Re: [IPsec] New method to resist replay attack in ikev2

["ramaswamy" <[e-mail]>]

Thanks for the response, I agree with your comments, I think we can use
certificates to avoid man in the middle attacks and error message flooding
in the INIT phase only, as certificates are signed by trusted certificate
authorities authenticity is ensured.

If certificates are used in INIT message exchanges [mutual authentication],
we can effectively avoid afore said attacks as it avoids huge computation of
IKE-keys before the client OR server is authenticated.

To avoid Replay attacks:
By using RSA private key of certificate to encrypt the nonce (Ni) in
INIT_REQUEST message we can avoid replay attacks, at the receiving end,
first certificate is verified using root CA and nonce is decrypted using
public key of the received certificate which ensures that sender holds the
valid private key of the certificate and not an attacker.  By using nonce we
can avoid Replay attacks[Packets can be rejected if the same nonce is
received within a particular session].

Please assert and also let us know if any related drafts/rfc to avoid these
attacks.

Best Regards ,
Ram

-----Original Message-----
From: Tero Kivinen [mailto:[e-mail]] 
Sent: Tuesday, August 30, 2011 2:41 PM
To: ramaswamy
Cc: [e-mail]; [e-mail];
[e-mail]; [e-mail]
Subject: [IPsec] New method to resist replay attack in ikev2

ramaswamy writes:
> Proposed new negotiations 
> 
> Before initial exchange begins initiator looks up to the pre shared
> secret with the intended responder and does the hash value on first
> half of pre shared secret, nonce of the initiator. Once the
> responder receives the request it looks up the correspondence pre
> shared key in its table and it takes the nonce form initiator
> request message then it does a hash value to authenticate the
> initiator.

This is bit like how IKEv1 did it, and it has same problem than IKEv1
had with that, meaning it does not provide ANY identity protection at
all. 

The responder needs to find the pre-shared key for the initiator based
only with the information that are in the first IKE_SA_INIT packet.
This DOES NOT include identity of the initiator, and SAi1, KEi, and Ni
does not help at all in this process. The only information that
responder has which it can use is the source IP-address of the
IKE_SA_INIT packet.

This has the effect that the pre-shared key will be tied to the source
IP-address of the initiator, which mean every passive listener will
also see that same IP-address and will know the identity of the
initiator.

The method in IKEv2 where the PSK is not tied to the IP-address of the
initiator offers much better identity protection, as now the responder
identity is only releaved to the active attacker.
-- 
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