Subject: [HOKEY] Changes proposals for rfc5296bis - 2: remove local vs. home distinction

From: Sebastien Decugis <[email-masked]>
Date: Wed, 20 Oct 2010 14:13:40 +0900

Hello again,

Following my previous mail, here is my second simplification proposal
for rfc5296bis.

I think the existence of "home" and "local" ER servers in the RFC are
very confusing, and really do not add any value.

In EAP, there is no concept of domain involved. There is a peer, an
authenticator, and a backend authentication server where the EAP server
is located.

In ERP, we add one entity: the ER server. This entity is inserted
"between" the authenticator and the backend authentication server.

We also add a new capability to derive key hierarchies. This capability
depends on the EAP server, for retrieving the EMSK. It is *not* an ER
server in the sense that it does not functionnaly terminate the ERP
exchanges. Since this capability depends on the EMSK, security dictates
that this function is placed in the same domain as the EAP server,
although it does not need to be physically collocated, the EMSK might be
shared by other mean. I propose to call this capability the EAP
Re-authentication Key Server, ERKS, in the document.

In order to summarize, we have now the following logical entities:
peer <--> authenticator <--> ER server <--> ERKS <--> EAP server.

There again, there is no concept of domain involved, except for the
following precisions:
 - the ERKS must be in the same domain as the EAP server.
 - depending on where the ER server is located, the functions of the
ERKS and the peer will be affected.

I think it would be very helpful to integrate these clarifications in
rfc5296bis.
Previous discussions here and elsewhere tend to prove that the terms
"home ER server" and "local ER server" and "bootstrapping" have led to
much confusion...

I can also help with wording this in the document, should it be deemed
useful.

As usual, comments are welcome :)

Best regards,
Sebastien.

-- 
Sebastien Decugis
Research fellow
Network Architecture Group
NICT (nict.go.jp)

---

From: Qin Wu <[email-masked]>
Date: Wed, 20 Oct 2010 17:00:42 +0800

Hi,
----- Original Message ----- 
From: "Sebastien Decugis" <[email-masked]>
To: <[email-masked]>
Sent: Wednesday, October 20, 2010 1:13 PM
Subject: [HOKEY] Changes proposals for rfc5296bis - 2: remove local vs. homedistinction

> very confusing, and really do not add any value.

[Qin] Yes, Distinguishing between home and local is not necssary, e.g., DSRK can be distributed to local ER server, also can be generated for home ER server.
but the the ER server should be somewhere, home or local. 
Also without local or home, we can not address inter-domain handover case.
Therefore I think it is more pratical to allow ERP
exhange with only one ERP server. This ERP server could be at the home or at the 
local. But it is not necessary to allow ERP exchange not only with the local ERP server
but also with home ERP server.

> Re-authentication Key Server, ERKS, in the document.

[Qin]: I think the concept of introducing independent key hierachies is to separate 
key management from authentication. ERKS is not new capability and could be
part of EAP server. becos the Key Derivation depends on EAP method exchange
and EAP server.

> peer <--> authenticator <--> ER server <--> ERKS <--> EAP server.

[Qin]: Separeate ERKS from EAP server may complicate protocol exchange.
I suggest we may only consider the following logical entities :

Peer<-->authenticator<-->local ER server<-->home EAP server

for inter-domain handover

Peer<-->authenticator<-->local ER server

for intra-domain handover.

> _______________________________________________
> HOKEY mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/hokey

---

From: Sebastien Decugis <[email-masked]>
Date: Thu, 21 Oct 2010 14:57:53 +0900

Hi Qin,

Thank you for your answer. Please see my comments inline.

> [Qin] Yes, Distinguishing between home and local is not necssary, e.g., DSRK can be distributed to local ER server, also can be generated for home ER server.
Indeed, you are right, the way the keys are computed should be the same
in any domain -- although that was not the intent of my sentence :-)

> but the the ER server should be somewhere, home or local. 
Yes :) I am just proposing to call it "the ER server" and do not
distinguish its location, since it has little impact.

> Also without local or home, we can not address inter-domain handover case.
Can you explain why you say that? I don't get it, sorry.

> but also with home ERP server.
Yes, my point, exactly. There is only one ER server involved in any ERP
exchange, so let's call it "the ER server". This will avoid all this
confusion around "home" or "local".

> part of EAP server. becos the Key Derivation depends on EAP method exchange
I disagree with your statement. The capability that I am calling ERKS is
*not* part of standard EAP (the EMSK is not used by a standard EAP
server). Therefore it is a new feature we are introducing for ERP.
If this ERKS capability might be useful to other systems beyond ERP, it
might be specified in some other document. However, how it interfaces
with the EAP server, and its security considerations must be described
somewhere.
In the ERP document, the interface between ER server and ERKS must be
described as well.

> [Qin]: Separeate ERKS from EAP server may complicate protocol exchange.
On the contrary, it avoids all the confusion that we are experiencing now.
Again, a "simple" EAP server is *not* capable of deriving the key
material we are dealing with.

Best regards,
Sebastien.

---

From: andy L <[email-masked]>
Date: Fri, 22 Oct 2010 15:25:28 +0800

to my understanding, the 'home' and 'local' concept is for bussiness only,
so Qin said 'Also without local or home, we can not address inter-domain
handover case.' thinking about a subscriber roaming from one operator to an
other, it is no possibility two operators share an ER server, it is also
convient  for the operators to deal with the finance report, when
subscribers annouce their home domain.
I think ERKS is a little confusing, I just browsed RFC 5247, I can't find
any necessity to put ERKS between two entities. although we need
re-authentication, we'd better follow the same key management framework.
thanks

Liu, Shu

2010/10/21 Sebastien Decugis <[email-masked]>

> > [Qin] Yes, Distinguishing between home and local is not necssary, e.g.,
> DSRK can be distributed to local ER server, also can be generated for home
> ER server.

---

From: Sebastien Decugis <[email-masked]>
Date: Fri, 22 Oct 2010 16:45:20 +0900

Hi,

> I think ERKS is a little confusing, I just browsed RFC 5247, I can't
> find any necessity to put ERKS between two entities. although we need
This ERKS performs the key derivation described in RFC 5295.

Best regards,
Sebastien.

---

From: Qin Wu <[email-masked]>
Date: Wed, 27 Oct 2010 12:47:03 +0800

Hi,
----- Original Message ----- 
From: "Sebastien Decugis" <[email-masked]>
To: "Qin Wu" <[email-masked]>
Cc: <[email-masked]>
Sent: Thursday, October 21, 2010 1:57 PM
Subject: Re: [HOKEY] Changes proposals for rfc5296bis - 2: remove local vs. homedistinction

> distinguish its location, since it has little impact.

[Qin]: According to the original text of RFC5296, ERP with Home ER server is only used when
there is no local ER server between the peer and the home EAP server. When ERP with Local ER
server is used, ERP with home ER server will not be used any more.
So to me, there is no confusion here.

> Can you explain why you say that? I don't get it, sorry.

[Qin]: As described in RFC5296, there is one use case for Implicit ER bootstapping, i.e.,
Peer<-->authenticator<-->Local ER server<-->Home EAP server,
this use case is used to address inter-domain handover case.
When Implicit ER bootstapping completes, the home EAP server will distribute DSRK to the local ER server,
the intra-domain handover will follow afterwards, i.e., the peer only perform ERP exchange with the local ER server.

> confusion around "home" or "local".

[Qin]: See above.

> In the ERP document, the interface between ER server and ERKS must be
 
[Qin]: No, EAP server will generate EMSK through EAP method exchange. EMSK will
not leave EAP server. and EMSK will be used to derive other keys for ERP and form ER Key Hierarchy.
Therefore Key Hierarchy is part of EAP server.

> material we are dealing with.

[Qin]: Okay, we can take it as one new functionality or capability. but it is still part of EAP server.

---

From: andy L <[email-masked]>
Date: Wed, 27 Oct 2010 14:48:20 +0800

Qin
I agree with you, RFC 5247 and RFC 5296 both emphasized 'The EMSK MUST NOT
be provided to an entity outside the EAP server or peer', to introduce a new
entity seems compromising  that restriction. so I think we'd better keep
ERKS integrated with ER server.

Shu

2010/10/27 Qin Wu <[email-masked]>

> the intra-domain handover will follow afterwards, i.e., the peer only
> perform ERP exchange with the local ER server.
>

---

From: Qin Wu <[email-masked]>
Date: Wed, 27 Oct 2010 15:04:45 +0800

Hi,
  ----- Original Message ----- 
  From: andy L 
  To: Qin Wu 
  Cc: Sebastien Decugis ; [email-masked] 
  Sent: Wednesday, October 27, 2010 2:48 PM
  Subject: Re: [HOKEY] Changes proposals for rfc5296bis - 2: remove local vs. homedistinction

  Qin
  I agree with you, RFC 5247 and RFC 5296 both emphasized 'The EMSK MUST NOT be provided to an entity outside the EAP server or peer', to introduce a new entity seems compromising  that restriction. so I think we'd better keep ERKS integrated with ER server.

  [Qin]:I think you mean ERKS should be integrated with EAP server.

  Shu

    Hi,
    ----- Original Message -----

    [Qin]: See above.

---

From: andy L <[email-masked]>
Date: Wed, 27 Oct 2010 15:33:28 +0800

Sorry, my mistake. Thank you.

Shu

> *From:* andy L <[email-masked]>
> *To:* Qin Wu <[email-masked]>
> *Cc:* Sebastien Decugis <[email-masked]> ; [email-masked]
> *Sent:* Wednesday, October 27, 2010 2:48 PM
> *Subject:* Re: [HOKEY] Changes proposals for rfc5296bis - 2: remove local
> vs. homedistinction
>
> Qin

---

From: Sebastien Decugis <[email-masked]>
Date: Wed, 27 Oct 2010 17:20:12 +0900

Hi Qin, Shu, all,

>   [Qin]:I think you mean ERKS should be integrated with EAP server.
I am fine with this, although this makes things more difficult for
networks with several EAP servers.
Anyway, it would be useful if the interface between this ERKS component
integrated in EAP server and the ER server was defined clearly in the
document.

Best regards,
Sebastien.

---

From: Qin Wu <[email-masked]>
Date: Wed, 27 Oct 2010 16:47:44 +0800

Hi,
----- Original Message ----- 
From: "Sebastien Decugis" <[email-masked]>
To: "Qin Wu" <[email-masked]>
Cc: "andy L" <[email-masked]>; <[email-masked]>
Sent: Wednesday, October 27, 2010 4:20 PM
Subject: Re: [HOKEY] Changes proposals for rfc5296bis - 2: remove local vs. homedistinction

> integrated in EAP server and the ER server was defined clearly in the

[Qin]: That is reasonable to me.