[SPKM] RE: Comments on draft-zhu-pku2u-01.txt

["Liqiang(Larry) Zhu" <[e-mail]>]

Olga Kornievskaia wrote:

> Why state this? In the motivation section, it has been stated that: 
> "there is no trusted third party in such environments." While it is 
> stated that "consequently the Kerberos protocol as defined in
[RFC4120] 
> and [RFC4556] is inadequate to provide security services ", this 
> document's writing heavily depends on it and PKU2U is basically
rfc4556 
> where the server is not a KDC.

This is designed for fast session resumption. When the initiator already
obtained a service ticket in prior sessions, it can just use that cached
ticket right away.

> Isn't there a missing reference to the Section 3.2.3 of RFC4556.
Unlike 
> KDC and principal, acceptor and initiator don't share any secrets. 
> PKINIT's PA_PK_AS_REP is needed here for the initiator to make use of 
> the ticket created by the acceptor.

RFC4556 updates RFC4120, unless there is something here specific to
RFC4556, I do not see the need here.

> Since this is a GSS API mechanism what about QoP handling and channel 
> bindings?

These are handled in the same way as described in RFC4121.

> This draft does not support non-Kerberos environments. By that I mean,
a 
> Kerberos domain must exist and users of PKU2U must have Kerberos 
> principal names.

How was this deduced? What is a Kerberos domain? And it should not be
needed. what environments are not supported? Can you expand on this? 

> Name type NT-X500-PRINCIPAL which is rfc2253 string representation of 
> the distinguished name does not produce a canonical name.

PKU2U requires little endian order:

   The Distinguished Name contained in the
   PKU2U Kerberos principal name MUST begin with the most specific
   attribute and continue with progressively broader attrbiutes.

With this constraint, is there a case where this does not produce a
canonical name?

> What happens when the initiator rejects the AS-REP tokens sent by the 
> acceptor (ie., fails to verify acceptor's certificate)?  Does it 
> generate an error token?

You can get an error token as in
http://www.watersprings.org/pub/id/draft-swift-win2k-krb-user2user-03.tx
t. but typically the acceptor returns an error and aborts.

> Naming needs work. Comments made about naming in SPKM3 apply here.

Can you point me to the comments, it would help. Thanks for the review.

--larry
-----Original Message-----
From: Olga Kornievskaia [mailto:[e-mail]] 
Sent: Friday, March 16, 2007 1:53 PM
To: Liqiang(Larry) Zhu
Cc: [e-mail]; [e-mail]; Nicolas Williams;
[e-mail]; [e-mail]
Subject: Re: Comments on draft-zhu-pku2u-01.txt

Section 3

   If initially the initiator has a service ticket to the acceptor, the
   initiator, acting as the client in the parlance of [RFC4120],
   performs the client-server authentication exchange according to
   [RFC4121] and Section 3.2 of [RFC4120], with the acceptor acting as
   the server.

Why state this? In the motivation section, it has been stated that: 
"there is no trusted third party in such environments." While it is 
stated that "consequently the Kerberos protocol as defined in [RFC4120] 
and [RFC4556] is inadequate to provide security services ", this 
document's writing heavily depends on it and PKU2U is basically rfc4556 
where the server is not a KDC.

   If all goes well, processing the KRB_AS_REQ message will result in
   the creation of a ticket for the initiator to present to the acceptor
   and the response is a KRB_AS_REP message generated according to
   Section 3.1.3 of [RFC4120].

Isn't there a missing reference to the Section 3.2.3 of RFC4556. Unlike 
KDC and principal, acceptor and initiator don't share any secrets. 
PKINIT's PA_PK_AS_REP is needed here for the initiator to make use of 
the ticket created by the acceptor.

   In all cases, GSS_Accept_security_context() returns
   GSS_S_CONTINUE_NEEDED status [RFC2743] and the output token is a
   KRB_AS_REP message if a ticket was created or a KRB_ERROR message if
   there was an error while processing the request or the local policy
   prevented a ticket from being issued.

If the acceptor returns GSS_S_CONTINUE_NEEDED in the case of an error, 
what happens when the initiator after processing the error token decides

to stop, will the server just hang there in the continue needed state?

Is having a MUST for PKINIT's EKUs too restrictive?

Since this is a GSS API mechanism what about QoP handling and channel 
bindings?

Token ids are defined for KRB_AS_REQ and KRB_AS_REP but not for
KRB_ERROR?

This draft does not support non-Kerberos environments. By that I mean, a

Kerberos domain must exist and users of PKU2U must have Kerberos 
principal names.

Name type NT-X500-PRINCIPAL which is rfc2253 string representation of 
the distinguished name does not produce a canonical name.

What happens when the initiator rejects the AS-REP tokens sent by the 
acceptor (ie., fails to verify acceptor's certificate)?  Does it 
generate an error token?

Perhaps last paragraph of Section 6 can have a more detailed explanation

that doesn't require the user to go search for a different draft to find

our that AP_REQ should carry TYPED_DATA of type TD_IAKERB_FINISHED.  I'm

sure i'm missing something but why is there a need to tie AS_REQ/REP to 
AP_REQ/REP no such ties exist in original Kerberos message flow?

Naming needs work. Comments made about naming in SPKM3 apply here.

Liqiang(Larry) Zhu wrote:
> Here is the updated PKU2U. Please review it and see if it has
addressed
> all concerns.
>
> Thanks,
>
> --Larry
>
> -----Original Message-----
> From: [e-mail] [mailto:[e-mail]] 
> Sent: Tuesday, February 27, 2007 3:50 PM
> To: [e-mail]
> Subject: I-D ACTION:draft-zhu-pku2u-01.txt 
>
> A New Internet-Draft is available from the on-line Internet-Drafts
> directories.
>
>
> 	Title		: Public Key Cryptography Based User-to-User
> Authentication - (PKU2U)
> 	Author(s)	: L. Zhu, et al.
> 	Filename	: draft-zhu-pku2u-01.txt
> 	Pages		: 10
> 	Date		: 2007-2-27
> 	
> This document defines the public key cryptography based user-to-user
>    authentication protocol - PKU2U. This mechanism provides security
>    services in peer to peer networking environments without requiring
a
>    trusted third party.  Furthermore, the binding of PKU2U for the
>    Generic Security Service Application Program Interface (GSS-API)
per
>    RFC2743 is defined based on RFC4121.
>
> A URL for this Internet-Draft is:
> http://www.ietf.org/internet-drafts/draft-zhu-pku2u-01.txt
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