I propose, as a strawman proposal, that when policies require the sender's
recipient list, they should be specified through XACML access-subject
attributes, NOT PLASMA-specific attributes (e.g. within <plasma:GetCMSToken>).
My position would be that PLASMA should only supplement XACML's pre-defined
attributes where necessary, not create PLASMA-specified attributes where
existing XACML-specified attributes are already defined and are sufficient.
Hence my position at the moment is I would NOT change the current PLASMA
semantics of <plasma:Recipient> which is specifically for specifying a lockbox
for a recipient (though I agree with Jim that the name of the element should be
changed to <LockBoxes> to avoid confusion) and, instead indicate in the
specification, that when a policy processing depends on knowing the list of
recipients, that those recipients be specified through a XACML <Attributes>
category for subjects which specifies the recipients through XACML
access-subject att
ributes.
Besides a list of recipients, I can imagine other policy-specific information
that could be used in a GetCMSToken request. Like the list of recipients, such
policy-specific information would also be included through non-PLASMA-specific,
XACML attributes.
For example, a XACML request for GetCMSToken which needs to specify the list of
recipients and other info could look like this...
<Request xmlns="urn:oasis:names:tc:xacml:3.0:core:schema:wd-17"
CombinedDecision="false" ReturnPolicyIdList="false">
<Attributes
Category="urn:oasis:names:tc:xacml:3.0:attribute-category:action">
<Attribute AttributeId="urn:plasma:action-id" IncludeInResult="false">
<AttributeValue
DataType="http://www.w3.org/2001/XMLSchema#string";>GetCMSToken</AttributeValue>
</Attribute>
</Attributes>
<Attributes Category="urn:ietf:plasma:data">
<Attribute AttributeId="urn:plasma:data-id" IncludeInResult="false">
<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string";>
<GetCMSToken xmlns="urn:ietf:schema:plasma:1.0">
<Leaf
PolicyId="urn:example:policies:only-allow-recipients-to-decrypt-this-email"/>
<Hash>
<DigestMethod xmlns="http://www.w3.org/2000/09/xmldsig#";
Algorithm ="http://www.w3.org/2001/04/xmlenc#sha256"/>
<DigestValue
xmlns="http://www.w3.org/2000/09/xmldsig#";>hrQkL07h1qZhPhgLXKlL0dVeFLAbUVy0no05EGDzK2Q=</DigestValue>
</Hash>
<CEK>1BF2BEB249EE8EF2CB373E9800AC6F01</CEK>
</GetCMSToken>
</AttributeValue>
</Attribute>
</Attributes>
<!-- Ed's NEW STUFF BEGINS HERE! -->
<Attributes
Category="urn:oasis:names:tc:xacml:3.0:attribute-category:access-subject">
<Attribute
AttributeId=""urn:oasis:names:tc:xacml:1.0:subject:subject-id""
IncludeInResult="false">
<AttributeValue
DataType="urn:oasis:names:tc:xacml:1.0:data-type:rfc822Name">[email protected]</AttributeValue>
</Attribute>
<Attribute
AttributeId=""urn:oasis:names:tc:xacml:1.0:subject:subject-id""
IncludeInResult="false">
<AttributeValue
DataType="urn:oasis:names:tc:xacml:1.0:data-type:rfc822Name">[email protected]</AttributeValue>
</Attribute>
<Attribute
AttributeId=""urn:oasis:names:tc:xacml:1.0:subject:subject-id""
IncludeInResult="false">
<AttributeValue
DataType="urn:oasis:names:tc:xacml:1.0:data-type:rfc822Name">[email protected]</AttributeValue>
</Attribute>
</Attributes>
<Attributes
Category="urn:example:some-other-attributes-related-to-processing-this-policy">
<Attribute AttributeId="urn:example:something-1" IncludeInResult="false">
<AttributeValue
DataType="urn:example:something-1-format">SomethingSomethingSomethingSomething</AttributeValue>
</Attribute>
<Attribute AttributeId="urn:example:something-2" IncludeInResult="false">
<AttributeValue
DataType="urn:example:something-2-format">asldkjfalskdjf32434534543dfjalkscxvkljzv2309080kjlkjlkj</AttributeValue>
</Attribute>
</Attributes>
</Request>
Ed
________________________________________
From: Jim Schaad [[email protected]]
Sent: Wednesday, November 21, 2012 01:39
To: 'Trevor Freeman'; Ed Simon; [email protected]
Subject: RE: [plasma] Clarification of how client applications handle the
LockBox in client in <plasma:GetCMSToken> elements
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:[email protected]]
> Sent: Tuesday, November 20, 2012 2:46 PM
> To: Jim Schaad; 'Ed Simon'; [email protected]
> 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:[email protected]]
> Sent: Monday, November 19, 2012 8:11 PM
> To: Trevor Freeman; 'Ed Simon'; [email protected]
> Subject: RE: [plasma] Clarification of how client applications handle the
> LockBox in client in <plasma:GetCMSToken> elements
>
>
>
> > -----Original Message-----
> > From: Trevor Freeman [mailto:[email protected]]
> > Sent: Monday, November 19, 2012 2:18 PM
> > To: Jim Schaad; 'Ed Simon'; [email protected]
> > 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>[email protected]</Subject>
> > </Recipient>
> > < Recipient>
> > <Subject>[email protected]</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 "[email protected] [email protected]"
>
> 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>[email protected]</Subject>
> > <LockBox>123456789</LockBox>
> > </Recipient>
> > < Recipient>
> > <Subject>[email protected]</Subject>
> > <LockBox>abcdef</LockBox>
> > </Recipient>
> >
> > Trevor
> >
> > -----Original Message-----
> > From: [email protected] [mailto:[email protected]] On
> > Behalf Of Jim Schaad
> > Sent: Monday, November 19, 2012 1:58 PM
> > To: 'Ed Simon'; [email protected]
> > Subject: Re: [plasma] Clarification of how client applications handle
> > the LockBox in client in <plasma:GetCMSToken> elements
> >
> >
> >
> > > -----Original Message-----
> > > From: [email protected] [mailto:[email protected]] On
> > > Behalf Of Ed Simon
> > > Sent: Saturday, November 17, 2012 1:07 PM
> > > To: [email protected]
> > > 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
> > > [email protected]
> > > https://www.ietf.org/mailman/listinfo/plasma
> >
> > _______________________________________________
> > plasma mailing list
> > [email protected]
> > https://www.ietf.org/mailman/listinfo/plasma
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