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

Trevor Freeman <trevorf@exchange.microsoft.com> Tue, 20 November 2012 22:48 UTC

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From: Trevor Freeman <trevorf@exchange.microsoft.com>
To: Jim Schaad <ietf@augustcellars.com>, 'Ed Simon' <Ed.Simon@titus.com>, "plasma@ietf.org" <plasma@ietf.org>
Thread-Topic: [plasma] Clarification of how client applications handle the LockBox in client in <plasma:GetCMSToken> elements
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Date: Tue, 20 Nov 2012 22:46:29 +0000
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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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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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