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Subject: Re: [ws-rx] Comments on Issue 66



Tom,

If an RMD has not received a LastMessage, is it still obligated to deliver retransmitted
messages?

I think that in the answer to the above question, you will find the answer to your concern.

The RMD does not need to know that the RMS thinks it has sent the last message in
a Sequence. The Sequence is either open (active) or in a closed state. That's pretty
straightforward IMO.

Cheers,

Christopher Ferris
STSM, Emerging e-business Industry Architecture
email: chrisfer@us.ibm.com
blog: http://webpages.charter.net/chrisfer/blog.html
phone: +1 508 377 9295


Doug Davis/Raleigh/IBM@IBMUS wrote on 11/30/2005 04:49:31 AM:

>
> Tom,
>   Right, it uses LastMessage to keep message numbers higher than X
> from being delivered - which is one of the two uses I stated it
> appeared to be used
> for.  However, we need to look at whether the use of LastMessage is
> appropriate
> for this type of security hole.  If people are concerned about
> hijacking of sequences
> then LastMessage is not a very good way to stop it - stopping peoplefrom using
> a msgNum higher than X but not less than X-1 is very arbitrary.  The
> real solution
> for this would be to use something like SecureConversation or some
> other security
> mechanism.  So, while the presence of LastMessage may (or may not - I need to
> think more about it) change the state table, I don't think the new
> state created by the
> presence of LastMessage is a worthwhile state - in other words, it doesn't add
> anything of value (see my thread with Anish) and should be removed.
> Just because
> there's something in the spec that creates a new state does not imply that the
> state itself is useful.
>
> thanks
> -Doug
>
>

>
> Tom Rutt <tom@coastin.com>

> 11/29/2005 03:28 PM
>
> Please respond to
> tom

>
> To

>
> wsrx <ws-rx@lists.oasis-open.org>

>
> cc

>
> Subject

>
> [ws-rx] Comments on Issue 66

>
>
>
>
> Description from Issue 66 states:
> "
>            The LastMessage element, as part of a Sequence header
> element, appears superfluous. It seems to serve 2 purposes:
>        
>            1 - force a SeqAck to be sent back from the RMD
>
>            2 - force the RMD to reject any messages with a higher message #
>
>            #1 can be done with an AckReq header.  We should avoid
> having multiple ways to do the same thing.
>        
>            #2 is really only an issue if someone tries to hijack the
> sequence - and to protect against that we should be using a
>            real security mechanism like WS-SC/Trust, not the
> LastMessage element.
>  
>            When an RMS is done with a sequence it is free to simply
> Close or Terminate it (whether or not it has all of the Acks
>            it wants - but normally it will wait) - having an additional
> message exchange to send a LastMessage is unnecessary
> "
>
> The ws-rm spec wording implies that there is a difference in behaviour
> (as described in the Hitachi proposed state tables) between
> the RMD in states "closed" and "lastReceived".
>   The RMD continues to "deliver" retransmitted messages with msgNo less
> than the last messageId value, when in the last state.
>   The RMD does not deliver any messages when in the closed state.
>
> This difference in behaviour is significant.  Last is used for orderly
> shutdown (with no lost messages at time of sequence terminiation).
>
> Tom Rutt
> .
>
> --
> The key issue here is
>
> ----------------------------------------------------
> Tom Rutt                 email: tom@coastin.com; trutt@us.fujitsu.com
> Tel: +1 732 801 5744          Fax: +1 732 774 5133
>
>


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