Network Working Group J. Schaad
Internet-Draft Soaring Hawk Consulting
Intended status: Standards Track August 24, 2012
Expires: February 25, 2013
Plasma Service Trust Processing
draft-schaad-plasma-service-03
Abstract
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. XML Nomenclature and Name Spaces . . . . . . . . . . . . . 4
1.2. Requirements Terminology . . . . . . . . . . . . . . . . . 5
2. Components . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. XACML 3.0 . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. SAML . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3. WS-Trust 1.4 . . . . . . . . . . . . . . . . . . . . . . . 7
3. Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Sender Processing . . . . . . . . . . . . . . . . . . . . 8
3.2. Recieving Agent Processing . . . . . . . . . . . . . . . . 9
4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 11
5. Plasma Request . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1. Authentication Element . . . . . . . . . . . . . . . . . . 13
5.1.1. SAML Assertion . . . . . . . . . . . . . . . . . . . . 15
5.1.2. WS Trust Tokens . . . . . . . . . . . . . . . . . . . 16
5.1.3. XML Signature Element . . . . . . . . . . . . . . . . 17
5.1.4. GSS-API Element . . . . . . . . . . . . . . . . . . . 18
5.2. xacml:Request Element . . . . . . . . . . . . . . . . . . 18
6. Plasma Response Element . . . . . . . . . . . . . . . . . . . 20
6.1. xacml:Response Element . . . . . . . . . . . . . . . . . . 20
7. Role Token and Policy Acquisition . . . . . . . . . . . . . . 23
7.1. Role Token Request . . . . . . . . . . . . . . . . . . . . 23
7.2. Request Role Token Response . . . . . . . . . . . . . . . 24
7.2.1. RoleToken XML element . . . . . . . . . . . . . . . . 25
7.2.2. Email Address List Options . . . . . . . . . . . . . . 28
8. Sending An Email . . . . . . . . . . . . . . . . . . . . . . . 29
8.1. Send Message Request . . . . . . . . . . . . . . . . . . . 29
8.1.1. CMS Message Token Data Structure . . . . . . . . . . . 30
8.1.2. XML Label Structure . . . . . . . . . . . . . . . . . 32
8.2. Send Message Response . . . . . . . . . . . . . . . . . . 37
9. Decoding A Message . . . . . . . . . . . . . . . . . . . . . . 39
9.1. Requesting Message Key . . . . . . . . . . . . . . . . . . 39
9.2. Requesting Message Key Response . . . . . . . . . . . . . 40
10. Plasma Attributes . . . . . . . . . . . . . . . . . . . . . . 42
10.1. Data Attributes . . . . . . . . . . . . . . . . . . . . . 42
10.1.1. Channel Binding Data Attribute . . . . . . . . . . . . 42
10.1.2. CMS Signer Info Data Attribute . . . . . . . . . . . . 43
10.1.3. S/MIME Capabilities Data Attribute . . . . . . . . . . 43
10.2. Obligations and Advice . . . . . . . . . . . . . . . . . . 44
10.2.1. Signature Required . . . . . . . . . . . . . . . . . . 44
10.2.2. Encryption Required . . . . . . . . . . . . . . . . . 44
11. Certificate Profiles . . . . . . . . . . . . . . . . . . . . . 46
12. Message Transmission . . . . . . . . . . . . . . . . . . . . . 47
13. Security Considerations . . . . . . . . . . . . . . . . . . . 48
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 49
14.1. Plasma Action Values . . . . . . . . . . . . . . . . . . . 49
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14.2. non . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
14.3. Port Assignment . . . . . . . . . . . . . . . . . . . . . 51
15. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 52
16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 53
16.1. Normative References . . . . . . . . . . . . . . . . . . . 53
16.2. Informative References . . . . . . . . . . . . . . . . . . 54
Editorial Comments . . . . . . . . . . . . . . . . . . . . . . . .
Appendix A. XML Schema . . . . . . . . . . . . . . . . . . . . . 57
Appendix B. Example: Get Roles Request . . . . . . . . . . . . . 62
Appendix C. Example: Get Roles Response . . . . . . . . . . . . . 63
Appendix D. Example: Get CMS Token Request . . . . . . . . . . . 64
Appendix E. Example: Get CMS Token Response . . . . . . . . . . . 66
Appendix F. Example: Get CMS Key Request . . . . . . . . . . . . 67
Appendix G. Example: Get CMS KeyResponse . . . . . . . . . . . . 68
Appendix H. Enabling the MultiRequests option . . . . . . . . . . 69
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 70
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1. Introduction
1.1. XML Nomenclature and Name Spaces
The following name spaces are used in this document:
+-----+--------------------------------------------+----------------+
| Pre | Namespace | Specification( |
| fix | | s) |
+-----+--------------------------------------------+----------------+
| eps | http://ietf.org/2011/plasma/ | This |
| | | Specification |
| | | |
| wst | http://docs.oasis-open.org/ws-sx/ws-trust/ | [WS-TRUST] |
| | 200512 | |
| | | |
| wsu | http://docs.oasis-open.org/wss/2004/01/oas | [WS-Security] |
| | is-200401-wss-wssecurity-utility-1.0.xsd | |
| | | |
| wss | http://docs.oasis-open.org/wss/2004/01/oas | [WS-Security] |
| e | is-200401-wss-wssecurity-secext-1.0.xsd | |
| | | |
| wss | http://docs.oasis-open.org/wss/oasis-wss-w | [WS-Security] |
| e11 | security-secext-1.1.xsd | |
| | | |
| xac | http://docs.oasis-open.org/xacml/3.0/xacml | [XACML] |
| ml | -3.0-core-spec-cs-01-en.html | |
| | | |
| ds | http://www.w3.org/2000/09/xmldsig# | [XML-Signature |
| | | ] |
| | | |
| xen | http://www.w3.org/2001/04/xmlenc# | [XML-Encrypt] |
| c | | |
| | | |
| wsp | http://schemas.xmlsoap.org/ws/2004/09/poli | [WS-Policy] |
| | cy | |
| | | |
| wsa | http://www.w3.org/2005/08/addressing | [WS-Addressing |
| | | ] |
| | | |
| xs | http://www.w3.org/2001/XMLSchema | [XML-Schema1][ |
| | | XML-Schema2] |
+-----+--------------------------------------------+----------------+
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1.2. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
When the words appear in lower case, their natural language meaning
is used.
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2. Components
In designing this specification we used a number of pre-existing
specifications as building blocks. In some cases we use the entirety
of the specification and in other case we use only select pieces.
2.1. XACML 3.0
The XACML specification (eXtensible Access Control Markup Language)
[XACML] provides a framework for writing access control policies and
for creating standardized access control queries and responses. The
request and response portion of the specification is used to build
the request (Section 5.2) and response (Section 6.1) messages in this
specification. The structure for writing the access control policies
is out of scope for this document, but XACML is one of the
possibilities that can be used for that purpose.
2.2. SAML
A number of different methods for carrying both identification and
attributes of the party requesting access is permitted in this
specification. SAML is one of the methods that is permitted for that
purpose.
SAML has defined three different types of assertions in it's core
specification [OASIS-CORE]:
o Authentication: The assertion subject was authenticated by a
particular means at a particular time.
o Attribute: The assertion subject is associated with the supplied
attributes.
o Authorization Decision:[anchor7] A request to allow the assertion
subject to access the specified resource has been granted or
denied.
While a PDP can use an Authorization Decision as input, this is
unexpected and MAY be supported. In addition there are three
different ways that the subject of a SAML statement can be
identified:
o A bearer statement: These statements are belong to anybody who
presents them. The owner is required to take the necessary
precautions to protect them.
o A holder of key statement: These statements belong to anybody who
can use the key associated with the statement.
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o Subject match:[anchor8] These statements can be associated to an
identity by matching the name of the entity.
We cannot pass a SAML assertion with attributes as a single attribute
in the XACML request as XACML wants each of the different attributes
to be individually listed in the request. This greatly simplifies
the XACML code, but means that one needs to do a mapping process from
the SAML attributes to the XACML attributes. This process has been
discussed in Section 2 of [SAML-XACML]. This mapping process MUST be
done by a trusted agent, as there are a number of steps that need to
be done including the validation of the signature on the SAML
assertion. This process cannot be done by the PEP that is residing
on the Plasma client's system as this is considered to be an
untrusted entity by the Plasma system as a whole. One method for
this to be addressed is to treat the Plasma server as both a PDP (for
the Plasma client) and a PDP for the true XACML policy evaluator. In
this model, the Plasma server becomes the trusted PEP party and has
the ability to do the necessary signature validation and mapping
processes. A new XACML request is then created and either re-
submitted to itself for complete evaluation or to a third party which
does the actual XACML processing.[anchor9]
2.3. WS-Trust 1.4
The WS-Trust 1.4 [WS-TRUST] standard provides for methods for
issuing, renewing, and validating security tokens. This
specification uses only a small portion of that standard,
specifically the structure that returns a trust token from the issuer
to the requester.
This specification makes no statements on the content and format of
the token returned from the Plasma server to the Plasma client in the
wst:RequestSecurityTokenResponse field. These tokens may be
parseable by the client, but there is no requirement that the client
be able to understand the token. The token can always be treated as
an opaque blob by the client which is simply reflected back to the
server at a later time. The attributes that client needs to
understand in order to use the token, such as the life time, are
returned as fields of the token response.
TODO: need to discuss the content model and say what elements need to
be supported and what elements can be ignored -- safely.
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3. Model
To be supplied from the problem statement document. [anchor11]
(1)(3) +----------+
+----------->|Sending |<------------+
| |Agent | |
(2) v +----------+ v
+----------+ ^ +---------+
|Email | | |Mail |
|Policy |<----------+ |Transfer |
|Service | |Agent |
+----------+ +---------+
() ^ +----------+ ^
| |Receiving | |
+----------->|Agent |<------------+
()() +----------+
Figure 1: Message Access Control Actors
List the boxes above and give some info about them.
Email Policy Service is the gateway controller for accessing a
message. Although it is represented as a single box in the
diagram, there is no reason for it to be in practice. Each of the
three protocols could be talking to different instances of a
common system. This would allow for a server to operated by
Company A, but be placed in Company B's network thus reducing the
traffic sent between the two networks.
Mail Transfer Agent is the entity or set of entities that is used to
move the message from the sender to the receiver. Although this
document describes the process in terms of mail, any method can be
used to transfer the message.
Receiving Agent is the entity that consumes the message.
Sending Agent is the entity that originates the message.
3.1. Sender Processing
We layout the general steps that need to be taken by the sender of an
EPS message. The numbers in the steps below refer to the numbers in
the upper half of Figure 1. A more detailed description of the
processing is found in Section 7 for obtaining the security policies
that can be applied to a messages and Section 8 for sending a
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message.
1. The Sending Agent sends a message to one or more Email Policy
Services in order to obtain the set of policies that it can apply
to a message along with a security token to be used in proving
the authorization. Details of the message send can be found in
Section 7.1.
2. The Email Policy Service examines the set of policies that it
understands and checks to see if the requester is authorized to
send messages with the policy.
3. The Email Policy Service returns the set of policies and an
security token to the Sending Agent. Details of the message sent
can be found in Section 7.2.
4. The Sending Agent selects the Email Policy(s) to be applied to
the message, along with the set of recipients for the message.
5. The Sending Agent relays the selected information to the Email
Policy Service along with the security token. Details of this
message can be found in Section 8.1.
6. The Email Policy Service creates the recipient info attribute as
defined in [EPS-CMS].
7. The Email Policy Service returns the created attribute to the
Sending Agent. Details of this message can be found in
Section 8.2.
8. The Sending Agent composes the CMS EnvelopedData content type
placing the returned attribute into a KEKRecipientInfo structure
and then send the message to the Mail Transport Agent.
3.2. Recieving Agent Processing
We layout the general steps that need to be taken by the sender of an
EPS message. The numbers in the steps below refer to the numbers in
the lower half of Figure 1. A more detailed description of the
processing is found in Section 9.
1. The Receiving Agent obtains the message from the Mail Transport
Agent.
2. The Receiving Agent starts to decode the message and in that
process locates an EvelopedData content type which has a
KEKRecipientInfo structure with a XXXX attribute.
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3. The Receiving Agent processes the SignedData content of the XXXX
attribute to determine that communicating with it falls within
accepted policy.
4. The Receiving Agent transmits the content of the XXXX attribute
to the referenced Email Policy Service. The details of this
message can be found in Section 9.1.
5. The Email Policy Service decrypts the content of the message and
applies the policy to the credentials provided by the Receiving
Agent.
6. If the policy passes, the Email Policy Service returns the
appropriate key or RecipientInfo structure to the Receiving
Agent. Details of this message can be found in Section 9.2.
7. The Receiving Agent proceeds to decrypt the message and perform
normal processing.
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4. Protocol Overview
The protocol defined in this document is designed to take place
between a Plasma server and a Plasma client. The protocol takes
place in terms of a request/response dialog from the client to the
server. A single dialog can consist of more than one request/
response message pair. Multiple round trips within allow a client to
provide additional authentication, authorization and attribute
information to the server.
Each dialog contains one or more action attributes specifying what
actions the client wishes the server to take. Depending on the
action requested, additional attributes may be present providing data
for the action to use as input. Finally, each dialog will contain
authentication and attributes supplied by one or more authorities
that the server can use either as input to the action or as input to
policy decisions about whether to perform the action.
The protocol MUST be run over a secure transport, while the protocol
allows for signature operations to occur on sections of the message
structure, the secure transport is responsible for providing the
confidentiality and integrity protection services over the entire
message.
Multiple dialogs may be run over a single secure transport. Before a
new dialog may be started, the previous dialog MUST have completed to
a state of success, failure or not applicable. A new dialog MUST NOT
be started after receiving a response with an indeterminate status.
This is an indicator that the dialog has not yet completed.[anchor14]
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5. Plasma Request
The specification is written using XACML as the basic structure to
frame a request for an operation. The request for operations to
occur are written using XACML action items. This specification
defines actions specific to Plasma in a CMS environment. Other
specifications can define additional action items for other
environments (for example the XML encryption environment) or other
purposes. (Future work could use this basic structure to standardize
the dialogs between PDPs and PAPs or to facilitate legal signatures
on emails.)
In addition to the XACML action request there is a set of structures
to allow for a variety of authentication mechanisms to be used. By
allowing for the use of SAML and GSS-API as base authentication
mechanisms, the mechanism used is contained in a sub-system and thus
does not directly impact the protocol.
The request message uses a single XML structure. This structure is
the eps:PlasmaRequest object. The XML Schema used to describe this
structure is:
<xs:element name="PlasmaRequest" type="eps:RequestType"/>
<xs:complexType name="RequestType">
<xs:sequence>
<xs:element ref="eps:Authentication" minOccurs="0"/>
<xs:element ref="xacml:Request"/>
</xs:sequence>
<xs:attribute name="Version" type="xs:string" default="1.0"/>
</xs:complexType>
The RequestType has two elements in it:
Authentication is an optional element that holds the structures used
for doing authentication and authorization. Unless no
authentication is required by the Plasma server, the element is
going to exist for one or more requests in the dialog.
xacml:Request is a required element that contains the control
information for the action requested. The control information
takes the form of an action request plus additional data to be
used as part of the action request. The data and actions are to
be treated as self-asserted, that is they are deemed not to come
from a reliable source even in the event that an authentication is
successfully completed. As self-asserted values, Plasma servers
need to exercise extreme care about which are included in the
policy enforcement decisions. As an example, it makes sense to
allow for the action identifier to be included in the policy
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enforcement, but assertions about the identity of the subject
should be omitted. This element is taken from the XACML
specification.
For some operations, display string values are returned as part of
the response from the server. The xml:lang attribute SHOULD be
included in the RequestType element to inform the server as to what
language client wishes to have the strings in. The server SHOULD
attempt to return strings in the language requested or a related
language if at all possible.
5.1. Authentication Element
One of the major goals in the Plasma work is to detach the process of
authentication specifics from the Plasma protocol. In order to
accomplish this we are specifying the use of two general mechanisms
(SAML and GSS-API) which can be configured and expanded without
changing the core Plasma protocol itself. The authentication element
has two main purposes: 1) to process the authentication being used by
the client and 2) to carry authenticated attributes for use in the
policy evaluation.
When transporting the authentication information, one needs to
recognize that there may be a single or multiple messages in the
dialog in order to complete the authentication process. In
performing the process of authenticating, any or all of the elements
in this structure can be used. If there are multiple elements filled
out, the server can choose to process the elements in any order.
This means that the Plasma protocol itself does not favor any
specific mechanism. The current set of mechanisms that are built
into the Plasma specification are:
o SAML Assertions - many different types of SAML assertions are
supported. The specification uses both bearer and holder of key
assertions.
o X.509 Certificates can be used for the purpose of authentication
by creating a signature with the XML Digital Signature standard.
o GSS-API - the specification allows for the use of GSS-API in
performing the authentication process. The ABFAB mechanism in
GSS-API is specifically designed for use in a federated community
and allows for both authentication and attribute information to be
queried from the identity server.
o WS-Trust[anchor16] tokens allow for much of the same type of
information to be passed as SAML assertions. The Plasma
specification has been designed mailing for the use of WS-Trust
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tokens to be used for caching prior authentication sessions.
More than one authentication element can be present in any single
message. This is because a client may need to provide more than one
piece of data to a server in order to authenticate, for example a
holder of key SAML Assertion along with a signature created with that
key. Additionally a client may want to provide the server an option
of different ways of doing the authentication. In a federated
scenario, an X.509 certificate with a signature can be presented and
the server may not be able to build a trust path to it's set of trust
anchors. In this case the client may need to use the GSS-API/EAP
protocol for doing the authentication. The client may want to
provide the server with one or more SAML Assertion that binds a
number of attributes to it's identities so that the server does not
need to ask for those attributes at a later time. Finally, multiple
entities may need to be validated (for example the user and the
user's machine).
When transporting the attribute information, one needs to recognize
that there may be single or multiple messages in the dialog in order
to complete the authorization process. The server will return a
status code of urn:oasis:names:xacml:1.0:status:missing-attribute in
the event that one or more attributes are needed in order to complete
the authorization process. The details on how XACML returns missing
attribute information is found in Section 7.17.3 of [XACML]. When
the list of attributes is returned, the client has two choices: 1) It
can close the dialog, look for a source of the missing attributes and
then start a new dialog, 2) it can just get an assertion for the
missing attributes and send the new assertion as in a new request
message within the same dialog. The decision of which process to use
will depend in part on how long it is expected to take to get the new
attribute assertion to be returned.
The same authentication data does not need to be re-transmitted to
the server in a subsequent message within a single dialog. The
server MUST retain all authenticated assertion information during a
single dialog.
The schema for the Authentication element directly maps to the
ability to hold the above elements. The schema for the
Authentication element is:
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<xs:element name="Authentication" type="eps:AuthenticationType"/>
<xs:complexType name="AuthenticationType">
<xs:choice maxOccurs="unbounded">
<xs:element ref="saml:Assertion"/>
<xs:element name="GSSAPI" type="xs:hexBinary"/>
<xs:element name="WS-Token">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:hexBinary">
<xs:attribute name="tokenType" type="xs:anyURI"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element ref="ds2:Signature"/>
<xs:element name="Other">
<xs:complexType>
<xs:sequence>
<xs:any namespace="##other"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:choice>
</xs:complexType>
The schema allows for multiple authentication elements to occur in
any order. It is suggested, but not required, that the ds2:Signature
element occur after the authentication element that has an assoicated
key. This makes it easier for servers to make a one pass validate of
all authentication elements.
The Other element is provided to allow for additional authentication
elements, include SAML version 1.1, to be used.
5.1.1. SAML Assertion
SAML Assertions can provide authentication or attribute information
to the server. A SAML statement only needs to be provided once
during a single dialog, the server MUST remember all attributes
during the dialog.
When a SAML Assertion contains a SubjectConformation element using
the KeyInfoConfirmationDataType as a subject conformation element,
the confirmation shall be performed by the creation of an XML
Signature authentication element. The signature element shall be
created using an appropriate algorithm for the key referenced in the
SAML statement.
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Identify a SAML statement in the delegation/subject/environment space
- need text for this
5.1.2. WS Trust Tokens
WS Trust tokens are used in two different ways by this specification.
They can be used as the primary introduction method of a client to
the server, or they can be used by the server to allow the client to
be re-introduced to the server in such a way that the server can use
cached information.
WS Trust tokens come in two basic flavors: Bearer tokens[anchor18]
and Holder of Key tokens. With the first flavor, presentation of the
token is considered to be sufficient to allow the server to validate
the identity of the presenter and know the appropriate attributes to
make a policy decision. In the second flavor some type of
cryptographic operation is needed in addition to just presenting the
token. The Signature element Section 5.1.3 provides necessary
infrastructure to permit the cryptographic result to be passed to the
server.
This document does not define the content or structure of any tokens
to be used. This is strictly an implementation issue for the servers
in question. This is because the client can treat the WS Token value
presented to it as an opaque blob.[anchor19] Only the servers need to
understand how to process the blob. However there are some
additional fields which can be returned in addition to the token that
need to be discussed:
wst:TokenType SHOULD be returned if more than one type of token is
used by the set of servers. If a token type is returned to the
client, the client MUST include the element when the token is
returned to the server.
wst:BinarySecret SHOULD be returned for moderate duration tokens.
If a binary secret is returned then the client MUST provide
protection for the secret value. When a binary secret has been
returned, then the client MUST create either a signature or MAC
value and place it into the Signature element Section 5.1.3.
[anchor20].
wst:Lifetime MUST be returned with the wsu:Expires element set. The
wsu:Created element MAY be included. The element provides the
client a way to know when a token is going to expire and obtain a
new one as needed.
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5.1.3. XML Signature Element
When a holder of key credential is used to determine the attributes
associated with an entity, there is a requirement that the key be
used in a proof of possession step so that the Plasma server can
validate that the entity does hold the key. The credentials can hold
either asymmetric keys (X.509 certificates and SAML Assertions) or
symmetric keys (WS Trust Tokens and SAML Assertions) which use
Digital Signatures or Message Authentication Codes (MACs)
respectively to create and validate a key usage statement. The XML
signature standard [XML-Signature] provides an infrastructure to for
conveying the proof of possession information.
The signature is computed over the XACML request element as a
detached signature. When a signature element exists in the message,
the ChannelBinding attribute (Section 10.1.1) MUST be included in the
request. By the use of a value which is derived from the
cryptographic keys used in for protecting the tunnel, it is possible
for the server to verify that the authentication values computed were
done specifically for this specific dialog and are not replayed.
When creating either a signature or a MAC, the following statements
hold:
o The canonicalization algorithm Canonical XML 1.1 [XML-C14N11]
without comments MUST be supported and SHOULD be used in preparing
the XML node set for hashing. Other canonicalization algorithms
MAY be used.
o The signature algorithms RSAwithSHA256 and ECDSAwithSHA256 MUST be
supported by servers. At least one of the algorithms MUST be
supported by clients. The MAC algorithm HMAC-SHA256 MUST be
supported by both clients and servers. Other signature and MAC
algorithms MAY be supported.
o Set the additional attributes that must be included in a signature
- what should they be?
o If an xacml:Request element is referenced by an XML Signature
element, the xacml:Request element MUST include the ChannelBinding
token (Section 10.1.1) as one of the attributes.
o The keys used in computing the authentication value need to be
identified for the recipient. For X509 certificates, the full raw
certificate will normally be included as part of the signature,
but MAY be referenced instead. For SAML assertions, the specific
assertion carrying the asymmetric key can be identified by TBD
HERE. In the event that symmetric keys are used by holder of key
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assertions, the specific assertion will be identified by TBD HERE.
In these cases the server is expected to be able to associated the
key with the assertion by some means (either locally or perhaps
encrypted into the assertion).
5.1.4. GSS-API Element
TBD - rules for using GSS-API in general and the EAP version from
ABFAB particularly.
o How to build the name.
o Must use a secure tunnel for the outer EAP method and an
appropriate inner EAP method(s) to accomplish the required level
of authentication.
o Server query of attributes and specification of LOA to the EAP
IdP.
o Any additional Trust model items.
o How round trips are accomplished - the only case that a server
will send back an Authentication element is on return processing
of GSS-API messages.
5.2. xacml:Request Element
The request for an action to be performed by the Plasma server along
with the data that needs to be supplied by the client in order for
the server to complete the action are placed into the xacml:Request
element of the request. This document defines a set of actions that
are to be understood by the Plasma server. One (or more) action is
to be placed in the request message.
In addition to the request for a specific action to occur, the client
can place additional attributes in the request as well. These
attributes are provided in order to assist the server either in
identifying who the various agents on the client side are or to
provide suggestions of attributes for using in making control
decisions. Any data provided by the client in this manner is to be
considered as a self-asserted value and to be treated as if it comes
from the client as oppose to a trusted attribute agent.
For convenience the schema for the xacml:Request element is
reproduced here:
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<xs:element name="Request" type="xacml:RequestType"/>
<xs:complexType name="RequestType">
<xs:sequence>
<xs:element ref="xacml:RequestDefaults" minOccurs="0"/>
<xs:element ref="xacml:Attributes" maxOccurs="unbounded"/>
<xs:element ref="xacml:MultiRequests" minOccurs="0"/>
</xs:sequence>
<xs:attribute name="ReturnPolicyIdList" type="xs:boolean" use="required"/>
<xs:attribute name="CombinedDecision" type="xs:boolean" use="required"/>
</xs:complexType>
The RequestDefaults element of the XACML Request MUST be omitted by
the clients. If present servers MUST ignore the RequestDefaults
element. The use of the MultiRequest element is current not defined
for a Plasma server and SHOULD be omitted by clients.
Clients MAY set ReturnPolicyIdList to true in order to find out which
policies where used by the server in making the decision. Server MAY
ignore this field and not return the policy list even if requested.
A number of different entities may need to be identified to Plasma
server as part of a request. These entities include:
1. The subject making the request to the server.
2. The machine on the subject is using.
3. The entity the subject is acting for. Converse about Delegation.
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6. Plasma Response Element
There is a single top level structure that is used by the server to
respond to a client request.
The XML Schema used to describe the top level response is as follows:
<xs:element name="PlasmaResponse" type="eps:ResponseType"/>
<xs:complexType name="ResponseType">
<xs:sequence>
<xs:element ref="xacml:Response"/>
<xs:element ref="eps:PlasmaReturnToken" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="Version" type="xs:string" default="1.0"/>
</xs:complexType>
<xs:element name="PlasmaReturnToken" type="eps:PlasmaReturnTokenType"/>
<xs:complexType name="PlasmaReturnTokenType" abstract="true">
<xs:attribute name="DecisionId" type="xs:string"/>
</xs:complexType>
A Plasma Response has two elements:
xacml:Response is a mandatory element that returns the status of the
access request.
PlasmaReturnToken is an optional element that will return one or
more PlasmaReturnToken elements. These tokens represent the
answer, for a success, of the request.
A Plasma Return Token is the base type from which return values are
derived. The optional attribute DecisionId is defined for
correlation of requests and results in the event that multiple
requests are made. This document defines the following items that
are derived from this type:
o RoleToken - used to return roles.
o CMSMessageToken - used to return one or more CMS RecipientInfo
strucutures.
o CMSKeyToken - used to return either a CMS RecipientInfo structure
or a bare content encryption key.
6.1. xacml:Response Element
The xacml:Response element has the ability to return both a decision,
but additionally information about why a decision was not made.
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The schema for the xacml:Response element is reproduced here for
convenience:
<xs:element name="Response" type="xacml:ResponseType"/>
<xs:complexType name="ResponseType">
<xs:sequence>
<xs:element ref="xacml:Result" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<xs:element name="Result" type="xacml:ResultType"/>
<xs:complexType name="ResultType">
<xs:sequence>
<xs:element ref="xacml:Decision"/>
<xs:element ref="xacml:Status" minOccurs="0"/>
<xs:element ref="xacml:Obligations" minOccurs="0"/>
<xs:element ref="xacml:AssociatedAdvice" minOccurs="0"/>
<xs:element ref="xacml:Attributes" minOccurs="0" maxOccurs="unbounded"/>
<xs:element ref="xacml:PolicyIdentifierList" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
The xacml:Response element consists of one child the Result.
The xacml:Response element consists of the following elements:
xacml:Decision is a mandatory element that returns the possible
decisions of the access control decision. The set of permitted
values are Permit, Deny, Indeterminate and No Policy.
xacml:Status is an optional element returned for the Indeterminate
status which provides for the reason that a decision was not able
to be reached. Additionally it can contain hints for remedying
the situation. This document defines a new set of status values
to be returned. Formal declaration may be found in Section 14.
* gss-api indicates that a gss-api message has been returned as
part of the authentication process.
xacml:Obligations is designed to force the PEP to perform specific
actions prior to allowing access to the resource. If a response
is returned with this element present, the processing MUST fail
unless the PEP can perform the required action. A set of Plasma
specific obligations are found in Section 10.2. [anchor23]
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xacml:AssocatedAdvice is designed to give suggestions to the PEP
about performing specific actions prior to allowing access to the
resource. This element is not used by Plasma and SHOULD be
absent. If the response is returned with this element present,
processing will succeed even if the PEP does not know how to
perform the required action. A set of Plasma specific advice
elements are found in Section 10.2.
xacml:Attributes provides a location for the server to return
attributes used in the access control evaluation process. Only
those attributes requested in the Attributes section of the
request are to be returned. Since Plasma does not generally
supply attributes for the evaluation process, this field will
normally be absent.
xacml:PolicyIdentifierList provides a location to return the set of
policies used to grant access to the resource. This element is
expected to be absent for Plasma. [anchor24][anchor25]
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7. Role Token and Policy Acquisition
In order to send an email using a Plasma server, the first step is to
obtain a role token that provides the description of the labels that
can be applied and the authorization to send an email using one or
more of the labels. The process of obtaining the role token is
designed to be a request/response round trip to the Plasma server.
In practice a number of round trips may be necessary in order to
provide all of the identity and attributes to the Plasma server that
are needed to evaluate the policies for the labels.
When a Plasma server receives a role token request from a client, it
needs to perform a policy evaluation for all of the policies that it
arbitrates along with all of the options for those policies. In
general, the first time that a client requests a role token from the
server, it will not know the level of authentication that is needed
or the set of attributes that needs to be presented in order to get
the set of tokens. A server MUST NOT issue a role token without
first attempting to retrieve from an attribute source (either the
client or a back end server) all of the attributes required to check
all policies. Since the work load required on the server is expected
to be potentially extensive for creating the role token, it is
expected that the token returned will be valid for a period of time.
This will allow for the frequency of the operation to be reduced.
While the use of an extant role token can be used for identity proof,
it is not generally suggested that a new token be issued without
doing a full evaluation of the attributes of the client as either the
policy or the set of client attributes may have changed in the mean
time.
7.1. Role Token Request
The process starts by a client sending a server a role token request.
Generally, but not always, the request will include some type of
identity proof information and a set of attributes. It is suggested
that, after the first successful conversation, the client cache hints
about the identity and attributes needed for a server. This allows
for fewer round trips in later conversations. An example of a
request token can be found in Appendix B.
The role token request, as with all requests, uses the eps:
PlasmaRequest XML structure. The eps:Authentication MAY be included
on the first message and MUST be included on subsequent
authentication round trips.
A role token request by a client MUST include the GetRoleTokens
Plasma action request as an attribute of the xacml:Request element.
Details on the action can be found in section Section 14.1. When
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role tokens are requested, no additional data needs to be supplied by
the requester.
An example of a message requesting the set of policy information is:
<esp:PlasmaRequest>
<eps:Authentication>...</eps:Authentication>
<xacml:Request>
<xacml:Attributes Category="...:action">
<xacml:Attribute AttributeId="urn:plasma:action-id">
<xacml:AttributeValue
DataType="http://www.w3.org/2001/XMLSchema#string">
GetRoleToken</xacml:AttributeValue>
</xacml:Attribute>
</xacml:Attributes>
</xacml:Request>
</esp:PlasmaRequest>
7.2. Request Role Token Response
In response to a role token request, the Plasma server returns a role
token response. The response uses the eps:PlasmaResponse XML
structure. When a response is create the following should be noted:
An xacml:Decision is always included in a response. The values
permitted are:
Permit is used to signal success. In this case the response MUST
include one or more eps:RoleToken element.
Deny is used to signal failure. In this case the xacml:Status
element MUST be present an contain a failure reason.
Indeterminate is used to signal that a final result has not yet been
reached. When this decision is reached, the server SHOULD return
a list of additional attributes to be returned and SHOULD return
the list of role tokens that have been granted based on the
attributes received to that point.
NotApplicable is returned if the Plasma server does not have the
capability to issue role tokens.
An example of a response returning the set of policy information is:
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<eps:PlasmaResponse>
<xacml:Response>
<xacml:Result>
<xacml:Decision>Permit</xacml:Decision>
</xacml:Result>
</xacml:Response>
<eps:PlasmaReturnToken xsi:type="RoleToken">
<eps:Name>Role Display Name</eps:Name>
<eps:PDP>PDP Url names</eps:PDP>
<eps:PolicyList>
<eps:Policy>
Details of a policy
</eps:Policy>
... More policies ...
</eps:PolicyList>
<wst:RequestSecurityTokenResponse>
<wst:TokenType>urn:...:plasma:roleToken</wst:TokenType>
<wst:RequestedSecurityToken>...</wst:RequestedSecurityToken>
</wst:RequestSecurityTokenResponse>
</eps:PlasmaReturnToken>
... More Role Tokens ...
</eps:PlasmaResponse>
7.2.1. RoleToken XML element
The eps:PlasmaReturnToken element is used to return a role token to
the client. Multiple role tokens can be returned by using multiple
eps:PlasmaReturnToken elements. Each role token returned contains
one or more policies that can be asserted, the role token, and
optionally one or more set of obligations or advice that need to be
observed when creating messages. Additionally the name of a Plasma
server to be used with the token can be included as well as
cryptographic information to be used with the token.
The schema used for the PlasmaTokens element is:
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<xs:complexType name="RoleToken">
<xs:complexContent>
<xs:extension base="eps:PlasmaReturnTokenType">
<xs:sequence>
<xs:element name="Name" type="xs:string"/>
<xs:element name="PDP" type="xs:anyURI" maxOccurs="unbounded"/>
<xs:choice>
<xs:element name="PolicyList">
<xs:complexType>
<xs:sequence>
<xs:element name="Policy" type="eps:PolicyType" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element ref="eps:Label"/>
</xs:choice>
<xs:element ref="wst:RequestSecurityTokenResponse"/>
<xs:element ref="xacml:Obligations" minOccurs="0"/>
<xs:element ref="xacml:AssociatedAdvice" minOccurs="0"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="PolicyType">
<xs:sequence>
<xs:element name="Name" type="xs:string"/>
<xs:element name="Options" minOccurs="0">
<xs:complexType>
<xs:complexContent>
<xs:extension base="xs:anyType">
<xs:attribute name="optionsType" type="xs:anyURI" use="required"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
</xs:element>
</xs:sequence>
<xs:attribute name="PolicyId" type="xs:anyURI" use="required"/>
</xs:complexType>
The eps:RoleToken element contains the following items:
Name This element returns a descriptive name of the role as a whole.
The string returned SHOULD be selected based on the language
attribute on the request message. The stri8ng is suitable for
display to the user and should be indicative of the scope of the
role. Examples of role descriptive strings would be "Company
President", "Senior Executive", "Project X Electrical Engineer".
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PDP The element provides one or more URLs to be used for contacting
a Plasma server for the purpose of sending a message. This
element allows for the use of different Plasma servers for issuing
role tokens and message tokens. No ranking of the servers is
implied by the order of the URLs returned.
PolicyList contains the description of one or more policies that can
be asserted using the issued role token. Any of the policies
contained in the list may be combined together using the policy
logic in constructing a label during the send message process.
Label contains a single specific label. This element is returned as
part of a read message token to allow for replies to be formulated
by an entity that cannot generally originate a message using the
policy.
wst:RequestSecurityTokenResponse contains the actual token itself.
The eps:PolicyType type is used to represent the elements of a policy
to the client. The elements in this type are:
Name contains a display string that represents the policy. This
element is localized in response to the TBD attribute in the TBD
field.
PolicyId This attribute contains a "unique" identifier for the
policy. This is the value that identifies the policy to the
software. The type for the value is defined as a URI.
Options This element is used to inform the client what the set of
options that need to be filled in as part of asserting the policy.
If the client software does not understand how to set the options
for the supplied type, then the client software MUST NOT allow the
user to assert the policy. The option structure is identified by
the URI in the optionsType attribute. This document defines one
option structure in section Section 7.2.2. This option structure
is used in the basic policies defined in [PlasmaBasicPolicy].
When building the wst:RequestSecurityTokenResponse element, the
following should be noted:
A wst:RequestedSecurityToken element containing the security token
MUST be included. The format of the security token is not
specified and is implementation specific, it is not expected
that[anchor27] . Examples of items that could be used as security
tokens are SAML statements, encrypted record numbers in a server
database.
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A wst:Lifetime giving the life time of the token SHOULD be
included. It is not expected that this should be determinable
from the token itself and thus must be independently provided.
There is no guarantee that the token will be good during the
lifetime as it make get revoked[anchor28] due to changes in
credentials, however the client is permitted to act as if it were.
The token provided may be used for duration. If this element is
absent, it should be assumed that the token is either a one time
token or of limited duration.
Talk about cryptographic information
7.2.2. Email Address List Options
Some policies are designed to be restricted to a set of explicitly
named people by the sender of the message. This policy is used for
the set of basic policies defined in [PlasmaBasicPolicy]. In these
cases the creator of the message specifies a set of recipients by
using email address names without any decoration.
The Email Address List Option is identified by the uri
"urn:ietf:plasma:options:emailAddrs". The type associated with the
structure is a string. The string contains a space separated set of
email addresses.
All Plasma clients and servers MUST be able to create, parse and use
the Email Address List Option for any policy.
As of the release of this document, Plasma clients and servers are
not expected to understand any other options.
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8. Sending An Email
After having obtained a role token from a Plasma server, the client
can then prepare to send an Email by requesting a message token from
the Plasma server. As part of the preparatory process, the client
will construct the label to be applied to the Email from the set of
policies that it can assert, determine the optional elements for
those policies which have options, generate the random key encryption
key and possible create the key recipient structures for the email.
Although this section is written in terms of a CMS Encrypted message,
there is nothing to prevent the specification of different formats
and still use this same basic protocol. An example of a request
token exchange can be found in Appendix D.
8.1. Send Message Request
The send message request is built using the eps:PlasmaRequest XML
structure. When building the request, the following applies:
o The eps:Authentication element SHOULD be included in the initial
message. The authorization is supplied by the role token returned
above, however authentication may be required as well. The
authentication data is placed here.
o The xacml:Request element MUST be included in the initial message.
o The client MUST include an action attribute. This document
defines the GetSendCMSTOken action attribute for this purpose.
o The client MUST include a data attribute. This attribute contains
the information that is used to build the CMS Message token to be
returned. There MAY be more than one data attribute, but this
will not be a normal case. More details on this attribute are in
Section 8.1.1.
o If the client is using the XML Digital Signature element in this
message, then the client MUST include the cryptographic channel
binding token (Section 10.1.1) in the set of XACML attributes.
A message requesting that a CMS message token be created looks like
this:
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<eps:PlasmaRequest>
<eps:Authentication>
<eps:WS_Token>
Role Token goes here
</eps:WS_Token>
</eps:Authentication>
<xacml:Request>
<xacml:Attributes Category="...:action">
<xacml:Attribute AttributeId="urn:plasma:action-id">
<xacml:AttributeValue>
GetSendCMSToken
</xacml:AttributeValue>
</xacml:Attribute>
</xacml:Attributes>
<xacml:Attributes Category="...:data">
<xcaml:Attribute AttributeId="urn:plasma:data-id">
<xacml:AttributeValue>
<eps:GetCMSToken>
<eps:Label>
... Label Tree for message ...
</eps:Label>
<eps:Hash>
... Hash algorithm and hash of encrypted content ...
</eps:Hash>
<eps:CEK>
... Content Encryption Key ...
</eps:CEK>
</eps:GetCMSToken>
</xacml:AttributeValue>
</xcaml:Attribute>
</xacml:Attributes>
</xacml:Request>
</eps:PlasmaRequest>
8.1.1. CMS Message Token Data Structure
The message token data structure is used as an attribute to carry the
necessary information to issue a CMS message token. The schema that
describes the structure is:
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<xs:element name="GetCMSToken" type="eps:CMSTokenRequestType"/>
<xs:complexType name="CMSTokenRequestType">
<xs:sequence>
<xs:choice>
<xs:element ref="eps:Label"/>
<xs:element ref="eps:Leaf"/>
</xs:choice>
<xs:element name="Hash">
<xs:complexType>
<xs:sequence>
<xs:element ref="ds2:DigestMethod"/>
<xs:element ref="ds2:DigestValue"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="Recipient" type="eps:RecipientInfoType" minOccurs="0" maxOccurs="unbounded"/>
<xs:element name="CEK" type="xs:hexBinary" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:element name="RecipientInfo" type="eps:RecipientInfoType"/>
<xs:complexType name="RecipientInfoType">
<xs:sequence>
<xs:element name="Subject" maxOccurs="unbounded">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:anySimpleType">
<xs:attribute name="type" type="xs:string" use="required"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name="LockBox" type="xs:base64Binary"/>
</xs:sequence>
</xs:complexType>
When used in an xacml:Attribute, the structure is identified by:
Category = "urn:oasis:name:tc:xacml:3.0:attribute-category:data"
AttributeId = "urn:ietf:plasma:data-id"
DataType = "http://www.w3.org/2001/XMLSchema#anyType"
The elements of the structure are used as:
Leaf
This element contains a the policy to be applied to the message
when a single policy is used.
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Label
This element contains the policy to be applied to the message when
a combination of policies is to be applied.
Hash
This element contains the hash of the encrypted content of the
message that the policy is being applied to. The algorithm used
to compute the hash is contained in the DigestMethod element and
the value is contained in the DigestValue element.
Recipients
This optional element contains a recipient info structure for a
message recipient. This element may be repeated when more than
one lock box is pre-computed for recipients by the message sender.
This element is used in those cases where the sender does not want
to share the content encryption key with the Plasma server and the
sender has the ability to retrieve the necessary keys for all of
the recipients. If the #### obligation was returned for the role
token, then a recipient info lock box MUST be created for the
Plasma server and the CEK element MUST absent.
CEK
This optional element contains the content encryption key (CEK) to
decrypt the message.
One or both of CEK and Recipients elements MUST be present.
The elements of the RecipientInfoType structure are:
Subject
This element contains a subject identifier. Since a CMS recipient
info structure does not contain a great deal of information about
the recipient, this element contains a string which can be used to
identify the subject. This will normally be an RFC 822 name.
Multiple subject names can be provided for a single lock box.
LockBox contains a base64 encoded CMS Recipient Info structure. If
the recipient info structure is placed here, it MUST NOT be placed
in the CMS EnvelopedData structure as well.
8.1.2. XML Label Structure
A client is allowed to build a complex label to be sent to the Plasma
server for evaluation. While there are some cases that a simple
single policy is applied to a message, it is expected that many, if
not most, messages will have more than one policy applied to it with
logical statements connected those policies.
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The schema for specifying a label is:
<xs:element name="Label" type="eps:LabelType"/>
<xs:complexType name="LabelType">
<xs:sequence>
<xs:choice maxOccurs="unbounded">
<xs:element ref="eps:Label"/>
<xs:element ref="eps:Leaf"/>
</xs:choice>
</xs:sequence>
<xs:attribute name="CombiningRule" type="eps:CombiningRuleType" use="required"/>
</xs:complexType>
<xs:simpleType name="CombiningRuleType">
<xs:restriction base="xs:string">
<xs:enumeration value="and"/>
<xs:enumeration value="or"/>
<xs:enumeration value="except"/>
</xs:restriction>
</xs:simpleType>
<xs:element name="Leaf" type="eps:LeafType"/>
<xs:complexType name="LeafType">
<xs:sequence>
<xs:any namespace="##any" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="PolicyId" type="xs:anyURI" use="required"/>
</xs:complexType>
The Label and the Leaf elements are used when specifying a policy for
a message depending on whether multiple policies or a single policy
is to be evaluated.
The Leaf element is used to specify a single policy to the server
along with any options that are defined for that policy. The Leaf
element contains:
PolicyId
Is an attribute that contains the URI which identifies a specific
policy to be evaluated.
The content of the Leaf element can be any XML element. The
content is to be a set of options for the policy. The schema
applied to the content is based on the policy selected.
The Label element is used to specify a logical set of policies to be
applied to the message. This element allows one to specify multiple
policies along with a logic operation to combine them togeither.
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Label
This element allows for a logical set of policies to be
recursively evaluated. This element can occur zero or more times.
Leaf
This element allows for a single policy and any options for the
policy to be specified. This element can occur zero or more
times.
CombiningRule
This attribute specifies the operation to be used in combining the
elements of the tree together. This attribute can contain either
a string or a URI. If it is a string it MUST be one of the
strings defined in this document. Examples of URIs that could be
used can be found in Section XX of [XACML]. Servers MUST be able
to evaluate the set of logical operations defined here, but other
combining rules can be implemented as well. The set of string
values defined in this document are:
and All policies referenced by this element MUST evaluate to
accept.
or At least one policy referenced by this element MUST evaluate to
accept.
except When this combining rule is used, there MUST be exactly
two policy elements. The rule evaluates to accept if and only
if the first element evaluates to accept and the second does
not evaluate to accept.
TODO: Correct the following text to make sense in the XML space
rather than in the ASN.1 space
8.1.2.1. Label Extensibility
The ASN.1 type OneLabel has been explicitly defined to allow for
later extensibility. When a new element is added, it will be added
with at the end of the choice with a different tag value. ASN.1
decoders need to following the current recommendations on dealing
with extensibility. This means that when the decoder finds a new
choice in this structure that is not part of the current syntax, the
element should be treated as an unknown blob and returned to the
caller as an unrecognized blob. This allows for the calling code to
make the decision on how the unknown element is treated.
However the extensibility is not handled the same in all cases. Each
of the four different cases is outlined below.
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8.1.2.1.1. Sender Composing
The set of policies that can be used by the sender in applying a
label is usually given as a list of policies, however under some
circumstances the sender may be handed structured policies either for
application or for checking that some policies can be used together.
If structured policies are provided to the sender, it will not matter
to the sender that they cannot evaluate the policy unless the details
are to be shown to the sending user. Following the current ASN.1
rules which allow for the decoding and then re-encoding of a type
which contains unknown nodes allows the sending agent the most
flexibility.
The protocol used to give the policy information to the sending
client may not use the ASN.1 structure provided here or configuration
purposes but would generally be expected to provide for a different
data format.
8.1.2.1.2. Sender to Email Policy Service
In the sending agent to Email Policy Service protocol (defined
external to this document) the ASN.1 type OneLabel may or may not be
used directly. If it is used, then the Email Policy Server is
expected to reject the label if it contains elements which it does
not understand. The general expectation is that the Email Policy
Service that the sender is communicating with is going to be the same
one as is later enforcing the policy. It makes no sense for this
server to accept a policy that it would later be unable to enforce.
The protocol should make provisions for the return of this as an
explicit error code. Having the ASN.1 decoded allows for the
communication of the exact tag that is causing the problem. Under
most policies, the evaluation of sender policy would be expected to
be different than laid out in the next session. As a general rule,
the sender should be permitted to assert all of the leaf policies for
the purpose of sending.
8.1.2.1.3. Recipient to Email Policy Service
The Email Policy Service which recipient communicates way is normally
the same server as the sender communicated with. However the server
can be a different server, or the server may have been downgraded in
the mean time. In this case the policy evaluation need to be
conservative. There are two different ways of doing this evaluation.
The first option is to say that if an unknown node is found, then the
policy evaluation results in "Deny" for all cases. The second option
is to try and evaluation the policy, but to do so in a conservative
manner. In this section we use the same terms as XACML [XACML] uses
in section 7.2.1. If the second option is chosen then the following
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rules are used:
uriLeaf results in "Permit", "Deny", "Not Applicable" or
"Indeterminate". "Not Applicable" results if the policy is
unknown. "Indeterminate" results if the policy cannot be
evaluated.
oidLeaf results in "Permit", "Deny", "Not Applicable" or
"Indeterminate". "Not Applicable" results if the policy is
unknown. "Indeterminate" results if the policy cannot be
evaluated.
andLabels results in "Deny" if any input node is "Deny" or "Not
Applicable". It results in "Permit" if all of the input nodes are
"Permit". Otherwise it results in "Indeterminate".
orLabels results in "Permit" if any input node is "Permit". It
results in "Deny" if all nodes are either "Deny" or "Not
Applicable". Otherwise it results in "Indeterminate".
exclude results in "Deny" if the first element is "Deny" or if the
second input is "Permit". It results in "Permit" if the first
input is "Permit" and the second is "Deny". It results in "Not
Applicable" if either element is "Not Applicable". Otherwise it
results in "Indeterminate".
If the final node results in "Permit", then access is granted. If
the final result is either "Deny" or "Not Applicable" then access is
denied. If the final result is "Indeterminate", then access is
denied, however if the protocol permits, then the result can be "Not
Applicable" and the attributes needed to do the policy evaluation can
be requested and policy evaluation may be re-attempted.
Any future element that is added to the choice needs to define a
similar rule to the set of rules above.
8.1.2.1.4. Recipient User Agent Display
Recipient user agents may want to display the policy to the user.
This policy may be communicated from the Email Policy Service to the
recipient using the OneLabel ASN.1 structure or using a different
type. The label has been successfully (or unsuccessfully) validated
so access has been granted (or denied) to the message. At this point
we are only talking about a user interface issue. The recipient user
agent should make some type of provision for indicating that an
operation was placed in that location of the tree, but the agent is
not aware of what the operation is.
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8.2. Send Message Response
In response to a send message request, the Plasma server returns a
send message response message. The response messages uses the eps:
PlasmaResponse XML structure. When the response message is created,
the following should be noted:
o The xacml:Decisions is always included in the response. If the
'Permit' value is returned then the eps:CMSToken element MUST be
present.
o The PlasmaReturnToken element with a eps:CMSToken content is
included with a permit response. The CMSToken contains one or
more CMS RecipientInfo objects to be included in the message sent.
An example of a message returning the set of policy information is:
<eps:PlasmaResponse>
<xacml:Response>
<xacml:Result>
<xacml:Decision>Permit</xacml:Decision>
</xacml:Result>
</xacml:Response>
<eps:PlasmaReturnToken xsi:"eps:CMSTokenResponseType">
<eps:RecipientInfo>234e34d3</eps:RecipientInfo>
</eps:PlasmaReturnToken>
</eps:PlasmaResponse>
The schema use for returning a CMS token is:
<xs:element name="CMSToken" type="eps:CMSTokenResponseType"/>
<xs:complexType name="CMSTokenResponseType">
<xs:complexContent>
<xs:extension base="eps:PlasmaReturnTokenType">
<xs:sequence>
<xs:element name="RecipientInfo" maxOccurs="unbounded">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:base64Binary">
<xs:attribute name="CMSType" type="xs:string"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
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This schema fragment extends the Plasma response token type and
allows for the return of one or more base64 encoded RecipientInfo
structures. The Plasma server can return recipient info information
for any recipient that it pre-authorizes to receive the message (see
Section ### of [Plasma] for examples of when this would occur).
Additionally the Plasma server can return a KEKRecipientInfo
structure with the Plasma Other Key attribute. (For details see
[EPS-CMS].) In some extremely rare cases where the Plasma server can
pre-authorize the entire set of recipients , the KEKRecipientInfo
structure with the Plasma Other Key Attribute may not be included in
the returned set of recipients. The recipient info structure for the
plasma server SHOULD be placed last in the list of recipients infos.
The CMSTokenResponse type has the following:
RecipientInfo
This element contains the ASN.1 encoding for a CMS RecipientInfo
structure to be placed in the final message.
CMSType
This attribute of the RecipientInfo structure is an optional text
value that identifies the type of recipient info structure
returned. NOTE: This attribute is currently optional and is
likely to disappear if I do not find it useful.
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9. Decoding A Message
When the receiving agent is ready to decrypt the email, it identifies
that there is a KEKRecipientInfo object which contains a key
attribute identified by id-keyatt-eps-token. It validates the
signature, determines that communicating with the Plasma Service is
within local policy, and then sends a request to the service to
obtain the decryption key for the message.
In some cases the recipient of a message is not authorized to use the
same set of labels for sending a message. For this purpose a token
can be returned in the message along with the key so that recipient
of the can reply to the message using the same set of security
labels.
9.1. Requesting Message Key
The client sends a request to the Plasma server that is identified in
the token. For the CMS base tokens, the address of the Plasma server
to use is defined in [EPS-CMS] this is located in the aa-eps-url
attribute.
The request uses the eps:PlasmaRequest XML structure. When building
the request, the following should be noted:
o The xacml:Request MUST be present in the first message of the
exchange.
o The action used to denote that a CMS token should be decrypted is
"ParseCMSToken".
o The CMS token to be cracked is identified by "CMSToken"
o In the event that a reply to role token is wanted as well, then
that is supplied as a separate action.[anchor33] In this case the
action is "GetReplyToken".
o If the client is using the XML Digital Signature element in this
message, then the client MUST include the cryptographic channel
binding token (Section 10.1.1) in the set of XACML attributes.
An example of a message returning the set of policy information is:
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<eps:PlasmaRequest>
<eps:Authentication>...</eps:Authentication>
<xacml:Request>
<xacml:Attributes Category="...:action">
<xacml:Attribute AttributeId="..:action-id">
<xacml:AttributeValue>ParseCMSToken</xacml:AttributeValue>
</xacml:Attribute>
</xacml:Attributes>
<xacml:Attribute Category="...:data">
<xacml:Attribute AttreibuteId="..:data:CMSToken">
<xacml:AttributeValue>
Base64 encoded CMS Token Value
</xacml:AttributeValue>
</xacml:Attribute>
</xacml:Attribute>
</xacml:Request>
</eps:PlasmaRequest>
9.2. Requesting Message Key Response
In response to a message key request, the Plasma server returns a
decrypted key in the message key response. The response message uses
the eps:Plasma XML structure. When a response message is create the
following should be noted:
o If the value of xacml:Decision is Permit, then response MUST
include an eps:CMSKey element.
o For all other decision types the eps:CMSKey MUST be absent.
o If a reply token was requested and granted, then the response MUST
include an eps:PlasmaToken element. The eps:PlasmaToken element
MUST use the Label option
An example of a message returning the set of policy information is:
<eps:PlasmaResponse>
<xacml:Response>
<xacml:Result>
<xacml:Decision>Permit</xacml:Decision>
</xacml:Result>
</xacml:Response>
<eps:CMSKey>
<eps:DisplayString>Label TExt</eps:DisplayString>
<eps:KEK>hex based KEK</eps:KEK>
</eps:CMSKey>
</eps:PlasmaResponse>
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The schema for returning the decrypted key is:
<xs:element name="CMSKey" type="eps:CMSKeyResponseType"/>
<xs:complexType name="CMSKeyResponseType">
<xs:complexContent>
<xs:extension base="eps:PlasmaReturnTokenType">
<xs:sequence>
<xs:element name="DisplayString" type="xs:string"/>
<xs:choice>
<xs:element name="CEK" type="xs:hexBinary"/>
<xs:element ref="eps:RecipientInfo"/>
</xs:choice>
<xs:element name="ResponseRoleToken" type="eps:RoleToken" minOccurs="0"/>
<xs:element name="EncryptionRequestor" type="xs:string"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
This schema extends the Plasma response token type and restricts the
content to the listed elements. The values returned are:
DisplayString returns a localized display string for the policy(s)
which were applied to the message. The lang attribute on the
request is used to determine which language to use for this
string.
KEK returns the base64 encoded key encryption key.
eps:RecipientInfo returns the encrypted key in the form of a CMS
RecipientInfo structure
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10. Plasma Attributes
In this document a number of different XAMCL attributes have been
defined, this section provides a more detailed description of these
elements.
10.1. Data Attributes
10.1.1. Channel Binding Data Attribute
The channel binding data attribute is used to provide for a binding
of the TLS session that is being used to transport the Plasma
messages with the content of the Plasma requests themselves. There
is a need for the server to be able to validate that the
cryptographic operations related to holder of key statements be made
specifically for the current conversation and not be left over from a
previous one as a replay attack. By deriving a cryptographic value
from the shared TLS session key and signing that value we are able to
do so.
The channel binding value to be used is created by the TLS key
exporter specification defined in RFC 5705 [RFC5705]. This allows
for a new cryptographic value to be derived from the existing shared
secret key with additional input to defined the context in which the
key is being derived. When using the exporter, the label to be input
into the key exporter is "EXPORTER_PLASMA". The value to be derived
will be 512 bits in length, and no context is provided to the
exporter.
When used as an XACML attribute in a request:
The category of the attribute is
"urn:oasis:names:tc:xacml:3.0:attribute-category:data".
The AttributeId attribute is
"urn:ietf:params:xml:plasma:data-id:ChannelBinding".
The Issuer attribute is absent.
The DataType is either base64Binary or hexBinary
The same value is used for both the XACML channel binding data
attribute and the XML channel binding structure defined in
Section 5.1.3.
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10.1.2. CMS Signer Info Data Attribute
In many cases a policy stays that the client is required to sign the
message before encrypting it. The server cannot verify that a
signature is applied to the message and included, but we can require
that a signature be supplied to the server. This signature can then
be validated by the server (except for the message digest attribute
value), and the server can take a hash of the value and return it as
part of the key returned to a decrypting agent. This agent can then
validate that the signature is a part of the message and complain if
it absent. This means we do not have an enforcement mechanism, but
we do have a way of performing an audit at a later time to see that
the signature operation was carried out correctly.
By requiring that a signature be supplied to the server as part of
the authentication process, the Plasma server can also be setup so
that the supplied signature is automatically setup for archival
operations. One way to do archiving is to use the data records
defined in [RFC4998].
The following applies when this data value is present:
The Category attribute is
"urn:oasis:names:tc:xacml:3.0:attribute-category:data".
The AttributeId attribute is
"urn:ietf:params:xml:plasma:data-id:CMSSignerInfo".
The Issuer attribute is absent.
The DataType attribute is either base64Binary or hexBinary.
10.1.3. S/MIME Capabilities Data Attribute
Policies sometimes require that specific algorithms be used in order
to meet the security needs of the policy. This attribute allows for
an S/MIME Capabilities to be carried in a DER encoded
SMIMECapabilities ASN.1 structure to be transmitted to the client.
Details on how the S/MIME Capabilities function can be found in
[SMIME-MSG].
The following attributes are to be set for the data value:
The Category attribute is
"urn:oasis:names:tc:xacml:3.0:attribute-category:data".
The AttributeId attribute is
"urn:ietf:params:xml:plasma:data-id:SMIME-Capabilties".
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The Issuer attribute is absent.
The DataType attribute is either base64binary or hexBinary.
10.2. Obligations and Advice
Obligations and advice consist of actions that the Plasma server
either requires or requests that the client PEP perform in order to
gain access or before granting access to the data. These normally
represent actions or restrictions that the PDP itself cannot enforce
and thus are not input attributes to the policy evaluation. The same
set of values can be used either as obligations or advice, the
difference being that if the PEP cannot do an obligation it is
required to change the policy decision.
10.2.1. Signature Required
Many policies require that a message be signed before it is encrypted
and sent. Since the unencrypted version of message is not sent to
the Plasma server, the policy cannot verify that a signature has been
placed onto the signed message. The attribute is not for use as a
returned obligation from an XACML decisions, rather it is for a pre-
request obligations used in role responses (Section 7.2).
When used as an Obligation:
The ObligationId attribute is
"urn:ietf:params:xml:plasma:obligation:signature-required".
A S/MIME Capabilities data value can optionally be included. If
it is included, then it contains the set of S/MIME capabilities
that describes the set of signature algorithms from which the
signature algorithm for the message MUST be selected.
10.2.2. Encryption Required
Occasionally a policy requires a specific set of encryption
algorithms be used for a message, when this is the case then the
encryption required obligation is included in the returned set of
obligations. If the default set of encryption algorithms is
sufficient then the obligation is omitted.
When used as an Obligation:
The ObligationId attribute is
"urn:ietf:params:xml:plasma:obligation:encryption-required".
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An S/MIME Capabilities data value MUST be included containing the
set of permitted encryption algorithms. The algorithms included
MUST include a sufficient set of algorithms for the message to be
encrypted. An absolute minimum would be a content encryption
algorithm and key encryption algorithm.
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11. Certificate Profiles
We need to put in text to express the following items:
DNS or IPAddr subject alt name to be present
Have one of four EKUs
Plasma Token EKU - Signals that it can sign and/or encrypt a
plasma object
Plasma Secure Session - Use for the TLS session
Plasma CEK Transport - Used for transporting the CEK to the
server in high security situations
MUST NOT have the anyPolicy EKU set
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12. Message Transmission
Plasma messages are sent over a TCP connection using port TBD1 on the
server. The client first setups up TLS on the connection, then sends
the UTF8 encoded XML message over the TLS connection as an atomic
message. The XML MUST be encoded as UTF8, however the Byte Order
Mark (BOM) is sent. The response comes back on the same connection.
The client is responsible for closing the TLS session and the TCP
connection when either no more messages are to be sent to the server
or a final indeterminate state has been reached.
If a Plasma server receives an XML request which is not well formed
XML, the server if free to close the connection without first sending
an error reply.
The Plasma server SHOULD support TLS resumption [RFC5077].
Plasma clients and server MUST support TLS 1.1 [RFC4346] and above.
Implementations SHOULD NOT allow for the use of TLS 1.0 or SSL.
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13. Security Considerations
To be supplied after we have a better idea of what the document looks
like.
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14. IANA Considerations
We define the following name spaces
New name space for the plasma documents urn:ietf:params:xml:ns:plasma
14.1. Plasma Action Values
A new registry is established for Plasma server action identifiers
using the tag "action-id". The full urn for the registry is
"urn:ietf:params:xml:ns:plasma:actions". This registry operates
under a specification required policy. All entries in this registry
require the following elements:
o A string in camel case which identifies the action to be
performed.
o An optional XML data structure used to carry the control data for
the action.
o An optional XML data structure used to return the result of the
action from the server.
o A document reference describing the steps to be taken by the
server.
The registry will be initially populated with the following:
+-----------------+-------------------------+------------------+
| Action Id | Input Structure | Output Structure |
+-----------------+-------------------------+------------------+
| GetRoleTokens | none | eps:RoleToken |
| | | |
| GetSendCMSToken | eps:MessageTokenRequest | eps:CMSToken |
| | | |
| ParseCMSToken | eps:CMSToken | eps:CMSKeyToken |
| | | |
| GetReplyToken | none | eps:RoleToken |
+-----------------+-------------------------+------------------+
When these actions are placed in an xacml:Request,
o the Category is
"urn:oasis:names:tc:xacml:3.0:attribute-category:action",
o the AttributeId is "urn:ietf:params:xml:ns:plasma:actions",
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o the DataType is "http://www.w3.org/2001/XMLSchema#string"
14.2. non
Define a new data name space urn:ietf:params:xml:ns:plasma:data-id
CMSToken
ChannelBinding
SMIME-Capabilities
Define a new name space for status codes at
urn:ietf:params:xml:ns:plasma:status. The initial set of values is
authentication-error This identifier indicates that the
authentication methods failed to successfully complete.
Define a new name space for obligations. The same namespace will be
used both for obligations and for advice and the values may appear in
either section.
signature-required This identifier indicates that that the encrypted
body must contain a signature element. The data value of this
type shall be "http://www.w3.org/2001/XMLSchema#hexBinary" and the
data structure shall consist of a DER encoded CMSCapabilities
structure [SMIME-MSG] with the list of permitted signature
algorithms. If there are no restrictions on the algorithms or the
restriction is implicit, then the data value MAY be omitted.
encryption-algorithms see above
ambigous-identity The identity of the client is either not stated in
a form the Plasma server understands, or there are multiple
identities in the authentication data. To remedy this situation,
the client includes an explicit identity in the xacml:Reqeust
element.
We define a schema in appendix A at
urn:ietf:params:xml:schema:plasma-RFCTBD
Define a new Status Code for use in the Status URI field.
urn:ietf:???:plasma:status:gss-api-response - This status is
returned only with Indefinite responses. Indicates a GSS-API
response object was returned in the GSSAPIResponse token type.
Will return until authentication has been completed.
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14.3. Port Assignment
We request that IANA assign a new port for the use of this protocol.
Service name: plasma
Port Number: TBD1
Transport Protocol: TCP
Description: Plasma Service Protocol
Reference: This document
Assignee: iesg@ietf.org
Contact: chair@ietf.org
Notes: The protocol requires that TLS be used to communicate over
this port. There is no provision for unsecure messages to be sent to
this protocol.
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15. Open Issues
List of Open Issues:
o JLS: URL definitions - do we need a new schema or do we just
overload https? For our URLs - do we require that they be passed
through the internationalization step first? Probably should
since the locale information is on the server and the client might
not agree.
o JLS: Should we require that any SignatureProperty be present for
XML Signature elements?
o JLS: Need to figure out an appropriate way to reference the
assertion from a dig sig element. Could use a special version of
RetrievalMethod with a transform, but that does not seem correct.
May need to define a new KeyInfo structure to do it.
o JLS: Should X.509 certificates and attribute certificates be fully
specified as an authentication method?
o JLS: Should a SignerInfo attribute be placed under the access-
subject Category for a senders version and under Environment for a
machine version? Currently both are under Data
o JLS: Need an obligation to say that CEK must be encrypted. Do we
also need to have recipient info structures encrypted?
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16. References
16.1. Normative References
[ABFAB] Hartman, S. and J. Howlett, "A GSS-API Mechanism for the
Extensible Authentication Protocol", Work In
Progress draft-ietf-abfab-gss-eap-04, Oct 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[EPS-CMS] Schaad, J., "Email Policy Service ASN.1 Processing", Work
In Progress draft-schaad-plamsa-cms, Jan 2011.
[XML-Signature]
Roessler, T., Reagle, J., Hirsch, F., Eastlake, D., and D.
Solo, "XML Signature Syntax and Processing (Second
Edition)", World Wide Web Consortium Recommendation REC-
xmldsig-core-20080610, June 2008,
<http://www.w3.org/TR/2008/REC-xmldsig-core-20080610>.
[XML-C14N11]
Boyer, J. and G. Marcy, "Canonical XML Version 1.1", World
Wide Web Consortium Recommendation REC-xml-c14n11-
20080502, May 2008,
<http://www.w3.org/TR/2008/REC-xml-c14n11-20080502>.
[WS-TRUST]
Lawrence, K., Kaler, C., Nadalin, A., Goodner, M., Gudgin,
M., Barbir, A., and H. Granqvist, "WS-Trust 1.4", OASIS
Standard ws-trust-200902, March 2007, <http://
docs.oasis-open.org/ws-sx/ws-trust/v1.4/ws-trust.html>.
[XACML] Rissanen, E., "eXtensible Access Control Markup Language
(XACML) Version 3.0", OASIS Standard xacml-201008,
August 2010, <http://docs.oasis-open.org/xacml/3.0/
xacml-3.0-core-spec-cs-01.en.doc>.
[Plasma] Freeman, T., Schaad, J., and P. Patterson, "Requirements
for Message Access Control", Work in
progress draft-freeman-message-access-control,
October 2011.
[OASIS-CORE]
Cantor, S., Kemp, J., Philpott, R., and E. Maler,
"Assertions and Protocols for the OASIS Security Assertion
Markup Language (SAML) V2.0", OASIS Standard saml-core-
2.0-os, March 2005.
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[RFC5705] Rescorla, E., "Keying Material Exporters for Transport
Layer Security (TLS)", RFC 5705, March 2010.
[SMIME-MSG]
Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message
Specification", RFC 5751, January 2010.
16.2. Informative References
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006.
[RFC4998] Gondrom, T., Brandner, R., and U. Pordesch, "Evidence
Record Syntax (ERS)", RFC 4998, August 2007.
[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
"Transport Layer Security (TLS) Session Resumption without
Server-Side State", RFC 5077, January 2008.
[SAML-XACML]
Anderson, A. and H. Lockhart, "SAML 2.0 profile of XACML
v2.0", OASIS Standard access_control-xacml-2.0-saml-
profile-spec-os.pdf, February 2005.
[PlasmaBasicPolicy]
Anon, A., "IETF Defined Plasma Policies", February 2005.
[SOAP11] Box, D., Ehnebuske, D., Kakivaya, G., Layman, A.,
Mendelsohn, N., Nielsen, H., Thatte, S., and D. Winer,
"Simple Object Access Protocol (SOAP) 1.1", W3C NOTE NOTE-
SOAP-20000508, May 2000.
[SOAP12] Lafon, Y., Gudgin, M., Hadley, M., Moreau, J., Mendelsohn,
N., Karmarkar, A., and H. Nielsen, "SOAP Version 1.2 Part
1: Messaging Framework (Second Edition)", World Wide Web
Consortium Recommendation REC-soap12-part1-20070427,
April 2007,
<http://www.w3.org/TR/2007/REC-soap12-part1-20070427>.
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Editorial Comments
[anchor7] Trevor: I don't see Plasma using this type
[anchor8] Trevor: What about attribute match?
[anchor9] Trevor: This sounds like we ignore the mapping on the
wire. There is no reason to mandate the mapping occurs
inside the PDP.
[anchor11] Brian: Should one be able to create a policy on the fly
for specific item where a set of attributes can be
defined by the sender of the message.
[anchor14] jimsch: Remove this?
[anchor16] Trevor: What is the difference between WS-trust SAML
assertions and the SAML assertions above?
[anchor18] Trevor: Would we use bearer tokens to reintroduce the
client? The main protection of bearer tokens is if they
are fresh so you have had little time to stream one
[anchor19] trevor: Is this totally true? Don't we need some kind of
identifier so the server can indicate when the token can
be replayed in a subsequence request? E.g. give me these
attributes or a foo token.
[anchor20] JLS: I don't know of any way to say use the asymmetric
key that you authenticated with originally - can this be
done?
[anchor23] Trevor: What about audit obligatiouns
[anchor24] Trevor: Should we ignore it if present?
[anchor25] JLS: I don't think we need to say anything about looking
at it or ignoring it. While it would be something for
debugging, as a general rule the client does not care
which policies where evaluated and passed to grant
access.
[anchor27] Trevor: Something missing.
[anchor28] Trevor: did not think you have a revocation mechanism in
SAML
[anchor33] jls: We may want to require that a reply token always be
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returned instead of just returning it on demand.
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Appendix A. XML Schema
This appendix represents the entirety of the XML Schema for Plasma
documents.
<?xml version="1.0" encoding="UTF-8"?>
<!-- edited with XMLSpy v2007 sp2 (http://www.altova.com) by James Schaad (exmsft) -->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xacml="urn:oasis:names:tc:xacml:3.0:core:schema:wd-17" xmlns:wst="http://schemas.xmlsoap.org/ws/2005/02/trust" xmlns:eps="urn:ietf:schema:plasma:1.0" xmlns:ds2="http://www.w3.org/2000/09/xmldsig#" xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion" targetNamespace="urn:ietf:schema:plasma:1.0" elementFormDefault="qualified" attributeFormDefault="unqualified">
<xs:annotation>
<xs:documentation>
The PlasmaRequest element is one of two top level elements defined by this XSD schema.
The PlasmaRequest element is sent from the client to the server in order to
</xs:documentation>
</xs:annotation>
<xs:element name="PlasmaRequest" type="eps:RequestType"/>
<xs:complexType name="RequestType">
<xs:sequence>
<xs:element ref="eps:Authentication" minOccurs="0"/>
<xs:element ref="xacml:Request"/>
</xs:sequence>
<xs:attribute name="Version" type="xs:string" default="1.0"/>
</xs:complexType>
<xs:element name="PlasmaResponse" type="eps:ResponseType"/>
<xs:complexType name="ResponseType">
<xs:sequence>
<xs:element ref="xacml:Response"/>
<xs:element ref="eps:PlasmaReturnToken" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="Version" type="xs:string" default="1.0"/>
</xs:complexType>
<xs:element name="PlasmaReturnToken" type="eps:PlasmaReturnTokenType"/>
<xs:complexType name="PlasmaReturnTokenType" abstract="true">
<xs:attribute name="DecisionId" type="xs:string"/>
</xs:complexType>
<!-- <xs:element name="RequestRoles">
<xs:complexType>
<xs:sequence>
<xs:element ref="eps:Authentication" minOccurs="0"/>
<xs:element name="Identity" type="xs:string"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="RequestMessageData">
<xs:complexType>
<xs:sequence>
<xs:element name="Label" type="eps:LabelType"/>
<xs:element name="RoleToken"/>
<xs:element name="Recipients"/>
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</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="ReadMessage"/> -->
<xs:element name="Authentication" type="eps:AuthenticationType"/>
<xs:complexType name="AuthenticationType">
<xs:choice maxOccurs="unbounded">
<xs:element ref="saml:Assertion"/>
<xs:element name="GSSAPI" type="xs:hexBinary"/>
<xs:element name="WS-Token">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:hexBinary">
<xs:attribute name="tokenType" type="xs:anyURI"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element ref="ds2:Signature"/>
<xs:element name="Other">
<xs:complexType>
<xs:sequence>
<xs:any namespace="##other"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:choice>
</xs:complexType>
<xs:complexType name="RoleToken">
<xs:complexContent>
<xs:extension base="eps:PlasmaReturnTokenType">
<xs:sequence>
<xs:element name="Name" type="xs:string"/>
<xs:element name="PDP" type="xs:anyURI" maxOccurs="unbounded"/>
<xs:choice>
<xs:element name="PolicyList">
<xs:complexType>
<xs:sequence>
<xs:element name="Policy" type="eps:PolicyType" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element ref="eps:Label"/>
</xs:choice>
<xs:element ref="wst:RequestSecurityTokenResponse"/>
<xs:element ref="xacml:Obligations" minOccurs="0"/>
<xs:element ref="xacml:AssociatedAdvice" minOccurs="0"/>
</xs:sequence>
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</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="PolicyType">
<xs:sequence>
<xs:element name="Name" type="xs:string"/>
<xs:element name="Options" minOccurs="0">
<xs:complexType>
<xs:complexContent>
<xs:extension base="xs:anyType">
<xs:attribute name="optionsType" type="xs:anyURI" use="required"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
</xs:element>
</xs:sequence>
<xs:attribute name="PolicyId" type="xs:anyURI" use="required"/>
</xs:complexType>
<xs:element name="Label" type="eps:LabelType"/>
<xs:complexType name="LabelType">
<xs:sequence>
<xs:choice maxOccurs="unbounded">
<xs:element ref="eps:Label"/>
<xs:element ref="eps:Leaf"/>
</xs:choice>
</xs:sequence>
<xs:attribute name="CombiningRule" type="eps:CombiningRuleType" use="required"/>
</xs:complexType>
<xs:simpleType name="CombiningRuleType">
<xs:restriction base="xs:string">
<xs:enumeration value="and"/>
<xs:enumeration value="or"/>
<xs:enumeration value="except"/>
</xs:restriction>
</xs:simpleType>
<xs:element name="Leaf" type="eps:LeafType"/>
<xs:complexType name="LeafType">
<xs:sequence>
<xs:any namespace="##any" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="PolicyId" type="xs:anyURI" use="required"/>
</xs:complexType>
<xs:element name="GetCMSToken" type="eps:CMSTokenRequestType"/>
<xs:complexType name="CMSTokenRequestType">
<xs:sequence>
<xs:choice>
<xs:element ref="eps:Label"/>
<xs:element ref="eps:Leaf"/>
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</xs:choice>
<xs:element name="Hash">
<xs:complexType>
<xs:sequence>
<xs:element ref="ds2:DigestMethod"/>
<xs:element ref="ds2:DigestValue"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="Recipient" type="eps:RecipientInfoType" minOccurs="0" maxOccurs="unbounded"/>
<xs:element name="CEK" type="xs:hexBinary" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:element name="RecipientInfo" type="eps:RecipientInfoType"/>
<xs:complexType name="RecipientInfoType">
<xs:sequence>
<xs:element name="Subject" maxOccurs="unbounded">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:anySimpleType">
<xs:attribute name="type" type="xs:string" use="required"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name="LockBox" type="xs:base64Binary"/>
</xs:sequence>
</xs:complexType>
<xs:element name="CMSKey" type="eps:CMSKeyResponseType"/>
<xs:complexType name="CMSKeyResponseType">
<xs:complexContent>
<xs:extension base="eps:PlasmaReturnTokenType">
<xs:sequence>
<xs:element name="DisplayString" type="xs:string"/>
<xs:choice>
<xs:element name="CEK" type="xs:hexBinary"/>
<xs:element ref="eps:RecipientInfo"/>
</xs:choice>
<xs:element name="ResponseRoleToken" type="eps:RoleToken" minOccurs="0"/>
<xs:element name="EncryptionRequestor" type="xs:string"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:element name="CMSToken" type="eps:CMSTokenResponseType"/>
<xs:complexType name="CMSTokenResponseType">
<xs:complexContent>
<xs:extension base="eps:PlasmaReturnTokenType">
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<xs:sequence>
<xs:element name="RecipientInfo" maxOccurs="unbounded">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:base64Binary">
<xs:attribute name="CMSType" type="xs:string"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
</xs:schema>
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Appendix B. Example: Get Roles Request
This section provides an example of a request message to obtain the
set of roles for an individual named 'bart@simpsons.com'. The
authentication provided in this is a SAML statement included in the
SAML_Collection element.
<?xml version="1.0" encoding="UTF-8"?>
<PlasmaRequest xmlns="urn:ietf:schema:plasma:1.0"
xmlns:xacml="urn:oasis:names:tc:xacml:3.0:core:schema:wd-17"
xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:schema:plasma:1.0 C:\ietf\drafts\Schema\Plasma.xsd" >
<Authentication>
<WS-Token>123456</WS-Token>
<!-- <saml:Assertion>....</saml:Assertion> -->
</Authentication>
<xacml:Request CombinedDecision="false" ReturnPolicyIdList="false">
<xacml:Attributes Category="urn:oasis:names:tc:xaml:3.0:attribute-catagory:action">
<xacml:Attribute IncludeInResult="false" AttributeId="urn:plasma:action-id">
<xacml:AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">GetRoleTokens</xacml:AttributeValue>
</xacml:Attribute>
</xacml:Attributes>
<xacml:Attributes Category="urn:oasis:names:tc:xacml:3.0:attribute-category:environment">
<xacml:Attribute AttributeId="urn:ietf:plasma:data:channel" IncludeInResult="false">
<xacml:AttributeValue DataType="http://www.w3.org/2001/XMLSchema#base64Binary">ABCDEFGH</xacml:AttributeValue>
</xacml:Attribute>
</xacml:Attributes>
</xacml:Request>
</PlasmaRequest>
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Appendix C. Example: Get Roles Response
This section provides an example response to a successful request for
a role sets.
<?xml version="1.0" encoding="UTF-8"?>
<PlasmaResponse xmlns="urn:ietf:schema:plasma:1.0"
xmlns:xacml="urn:oasis:names:tc:xacml:3.0:core:schema:wd-17"
xmlns:wst="http://schemas.xmlsoap.org/ws/2005/02/trust"
xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:schema:plasma:1.0 C:\ietf\drafts\Schema\Plasma.xsd">
<xacml:Response>
<xacml:Result>
<xacml:Decision>Permit</xacml:Decision>
</xacml:Result>
</xacml:Response>
<PlasmaReturnToken xsi:type="RoleToken">
<Name>Example Role Name</Name>
<PDP>https://pdp.example.com/companyPolicies</PDP>
<PolicyList>
<Policy PolicyId="urn:example:policies:confidential">
<Name>Company Confidential</Name>
</Policy>
<Policy PolicyId="urn:example:policies:plasma">
<Name>Plasma Project</Name>
</Policy>
</PolicyList>
<wst:RequestSecurityTokenResponse>
<wst:TokenType>urn:plasma:roleToken</wst:TokenType>
<wst:RequestedSecruityToken>....</wst:RequestedSecruityToken>
<wst:Entropy><wst:BinarySecret>12345678</wst:BinarySecret></wst:Entropy>
<wst:Lifetime><wsu:Expires>2012-02-01T00:00:00</wsu:Expires></wst:Lifetime>
</wst:RequestSecurityTokenResponse>
</PlasmaReturnToken>
</PlasmaResponse>
In this example a role is returned that has two different policies
that can be used by that role. Along with the role token, a binary
secret is returned that is to be used in proving that the same entity
is returning to use the roles.
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Appendix D. Example: Get CMS Token Request
This section contains an example of a request from a client to a
server for a CMS message token to be issued. The authentication for
the request is provided by using a WS-Trust token previously issued
as part of a role request/response dialog. The request contains the
following elements:
o A complex rule set is requested where permission to is to be
granted to anyone who meets either of the two policies given.
o A specific recipient info structure is provided for a subject
who's name is 'lisa@simpsons.com'. The details of the recipient
info structure are skipped but it would be any encoding of a
RecipientInfo structure from CMS.
o A generic key encryption key is provided for any other subject who
meets the policies specified.
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<?xml version="1.0" encoding="UTF-8"?>
<PlasmaRequest xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:schema:plasma:1.0 C:\ietf\drafts\Schema\Plasma.xsd"
xmlns="urn:ietf:schema:plasma:1.0"
xmlns:ds2="http://www.w3.org/2000/09/xmldsig#"
xmlns:xacml="urn:oasis:names:tc:xacml:3.0:core:schema:wd-17">
<Authentication>
<WS-Token>123456</WS-Token>
</Authentication>
<xacml:Request CombinedDecision="false" ReturnPolicyIdList="false">
<xacml:Attributes Category="urn:oasis:names:tc:xaml:3.0:attribute-catagory:action">
<xacml:Attribute IncludeInResult="false" AttributeId="urn:plasma:action-id">
<xacml:AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">GetCMSToken</xacml:AttributeValue>
</xacml:Attribute>
</xacml:Attributes>
<xacml:Attributes Category="urn:ietf:plasma:attribute-category:data">
<xacml:Attribute AttributeId="urn:plasma:data-id" IncludeInResult="false">
<xacml:AttributeValue DataType="xml">
<GetCMSToken>
<Label CombiningRule="or">
<Leaf Label="urn:example:policies:confidential"/>
<Leaf Label="urn:example:policies:plasma"/>
</Label>
<Hash>
<ds2:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"></ds2:DigestMethod>
<ds2:DigestValue>ABCDEFG0</ds2:DigestValue>
</Hash>
<Recipient>
<Subject type="urn:oasis:names:tc:xacml:1.0:data-type:rfc822Name">
lisa@simpsons.com
</Subject>
<LockBox>FF33eeddccaa002234</LockBox>
</Recipient>
<CEK>AB123456</CEK>
</GetCMSToken>
</xacml:AttributeValue>
</xacml:Attribute>
</xacml:Attributes>
</xacml:Request>
</PlasmaRequest>
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Appendix E. Example: Get CMS Token Response
This section contains an example of a response from a server to a
client for a CMS message token to be issued. The token is returned
in the CMSToken element. This element would then be placed into the
CMS message being created by the client.
<?xml version="1.0" encoding="UTF-8"?>
<PlasmaResponse xmlns="urn:ietf:schema:plasma:1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:schema:plasma:1.0 C:\ietf\drafts\Schema\Plasma.xsd"
xmlns:xacml="urn:oasis:names:tc:xacml:3.0:core:schema:wd-17">
<xacml:Response>
<xacml:Result>
<xacml:Decision>Permit</xacml:Decision>
</xacml:Result>
</xacml:Response>
<PlasmaReturnToken xsi:type="CMSTokenResponseType">
<RecipientInfo>3425342352343243</RecipientInfo>
</PlasmaReturnToken>
</PlasmaResponse>
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Appendix F. Example: Get CMS Key Request
<?xml version="1.0" encoding="UTF-8"?>
<PlasmaRequest xmlns="urn:ietf:schema:plasma:1.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:schema:plasma:1.0 C:\ietf\drafts\Schema\Plasma.xsd"
xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion"
xmlns:xacml="urn:oasis:names:tc:xacml:3.0:core:schema:wd-17">
<Authentication>
<!-- <saml:Assertion></saml:Assertion> -->
<GSSAPI></GSSAPI>
</Authentication>
<xacml:Request CombinedDecision="false" ReturnPolicyIdList="false">
<xacml:Attributes Category="urn:oasis:names:tc:xacml:3.0:attribute-catagory:action">
<xacml:Attribute AttributeId="urn:plasma:action-id" IncludeInResult="false">
<xacml:AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">ParseCMSToken</xacml:AttributeValue>
</xacml:Attribute>
<xacml:Attribute AttributeId="urn:plasma:action-id" IncludeInResult="false">
<xacml:AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">GetReplyToken</xacml:AttributeValue>
</xacml:Attribute>
</xacml:Attributes>
<xacml:Attributes Category="urn:oasis:names:tc:xacml:3.0:attribute-category:data">
<xacml:Attribute AttributeId="urn:plasma:data-id:CMSToken" IncludeInResult="false">
<xacml:AttributeValue DataType="http://www.w3.org/2001/XMLSchema#base64Binary">AABBDDEEFF1122344</xacml:AttributeValue>
</xacml:Attribute>
</xacml:Attributes>
</xacml:Request>
</PlasmaRequest>
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Appendix G. Example: Get CMS KeyResponse
<?xml version="1.0" encoding="UTF-8"?>
<PlasmaResponse xmlns="urn:ietf:schema:plasma:1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:schema:plasma:1.0 C:\ietf\drafts\Schema\Plasma.xsd"
xmlns:xacml="urn:oasis:names:tc:xacml:3.0:core:schema:wd-17"
xmlns:wst="http://schemas.xmlsoap.org/ws/2005/02/trust"
xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd">
<xacml:Response>
<xacml:Result>
<xacml:Decision>Permit</xacml:Decision>
</xacml:Result>
</xacml:Response>
<PlasmaReturnToken xsi:type="CMSKeyResponseType">
<DisplayString>Company Confidential</DisplayString>
<CEK>3425342352343243</CEK>
<ResponseRoleToken>
<Name>Message Response Role</Name>
<PDP>https://pdp.example.com/companyPolicies</PDP>
<Label CombiningRule="or">
<Leaf PolicyId="urn:example:policies:confidential"/>
<Leaf PolicyId="urn:example:policies:plasma"/>
</Label>
<wst:RequestSecurityTokenResponse>
<wst:TokenType>urn:plasma:roleToken</wst:TokenType>
<wst:RequestedSecurityToken>ABCDEF</wst:RequestedSecurityToken>
<wst:Lifetime><wsu:Expires>2012-02-01T00:00:00</wsu:Expires></wst:Lifetime>
</wst:RequestSecurityTokenResponse>
</ResponseRoleToken>
</PlasmaReturnToken>
</PlasmaResponse>
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Appendix H. Enabling the MultiRequests option
NOTE: RFC Editor please remove this section prior to publication.
This section exists as a note to the author to make sure that it can
be done. It will be published as a separate document if desired.
One of the issues in doing multiple requests in a single message is
the issue of correlation between the request and the results. We
have make this issue even worse by the fact that we are return
results that are not input attributes for the decision and that we
are not returning as attributes of the decision.
The best way to deal with this is by putting tags into the request
and reflect them in the return values for the response. The only
place that this does not work is for the GSS-API response token as
this element would normally be part of the response of multiple
requests. You want to finish that authentication step before issuing
final decisions if the input is needed as part of that decision.
With this in mind what we do is the following:
o Define a new data attribute for plasma as plasma-request-id. The
category for it is urn:...:data. The type will be a string.
o When the new attribute is used, then the return attribute flag
MUST be set on the attribute.
o There MUST be one entity of the new attribute, with a unique
value, for each of the requests in the MultiRequest element.
o Exactly one of the new attributes MUST be referenced in each
request in the MultiRequest element.
o The server copies the value of the attribute into the ***
attribute of the returned token.
We could probably relax the restrictions if we know that the token
can only be returned by one request, however using the token to
correlate the request and the decision is still probably desired so
that those values can be correlated.
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Author's Address
Jim Schaad
Soaring Hawk Consulting
Email: ietf@augustcellars.com
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