSK a1b2c3
> 
> EAP- MSCHAPv2
> AAA User ID at xxx.xxx.net<mailto:ID at xxx.xxx.net>
> AAA Password d3e4f5g6

EAP authentication in conjunction with PSK server authentication can be
very problematic, and is therefore not allowed by RFC 5996, and not
supported by our Android client.

If I understand correctly, you'd like to authenticate a large set of
users to a security gateway. Each user authenticates itself using the
mentioned AAA credentials. The gateway, on the other hand, uses a single
(?) PSK to authenticate itself against all users.

The problem is that each client has to know the security gateway PSK to
verify it. Having that PSK, it can easily impersonate the gateway
against all other users, and collect all the AAA credentials of all
users. Something you really should avoid, especially with larger/open
user groups.

It is therefore recommended to use public key authentication together
with EAP. There also is the mutual EAP-only authentication extension
[1], which is supported in strongSwan. However, EAP-MSCHAPv2 can not be
considered secure, so you can't use it with that extension.

Regards
Martin

[1]http://tools.ietf.org/html/rfc5998