Re: [Dime] [IPsec] Last Call: <draft-ietf-dime-ikev2-psk-diameter-06.txt> (Diameter IKEv2 PSK: Pre-Shared Secret-based Support for IKEv2 Server to Diameter Server Interaction) to Proposed Standard

["Cakulev, Violeta (Violeta)" <[e-mail]>]

Hi Yaron,
Thanks for the comments.
Please see inline [VC].

-Violeta

-----Original Message-----
From: [e-mail] [mailto:[e-mail]] On Behalf Of Yaron Sheffer
Sent: Sunday, May 22, 2011 2:38 PM
To: [e-mail]
Cc: IPsecme WG; [e-mail]; [e-mail]
Subject: Re: [IPsec] Last Call: <draft-ietf-dime-ikev2-psk-diameter-06.txt> (Diameter IKEv2 PSK: Pre-Shared Secret-based Support for IKEv2 Server to Diameter Server Interaction) to Proposed Standard

Hi,

Having read this document only now, I think there's a number of serious issues with it. This document was sent to the ipsec mailing list a while ago but unfortunately got no review.

Summary:
1. I think the wrong architectural choice was made, in preferring PSK over EAP authentication.
2. There is not enough detail in the document to result in interoperable implementations.
[VC] Please see responses to detailed comments.

Detailed comments:
* The appropriate ref for IKEv2 is RFC 5996. This was actually noted in the shepherd review back in March.
[VC] This is fixed in v7.


* The document notes that EAP is one of the authentication modes supported by IKEv2. EAP is designed for interaction with backend AAA servers, and is quite capable of performing shared-secret authentication, using a variety of EAP methods (and see also RFC 5998, on IKEv2 mutual auth with EAP). Yet the document does not explain why EAP is not used, instead preferring the IKE PSK authentication method.
[VC] Diameter application for Diameter client to server communication for IKEv2 with EAP has been specified in RFC 5778. However, there is no Diameter application specified for IKE PSK authentication method. This is stated in the draft both in Abstract and Introduction. The draft does not recommend one or the other, it is simply specifying what is not specified. It is up to a specific use case to decide what to use. For example 3GPP2 decided to use IKEv2 PSK (in 2 of its specifications), and that is what triggered this effort in IETF.


* 4.1: how can the incoming SPI be used to identify the peer?
[VC] As stated in Section 4.1 IDi payload is extracted from the IKE_AUTH message and this payload 'MUST contain an identity that is meaningful
   for the Diameter infrastructure, such as a Network Access Identifier (NAI), since it is used by the IKEv2 Server to populate the User-Name
   AVP in the Diameter message'. SPI is not used to identify the peer.


* Packing additional semantics into SPI may conflict with elements of the IPsec architecture (see for example Sec. 9.3 of draft-ietf-ipsecme-failure-detection-08).
[VC] Agreed.


* 4.1, 2nd paragraph: generation of the PSK is central to this solution, so it cannot be "outside the scope" of the document. There is no way to interoperate otherwise.
[VC] This draft focuses on IKEv2 server, as a Diameter client, to the Diameter server communication for IKEv2 with pre-
   shared secret based authentication, and specifies Diameter application for this communication. It is left to specifications that make use of this Diameter application to specify where the PSK comes from and how it is generated. As mentioned above, there are two 3GPP2 specs that make use of this Diameter application and both of those specs specify generation of the PSK.


* Moreover, if a single client is expected to sometimes use EAP and sometimes PSK, there must be a way to notify it which one to use.
[VC] This is not the assumption. Again this draft specifies Diameter application for Diameter client to the Diameter server communication for IKEv2 with PSK. IKEv2 server knows whether EAP or PSK is used.


* How does key-lifetime relate to the lifetime of the IKE SA?
[VC] This should be the same as in RFC 5996, how pre-shared secret lifetime relates to the lifetime of the IKE SA. This draft should not make any changes.


* Sec. 10 refers to the PSK as a "session key" which is incorrect, as PSK is only used for authentication and does not encrypt anything.
[VC] Good point. It is changed to PSK in v7.


* The same paragraph is very vague about the security properties of PSK.
RFC 5996 takes PSK much more seriously, e.g. "When using pre-shared keys, a critical consideration is how to assure the randomness of these secrets." Again, I believe the document should specify how the PSK is derived.
[VC] I absolutely agree that derivation of PSK is critical. However, as stated above, this draft specifies Diameter application only. Therefore, security consideration section cannot include much more details on derivation of PSK as it is specified elsewhere.


* Why "if nonces are included" where the document says that they *must* be included (in the AVP occurrence table).
[VC] Good point. This is removed in v7.


Thanks,
Yaron

On 05/20/2011 04:50 PM, The IESG wrote:
> The IESG has received a request from the Diameter Maintenance and
> Extensions WG (dime) to consider the following document:
> - 'Diameter IKEv2 PSK: Pre-Shared Secret-based Support for IKEv2 Server
>     to Diameter Server Interaction'
>    <draft-ietf-dime-ikev2-psk-diameter-06.txt>  as a Proposed Standard
>
> The IESG plans to make a decision in the next few weeks, and solicits
> final comments on this action. Please send substantive comments to the
> [e-mail] mailing lists by 2011-06-03. Exceptionally, comments may
> be sent to [e-mail] instead. In either case, please retain the
> beginning of the Subject line to allow automated sorting.
>
> Abstract
>
>
>     The Internet Key Exchange protocol version 2 (IKEv2) is a component
>     of the IPsec architecture and is used to perform mutual
>     authentication as well as to establish and to maintain IPsec security
>     associations (SAs) between the respective parties.  IKEv2 supports
>     several different authentication mechanisms, such as the Extensible
>     Authentication Protocol (EAP), certificates, and pre-shared secrets.
>
>     With [RFC5778] the Diameter interworking for Mobile IPv6 between the
>     Home Agent, as a Diameter client, and the Diameter server has been
>     specified.  However, that specification focused on the usage of EAP
>     and did not include support for pre-shared secret based
>     authentication available with IKEv2.  This document specifies IKEv2
>     server, as a Diameter client, to the Diameter server communication
>     for IKEv2 with pre-shared secret based authentication.
>
>
>
>
> The file can be obtained via
> http://datatracker.ietf.org/doc/draft-ietf-dime-ikev2-psk-diameter/
>
> IESG discussion can be tracked via
> http://datatracker.ietf.org/doc/draft-ietf-dime-ikev2-psk-diameter/
>
>
> No IPR declarations have been submitted directly on this I-D.
>
>
> _______________________________________________
> IETF-Announce mailing list
> [e-mail]
> https://www.ietf.org/mailman/listinfo/ietf-announce
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