Re: [plasma] Clarification of how client applications handle the LockBox in client in <plasma:GetCMSToken> elements

"Jim Schaad" <ietf@augustcellars.com> Wed, 21 November 2012 06:40 UTC

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From: "Jim Schaad" <ietf@augustcellars.com>
To: "'Trevor Freeman'" <trevorf@exchange.microsoft.com>, "'Ed Simon'" <Ed.Simon@titus.com>, <plasma@ietf.org>
References: <DCD8C7A5A8B3E844AA2E2CBE327CDC92013D21D4@E10MB3.tituscorp.local> <002601cdc6a0$fa38dcf0$eeaa96d0$@augustcellars.com> <3020AC5E95452D43B5D8D0FB02F881D30A6DA4@DF-M14-10.exchange.corp.microsoft.com> <005d01cdc6d5$04f967c0$0eec3740$@augustcellars.com> <3020AC5E95452D43B5D8D0FB02F881D30A77B8@DF-M14-10.exchange.corp.microsoft.com>
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Date: Tue, 20 Nov 2012 22:39:48 -0800
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Subject: Re: [plasma] Clarification of how client applications handle the LockBox in client in <plasma:GetCMSToken> elements
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What does it mean to have a recipient list if you are not looking at Email?

If one has a recipient list, and that recipient list is updated during
processing (for example mail list expansion) does that change the original
policy set by the sender?

I should have called the structure <LockBoxes> rather than <Recipients> to
prevent the confusion.  However, I can see that this could be an input that
is of interest to the policy.  However doing so means that we have to figure
out what it means in a number of different cases that I am currently not
ready to think about

Jim


> -----Original Message-----
> From: Trevor Freeman [mailto:trevorf@exchange.microsoft.com]
> Sent: Tuesday, November 20, 2012 2:46 PM
> To: Jim Schaad; 'Ed Simon'; plasma@ietf.org
> Subject: RE: [plasma] Clarification of how client applications handle the
> LockBox in client in <plasma:GetCMSToken> elements
> 
> Hi Jim,
> 
> The list of recipients for a message is a single list per message. There
are no
> policy dependent recipient lists.  The need for the list is policy
dependent but
> One or more policies may want that data as input to the policy. It seems
> pointless duplication to include the list of recipients as part of the
policy as
> you have to repeat the same data to each policy.
> 
> We have a per-message recipient list structure defined. If the lock box
> element is optional, we can use the same structure for both #1 and #2
below
> i.e. if I just want a recipient list with no lock boxes or if I want a
recipient list
> with lock boxes.
> 
> Trevor
> 
> 
> -----Original Message-----
> From: Jim Schaad [mailto:ietf@augustcellars.com]
> Sent: Monday, November 19, 2012 8:11 PM
> To: Trevor Freeman; 'Ed Simon'; plasma@ietf.org
> Subject: RE: [plasma] Clarification of how client applications handle the
> LockBox in client in <plasma:GetCMSToken> elements
> 
> 
> 
> > -----Original Message-----
> > From: Trevor Freeman [mailto:trevorf@exchange.microsoft.com]
> > Sent: Monday, November 19, 2012 2:18 PM
> > To: Jim Schaad; 'Ed Simon'; plasma@ietf.org
> > Subject: RE: [plasma] Clarification of how client applications handle
> > the LockBox in client in <plasma:GetCMSToken> elements
> >
> > Hi Jim,
> >
> > Let me restate things to see if I understood you correctly.
> >
> > The list of recipient is one per message not one per policy. While one
> > or
> more
> > policies may require the list be supplied; only one list would be
> > included
> in
> > the GetCMSToken request via the recipient structure.
> >
> > < Recipient>
> > <Subject>lisa@simpsons.com</Subject>;
> > </Recipient>
> > < Recipient>
> > <Subject>bart@simpsons.com</Subject>;
> > </Recipient>
> 
> No that is not correct.
> 
> There are three distinct ways that a list of recipients may be supplied to
the
> system.  These each have different outcomes.
> 
> 1.  A recipient may be supplied with a lock box created by the sender.
This
> supports a mode where the Plasma server does not know the CEK.   This is
> done through the <Recipient/> element.  (As you did below here)
> 
> 2.  A recipient list may be supplied as part of a policy.   This allows
for
> a policy to have a set of names to evaluate as part of the policy.  This
will
> (normally) be combined with giving a CEK to the server and allowing it to
> determine who gets the CEK back.
> 
> 3.  A recipient lists specific to email may be provided as part of the
input data.
> This behavior (perhaps not currently in the document) is provided for the
> purpose of doing pre-authorization of gateways and is specific to email.
> 
> 
> Currently the above is better expressed as
> 
> Policy=basic Policy
> BasicPolicy Recipient List is "lisa@simpsons.com bart@simpsons.com";
> 
> Jim
> 
> >
> > Policies may also require that lock boxes be generated for receipts
> > rather than supply the CEK to the Plasma server. In that instance, the
> > list of
> receipts
> > together with the associated lock box would be included in the
> > GetCMSToken request.
> >
> > < Recipient>
> > <Subject>lisa@simpsons.com</Subject>;
> > <LockBox>123456789</LockBox>
> > </Recipient>
> > < Recipient>
> > <Subject>bart@simpsons.com</Subject>;
> > <LockBox>abcdef</LockBox>
> > </Recipient>
> >
> > Trevor
> >
> > -----Original Message-----
> > From: plasma-bounces@ietf.org [mailto:plasma-bounces@ietf.org] On
> > Behalf Of Jim Schaad
> > Sent: Monday, November 19, 2012 1:58 PM
> > To: 'Ed Simon'; plasma@ietf.org
> > Subject: Re: [plasma] Clarification of how client applications handle
> > the LockBox in client in <plasma:GetCMSToken> elements
> >
> >
> >
> > > -----Original Message-----
> > > From: plasma-bounces@ietf.org [mailto:plasma-bounces@ietf.org] On
> > > Behalf Of Ed Simon
> > > Sent: Saturday, November 17, 2012 1:07 PM
> > > To: plasma@ietf.org
> > > Subject: Re: [plasma] Clarification of how client applications
> > > handle the LockBox in client in <plasma:GetCMSToken> elements
> > >
> > > Based on discussions with others on this mailing list, and
> > >
> > > http://www.ietf.org/mail-archive/web/plasma/current/msg00118.html
> > >
> > > ...I have drawn up the following three scenarios regarding the
> > construction of
> > > the <GetCMSToken> element sent to the PLASMA Server by the Sending
> > > Agent, and the construction of the LockBox by the PLASMA Server.
> > >
> > > Does what I've described in these scenarios, particularly Scenario B
> > > in
> > which
> > > the Sending Agent leaves it to the PLASMA Server to construct a
> > > LockBox
> > for
> > > a named recipient, sound reasonable? Scenario B follows from the text
> > >    "Additionally the Plasma server could return the standard
> > >    recipient info structures to be added to the message for recipients
> > >    if it can pre-authorize them to have access the message and knows
the
> > >    appropriate keying material."
> > > in the PLASMA Service CMS Processing v2 document.
> >
> > This text is intended to deal with the case of creating lockboxes for
> entities
> > such as virus checking gateways in a mail system.  The lockboxes that
> > are being returned with here are placed parallel to the Plasma Lockbox
> > in the CMS Enveloped data object and are not embedded into the lockbox
> > created by the Plasma server.
> >
> > >
> > > Here are the scenarios:
> > >
> > > Scenario A: The Sending Agent does NOT share the CEK with the PLASMA
> > > server and specifies a limited set of recipients who can decrypt the
> > message
> > > (for example, due to section 7.2.2 of PLASMA Service Trust
> > > processing
> v3).
> > >
> > > Sending Agent: In the <GetCMSToken> element of the PLASMA Request,
> > the
> > > sender will construct a <Recipient> list specifying, for each
> > recipient, both
> > > the <Subject> element (to identify the recipient), and the <LockBox>
> > > element to contain the encrypted CEK for that recipient (encrypted
> > > so only that recipient can decrypt it). There will be no <CEK>
element.
> > >
> > > PLASMA Server: Will construct an ASN.1 PLASMA LockBox (as described
> > > in PLASMA Service CMS Processing v2). The LockBox constructed by the
> > > PLASMA Server will comprise, in the namedRecipients, the LockBox-es
> > > provided by the Sending Agent. There will be no defaultRecipients
> > structure.
> > > Note that in this scenario, the PLASMA Server will not be able,
> > > barring
> > further
> > > communication with the Sending Agent, be able to supplement the list
> > > of recipients.
> >
> > This looks correct
> >
> > >
> > > Scenario B: The sender shares the CEK with the PLASMA server and
> > > specifies a limited set of recipients who can decrypt the message
> > > (for example,
> > again,
> > > due to section 7.2.2 of PLASMA Trust processing). For each recipient
> > > specified, there may or may not be a LockBox specified by the
> > > Sending Agent.
> > >
> > > Sending Agent: In the <GetCMSToken> element of the PLASMA Request,
> > the
> > > sender will construct a <Recipient> list specifying, for each
> > recipient, both
> > > the <Subject> element (to identify the recipient), and, optionally,
> > > the <LockBox> element to contain the encrypted CEK for that
> > > recipient (encrypted so only that recipient can decrypt it). The
> > > Sending Agent will
> > also
> > > construct a <CEK> element to contain the CEK.
> > >
> > > PLASMA Server: Where a LockBox for a recipient was specified by the
> > > Sending Agent, it will be treated as in Scenario A; otherwise, the
> > > PLASMA Server will create a LockBox for that recipient to populate
> > > the namedRecipients structure. It will also create a
> > > defaultRecipients
> > structure
> > > using the CEK provided by the Sending Agent. Note that in this
> > > scenario,
> > the
> > > PLASMA Server will be able to, independently of the Sending Agent,
> > > be able to supplement the list of recipients.
> > >
> > > Note that for Scenario B, the schema definition for the <LockBox>
> > > element will need to have the attribute minOccurs=0.
> >
> > This is not currently an envisioned scenario in terms of the Plasma
> > server creating the lock boxes at send time.  Currently if there is a
> > list of
> recipients
> > that the sender does not create lockboxes for, it is envisioned that
> > this
> would
> > be handled as part of the policy set on the message.  The Plasma
> > server would then deal with potentially creating a lock box (as oppose
> > to
> returning a
> > bare key) when the recipient tries to get the key from the server.
> >
> > >
> > > Scenario C: The Sending Agent shares the CEK with the PLASMA server
> > > and does NOT specify any recipients.
> > >
> > > Sending Agent: The Sending Agent will also construct a <CEK> element
> > > to contain the CEK; no <Recipient> element will be created.
> > >
> > > PLASMA Server: The PLASMA Server will also create a
> > > defaultRecipients structure using the CEK provided by the Sending
> > > Agent; it may or may not create a namedRecipients structure
> > > (populated independently of the Sending Agent). As in Scenario B,
> > > the PLASMA Server will be able to, independently of the Sending
> > > Agent, be able to supplement the list of recipients.
> >
> > This is what I would expect to see.
> >
> > Jim
> >
> > >
> > > _______________________________________________
> > > plasma mailing list
> > > plasma@ietf.org
> > > https://www.ietf.org/mailman/listinfo/plasma
> >
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