Re: [IPsec] Identifying encrypted traffic (was: Reauthentication extension for IKEv2)

["Grewal, Ken" <[e-mail]>]

Agreed!

________________________________
From: Yoav Nir [mailto:[e-mail]]
Sent: Tuesday, October 21, 2008 11:40 PM
To: Gary Hemminger
Cc: Yaron Sheffer; Grewal, Ken; [e-mail]
Subject: Re: [IPsec] Identifying encrypted traffic (was: Reauthentication extension for IKEv2)

Hi Gary

If that's the case, then the load balancer would need neither heuristics nor a wrapper. Having terminated the IKE, the load balancer would have the child SA, and would know for certain whether the algorithm is ESP-NULL or something encrypted. In fact, the load balancer would even be able to enforce such a policy.

Yoav

On Oct 22, 2008, at 2:00 AM, Gary Hemminger wrote:


The client would negotiate IKE  with the load balancer and would not directly negotiate with the Server.

Gary

From: Yaron Sheffer [mailto:[e-mail]]
Sent: Tuesday, October 21, 2008 3:23 PM
To: Grewal, Ken; Gary Hemminger; Yoav Nir
Cc: [e-mail]<mailto:[e-mail]>
Subject: RE: [IPsec] Identifying encrypted traffic (was: Reauthentication extension for IKEv2)

Hi Ken,

Thanks for the clarification. But I still don't understand how your scenario works.

Assume for simplicity an environment where everybody uses ESP in transport mode, with null encryption.

Client C1 does an IKE negotiation with a random server (as selected by the load balancer) S1. They negotiate some ESP traffic stream, denoted by an SPI. This whole thing is encrypted, so the load balancer cannot learn the SPI value.

Now when the first ESP packet is sent from C1 towards the load balancer, there is not enough information for it to forward the packet to S1, regardless of its being able to look into the cleartext packet! Only S1 has the ESP keying material, and if LB forwards the packet elsewhere, the receiver will not be able to verify its integrity.

Regards,
            Yaron

________________________________
From: Grewal, Ken [mailto:[e-mail]]
Sent: Tuesday, October 21, 2008 23:56
To: Yaron Sheffer; Gary Hemminger; Yoav Nir
Cc: [e-mail]<mailto:[e-mail]>
Subject: RE: [IPsec] Identifying encrypted traffic (was: Reauthentication extension for IKEv2)

Some observations below:


 1.  I agree with Yaron in that if a load balancer needs to 'terminate' the traffic before applying any rules to distribute the load, then it should have the keys to do so without any modifications to the current protocol. In this case, the session setup (via IKE) should have been negotiated with the load balancer and it is the natural termination point of the IPsec SA. The load balancer is essentially acting as a VPN gateway for tunnel mode or some kind of front end proxy to the multiple servers behind it in transport mode.
 2.  My understanding of a 'pure' load balancer is that it distributes traffic streams to different resources available to it and this is typically based on rules such as source / destination IP protocols, ports (e.g. TCP ports) and potentially some other information. Furthermore, as some of the upper layer protocols are stateful (e.g. TCP), it is desirable for the load balancer to ensure that a higher layer 'session' (e.g. TCP session) is 'pegged' to a resource (server) that has been handling the same session - this allows efficient state maintenance on a given resource / server, instead of all resources needing access to that state. Now if the traffic is protected using IPsec, then the load balancer needs access to upper layer payload data in the packet in order to apply the aforementioned rules for load balancing decisions. The charter item on traffic visibility provides for a clean solution where the load-balancer (as well as other network monitoring tools) is able to ascertain that the packet if not encrypted and hence look inside the packet to analyze the protocol / ports to make load balancing decisions. In this case, IPsec is still being terminated on the server behind the load balancer, but the load balancer can examine the IPsec protected packet en-route to ensure it gets to the right server. In essence, this charter item allows the load balancer (and other network tools) to continue to function in IPsec environments.
 3.  I agree with Gary on his observations about heuristics as being complex in HW, undeterministic and the associated parsing rules liable to change based on new protocols / payloads.

Thanks,
- Ken

________________________________
From: [e-mail]<mailto:[e-mail]> [mailto:[e-mail]] On Behalf Of Yaron Sheffer
Sent: Tuesday, October 21, 2008 1:37 PM
To: Gary Hemminger; Yoav Nir
Cc: [e-mail]<mailto:[e-mail]>
Subject: Re: [IPsec] Identifying encrypted traffic (was: Reauthentication extension for IKEv2)

OK. But if your load balancer is able to decrypt the traffic (i.e. it has the credentials or secret keys), then it can do that with today's normal IKE/IPsec. There is no need in this case to modify the protocol to make it easier to detect encrypted traffic.

Thanks,
            Yaron

________________________________
From: Gary Hemminger [mailto:[e-mail]]
Sent: Tuesday, October 21, 2008 19:02
To: Yaron Sheffer; Yoav Nir
Cc: [e-mail]<mailto:[e-mail]>
Subject: RE: Identifying encrypted traffic (was: [IPsec] Reauthentication extension for IKEv2)

The use case you are thinking about is probably pure IPsec VPN, where an encrypted stream only lives across the WAN.  But what if you are a load balancer and the IPsec traffic is end to end?  In this case, you may have a load balancer that needs to terminate the traffic so it can make the decision which server to handle the request.  All load balancers today support SSL termination.  Same thing applies to IPsec traffic.  We cannot make the decision which server to handle the request, nor can we maintain persistence without decrypting the traffic.

Gary

From: Yaron Sheffer [mailto:[e-mail]]
Sent: Tuesday, October 21, 2008 6:10 AM
To: Gary Hemminger; Yoav Nir
Cc: [e-mail]<mailto:[e-mail]>
Subject: Identifying encrypted traffic (was: [IPsec] Reauthentication extension for IKEv2)

Hi Gary,

I'm puzzled by the scenario you are presenting. I've been considering the work on ESP-null detection (e.g. draft-grewal-ipsec-traffic-visibility-01) as useful for middleboxes that want to look at the IPsec-protected traffic, but do NOT want to terminate IPsec (i.e. decapsulate the traffic). In general, if you can terminate IPsec, that means that you have access to the encryption keys and you can easily differentiate protected and unprotected traffic, Can you explain the use case that you have in mind?

Thanks,
            Yaron

________________________________
From: [e-mail]<mailto:[e-mail]> [mailto:[e-mail]] On Behalf Of Gary Hemminger
Sent: Monday, October 20, 2008 20:26
To: Yoav Nir
Cc: [e-mail]<mailto:[e-mail]>
Subject: Re: [IPsec] Reauthentication extension for IKEv2

I was talking about how to make the determination that the payload is encrypted.  Evidently there are two approaches:  one based on a heuristic, another based on a payload wrapper that flags the payload is encrypted.  We would need some mechanism to determine the payload is encryped if we need to terminate the IPSEC traffic and make a determination of which server to send it to.  Sorry about the confusion.

Gary

________________________________
From: Yoav Nir [mailto:[e-mail]]
Sent: Sat 10/18/2008 2:03 PM
To: Gary Hemminger
Cc: [e-mail]<mailto:[e-mail]>
Subject: Re: [IPsec] Reauthentication extension for IKEv2
Hi Gary.

I'm not sure what heuristics you are talking about. The problem of re-authentication is simply this. The owner of the remote access gateway has a security policy that says that connections can be open for only so long (say, 2 hours) without authenticating the user again. This is a favorite requirement by auditors, who believe that this is an important part of risk management. If somebody steals your laptop (or mobile phone) or sits down at the Internet Cafe station where you were logged on, we want to limit the amount of time they are connected to the internal network. This requirement makes sense if the user has to type in their password to authenticate. It makes less sense if there are user certificates that are stored on the computer, or if the client software has a "save password" feature.

Whether it makes sense or not, this is a requirement by auditors and regulators. If the user does not re-authenticate within the specified time, the IKE SA and all dependent child SAs are deleted.  This creates a usability problem, because the SA is deleted without any advance warning to the user, so the user is likely to get a relatively long time with no connectivity. This can break TCP connections such as FTP, HTTP, and IMAP. Outlook tends to make accounts permanently offline when this happens.

RFC 4778 and the improvement that Martin Willi is proposing, are aimed at solving this usability problem by informing the client software in advance when the re-authentication needs to be done, and allowing them to re-authenticate early enough, so that connections are not broken. The heuristic does not affect the security or the IPsec streams.

Yoav

On Oct 18, 2008, at 2:35 AM, Gary Hemminger wrote:

One comment on the heuristics approach.  As a hardware vendor of L4-7 ADC boxes, I am a little concerned about having to terminate IPSEC streams based on the heuristics approach, because this is open ended.  What I mean is that the heuristic may be easy to define now, but there is no certainty that it would remain this way.  My past experience suggests that eventually the heuristic would become too complex, and a well defined mechanism for determining which payload is encrypted would need to be employed anyway.
While I like the idea of some "other" box having to solve this issue, which prevents clients from having to be changed, as we are a vendor of the "other" box, I think we should think about the long term, not the short term.  Just my opinion, and I am certainly flexible, but the heuristics approach worries me a bit.

Gary

[IPsec] Reauthentication extension for IKEv2
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 *   Subject: [IPsec] Reauthentication extension for IKEv2
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________________________________

Martin Willi writes:

> What do you think about such an extension? Already considered something

> similar, or does your reauthentication procedure work hassle-free? I'm

> wondering if we are the only ones facing these problems or if such an

> extension would gain broader acceptance...



The first question I have is why are you doing reauthentication at

all?



What is the benefits of the reauthentication?



What is the benefits of the reauthentication that can be done WITHOUT

user intervention (i.e. no user typing in password or pin code or

fingerprint or similar)?



I myself can only really see benefits from reauthentication when it

does require that user is really sitting there on the machine, and

gives something that the machine itself cannot give. In those cases

the user is required to type in something or do something anyways,

thus it does not really matter if the communications is interrupted

for second if user must stop his work for much longer time to type in

his passphrase or pin code.



The RFC 4478 simply skips this question and says "With some IPsec

peers, particularly in the remote access scenario, it is desirable to

repeat the mutual authentication periodically. The purpose of this is

to limit the time that security associations (SAs) can be used by a

third party who has gained control of the IPsec peer."



In most cases if third party has gained control of the IPsec peer he

will also get control of all authentication information inside the

peer, including private keys and pre shared keys. Only way to make

sure that he does not get access to those is to protect them with

passphrase, or pin code or similar that is only known by the user.



This is also said out in the RFC 4478: "However, in the remote access

scenario it is usually up to a human user to supply the

authentication credentials ..."



Because of this I do not think there is that much requirement for

reauthentication protocol that is faster than what we already have.

--

kivinen at safenet-inc.com

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