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Network Working Group                                         T. Freeman
Internet-Draft                                           Microsoft Corp.
Intended status: Informational                                 J. Schaad
Expires: February 21, 2014                       Soaring Hawk Consulting
                                                            P. Patterson
                                       Carillon Information Security Inc
                                                         August 20, 2013


                Requirements for Message Access Control
                  draft-freeman-plasma-requirements-07

Abstract

   There are many situations where organizations want to protect
   information with robust access control, either for implementation of
   intellectual property right protections, enforcement of contractual
   confidentiality agreements or because of legal regulations.  The
   Enhanced Security Services (ESS) for S/MIME defines an access control
   mechanism for email which is enforced by the recipient's client after
   decryption of the message. The ESS mechanism therefore is dependent
   on the correct access policy configuration of every recipient's
   client. This mechanism also provides full access to the data to all
   recipients prior to the access control check, which is considered to
   be inadequate for robust access control due to the difficulty in
   demonstrating policy compliance.

   This document lays out the deficiencies of the current ESS security
   label, and presents requirements for a new model for providing access
   control to messages where the access check is performed prior to
   message content decryption. This new model also does not require
   policy configuration on the client thereby simplifying deployment and
   compliance verification.

   The proposed model additionally provides a method where non-X.509
   certificate credentials can be used for encryption/decryption of
   S/MIME messages.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.




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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on January 20, 2012. 99

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.






























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Table of Contents

   1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1  Data Access Control . . . . . . . . . . . . . . . . . . . .  4
     1.2  Encrypted E-Mail Using Web-based Credentials  . . . . . . .  5
     1.3  Vocabulary  . . . . . . . . . . . . . . . . . . . . . . . .  6
     1.4 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     2.1.  ESS Security Labels  . . . . . . . . . . . . . . . . . . . 12
     2.2.  Access Control and the Web . . . . . . . . . . . . . . . . 14
     2.3.  Information Asset Protection . . . . . . . . . . . . . . . 16
     2.4.  Authentication Assurance Frameworks  . . . . . . . . . . . 17
     2.5 Electronic Signatures:  Authentication vs. Authorization . . 17
   3.  Use Case Scenarios . . . . . . . . . . . . . . . . . . . . . . 18
     3.1 Consumer to Consumer Secure Email  . . . . . . . . . . . . . 18
     3.2.  Business to Consumer Secure Email  . . . . . . . . . . . . 19
     3.3  Business to Business Ad-Hoc Email . . . . . . . . . . . . . 22
     3.4  Business to Business Regulated Email  . . . . . . . . . . . 23
     3.5 Delegation of Access to Email  . . . . . . . . . . . . . . . 28
     3.6 Regulated Industry Email . . . . . . . . . . . . . . . . . . 28
     3.7 Email Compliance Verification  . . . . . . . . . . . . . . . 30
     3.8  Email Pipeline Inspection . . . . . . . . . . . . . . . . . 30
     3.9 Distribution List Expansion  . . . . . . . . . . . . . . . . 32
     3.10 Scalable Decision Making  . . . . . . . . . . . . . . . . . 32
     3.11  Related Use Case Scenarios . . . . . . . . . . . . . . . . 33
   4. Plasma Data Centric Security Model  . . . . . . . . . . . . . . 36
     4.1 Plasma Client/Server Key Exchange Level of Assurance . . . . 43
     4.2 Policy Data Binding  . . . . . . . . . . . . . . . . . . . . 43
     4.3 Content Creation Workflow  . . . . . . . . . . . . . . . . . 45
     4.4 Content Consumption Workflow . . . . . . . . . . . . . . . . 47
     4.5 Plasma Proxy Servers . . . . . . . . . . . . . . . . . . . . 47
     4.6 Policy Types . . . . . . . . . . . . . . . . . . . . . . . . 49
   5.  Message Protection Requirements  . . . . . . . . . . . . . . . 50
     5.1.  General Requirements . . . . . . . . . . . . . . . . . . . 50
     5.2.  Basic Policy Requirements  . . . . . . . . . . . . . . . . 52
     5.3.  Advanced Policy Requirements . . . . . . . . . . . . . . . 53
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 55
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 56
   Editorial Comments . . . . . . . . . . . . . . . . . . . . . . . . 57
   Appendix A.  References  . . . . . . . . . . . . . . . . . . . . . 58
     A.1.  Normative References . . . . . . . . . . . . . . . . . . . 58
     A.2.  Informative References . . . . . . . . . . . . . . . . . . 58
   Appendix B Authors' Addresses  . . . . . . . . . . . . . . . . . . 59
   Appendix C Document Change History . . . . . . . . . . . . . . . . 60







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1 Introduction

   The S/MIME (Secure/Multipurpose Internet Mail Extensions) standard
   [RFC5652] today provides digital signatures (for message integrity
   and data origin authentication) and encryption (for data
   confidentiality).  The Enhanced Security Services (ESS) for S/MIME
   [RFC5035] provides for additional services including security labels
   (eSSSecurityLabel) which represent the access control policy. The
   label is a signed attribute in the signed data block of a message.
   The recipient of the message is responsible for checking that the
   recipient has a legitimate right to see the message based on the
   label.  This type of security labeling is similar to that of stamping
   "Top Secret" on the cover of a document.  It relies on the reader to
   not open and read the document when the policy is discovered.

   The Cryptographic Message Syntax (CMS) [RFC5652] allows for a variety
   of different types of lock boxes to be applied to an encrypted
   message.  This allows for a variety of security mechanisms to be used
   by the sender and the recipient to process the message.  However the
   S/MIME standard is currently solely based on X.509 certificates. This
   means anyone without an X.509 certificate is unable to leverage the
   S/MIME protocol for securing email.  The vast majority of users on
   the Internet have other forms of credentials (passwords, one time
   passwords, PGP keys etc.).

1.1  Data Access Control

   There are many situations where organizations want to include
   information which is subject to regulatory or other complex access
   control policy in email.  Regulated information requires some form of
   robust access control to protect the confidentiality of the
   information.  While ESS for S/MIME [RFC5035] defines an access
   control mechanism for S/MIME (eSSSecurityLabel), it is an extremely
   weak form of access control as the recipient is responsible for the
   enforcement and is given access to the data even if the recipient
   fails to meet the access criteria as defined by the label.

   An access control policy defines a set of criteria and evaluation
   logic that must be satisfied in order to grant access to the
   information.

   * With  Discretionary Access Control (DAC), policies are defined in
     terms of group membership the subject needs to meet the policy.

   * With Role Based Access Control (RBAC), policies are defined in
     terms of what role the subject needs to belong to to meet the
     policy.




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   * With Attribute Based Access Control (ABAC),  policies are defined
     in terms of what attributes about the subject, their device or
     environment, their intended action on or use of the information and
     the resource are needed to meet hte policy.

   Examples of the types of attributes used in ABAC would include
   attributes about the subject such as their employers identity, their
   nationality, citizenship etc.,  or attributes about their device such
   as its name, boot state.  Standards now exist that enable the
   transport of attributes [SAML-overview].

   An ESS Security label is a signed attribute of a SignedData object
   which indicates the access control policy for the message.  While an
   ESS Security Label provides a standardized representation of an
   access policy identifier, it does not define any methods of obtaining
   the necessary information to satisfy the policy or policy description
   in order to enforce the policy. The fact that this is a signed
   attribute protects the integrity of the ESS label and provides a
   tamper evident binding of the label to the message but does not by
   itself protect the confidentiality of the message. At the point where
   the recipient learns the access control policy to enforce on the data
   the recipient already has access to the data.  While the signature
   provides tamper evident integrity for the label over the clear text,
   it is not tamper proof because it is susceptible to unauthorized
   removal if the message only contains a SignedData element,  i.e. any
   Message Transport Agent (MTA) in the path can remove a signature
   layer of a SignedData message thereby altering the access control
   data.  Encrypting the signed message protects the confidentiality of
   the data and protects the SignedData from tampering from anyone
   unable to decrypt the message. However, encrypting the message means
   that no intermediate agent can enforce the label policy and it does
   not protect the label from any entity that has the ability to decrypt
   the message.

   From a regulatory enforcement perspective, ESS labels are an
   extremely weak form of access control because cryptographic access to
   the data is given before the access check.  The correct enforcement
   of the access check is dependent on the configuration of every
   recipient's email client.  Since the cryptographic access is granted
   before the access policy check, there is no cryptographic impediment
   for a recipient who is able to decrypt the data but is unauthorized
   under the policy, to ignore the policy and access the data.  A
   stronger enforcement model is needed for regulatory control for email
   where cryptographic access is only granted after the access check is
   successful.

1.2  Encrypted E-Mail Using Web-based Credentials




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   There are many users on the Internet today who have forms of
   authentication credentials other than X.509 certificates. S/MIME
   today can only use X.509 certificates to protect the confidentiality
   or the data origin authentication of the messages.  This means the
   many users without X.509 certificates cannot use S/MIME. Standards-
   based services (e.g.  [SAML-overview])are now available which
   abstract the specifics of an authentication technology used to
   identify a subject from the application itself (S/MIME in this case).
    Adoption of this abstraction model would enable a broader set of
   authentication technologies to be able to use S/MIME to secure email
   for confidentiality or data origin authentication.  It also allows
   for new authentication technology to be deployed without impacting
   the core protocol.

1.3  Vocabulary

   Many of the terms used in this document are the same as as defined by
   RFC3198[RFC3198]. Some  terms however though representing broadly the
   same concept, have some minor differences in the definitions from
   RFC3198.

 Attribute Based         Where the access control policy is specified by
 Access Control (ABAC)   a set of attributes, their values, and any
                         relationship between attributes required to
                         authorize an action on a resource. These
                         attributes may be provided by the subject as
                         part of the decision request (Front End
                         Attribute Exchange) or discovered by the policy
                         decision service itself (Back End Attribute
                         Exchange). The policy, for example, may require
                         attributes about the subject, their device or
                         environment, a resource, or the intended use of
                         the information.

 Back End Attribute      When attributes are directly sent
 Exchange (BAE)          from the attribute issuer to the  Policy
                         Decision and Enforcement Point (PDEP).

 Capability Based Access Where access control is via a communicable,
 Control (CBAC)          unforgeable token. A capability token is a
                         protected object which, by virtue of its
                         possession by a subject, grants that subject
                         the capability.

 Cipher text             Plain text which has been processed by an
                         encryption algorithm to render it unreadable by
                         a program or human without the appropriate
                         cryptographic key.



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 Confidential            A message has been protected to a known level
                         of confidence so that the contents are not
                         decipherable by unauthorized users.

 Content Encryption Key  A key used to encrypt protected end user data.
 (CEK)                  (See Key Encryption Key)

 Cryptographic Lock Box  A data structure which holds a CEK encrypted
                         for a specific user. CMS implements
                         Cryptographic Lock Boxes as RecipientInfo
                         structures.

 Data Origin             Enables the recipient to verify that
 Authentication          message has not been tampered with in transit
                         or in storage, and the subject who originated
                         the message.

 Decision Requester (DR) The service responsible for making policy
                         decision requests to the PDEP. In this model
                         the policy decision is enforced by the PDEP by
                         its control of cryptographic keys. The DR
                         enforces any obligations the PDEP may require
                         such as signing or encryption of the data,
                         generating audit events etc. A DR is distinct
                         from a PEP in other models such as XACML in
                         that a DR is not by default trusted with the
                         clear text data. Policy enforcement is
                         performed by the PDEP. A DR may establish trust
                         by presentation of attributes about itself and
                         its environment to show it is trustworthy.

 Early Binding           The concept of creating the cryptographic lock
                         box for a recipient at the time the message is
                         sent. (Compare with Late Binding)

 Front End Attribute     When subject attributes are relayed from the
 Exchange (FEE)          attribute issuer to the PDEP party via the DR.

 Integrity Protected     A recipient of a message can determine to a
                         known level of confidence that a message has
                         not been modified between the time that it was
                         created and when it was received by the
                         recipient.

 Key Encryption Key      A key used to encrypt another cryptographic
 (KEK)                   key, often a CEK. (See Content Encryption Key)

 Late Binding            The concept of creating the cryptographic lock



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                         box for a recipient when the recipient attempts
                         to decrypt the message.  Late binding has a
                         potential downside because the sender cannot
                         know what symmetric algorithms the recipient
                         supports which can lead to interoperability
                         issues. (See Early Binding)

 Mail Transfer Agent     A program that transfers email from one
 (MTA)                   computer to another. An MTA implements both the
                         sending and receiving of email.

 Mail User Agent         A program or service used to manage a user's
 (MUA)                   email. The MUA may be a program run on the
                         users computer or a Web service accessed via
                         the users browser.

 Metadata                Metadata is data about data. There are three
                         kinds of metadata.

                         (1) Content metadata is metadata about an
                         instance of data, the actual data content. An
                         example of content metadata would be "this data
                         contains Company Foo intellectual Property" or
                         " this is a patient record".

                         (2) Policy metadata is metadata about the
                         policies to apply to an instance of data. An
                         example of policy metadata would be "apply
                         Company Foo XYZ policy".

                         (3) Structural metadata is metadata about the
                         design and specification of the data. An
                         example of structural metadata would be "this
                         is a patient record table".

 Orthonym                The correct or legal name of a place, person or
                         thing. (See Pseudonym.)

 Plain text              The information in a state which can be
                         directly read by a human or an appropriate
                         application.

 Policy                  (1) A statement in a human language which
                         defines a course of action by an individual or
                         organization. These statements may be in the
                         form of legislation, regulation, a legal
                         contract, or organization goals.
                         (2) Technical controls for implementation of



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                         the human-readable policies. Policies may
                         stipulate many forms of technical controls
                         requirements such as data protection, access
                         control, data integrity, data origination, data
                         retention, etc.

 Policy Administration   The system entity that creates, maintains and
 Point (PAP)             publishes policies or policy collections. The
                         policies define the rules, their conditions and
                         actions associated with the policy.

 Policy Collection       A collection of one or more policies which is
                         associated with a role. The policy collection
                         may also define the logical relationship
                         between the policies.

 Policy Decision Point   The system entity that evaluates the policy
 (PDP)                   using attributes supplied by a PIP to render
                         decisions on requests made by PEPs. The PDP
                         does not enforce the decision.

 Policy Decision and     The system entity that evaluates the policy
 Enforcement Point       criteria published by a PAP, using attributes
 (PDEP)                  supplied by a PIP to render decisions on
                         requests made by DRs. The PDEP is able to
                         enforce its decision via the use of
                         cryptographic keys.

 Policy Enforcement      The service responsible for making policy
 Point(PEP)                   decision requests to the PDP. A PEP has
                         access to the plain text data and metadata and
                         enforces the decisions made by the PDP.


 Policy Identifier       The tag that is used to identify a policy. For
                         the purposes of this document the focus is on
                         two different types of policy identifiers.
                         Object Identifiers (OIDs) are what are
                         currently used in many security policy systems
                         and are the only method of policy
                         identification supported by ESS security
                         labels.  Additionally URIs are supported as
                         policy identifiers  as they provide a more user
                         friendly method to uniquely identify a policy
                         and allow discovery of the policy.

 Policy Information      A service which issues assertions for example
 Point (PIP)             about a subject, their device, or environment



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                         e.g., a SAML Security Token Service. This model
                         supports both front end and back end exchange
                         of assertions between the PIP and the PDEP.
                         Attributes can be distributed directly between
                         the PIP and the PDEP (BAE). Alternatively
                         attributes may be distributed via the DR (FAE)
                         There are two types of PIP based on the types
                         of attribute the PIP would assert about the
                         subject. An Identity Provider (IdP) PIP will
                         issue authentication attributes  e.g.,
                         information about how and when the subject
                         authenticated to the IdP. An IdP may also issue
                         attributes about the subject themselves, e.g.,
                         their full name, age, or citizenship. An
                         attribute provider (AtP)PIP only issues
                         attributes about the subject or the subject's
                         environment.

 Policy Label            The data structure which holds one or more
                         policy identifiers and their logical
                         relationship.

 Pseudonym               A name that a person or group assumes for a
                         particular purpose, which differs from their
                         original or true name. (See Orthonym.)

 Role                    An abstract subject which has a series of
                         authorizations assigned to it. Users are
                         assigned to roles to perform the duties of the
                         role. Users typically select a role to perform
                         a function to disambiguate which role they are
                         currently  functioning as.  A role is distinct
                         from a group because a group is a collection of
                         subjects which has no intrinsic authorizations.

 Role Based Access       Access control based on the assignment of
 Control (RBAC)          a role.  Subjects are then allowed to assume
                         one or more roles based on their job needs as
                         for as long as their job requires.

   We additionally make use of the following terms:

 Attribute               The act of a client requesting and obtaining a
 Request/Issuance        set of attributes for a subject.  The issuance
                         of attributes will itself be controlled by
                         policy and thus recursively embeds this same
                         picture in that process.  The attributes can be
                         requested either by the DR (FAE) or the PDEP



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                         (BAE).

 Content Protection      The protocol to be run by the DR to get the set
 Request/Response        of decisions and information required to
                         successfully create and encode a data block
                         with appropriate labeling. This protocol is
                         part of the work to be defined by this group.

 Content Consumption     The protocol run by a DR to obtain the
 Request/Response        permissions and information needed to decode
                         and  access  data with appropriate labeling.

 Content Distribution    Can be any of a number of methods by which the
                         content is transmitted from the Content Creator
                         to the Content Consumer.  These methods
                         include, but are limited to: email, FTP, XMPP,
                         HTTP and physical distribution.


1.4 Keywords

   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 RFC 2119.

2 Background

   The S/MIME standard [RFC5751] provides a method to send and receive
   secure MIME messages. S/MIME uses CMS[RFC5652] as the means to
   protect the message.  While CMS allows for many types of security
   credentials to be used, S/MIME exclusively [RFC5750] uses X.509
   certificates [RFC5280] for the security credentials for signing and
   encryption operations.  S/MIME uses an early binding mechanism for
   encryption keys where the sender needs to discover the public key for
   each recipient of an encrypted message before it can be sent.  This
   requires the sender to maintain a cache of all potential recipient
   certificates (e.g. in a personal address book) and/or have the
   ability to find an acceptable certificate for every recipient from a
   repository at message creation.  This key management model has
   limited the use of S/MIME for encryption for a variety of reasons.
   For example:

   o  The recipient may not have an X.509 encryption certificate

   o  The sender may not have received a signed email with the
      recipient's certificate

   o  The recipient may not have an available repository from which to



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      retrieve the recipient's certificate

   o  The sender may be unaware of the location of the recipient's
      repository

   o  The recipient's repository may not be accessible to the sender,
      e.g., it's behind a firewall

   o  The sender may not have a valid certificate path to a trust anchor
      for the recipient's certificate

   If one or more recipient certificates are missing, then the sender is
   left with a stark choice: send the message unencrypted or remove the
   recipients without certificates from the message.

   The use of secure mailing lists has the ability to provide some
   relief to the problem. The original sender does not need to know the
   appropriate encryption information for all of the recipients of the
   mailing list, just for the mailing list itself.  It can thus be
   thought of as a form of late-binding of recipient information for the
   originating sender.  However it is still early-binding encryption for
   the mail list agent; as it needs to perform all of the gathering and
   processing of certificate information for every recipient that the
   agent will relay the message to.

   In many regulated environments end-to-end confidentiality between
   sender and recipients by itself is not enough.  The regulatory policy
   requires some form of access control check before access to the data
   is granted.  In many inter-organization collaboration scenarios it's
   impossible for the sender to satisfy the access checks on behalf of
   all recipients since they don't have, and frequently should not have
   access to, all the recipient's attributes because to do so may be a
   breach of the recipients privacy. Indeed to release the attributes to
   the sender may require that the sender's attributes first be released
   to the recipient's attributes provider.  It's a fundamental tenet of
   good security practice that users should control the release of data
   about themselves.

2.1.  ESS Security Labels

   Security labels are an optional security service for S/MIME defined
   in Enhanced Security Services for S/MIME [RFC5035].  The ESS security
   label allows classification of the sensitivity of the message
   contents using a hierarchical taxonomy in terms of the impact of
   unauthorized disclosure of the information [RFC3114].  The security
   label can also indicate access control such as full time employees
   only or US nationals only.  ESS security labels are authenticated
   attributes of a CMS signer-info structure in a SignedData object.



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   The label when applied to signed clear text data provides the access
   control decisions for the plain text.  If applied to cipher text such
   as the outer layer of a triple wrapped S/MIME message the label is
   used for coarse grained optimization such as routing.

2.1.1.  Problems With ESS Security Labels

   ESS Security Labels have been found to have a number of limitations.

   1.  When the label is on the innermost content, access to the plain
       text is provided to the recipient (in some form) independent of
       the label evaluation as it will be processed for the purpose of
       hash computation as part of signature validation.  Depending on
       how a triple wrapped message is processed by the recipient's CMS
       code, the inner content may be processed for signature validation
       even before the outer signature is validated.  This would happen
       for a stream based CMS processor which starts processing inner-
       layers immediately rather than finishing processing of each layer
       and caching the intermediate results.

   2.  Labels applied can be removed in transit.  If a signed layer is
       seen then it can be removed by any agent that processes the
       message (such as a Message Tranfer Agent).  If the label is
       protected by an encryption layer then it can only be removed by
       any agent that has a decryption key (Encryption Mail List agents
       or Spam Filtering software would be two such examples).

   3.  Policies are identified by Object Identifiers.  This makes for a
       small tight encoding, but it does not provide any mechanism for
       an email client to discover how to enforce a new access control
       policy if the message contains a policy the client is unaware of.
       This provides an impossible choice: ignore the access control
       policy and grant access to the message or block access to the
       message. Object identifiers also do not provide a good display
       name for a user so that they could manually find and download a
       new policy.

   4.  The current ESS standard only allows for a single policy label in
       a message; no standardized method of composing multiple policy
       labels together has been defined.  This is adequate for coarse-
       grained policy binding to express a limited set of choices such
       as with information sensitivity which typically provides a
       hierarchy of 3-5 choices. Many data sets need to be subject to
       multiple access control policies.  For instance, a message may
       contain information that is both propriety and export controlled.
        Trying to represent combinations of policies via a single policy
       label would lead to an exponential growth in the number of policy
       labels.



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   5.  ESS Labels do not provide for any auditing of who has been
       granted access to the message.  All policy evaluation is local to
       the recipient's machine; no centralized logging of access to the
       message can be performed

   6.  Enforcement of the policy occurs on the recipient's machine; the
       compliance with the policy is dependent on the state of the
       configuration of every receiving agent.  The policy is enforce by
       whatever module is located on the user's system. For cross
       corporate systems, this means that the policy provided by Company
       A must be installed on Company B machines, or Company B must
       install a policy that Company A will accept as being equivalent
       to their own policy. Additionally, any time that a new version of
       the policy module is rolled out, there will be a time lag before
       every recipients machine will have the updated module.  This
       makes policy compliance practically impossible in anything but a
       small, closed environment.

   7.  Access to the message cannot be granted or removed after the
       message has been sent. Therefore, if a recipient has a designated
       alternate recipient they will not be able to read the message.
       Also, if the sender subsequently learns one of the recipients was
       in error, they cannot correct the mistake.

2.2.  Access Control and the Web

   A prerequisite for many Web transactions is the disclosure of
   attributes about the subject such as name, age, email address,
   physical location, address, credit card number, social security
   number, etc. Some attributes lend themselves to easy verification but
   many do not. An assertion of an email address can be verified by
   sending an email to the address containing a secret ephemeral
   challenge. Subsequent demonstration of knowledge of the ephemeral
   challenge verifies the email address assertion.  Other assertions
   such as "this is my credit card account number" are not easily
   verified.  The fact that it is a valid credit card number can be
   verified but not the binding to the subject attempting to use it.
   Where a claim is not easily verified it is often combined with other
   assertions under the assumption that knowledge of this larger data
   set verifies all the assertions in the data set.  If you know the
   account number, billing address, etc., 'of course' you must be the
   account holder. This is a very weak form of verification as is often
   demonstrated by the growth of identity theft; much of this bigger
   data set is often publicly available via social networks or easily
   guessed, e.g., the most popular professions for a parent is dead or
   retired. Many of the assertions which are harder to verify are based
   on government issued documents such as a birth certificate, driver's
   license, identity card, or passport.  This requires an exchange of



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   the documents between the relying party and the subject. For a small
   number of high value transactions (e.g., opening a new account) with
   relying parties that have widespread physical presence (e.g., a bank
   or Post Office) this is acceptable because the applicant can present
   themselves with the required documentation in person. However,Web-
   based relying parties cannot perform an in person exchange of
   documents to verify information on government issued documents. The
   approach taken with such relying parties is to have trusted assertion
   providers where the assertion provider can perform an in-person
   exchange of documents with the subject then vouch for the set of
   assertions they have verified.

   SAML [SAML-core] defines an XML framework for describing and
   exchanging attributes about subjects.  The entity issuing the
   attributes about the subject is known as the attribute provider. The
   entity consuming the attributes is known as the relying party.  The
   well-known scenarios for using SAML are:

   o  Single Sign On across systems on different platform technology

   o  Federated Identity between business partners

   o  Web Services and other standards, e.g.,  -SOAP based protocols

   is able to exchange the rich and variable set of attributes which are
   necessary for authorizing transactions.


   X.509 identity certificates are a signed token that can exchange a
   limited set of identity attributes about a subject such as an X.500
   distinguished name, email address, Kerberos principal name, etc. The
   X.509 identity certificate always contains a public key issued to the
   subject and the subject proves their identity to a replying party by
   a challenge by the relying party to the associated private key. The
   X.509 identity certificate can be supplemented by an X.509 attribute
   certificate with can contain additional attributes about the subject
   such as date of birth, business sign-off limit levels, etc.

   SAML also uses signed tokens and supports an extensible set of
   attributes about the subject as is supported by X.509 identity and
   attribute certificates.  SAML tokens can be either Bearer Tokens or
   Holder-of-Key tokens. Bearer tokens have no cryptographic key and
   their security is based on the time between when the token was issued
   and time it was presented to the replying party together with the
   token being issued for use with the replying party. Low value
   transactions can use Bearer tokens where possession of the token
   alone is considered acceptable for the transaction risk. Holder-of-
   Key tokens contain a cryptographic key (either public or symmetric)



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   and like X.509 identity certificate the subject proves their identity
   to the replying party by the replying party challenging the key in
   the token. Higher value transactions can therefor have a stronger
   proof of identity by the demonstration of proof of possession of
   cryptographic keys. SAML also defines a number of query/response
   style profiles for issuing the tokens enabling both client and
   relying parties to request SAML tokens of different types.

   The critical difference between SAML and pure X.509 identity
   certificates is that SAML [SAML-QUERY] also abstracts the details of
   the authentication protocol from the relying party. The attribute
   provider can use a broad range of authentication mechanisms such as
   passwords, one-time passwords, biometrics, X.509 certificates, etc.,
   to authenticate the subject without impacting the relying party as
   part of the token issuing process.  The attribute provider includes
   the details of the authentication mechanism used or its strength
   using an established strength of authentication scale such as NIST
   SP800-63-1 [SP800-63-1].  The relying party then inspects the
   attributes in the token to the identity provider to determine if it
   complies with its access policy.

2.3.  Information Asset Protection

   Information Asset Protection (IAP) is a concept developed by the
   Transglobal Secure Collaboration Program (TSCP), a working group
   comprised of the major players in the western Aerospace and Defense
   industry.  The industry is highly regulated and operates in an
   environment with many policies governing the access to information
   assets.  These policies are motivated by the desire to protect
   intellectual property, the confidentiality of information, or are
   imposed by government regulations such as the US International
   Traffic in Arms Regulations (ITAR) from the US Department of State.
   They apply to the information assets in whatever form the asset may
   take and are independent of the application used to create the
   information.  These policies take many forms, e.g., verification the
   recipient has demonstrated a need to know the information because
   they are working on a specific project, that they have passed the
   appropriate background and nationality checks, or that they have
   signed the appropriate non-disclosure agreement.  What is needed is a
   policy driven, information-centric protection where the applicable
   policies either is manually or automatically attached to the
   information, and based on the policy, the system understands what
   access control and data protection is necessary.

   Email is an application widely used in the Aerospace and Defense
   industry.  S/MIME is widely used today and provides sender to
   recipient confidentiality.  This protects the contents of the message
   from discloser to unauthorized third parties, e.g., while it is in



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   transit between MTA's or while at rest in an MTA message queue or
   recipient's mailbox.  However, it does not impose any finer-grained
   access control such as those required by many policies.  S/MIME does
   define an extension mechanism for access control via an ESS security
   label [RFC5035] though this mechanism has drawbacks (see above).

2.4.  Authentication Assurance Frameworks

   A number of organizations have created taxonomies to define the
   possible levels of identity assurance for electronic authentication.
   The objective of the framework is to provide a simple abstraction of
   the details of:

     o  Identity proofing and registration of subjects

     o  Tokens used by subjects for providing electronic identity

     o  The token management mechanisms

     o  Protocols used for subject to employ tokens to authenticate to
     an identity provider

     o  Protocols used by subjects to authenticate and pass attributes
     to a relying party

   These framework have been drafted by industry organizations [lib-
   iaf][kan-iaf] and governments [SP800-63-1].  While all of these
   frameworks may not agree on every aspect, at a macro level they do
   exhibit many similarities.  A common theme in many is the adoption of
   a small number of levels of identity assurance, typically between 3
   and 5. A simplified description of the levels is:

        Level 1  Negligible confidence in the asserted identity

        Level 2  Some confidence in the asserted identity

        Level 3  Significant confidence in the asserted identity

        Level 4  High confidence in the asserted identity

   A framework defines broad characteristics in the area of identity
   proofing, credential type and management, identity provider
   authentication and relying party authentication.

2.5 Electronic Signatures:  Authentication vs. Authorization

   Electronic signatures on email are used today to show data
   origination so only authentication is required. However, with



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   transactions that are legally or regulatory significant,
   authentication alone is frequently insufficient. Policy requires
   other factors to be considered to ensure that the transaction meets
   policy requirements. Examples of these factors include:

     o The state of the system generating the signature

     o An indication of the signer's intent

     o Attributes about the signer to indicate, for example, job
     function in the company, job assignments, professional
     qualifications, signing authority, etc.


   Many organizations would like email based work flows to be an option
   for these transactions.

3.  Use Case Scenarios

   This section documents some email based use cases that the new
   protocol aims to support. Also included are some related scenarios
   where the same underlying theme of consistent policy enforcement
   equally applies.

3.1 Consumer to Consumer Secure Email

   One of the issues that is stopping the use of secure email in
   personal mail is the fact that consumers find X.509 certificates
   difficult and expensive to obtain and then use - especially across a
   set of devices (phone, tablet, workstation). One of the possible use
   cases of Plasma is to try and deal with this by removing the
   dependency on X.509 certificates.  The details of the use case are
   therefore: Alice wants to send an email message to Bob that contains
   sensitive, personal data so she is concerted about ensuring only Bob
   can read it. Bob has a strong credential he can use to identity
   himself, but it's not an X.509 certificate.  Alice needs to ensure
   the following:

   (a)  Only Bob can read the email.

   (b)  Bob has the ability to verify the email is from Alice.

   (c)  Bob has the ability to verify the email message has not been
        modified since Alice sent it.


   The sequence of events could be as follows:




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   1.  Alice composes the email to Bob.

   2.  Alice's email client allows here to classify the email.  Alice
        classifies the email as Personal Communication which is a policy
        provided by her ISP.

   3.  Alice's email client knows the protections to apply to a Personal
        Communication; it knows to encrypt and sign the message.

   4.  The protected email is able to flow securely and seamlessly
        through existing email infrastructure to Bob. The data is
        protected while in transit and rest.

   5.  Bob receives the email and sees that it is a secure message.  Bob
        can verify that the secure message has not been altered. Bob
        attempts to open and decrypt the email.  If Bob is on the same
        ISP as Alice, then the same username/password as he uses to get
        his Email is used to obtain the needed keys.  If Bob is on an
        ISP that is federated with Alice's ISP then an infrastructure
        such as SAML, OpenID, OAUTH or ABFAB could be used to validate
        Bob's identity and allow the needed decryption keys to be
        released.

3.2.  Business to Consumer Secure Email
   There are many examples of business-to-consumer secure email
   scenarios where the email could potentially contain sensitive medical
   or financial data. This would include doctor-patient; bank-account
   holder; Medical insurance-insured person and mortgage broker-customer
   communications. Two examples are presented here.

3.2.1 Bank Statement Email

   A bank (The Bank of Foo) has determined that it will be using email
   to distribute statements to its customers (Bob).  The information is
   confidential, so any channel of communication the bank selects must
   protect Bob's privacy.  The bank needs to ensure the following:

   (a)  Only Bob (or additional owners of the account) can read the
        email

   (b)  Bob authenticates with a sufficient level of identity assurance.
        The same identity assurance authentication level used to do on-
        line banking would be considered sufficient

   (c)  Bob can verify the statement is from his bank

   (d)  Bob can verify the statement has not been modified since his
        bank sent it.



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   The sequence of events would be as follows:

   1.  As part of routine end-of-the-month processing, the bank composes
   an email to Bob. They include the statement of balances and activity
   either as an attachment or as the body of the message.

   2.  The statement mailer for the Bank of Foo has been configured to
   apply a specific policy to the email.

   3.  The statement mailer for the Bank of Foo knows the protections to
   apply based on the policy; it knows to encrypt and integrity protect
   the message and what level of assurance is required for the
   recipients identity.

   4.   The protected email is able to flow securely and seamlessly
   through existing email infrastructure to Bob. The data is protected
   while in transit and at rest.

   5.   Bob receives the email and sees it is a secure message from the
   Bank of Foo. Bob can verify the message has not been altered as it is
   signed by his bank.  Bob uses the same credential as he would for on-
   line banking to prove his identity to the email system and obtain the
   keys necessary to decrypt the message.

   The same process could be used for any messages sent between the bank
   and its customers.  Thus, messages dealing with loan applications and
   changes in bank policies can be sent out in the same manner,
   potentially using different policies.  In some of these cases it
   might be in the bank's interests to record in an audit trail if and
   when the keys were handed out on certain emails.  For a statement,
   the bank would not expect a reply to occur, however, for other types
   of messages it should be possible for Bob to reply under the same
   level of protection.  If Bob is able to use the same credential when
   sending a message, as the one he uses for accessing the bank's Web
   site then the bank has the same assurance of the message sender's
   identity.

3.2.2  Doctor-Patient Communications

   In the second example, let's say that Alice is a doctor and has
   received test results for her patient Bob. This information is
   confidential and regulated, so any channel of communication she
   selects must protect Bob's privacy and comply with regulatory
   requirements.  Alice elects to use email to reach Bob quickly and
   easily with news of the results.  In this respect it is similar to
   the previous use case; however there are some additional
   complications that might need to be dealt with as well.  Depending on
   who Bob is and where he is currently, there are additional people



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   that may also need to be automatically informed of the same
   information, or need to have the ability to access the contents of
   the message. Examples of these would be Bob's spouse, an individual
   who is making care decisions for Bob (i.e., one of Bob's parents), or
   an individual in charge of dealing with Bob's day-to-day health care
   (i.e., a charge nurse in a hospital or a visiting nurse).  All of
   these people may have the same need-to-know as Bob. There is also the
   possibility that some parts of the message may need to be released to
   some individuals but not to others.  As an example, the mail message
   could contain a prescription; that specific portion of the message
   may need to be read by Bob's pharmacist.  Alice needs to ensure the
   following:

   (a)  Recipients can read the parts of the email they are authorized
        to see.  The definition of authorized will vary with the content
        of the message and thus the policy applied. (For example.
        general health issues will certainly be treated differently than
        mental health issues, even by a General Practitioner.)

   (b)  That Bob is required to authenticate with an identity assurance
        level 2 or above level.

   (c)  That Bob can verify the email is from Alice.

   (d)  That Bob can verify the email has not been modified after Alice
        sent it.

   The sequence of events would be as follows:

   1.  Alice composes the email to Bob. She includes some comments and
        suggestions for Bob and attaches the test results.

   2.  Alice's email client allows her to classify the email.  Alice
        classifies the email as a Doctor-Patient communication. As a
        side effect of classifying the email message, the policy may
        suggest or mandate additional individuals that the communication
        should be addressed to.

   3.  Alice's email client knows the protections to apply to Doctor-
        Patient communication; it knows to encrypt and integrity protect
        the message.

   4.  The protected email is able to flow securely and seamlessly
        through existing email infrastructure to Bob. The data is
        protected while in transit and at rest.

   5.  Bob receives the email and sees it is a secure message from
        Alice. Bob can verify the message has not been altered. Bob



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        attempts to opens the email.  Bob provides a Level 2 password to
        retrieve the necessary decryption keys. After Bob has proved his
        identity, he is able to read the email.

   There are number of different places where the identity provider for
   Bob could live.  The first is at Alice's office; Bob already has a
   face-to-face relationship with Alice and the credential could be
   setup in her office.  A second  could be Bob's insurance provider.
   Bob has a relationship with his insurance provider as does Alice,
   thus it can serve as an trusted identity provider to healthcare
   providers.  A third  location could be a federation of doctors in an
   area, potentially  with other health providers (such as hospitals and
   convalescent centers). Bob has setup an identity with Alice, but if
   he gets referred to Charlie by Alice for some procedures, Charlie
   would not need to setup a new identity for Bob but instead could just
   refer to  Alice for the necessary identity proof.  Many of these
   types of situations are dealt with by [I-D.ietf-abfab-arch].

   There are a number of other additional services that could be
   provided by the policy system.  One example would be that if the
   information was time critical, if Bob does not access his message
   within a given time period, the policy server could notify Alice of
   this fact so that an alternate method of communication can be
   attempted with the same information.

3.3  Business to Business Ad-Hoc Email

   Early in the relationship between two companies, it is frequently
   necessary to exchange sensitive information as a preliminary to a
   more formal business relationship e.g., contract negotiations.  This
   needs to occur before the relationship has matured to the point that
   a formal relationship is reflected through a specific legal
   agreement. Business owners need the agility to interact with
   potential partners without having to engage their respective IT
   staffs as a prerequisite of the communication.

   As an example, Charlie works for Company Foo. He has just met Dave
   from Company Bar to discuss the prospect of a potential new business
   opportunity.  Following the meeting, Charlie wants to send Dave some
   sensitive information relating to the new business opportunity.  When
   Charlie sends the email to Dave with the sensitive content, he must
   ensure the following objectives:

   (a)  Only Dave can read the email

   (b)  Dave is required to authenticate with an identity assurance
        level 2 or above




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   (c)  That Dave can verify the email is from Charlie

   (d)  That Dave can verify the email has not been tampered with

   (e)  Charlie may also need to keep a record of the fact that Dave
        accessed the message and when it was done.

   The sequence of events Charlie would use is as follows:

   1.   Charlie composes the email to Dave.  He include some sensitive
        information relating to potential terms and conditions for the
        new contract that Foo and Bar would sign to form a partnership
        for the business opportunity.

   2.   Charlie's email client allows him to classify the email.  He
        classifies the email as an ad-hoc pre-contractual communication.

   3.   Charlie's client knows the protections to apply to ad-hoc pre-
        contractual communication; it knows to encrypt and integrity-
        protect the message and the level of assurance required for the
        recipients identity.

   4.   The protected email is able to flow securely and seamlessly
        through existing email infrastructure to the recipient (Dave in
        this case).  The data is protected while in transit and at rest.

   5.   Dave receives the email and sees it is a secure message from
        Charlie. (Charlie policy requires level 2 authentication for
        which, Dave uses a password). Dave is able to prove his identity
        to the level of assurance requested by Charlie so he is able to
        read the email. The organization Dave works for has an identity
        service which he uses to prove his identity for Charlie's email.
        Dave opens the email.

   If Dave or his delegate replies to the email from Charlie, the new
   message inherits the policy from the original messages so the entire
   message thread has the same policy.  The policy also applies to
   messages forwarded by Dave because it contains information from
   Charlie and Company Foo wants consistent policy enforcement on its
   information.

3.4  Business to Business Regulated Email

   As business relationships mature they often result in a formal
   contractual agreement to work together. Contractual agreements would
   define a number of work areas and deliverables. These deliverables
   may be subject to multiple corporate and/or regulatory policies for
   access control, authentication and integrity. Some classes of email



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   may have information which is legally binding or the sender needs to
   demonstrate authorization to send some types of message where
   authority to send the message is derived from their role or function.
   Also many regulated environments need to be able to verify the
   information for an extended period - well beyond the typical lifetime
   of a user's certificate.  The set of policies applicable to an email
   is potentially subject to change as the different user's contribute
   information to the email thread.

3.4.1 Regulated Email Requiring a Confidentiality Policy

   Company Foo has been awarded a contract to build some equipment
   (Program X).  The equipment is covered by export control which
   requires information only be released to authorized recipients under
   the terms of the export control license.  Company Bar is a foreign
   subcontractor to Company Foo working on Program X. Company Foo sets
   up some business rules for access to program X data to ensure
   compliance with the  export control license requirements.  Company
   Foo also set up separate rules to cover the confidentiality of its
   intellectual property contributed to Program X. Company Bar also sets
   up its own policies to protect the confidentiality  its own
   intellectual property it contributes to Program X. As part of the
   agreement between Foo and Bar, they have agreed to mutually respect
   each other's policies.

   Confidentiality policies can change over time. It is important to be
   able to implement the changes without the need to update the data
   itself to reflect the change as finding all instances of the data in
   an intrinsically impossible problem to solve.

     Frank is an employee of Company Foo. He has been assigned as a
     design team leader on Program X and as an individual contributor on
     Program X integration. Frank wants to send some email as a team
     leader to colleagues working on Program X in both Companies Foo and
     Bar.

     Grace is an employee of Company Bar. She has also been assigned to
     the design team of Program X.

     When Frank sends the email with Program X regulated content he must
     ensure compliance with the export control policies. When Frank
     sends a Program X email he must ensure recipients are authorized to
     read the contents to ensure Company Foo remains in compliance with
     its export control license.

     If Frank also includes Company Foo intellectual property in an
     email, he must also ensure recipients are authorized to read the
     intellectual property contents.



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     When Grace receives a Program X email, she must provide attributes
     about herself to prove compliance with the export control policy.
     If the email also contains Company Foo intellectual property, she
     must also provide attributes to show she is authorized to read the
     information under the agreement between Company Foo and Company
     Bar.

     If Grace sends an email with Company Bar intellectual property, she
     must ensure recipients are authorized to read the contents under
     the agreement between Company Bar and Company Foo.

   When Frank sends a Program X email he must ensure the following
   objectives:

   (a)  Only recipients who meet the Program X export control policy
        and/or Company Foo's intellectual property protection policy can
        read the email.
   (b)  Recipients authenticate with a identity assurance level of level
        3 or above.
   (c)  Recipients present all other attributes about themselves
        necessary to verify compliance with the applicable policies
        (their program assignment, nationality, professional or industry
        certifications, etc.).

   (d)  Recipients can verify the email is from Frank to the level of
        identity assurance as defined by the message policy (i.e., level
        3 or above).

   (e) Recipients can verify the email has not been tampered with to the
        level of identity assurance as defined by the message policy.

   (f) Recipients are made aware that the message is a Program X email
        (and the contents can only be shared with other Program X
        workers) and/or the message contains Company Foo's intellectual
        property.

   The sequence of events Frank would use is as follows:

   (1)  Frank composes the email and includes a Program X distribution
        list as a recipient. He include some information related to
        Program X. Frank also includes some information which is Company
        Foo's Intellectual Property.
   (2)  Frank's email client allows him to select the Program X role.
        The client then allows Frank to select from a set of policies
        appropriate for Program X.
   (3)  Frank selects the Program X content and Company Foo IP policies
        from the list of available policies.
   (4)  The email client knows to encrypt the message, the key size and



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        algorithm to use. It also knows that the message needs to be
        signed with a level 3 or above private key.
   (5)  Frank clicks the "send email" button. The client signs the email
        using his smart card private key and includes the certificate
        with the appropriate public key for verification of the
        signature by recipients. The Client then encrypts the message
        and obtains data from a server that will enforce the access
        control requirements for Frank, and sends it to his email
        server.

   The email is able to flow securely and seamlessly through existing
   email infrastructure to recipients of the distribution list. Grace is
   on the distribution list so she receives the email from Frank.

   (6)  Grace receives the email. Grace's client provides the attributes
        necessary to comply with the policy which includes her level 3
        encryption certificate to the PDEP.
   (7)  Once Grace has shown she passes the policy requirements, the
        PDEP releases the message CEK to Grace using her level 3
        encryption certificate.
   (8)  Grace uses her smart card to open the message. She sees the
        message is signed by Frank and marked with both the Program X
        and Company Foo IP policies

   If Grace replies to the email from Frank, the new message inherits
   the policy from the original message.  If Grace includes some
   information which is Company Bar's IP she also adds her company's IP
   protection policy requirements to the message.

   Frank receives the reply from Grace.  Frank is able to prove his
   identity to the level requested by Grace and provides the requested
   attributes about himself to satisfy both the Program X export
   control, the Company Foo IP protection policies, as well as the
   Company Bar IP protection policies.  Frank opens the email.

   The policy also applies to messages forwarded by Frank and Grace
   because they contain information from Company Foo and Company Bar and
   both companies wants consistent policy enforcement on their
   information.

   After some time, Company Bar fails an audit to show they are
   complying which all the requirements for Program X. As a result,
   Company Foo updates its policies for Program X to remove Company Bar
   as an entity approved to access Program X data. Grace will no longer
   be able to access the Program X email as she can no longer satisfy
   the Program X policy requirements.

3.4.2  Regulated Email Requiring an Integrity Policy



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   Company Foo has been awarded a contract to build some equipment
   (Program X). This equipment is regulated by the National Aviation
   Authority (NAA) that has oversight of Company Foo.  The NAA requires
   strict procedures at a number of significant events for Program X
   such as in the design and maintenance of the Project X (e.g., when a
   design is complete and released to manufacturing). The sign-off
   process requires personal be suitability qualified and that the
   documentation needs to be maintained for the service life of the
   project (25 years for Program X).

   Company Foo has instigated an email based sign off procedure to
   simplify sign-off and reduce costs. It also has authored a policy for
   compliance with the NAA requirements. At the appropriate time,
   signoff email is sent to the designated program members. Recipients
   apply the NAA policy  when they reply to the sign-off request
   message.

   Frank is the lead on the Program X design team. They have a design
   which they believe can be released to the integration team. Frank
   initiates the sign-off process for the design.

   Grace is one of the sign-off design team members for Program X. She
   receives the sign-off email. Grace responds and applies the sign-off
   signature policy to the email. The policy requires Grace to
   authenticate with the required level of assurance,  present
   attributes about herself, her work effort assignments and
   professional qualifications to demonstrate compliance with the policy
   to send the message. The message is signed to indicate Grace met the
   policy.

   When Frank initiates a Program X sign-off email the system must
   ensure the following objectives:

   (a)  Frank was authenticated to the level of identity assurance
        required under the policy to initiate the sign-off process.
   (b)  Frank possessed the necessary attributes as required by policy
        to initiate the sign-off process.
   (c)  The contents of the email are accurate to the level of integrity
        assurance required by the policy.
   (d)  Frank was fully aware and intended to initiate the sign-off
        process.
   (e)  The state of Franks system was known to the level of assurance
        required under the policy to be free from agents which might
        interfere with the sign off process.
   (f)  Recipients can easily confirm over the lifetime of the design as
        required by the policy that the sign-off process met the policy
        without having to know the specifics of what the policy
        entailed.



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   The sequence of events Grace would use is as follows:

   (1)  Grace receives the sign-off request email.
   (2)  Grace replies to the email and completes the form data in the
        email to show she is approving the sign-off.
   (3)  Grace clicks the send button to send the email.
   (4)  Grace receives a sign-off confirmation dialogue before the email
        is sent where she is able to confirm her intent is to approve
        the sign-off of the component.

   Grace's system submits the decision request to send the sign-off
   email. Her system is asked to provide data about Grace, the state of
   her system and the data being authenticated. If Grace's request meets
   the policy, her system receives a signed statement that the message
   meets the policy which is attached to the email and the message
   sent.


3.5 Delegation of Access to Email
   There are a number of times when others are given access to a
   recipient's mailbox or email is forwarded to other recipients based
   on the original recipient's rules. This may be a long-standing
   relationship such as when an assistant is given access to an
   executive's mailbox. Alternatively, it may be a temporary
   relationship due to short-term needs (e.g., to cover for a
   vacation).  There are also organizational role mailboxes where the
   recipient is a role and one or more users are assigned to the role.

   Grace is going on vacation. While Grace is away, Brian will act as a
   delegate for Grace. Grace configures a mailbox rule to forward
   Program X email to Brian for the duration of her vacation. Brian is
   able to satisfy the policy requirements for the Program X email as
   outlined above and is therefore able to open the protected email sent
   to Grace. Frank does not need to take any actions to allow Brian to
   access the email.

3.6 Regulated Industry Email

   Some organizations work in areas which are intrinsically subject to
   policy such as regulatory policy, e.g., healthcare. In such
   environments the policies are often tied to the roles of the
   participants, the institution they are working at, and the subject of
   the exchange.

   Hanna is a primary care physician working for FooBar Healthcare. She
   has a patient whom she is referring to a specialist at another
   healthcare facility for further diagnosis. Ida works as a specialist
   at the Bar Hospital. Hanna needs to send the relevant patient notes,



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   test results, and comments to the specialist at Bar Hospital. Hanna
   knows she needs to comply with the confidentiality regulations and
   needs to respect her patient's consent decree for the privacy of her
   healthcare information. When Hanna sends the referral message she
   must ensure:

   (a)  Only recipients who meet the healthcare regulatory policy and
        the patients consent decree can read the email.
   (b)  The message has the appropriate level of integrity protection
        and includes the data required by recipients to establish the
        data origin of the message as required by the policies.
   (c)  The recipients authenticate with an acceptable level of
        assurance (i.e. level 3 or above).
   (d)  Recipients present attributes about themselves necessary to
        verify compliance with the policies (e.g., their professional
        qualification, professional registration, affiliated healthcare
        facility and department).
   (e)  Recipients can verify the email is from the sender (Hanna) to
        the level of assurance as defined by the message policy (i.e.,
        level 3 or above).
   (f)  Recipients can verify the email has not been tampered with to
        the level of assurance as defined by the message policy.
   (g)  Recipients are made aware that the message is a patient referral
        and contains sensitive patient data.

   The sequence of events Hanna would use is as follows:

   (1)  Hanna composes the email and adds an email address for the
        relevant department at Bar Hospital as a recipient of the
        message. She includes the patient information, test results, and
        comments in the email
   (2)  Hanna's email client allows her to select a policy which is
        appropriate for her work.
   (3)  Hanna selects the Patient Referral and Patient Consent Decree
        policies from the list of available policies.
   (4)  The email client knows the protection to apply to the email: it
        integrity-protects the message by signing with the private key
        on Hanna's smart card, then encrypts the message. It attaches
        the policy metadata to the message which contains the message
        CEK and the list of policies to apply to the message.
   (5)  Hanna clicks the "send email" button. The client signs the email
        using the private key on Hanna's smart card. The client then
        encrypts the message and sends it to the email server.

   The email is able to flow securely and seamlessly through existing
   email infrastructure to the message recipients. Ida is on the
   distribution list for the specialist department at Bar Hospital so
   receives the email from Hanna.



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   (6)  Ida sees the secure message from Hanna. Ida's client provides
        the attributes necessary to comply with the policy, which
        includes her level 3 encryption certificate.
   (7)  Once Ida has shown she passes the policy requirements, the
        message CEK is released to Ida using her level 3 encryption
        certificate.
   (8)  Ida uses the private key on her smart card to open the message.
        She sees the message is marked with both the Patient Referral
        and Patient Consent Decree policies.

3.7 Email Compliance Verification
   Verification is an essential part of compliance. Verification may be
   conducted by internal staff or external auditors. The verification
   need to confirm that the policy rules are being enforced.  Auditing
   relies on the generation of artifacts to capture information about
   events. Typically, this is done via some form of logging. A challenge
   here is that for distributed system, the set of logs which completely
   describes the transaction are scattered across many systems so
   consistency of the audit settings and correlating all the audit data
   is problematic. Another consideration is accurately capturing only
   the set of desired data, i.e., accurately targeting the set of events
   that needs to be logged

   Jerry is the compliance officer for Company Foo. He has a procedure
   for ensuring compliance for Program X. The procedure defines what to
   log and when to audit access to Program X data. Jerry has tools to
   collect the audit data and run an analysis to verify the polices are
   being followed.

   The sequence of events Jerry would use is as follows:

   (1)  Jerry configures an audit obligation for access to Program X
        data. The obligation defines the set of attributes to capture
        when Program X data is accessed. The obligation is part of the
        Program X policy. Part of the Program X policy is the set of
        PDEPs which can process policy decisions on Program X data.

   (2)  Jerry configures his audit log collection to download Program X
        audit log entries from the designated PDEPs.

   (3)  Jerry also has an audit confirmation tool which "pings" the
        PDEPs for access to Program X data. Jerry's audit log analysis
        tool looks for these pings to confirm that auditing is taking
        place as expected.

3.8  Email Pipeline Inspection

   Organizations have a huge incentive to inspect emails entering or



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   leaving the organization.  Such inspection is desired for many
   different reasons.  Inspection of mail leaving an organization is
   targeted towards making sure that it does not leak confidential
   information. It also behooves organizations to check that they are
   not a source of malicious content or spam.  Inbound mail is checked
   primarily for malicious content and phishing attempts as well as
   spam. For domains with a high volume of messages there is a strong
   need to process email with minimal overhead. Such domains may mandate
   that they be pre-authorized to process an email due to the overhead a
   per-message request to an external service would add to message
   processing.

   Company Foo has a policy to scan all inbound and outbound email to
   ensure it is free from malware. Company Foo also wants to ensure
   email is not spam. Company Foo can own their scanning servers or such
   checks may be outsourced to a third party service.  Company Foo wants
   to ensure that its policy of scanning message contents also applies
   to encrypted email.

   The ability to decrypt and check the message content for malicious
   content is highly desirable. There are a number of methods that can
   accomplish this:

   1.   When a Company Foo client requests to send a Plasma email, the
        PDEP is able to check to see if the policy allows email content
        inspection by MTA for this policy, and if it does, that Company
        Foo has an outbound email scanning, and that the scanning
        servers meet the policy requirements. It is able to pre-
        authorize the Company Foo email scanning servers to access the
        email.

   2.   The scanning MTA authenticates to the PDEP as an entity doing
        virus and malware scanning on a protected message.  If the PDEP
        has specific policy that allows for access to such a scanning
        MTA service, the appropriate decryption keys will be released
        and the server will scan the mail and take appropriate action.

   3.   The policy server is configured with information about various
        gateways (both internal and external) and has certificates for
        the known gateways.  The policy server can then return a normal
        X.509 recipient info structure (cryptographic lockbox) to the
        sender of the message for direct inclusion in the recipient info
        list of the message.  This allows normal S/MIME processing by
        the scanning MTA without the necessity to query the PDEP server
        for keys for specific messages.

   4.   If the scanning MTA server cannot gain access to the decrypted
        content using one of the two proceeding methods, it either



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        passes the encrypted mail on to the recipient(s) without
        scanning it or it rejects the mail.  This decision is based on
        local policy of the scanning MTA.  If the message is passed to
        the recipient(s), then the necessary scanning either will not be
        done, done by a downstream MTA,  or done on the recipient's
        client's system after the message has been decrypted.


3.9 Distribution List Expansion

   A distribution list (DL) is a function of an MTA that allows a user
   to send an email to a group of recipients without having to address
   all the recipients individually. The membership of the DL may be
   confidential so the sender may not know all the recipients. The DL
   may be maintained by an external organization. Since a DL is
   identified by an email address, the user may be unaware they are
   sending to a DL.

   Plasma polices may have the list of recipients as a parameter,
   therefor the fact that the message is being process by the
   distribution list means the MTA processing the message needs to
   update the policy to allow the new recipients to access the message.
   Organizations may also require inbound scanning of email and have
   therefore published keys to enable pre-authentication of the MTA by
   the sender to expedite processing. For both scenarios the DL MTA has
   to notify the Plasma server that it is adding recipients to the
   message and supply the list of new recipients. The Plasma server can
   then take appropriate action on the message token and return an
   updated token if required.

3.10 Scalable Decision Making

   Collaboration involves working with external organizations; e.g.,
   partners and suppliers. These collaborations may be short or long-
   lived, with a small or very large number of participants.
   Organizations therefore need flexibility in deployment and scaling.
   Organizations do not want to be forced into having to provide
   capacity themselves for all decision making over their data. Senders
   would be happy to delegate decisions where appropriate to partners or
   external services provided those decisions use the rules they define
   for their data. Likewise, partners would be happy to leverage their
   local decision capacity providing they don't have to duplicate rules
   of the partners, and can simply and easily use policies published by
   their partners publish. An organization may also want to use cloud
   based PDEPs where appropriate as a cost effective way to add capacity
   and to be able to respond to transient capacity fluctuations.

   See section 3.4.1 for description of the scenario.



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   The Program Managers for Program X at Companies Foo and Bar agree to
   a series of roles which are used to manage personnel and their
   assigned policy groups. The policy administrators for Company Foo and
   Bar respectively publish the roles and a policy collection for each
   role. There are rules associated with the policy collection, for
   example every roles uses the Program X policies published by Company
   Foo. Employees from Company Foo also get the Company Foo Intellectual
   Property polices for those roles, whereas employees from Company Bar
   get the Company Bar intellectual property polices for Program X.
   Company Foo has also decided to allow enforcement of Program X
   policies by decision engines in both Company Foo and Company Bar.
   Company Foo has also decided to use a cloud-based decision engine for
   Program X to allow lower cost capacity and scaling. Company Foo is
   able to add new instances of the cloud-based decision services as the
   program scales up and more uses start working on the program. Each
   decision engine dynamically discovers the policies it needs from the
   set published by Company Foo and Company Bar. Both Company Foo and
   Company Bar can add new polices to the policy collections at any time
   and they are dynamically discovered by all the policy decision
   engines.

3.11  Related Use Case Scenarios

   There are other use case scenarios which are related to the email
   cases because they would be subject to the same policy requirements.
   Email allows users to create content and transport it to a set of
   recipients.  Similar use cases to the above can be performed with
   other data formats such as documents and instant messages.  Policy is
   tied to the information so is agnostic to the underlying data format
   therefore if an organization has a policy relating to a type of
   information, then that same policy would apply to the same
   information in an email, a document, or an instant message, etc.

3.11.1.  Document Protection

   This use case scenario is very similar to 3.4 and 3.6 above.  The
   difference is that the information being generated is in the form of
   a document not an email.  It could be as part of an ad-hoc sharing or
   a regulated sharing of information.

   Frank is an employee of Company Foo. He has been assigned to Program
   X. Grace is an employee of Company Bar. She has been assigned to
   Program X. Frank creates a document for the program.  He also
   includes some Company Foo IP in the document.  When Frank creates the
   document he must ensure compliance with export control regulations
   and his corporate IP protection policies.  Frank must ensure:

   1.  Only users who meet the Program X policy or Company Foo's



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        intellectual property protection policy can open the document.

   2.  Users authenticate with an acceptable level of assurance as
        defined by the set of policies applied to the document.

   3.  Users present any other attributes about themselves necessary to
        verify compliance with the applicable policies.

   4.  Users can verify who the author was to an acceptable level of
        assurance as defined by the document policy.

   5.  Users can verify the document has not been tampered with to an
        acceptable level of assurance as defined by the document policy.

   6.  They can also tell it is a Program X document and that the
        contents can only be shared with other Program X workers.

   Frank creates a document for Program X. He includes some information
   related to Program X. Frank also includes some information which is
   Company Foo's IP.

   Franks word processor application allows him to classify the
   document. Frank classifies the document as Program X and Company Foo
   proprietary information.

   The word processor application knows the protection to apply to the
   document; it integrity-protects and encrypts the document then
   attaches the policy metadata to the document which contains the
   policies to apply to the document and the document CEK.

   The document is able to be published on a cloud-based Web portal. The
   document is protected while in transit to the portal and at rest on
   the portal.  The document is also protected on any backup or replica
   of the portal data.  Frank does not need to worry about where on the
   portal he publishes the document.  He can make the most appropriate
   choice based on the project and the document content.

   Grace sees the document on the portal and tries to open the document.
   Grace is able to prove her identity to the level required by the
   policies applied to the document and provides the requested
   attributes about herself to satisfy both the Program X export control
   and the Company Foo IP protection policies.  Grace opens the
   document.

   If Grace edits the document and includes some information which is
   Company Bar's IP she adds her company's IP protection policy
   requirements to the document.  Grace saves the updated document to
   the same location on the portal.



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   Frank sees that Grace has updated the document on the portal.  Frank
   is able to prove his identity to the level required by both the
   Company Foo and Company Bar policies and provides the requested
   attributes about himself to satisfy both the Program X export
   control, the Company Foo IP protection policies as well as the
   Company Bar IP protection policies.  Frank opens the document.

3.11.2 Instant Message Protection

   This scenario is very similar to 3.4 and 3.6 above.  The difference
   is that the information being generated is in the form of an instant
   message not an email.  It could be as part of an ad-hoc sharing or a
   regulated sharing of information.

   Frank is an employee of Company Foo. He has been assigned to Program
   X. Grace and Hank are employees of Company Bar and also have been
   assigned to Program X. Frank wants to discuss an urgent topic with
   Grace and Hank. The topic necessitates  discussion of Company Foo IP.
   Because of the urgency, Frank wants to use IM. Frank must ensure:

   (a) Only users who meet the Program X policy or Company Foo's
       intellectual property protection policy can join the IM session.

   (b) Users authenticate with an acceptable level of assurance as
       defined by the set of policies applied to the IM session.

   (c) Users present any attributes about themselves necessary to verify
       compliance with the applicable policies.

   (d) Users can verify who the IM initiator is to an acceptable level
       of assurance as defined by the session policy.

   (e) Users can verify the IM data has not been tampered with to an
       acceptable level of assurance as defined by the session policy.

   (f) They can also tell the session is a Program X  session and the
       contents can only be shared with other Program X workers.

   The sequence of events Frank would use is as follows:

   (1)  Frank initiates the IM session and includes Grace as a
        participant.
   (2)  Frank's IM client allows him to select a role which is
        appropriate for the session. Frank then selects the Program X
        and Company Foo IP policies for the session.

   The IM application knows what protection to apply to the IM session;
   it encrypts and integrity-protects the session, it attaches the



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   policy metadata to the session messages which contain the list of
   policies and the session CEK.

   The IM is able to flow securely and seamlessly through the existing
   IM infrastructure to session participants. Grace is a session
   participant so her IM application attempts to join the IM session
   with Frank. Hank is in a meeting so does not join the IM session at
   that time.

   (3)  Grace receives the IM and sees it is a secure IM from Frank.
        Grace's IM application provides the attributes necessary to
        comply with the policy which includes her level 3 encryption
        certificate.
   (4)  Once Grace has shown she passes the policy requirements, the she
        receives the IM session CEK protected by her level 3 encryption
        certificate.
   (5)  Grace uses the private key on her smart card to decrypt the
        session CEK and opens the IM session. She sees the from Frank is
        marked with both the Program X and Company Foo IP policies.
   (6)  Grace composes a response to Frank's question and hits send.
   (7)  When Hank's other meeting is finished, he sees the IM invitation
        from Frank and attempts to joins the IM session and is able to
        do so because he to meets the policy requirements and sees the
        messages from Frank and Grace.

4. Plasma Data Centric Security Model

   A common theme from these scenarios is the need to closely tie the
   information asset to the set of technical controls via the data
   owner's policies in such a way so it is possible to consistently
   apply the technical controls across a broad set of applications (not
   just email), for a broad set of users (not just those within an
   organization), and in a broad set of environments. Assumptions based
   on closed-world, enterprise security models are increasingly breaking
   down. Perimeter security continues to diminish in relevance and focus
   needs to be shifted to self-protecting data as opposed to protecting
   the machines that stores such data. The binding between the data and
   the applicable polices needs to happen as close to the data creation
   time as possible so ad-hoc trust decisions are not required.

   The delivery of the documented use cases will require the integration
   of many existing and some new protocols. In order to ensure the right
   overall direction for Plasma as each part of the work proceeds, a
   high level data model is documented here to  act as a guide. While
   this is technically informative to the developments of each
   individual component, it is normative to the work overall.

   This Data Centric Security model is based on a well-established set



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   of actors for policy enforcement used elsewhere [RFC3198] [XACML-
   core].


   Figure 1 shows the relationship between the actors.
                           ------------------
                           |                |
                           |     Policy     |
                           | Administration |
                           |     Point      |
                           |                |
                           ------------------
                                    |
   -----------------                |               -----------------
   |               |                |               |               |
   |   Policy      |                |  Read         |   Policy      |
   |  Information  |                |  Policy       |  Information  |
   |   Point       |                |               |   Point       |
   |               |                |               |               |
   -----------------                v               -----------------
        |  |                        v                       |  |
        |  |Issue          -----------------      Issue     |  |
        |  |Attributes     |               |      Attributes|  |
        |  |(BAE)          |     Policy    |      (BAE)     |  |
        |  -------------->>|    Decision   |<<---------------  |
        |                  |      and      |                   |
        |                  |  Enforcement  |                   |
        |  -------------->>|     Point     |<<-----------      |
        |  |Protect        |               |  Consume   |      |
        |  |Content        -----------------  Content   |      |
        |  |Request+                          Request+  |      |
        |  |Attributes                        Attributes|      |
        |  |(FAE)                             (FAE)     |      |
        v  |                                            v      v
        v  |                                            v      v
    -----------------                               -----------------
    |               |                               |               |
    |   Content     |           Distribute          |   Content     |
    |  Creation     |           Content             |  Consumption  |
    |  Decision     | ---------------------------->>|  Decision     |
    |  Requestor    |                               |  Requestor    |
    |               |                               |               |
    -----------------                               -----------------
  Figure 1 General Scheme for Publishing and Consuming Protected Content


   The Plasma model is applicable to any type data (email, documents,
   databases, IM, VoIP, etc.). This is to facilitate consistent policy



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   enforcement for data across multiple applications.  Another objective
   is to not require the data holder to have access to the plain text
   data in order to be able to make decision requests to the PDEP. The
   policy decision is complex so the content creation DR in Plasma just
   uses policy pointers or labels to indicate the set of policies
   applicable to content. The content consuming DR dynamically discovers
   the PDEP's that are authoritative for the decisions on protected
   content in question. The PDEP's dynamically discover the specifics of
   a policy from a PAP using the policy references. The specifics of
   policy authoring and policy decision logic modules are matters beyond
   the scope of this document. It is important to note that the actors
   in this model are logical entities and as such can be combined
   physically in different configurations.


     o The Plasma model uses references to bind the data and the policy.
     When information is created, it is encrypted and a list of policies
     that must be enforce by the PDEP is bound to the protected data.

     o The Plasma model is an Attribute-Based Access Control (ABAC)
     model where the ABAC policy is specified in terms of a set of
     attributes, their values, and their relationships. The policy may
     specify attributes about the subject, their device, or their
     environment, or attributes about a resource.

     o The ABAC policy does not require the subject provide their
     orthonym.  Subjects could be anonymous or pseudonymous. What is
     required is the presentation of a set of attributes that satisfies
     the policy.

     o The requestor can be required to bind the supplied attributes to
     the channel with the PDEP to a level of assurance as required by
     the PDEP. If the PDEP only requires low assurance, bearer tokens
     over TLS would be suitable. If the PDEP requires higher assurance,
     then the holder of key tokens over TLS would be required where the
     token key is bound to the TLS channel.

     o This model also supports Capability-Based Access Control (CBAC)
     where security tokens represent a capability to meet a policy. Once
     a subject has proven compliance with a policy, they can be issued a
     capability token. The client can subsequently  present this
     capability token in lieu of a token or tokens with the set of
     subject attributes.  The net result is that the model can
     transition to a Capability-Based Access Control because the
     capability token is an un-forgeable token of compliance with a
     policy. The token can be used with any resource tagged with the
     same policy.




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     o Plasma has a baseline of a secure transport between the DR and
     the PDEP. One of the decisions the PDEP has to make is the level of
     assurance on the release of the CEK to the subject. For example,
     the PDEP can release a clear text CEK over the secure transport to
     the DR. Alternatively, the PDEP could require the production of a
     high-assurance X.509 encryption certificate as a subject attribute
     to generate an encrypted CEK.


   For the purpose of the Plasma work, it is desirable that the DR and
   PDEP be clearly defined as separate services which may be on separate
   systems.  This allows for a generalization of the model and makes it
   less dependent on any specific deployment model, policy
   representation or implementation method. It also allows for a greater
   degree of control of the PDEP by an organization such that it is
   possible to keep all of the PDEP resources directly under it's
   control and independent of the data storage location.

   The base set of information for a Plasma client is as follows:

   o The address of one or more IdP(s) able to issue identity attributes
     to the subject

   o A means to authenticate to the IdP(s)and issue attributes to the
     subject

   o The address of zero or more AtP(s) able to issue additional
     attributes to the subject

   o The address of one or more Plasma PDEPs able to issue role tokens
     to the subject to initiate Plasma policy discovery.


   From this base set of data, the subject is able to authenticate to
   each Plasma PDEP in turn using the identity token from the IdP and
   discover the set of assigned roles. Each role has a set of policies
   which can be applied to data. A subject may be assigned to multiple
   roles and therefore has the ability to select the most appropriate
   role for the content being created. Once a role is selected, the
   subject is able to choose one or more policies from the policy
   collection for that role. Role assignment is dynamic so the role
   discovery needs to be done on a regular (but not frequent) basis.
   Policy selection during content creation can be either manual or
   automatic. A DR may have sufficient context to be able to select the
   role and policies for the subject or have some rules that facilitate
   policy selection.

   The model allows the content creation DR to discover the role



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   assignments from multiple PDEP which would allow the subject to
   access policies based on roles from within their organization and
   from any partner organization due to cross-organization
   collaboration. The PDEP's that are authoritative for the role
   assignment for a subject may be different from the PDEP that are
   authoritative for enforcement of a policy collection in question. The
   DR uses the role token to authenticate the content creation request.
   The PDEP will check that the requested list of policies for the
   information is a subset of the policies in the role token. If the set
   of policies is a subset of the policies in the role token, then it
   will issue the policy metadata token to be attached to the protected
   data.

   The policy metadata token is an signed data structure created by the
   PDEP which is bound to the protected data. It contains public policy
   metadata attributes which are used by the DR. An example of a public
   policy metadata attribute is a list of one or more URLs which
   represent the PDEPs that can make policy decisions using the policy
   metadata token. The DR can submit the decision request to any PDEP in
   the list. The policy metadata token also has a confidential payload
   containing private policy metadata attributes used by the PDEP to
   make policy decisions. An examples of a confidential policy metadata
   attribute is the list of CEKs for the protected data which would be
   released to the DR if it passes the policy checks.

   Policy rule processing and distribution is complex, so the Plasma
   model does not require policy rules to be distributed to the DR. The
   DR submits the policy metadata token as part of the decision request.
    The confidential portion of the policy metadata token contains a
   logic tree of policy references. The PDEP uses the policy references
   to discover the policy rules to apply to the request.  The logic thee
   defines the logical relationship between the polices e.g., are they
   combined via and AND clause or an OR clause. The use of policy
   references minimizes any policy maintenance issues relating to the
   protected data due to policy updates. The policy rues can be updated
   and the new rules discovered on subsequent decision requests.

   The DR and PDEP are required to carry out obligations of the policy
   such as specific encryption requirements, e.g., key size or
   algorithm, data integrity requirements, time-to-live of CEK, or
   audit record creation requirements. It is a matter for the policy on
   how to determine if the DR or PDEP is trusted to carry out the
   obligations. This could be achieved by devise type and state
   attributes.

   The PDEP makes its decisions based on the requested action from the
   DR, the policy requirements from the PAP(s), and the information from
   the PIP(s) about the subject, the subject's device, and the subject's



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   environment. The information about the subject may be exchanged
   directly between the PIP(s) and the PDEP (Back end Attribute
   Exchange) or indirectly via the DR (Front end Attribute Exchange) or
   both. The content creator can also include attributes in the policy
   metadata.

   There is no guarantee that identity and attribute providers will
   consistently use the same name to identity a specific attribute or
   attribute data. For example they may use different schemas to
   identify an email address or use localized names to describe job
   functions or roles. These kinds of values may be standardized within
   communities of interest, but not globally across all identity and
   attribute providers. Therefore it is necessary to canoicalize the
   attribute names and values before processing by the policy. The
   attribute name and value mapping is part of the policy data set,
   i.e., it is in addition to the policy processing rules.



































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    ---------------          -----------------         -----------------
    |             |          |               |         |               |
    |             |          |   Policy      |         |  Policy       |
    |  Policy     |          |  Decision and |         |  Decision and |
    | Decision    |          |  Enforcement  |         |  Enforcement  |
    |  Point      |          |   Point       |         |  Point        |
    |             |          |               |         |               |
    ---------------          -----------------         -----------------
           |                         |                         |
           |                  T      |      T                  |
           |                  TTTTTTT|TTTTTTT                  |
           V                         V                         V
           V                         V                         V
    ---------------           ---------------           ---------------
    |             |           |             |           |             |
    |  Policy     |           | Decision    |           | Decision    |
    | Enforcement |           | Requestor   |           | Requestor   |
    |  Point      |           |             |           |             |
    |             |           |             |           |             |
    ---------------           ---------------           ---------------
           |                         |                         |
    T      |     T                   |                         |
    TTTTTTT|TTTTTT                   |                         |
           V                         V                         V
           V                         V                         V
    ---------------           ---------------           ---------------
    |             |           |             |           |             |
    |  End        |           |  End        |           |  End        |
    |  User       |           |  User       |           |  User       |
    | Application |           | Application |           | Application |
    |             |           |             |           |             |
    ---------------           ---------------           ---------------
          (a)                        (b)                      (c)

   Figure 2 Options For Trusted Actors with Data.

   When drawing a line where the actors in the model are full trusted
   with the clear text data there are three possibilities (see figure
   2).

   Figure 2a shows the full trust line between the user application and
   the Policy Enforcement Point(PEP). This is the model for current
   standard access control mechanism, e.g., XACML [XACML-core]. In 2a,
   the PEP has full access to the plain text data. It makes decision
   requests to the PDP and if the decision is affirmative, allows the
   PEP to release the data to the application. To use fig 2a for secure
   email would require every MTA and MUA to be fully trusted with plain
   text data which is impossible.



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   Figure 2b shows the full trust line between the PDEP and the DR. In
   2b, the DR only has cipher text data. The data is encrypted with a
   content encryption key (CEK) and the PDEP has access to the CEK. The
   PDEP releases the CEK to the end-user application when access is
   granted so the application can recover the plain text. This mode is
   viable for secure email as it does not require the MTA to be trusted
   with the plain text data and either the MTA or MUA can act as a DR.

   In figure 2c, no actor is given full trust. When the data is
   encrypted, the CEK is encrypted for each recipient just as S/MIME
   does today. The encrypted CEKs are given to the PDEP and the PDEP
   releases the encrypted CEK when access is granted. This mode is also
   viable for secure email as the sender can use either conventional
   public key cryptography or Identity-Based Encryption[RFC5408] to
   protect the CEK for each recipient.

4.1 Plasma Client/Server Key Exchange Level of Assurance

   There are a number of mechanisms by which a client and servers can
   exchange CEKs. As a baseline, Plasma is establishing a secure
   transport between the client and server via TLS. However the client
   may be a proxy acting on behalf of the subject, therefore
   transporting a clear text CEK over the TLS transport would expose the
   key to the proxy. There also may be a proxy at the server which is
   terminating the TLS transports and forwarding the requests to another
   server which would mean a clear text CEK sent over the transport
   would be exposed to the server proxy. Policies may require a higher
   level of assurance that the CEK is not exposed to unauthorized
   principals. This requires encrypting the CEK for the subject before
   transport. This would further require the client or the server to
   provide a public key to the other party to be used to protect the CEK
   before sending it over the secure transport.

4.2 Policy Data Binding

   There are three ways to bind policy to data:-

   o By value. This is where a copy of the machine-readable rule set is
     directly associated with the data, e.g., where a file system has an
     Access Control List for the file or directory, or where a rights
     management agent embeddeds a copy of the policy expressed in a
     policy expression language in the rights-protected data. When an
     access request is made to the data, the PDEP compares the access
     request to the policy on the data itself.

   o By reference. This is where a reference to the policy is directly
     associated with the data, e.g., a URI or a URN which identifies the
     policy to be enforced or points to where the policy is published.



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     For example with S/MIME, the ESS label identifies the applicable
     policy by an OID. When an decision request is made to the data, the
     PDP finds the policy based on the identifier and then compares the
     access request to the referenced policy.

   o By inference. This is where the policy has a target description in
     terms of resource attributes the policy applies to. When an
     decision request is made, a set of attributes describing the
     resource which is the subject of the decision request is included
     in the request by a PEP. The PDP then compares the resource
     attributes to the set of target descriptions of the policies in its
     policy store to determine the set of policies to apply to the
     request. For example when an XACML policy is authored, a target
     description in terms of the attributes of the resource for the
     policy is also defined. When an XACML decision request is made, the
     PDP finds the policy set to apply to the request by matching the
     set of attributes in the request against the target description
     associated with the policies in its store. It then processes the
     decision request using the identified policy set.

   The chief strength of binding policy by value is its simplicity. The
   policy, being local to the data, can easily and quickly be read by
   the PDP. The chief weakness in binding policy by value is maintaining
   policy over time as binding by value results in the policy being
   replicated for every instance of data the policy is applied to. Many
   policies have a multi-year life span and over the course of time,
   there is a very high probability that the policy would need to be
   updated. Given the high number of copies, updating by value bound
   policy has proven to be a very costly and imperfect process both from
   an enforcement and audit perspective. This process is complicated by
   the fact that because only the result is stored and not an
   identifier, it is hard to identify the policy that has to be updated.

   The chief strength of binding by names is that once the policies are
   bound to the data, the same policies continue to be applied
   regardless of PDEP configuration or state. These polices may change
   their rules over time, but there is no doubt which policies would be
   enforced on the data. Another strength of binding policy by reference
   is it has a clear result as to the set of policies the PDEP has to
   apply. It the PDP does not have a policy, the reference allows the
   PDEP to discover the missing policy. If the PDEP is unable to access
   a policy for whatever reason, it knows to fail the decision request
   with a different error, i.e., don't know, which means the DR can
   reasonably try other PDEPs. The chief weakness in binding by name is
   adding or removing policies requires updating the policy metadata.
   Adding or removing policies has the same difficulties as maintaining
   polices by value.




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   The chief strength of binding by inference is it can often be applied
   to data without impacting the storage format providing the data
   already has rich and well defined set of metadata such as the
   structural metadata of an SQL table. It also allows new polices to be
   applied to the data without updating the metadata.  Unstructured data
   such as documents have the ability to store metadata but the
   challenge here is what metadata to capture. The nature of the
   metadata is also context specific, e.g., the policy target
   description required to match structural metadata from an SQL query
   would be different to the policy target description for matching
   content metadata for a document. The chief weakness in binding by
   inference is the reliability of the matching of the metadata to the
   policy target description. There are a number of factors which
   affects the policy matching process.

   *    The set of available metadata varies with different data types
        which makes the policy target definition more complex e.g.,
        structured data such as SQL databases have structural metadata
        whereas unstructured data such as documents have content
        metadata.
   &    There is a relationship between the metadata you need to capture
        and the polices you need to enforce. Its therefore hard to
        generalize the rules for what metadata is necessary independent
        of knowing what metadata policies require.
   *    The resultant set of policies to enforce for a decision request
        is dependent on the the PDP having a complete the set of
        policies. It is impossible  however, to detect missing policies
        based on the request. Likewise it is also impossible to detect
        if erroneous polices have been selected based on the request.
        If data moves from store to store and thereby uses a different
        PDPs. It's impossible to determine the correctness of the result
        of the policy matching process by the new PDP.

        The Plasma model is choosing to use binding by name for two
        reasons:

 1   The overarching need to consistently enforce the policies selected
     at creation time over the lifetime of the data. The typical use
     case is that the set of polices to be enforced on the data may
     change their rules over time but is the same set of policies to
     enforce over the lifetime of the data.
 2   Data in many cases is mobile and travels between users and
     organizations. Any dependency on consistency of the decision making
     entity would be difficult to enforce or verify.


4.3 Content Creation Workflow




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     The Content Creation DR bootstraps itself via the following
     sequence of events:

   (1)  The content creation DR is configured with the set PIPs and
        PDEPs it trusts.
   (2)  The content creation DR submits a request to all the trusted
        PDEPs for the set of roles it allows for the subject. The
        subject is authenticated and authorized for via attributes from
        the PIP(s). The PIP attributes can be obtained by the PDEP
        either via front-end (relayed to the PDEP from the PIP via the
        subject) or back-end (direct exchange between the PDEP and the
        PIP) processing.
   (3)  The content creation DR receives zero or more roles tokens from
        each of the PDEP. Each role token has a policy collection
        defining the set of allowed polices for that role when creating
        new content.

   the DR is then bootstrapped with a list of roles and role tokens. It
   is now ready to create content. This process would typically be
   performed as part of the application initialization process. When the
   user wants to create new content, they use the following sequence of
   events:

    (i)   The user creates the new content
    (ii)  The user selects the appropriate role for the content, then
          selects one or more policies from the policy set that are
          applicable to the content.
    (iii) The DR encrypts the content with one or more locally-generated
          CEKs
    (iv)  The DR submits a policy metadata token request to the PDEP
          together with the CEK(s), the set of required policies to be
          applied, teh role token, and the hash of the encrypted
          content. The CEK(s) in the request can be either raw key(s) or
          CEK(s) key encrypted by a KEK if the policy does not want the
          PDEP to have the ability to access the plain text data.
    (v)   The PDEP verifies the set of requested policies is a subset of
          the policy set in the role token.  It may also verify any
          other

          If ok, it generates the encrypted policy metadata which
          contains the list of policies and the CEKs. The metadata is
          encrypted by the PDEP for all the PDEPs allowed to make
          decision requests for the data (the content creation PDEP does
          not have to be in the set of PDEPS allowed to make access
          control decisions). The PDEP includes a URL all of the PDEPs
          allowed to make decision requests and the hash of the
          protected content as signed authenticated attributes in the
          policy metadata token then signs the encrypted metadata.



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    (vi)  The PDEP returns the policy metadata token to the DR
    (vii) The DR attaches the policy metadata token to the protected
          content and distributes the content.

4.4 Content Consumption Workflow

   When a user wants to open some protected content they would use the
   following workflow.

   (a)    The DR verifies the certificate in the signed policy metadata
          then determines via local policy if it wants to process the
          protected information based on the identity of the PDEP.
   (b)    The DR verifies the signature on the policy metadata token and
          the binding to the encrypted data by hashing the encrypted
          information and comparing it to the authenticated attribute in
          the policy metadata
   (c)    The DR forwards the signed policy metadata and requests a read
          token for the content from the PDEP using the address of the
          PDEP in the authenticated attributes in the policy metadata.
   (d)    The PDEP decrypts the policy metadata, de-references the
          policy pointers, and determines the set of rules to apply to
          the request based on the policy published by the PAP. The PDEP
          then determines the set of attributes it needs to evaluate the
          policy rules. The PDEP can use PIPs is has direct
          relationships with to query attributes about the subject. If
          the PDEP is missing attributes it need to process the policy,
          it returns a list of the missing attributes to the DR.
   (e)    If the DR receives a list of missing attributes from the PDEP,
          it obtains the missing attributes requested by the PDEP and
          sends them to the PDEP in a new read token request.
   (f)    Once the PDEP has a complete set of attributes, and the
          attribute values match those required under the access policy,
          the PDEP releases the CEK to the DR along with a TTL which
          defines how long the DR can use the CEK before it must discard
          the CEK and reapply for access.
   (g)    Once the DR has the CEK it decrypts the information. It caches
          the CEK until the TTL expires.


4.5 Plasma Proxy Servers

   There are two separate use cases for proxy servers in Plasma use
   cases. The forward proxy use case where the DR client needs to
   connect to a PDEP outside of its organization and the reverse proxy
   use case where the DR client outside an organization, need to connect
   to a PDEP.

   A recipient has no control over senders creating Plasma email (or any



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   other type of Plasma protected content) and sending to them.
   Malicious sender can craft harmful payloads and protect it in a
   Plasma envelope. Therefore Plasma recipients need a policy to
   determine the set of Plasma DPEP services they are willing to
   interact with. This can be a local policy i.e., the policy for the
   allowed set of PDEPs a DR client can interact. This policy would need
   to be distributed to every DR client. An alternate approach is to
   have a forward proxy manage the policy on behalf of the DR client. A
   forward proxy would eliminate the need to distribute policy by
   mediating the connection requests from the DR clients to the PDEP
   services. The forward proxy could be a server belonging to the DR
   client organization or a cloud service.

   In the no-proxy use case the DR client would connect via TLS directly
   to the URL contained in the policy metadata. The DR would need
   therefore local policy to determine whether to connect to the PDEP
   URL. If a forward proxy is preset, the DR client would connect via
   TLS to the forward proxy. The forward proxy would then connect to the
   PDEP if its policy allowed.

         Internet |         DMZ             |       Intranet
                  |                         |
                  |                         |
                  |                         |      ---------------
                  |                         |      |             |
            TLS   |                         | TLS  |  DR         |
        ----------|<------------------------|------|  Client     |
                  |                         |      |             |
           (a)    |                         |      ---------------
         no proxy |                         |
                  |                         |
                  |                         |
                  |      ---------------    |      ---------------
                  |      |             |    |      |             |
            TLS   |      |  Plasma     |    | TLS  |  DR         |
        ----------|<-----|  Forward    |<---|------|  Client     |
                  |      |  Proxy      |    |      |             |
            (b)   |      |             |    |      ---------------
          Forward |      ---------------    |
          Proxy   |                         |

                          Forward Plasma Proxy

   Since the Plasma service has sensitive cryptographic keys used to
   protect the data CEKs, it would be unwise to host those servers
   directly connected to the Internet. However, PDEPs will need to be
   Internet addressable for requests from DR clients outside the
   organization.  The simplest possible configuration would be to have a



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   passive reverse  proxy in front of the Plasma server. Since Plasma is
   using TLS, a passive proxy cannot inspect the data inside the TLS
   session. The passive proxy has therefore a limited function and would
   be only able to filter based on session characteristics e.g., Source
   IP addresses.  The Plasma protocol is a series of request-response
   messages, so an active reverse proxy can be implemented like other
   store-and-forward message based services (e.g., SMTP). The Internet
   facing proxy server would terminate the TLS connections from the
   external DRs. The active proxy can then scan submitted requests to
   ensure they are not malformed and are free from malicious content
   before relaying messages to a full PDEP server further inside the
   network for processing of the request.


         Internet |         DMZ             |       Intranet
                  |                         |
                  |                         |
                  |      ---------------    |      ---------------
                  |      |             |    |      |             |
            TLS   |      |  Passive    |    | TLS  |  Full       |
        ----------|------|-------------|----|----->|  PDEP       |
                  |      |  Reverse    |    |      |  Server     |
                  |      |  Proxy      |    |      |             |
           (a)    |      |             |    |      |             |
                  |      ---------------    |      |  TLS Keys   |
                  |                         |      |  Message    |
                  |                         |      |  Encryption |
                  |                         |      |  Keys       |
                  |                         |      |             |
                  |                         |      ---------------
                  |                         |
                  |      ---------------    |      ---------------
                  |      |             |    |      |             |
            TLS   |      |  Active     |    | TLS  |  Full       |
        ----------|----->|  Reverse    |----|----->|  PDEP       |
                  |      |  Proxy      |    |      |  Server     |
            (b)   |      |             |    |      |             |
                  |      |  TLS keys   |    |      |  TLS Keys   |
                  |      |             |    |      |  Message    |
                  |      ---------------    |      |  Encryption |
                  |                         |      |  Keys       |
                  |                         |      |             |
                  |                         |      ---------------
                  |                         |
                  |                         |
                          Reverse Plasma Proxy

4.6 Policy Types



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   Policies range from very simple to very complex. Policies have
   dependencies not only on the technical implementation of the software
   but on the range of attributes a PIP would issue to subjects. This is
   likely constrained by the physical procedures a PIP could support to
   capture and verify the information about the subject. To manage this
   range of requirements, this model uses two type types of policy.

4.6.1 Basic Policies

   Basic policies are intended to be universally usable by employing a
   small, fixed set of attributes which are available from all PIPs. For
   example, basic policies are intended to be equivalent to sending
   encrypted email with S/MIME today i.e., authenticated recipients of
   the email get access to the message.  Basic policies target scenarios
   involving consumers and small businesses who are using public PIPs
   which issue a limited set of attributes. It is expected that all
   Plasma clients and commercial IdPs would be capable of supporting
   basic policies due to the limited set of attribute set required. The
   universally available set of attributes may increases over time,
   therefore, later standards may define richer basic polices which
   leverage the expanded set of attributes types.

4.6.2 Advanced Policies

   Advanced policies are intended to be used where one or more policies
   are required on the content that require an expanded set of
   attributes from an IdP. They are intended to target more complex
   policy requirements such as content with regulated information or
   content subject to organization and contractual policies. The input
   set of attributes are defined by the policies. These attributes are,
   in theory, unbounded and can be either primordial such as date of
   birth, or derived attributes such as age, or both. In practice,
   advanced polices are constrained by the set of attributes  available
   under the IdP Trust Framework for the subjects. A data object may
   require multiple policies and any instance of multiple policies
   requires a logical relationships between the polices e.g., they can
   be AND-ed or OR-ed together. It is not expected that all Plasma
   clients support the rich set of attributes necessary for advanced
   policies.

5.  Message Protection Requirements

5.1.  General Requirements

   Confidentiality policy protected data MUST be protected from
   unauthorized disclosure, protected from unauthorized alteration and
   provide data origin authentication.




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   Integrity policy protected data MUST be integrity protected from
   unauthorized alteration and provide data origin authentication.

   Every authentication has a level of identity assurance associated
   with it depending on attributes such as the identity checks made
   about the subject and the authentication technology used by the
   subject.  The authentication of content creators and content
   consumers MUST support the multiple levels of identity assurance
   framework(see sections 3.1, 3.2, 3.3, and 3.4.)

   The specifics of every possible authentication mechanism or every
   detail about how the subject's identity was proofed by the IdP cannot
   be known to the DR and PDEP, therefore the specifics of how the
   sender or recipient achieves the required level of identity assurance
   MUST be abstracted from the PDEP and DR by use of a simple numeric
   scale, e,g., 0-n where n is linked to an identity assurance framework
   that defines the specifics of how to derive the LoA(see sections 3.1,
   3.2, 3.3, and 3.4.)

   Access policies are complex and subject to change over time.  For
   this reason, policies MUST be identified by reference rather than
   inclusion of the actual policy with the data so the policy change can
   be implemented without updating the data.(see section 3.4.1.)

   Access to the plaintext of the content MUST only be provided after
   the recipient has either provided suitable valid attributes to the
   PDEP or the PDEP finds attributes about recipient directly from a
   PIP, thus satisfying the policy as defined by the sender.(see
   sections 3.1 3.2, 3.3, 3.4.1, and 3.5.)

   The sender MUST be provided with a list of policies applicable to
   content they create and scoped to their current role, i.e., what
   tasks they are currently assigned to deliver.(see sections 3.1, 3.2,
   and 3.3.)

   The specifics of the access control policy used by the PDEP MUST be
   abstracted from both the sender and recipients DR, i.e., the DR MUST
   NOT make the access control decision or need specifics of the access
   policy requirements.(see sections 3.1, 3.2, 3.3, and 3.4.)

   A content consumer DR MUST receive authenticated attributes of the
   identity of the creator, the level of identity assurance of the
   creator, and the cryptographic fingerprint of the original content so
   that the DR can confirm who created the content and that the content
   has not been altered.(see sections 3.1, 3.2, 3.3, and 3.4)

   The key exchange between content creator and content consumer and the
   PDEP MUST support multiple levels of assurance so an appropriate



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   strength of mechanism can be selected based on the level of assurance
   required. For example, for low assurance situations this could be via
   a plan text CEK over a secure transport such as TLS.  For high
   assurance situations, the recipient MAY be required to provide a
   suitable key exchange key such as an X.509 certificate to encrypt the
   CEK.(see sections 3.3 and 3.4)

   The level of key exchange assurance requited MUST be selected by the
   sender's policy and enforced by the PDEP. (See sections 3.1, 3.2,
   3.3, and 3.4.)

   If the recipient is unable to initially comply with the sender's
   policy, if they are able to subsequently get the required credentials
   or attributes  it MUST be possible  for to retry access to the
   contnet without intervention from the content creator.

   A time-to-live (TTL) MUST be provided to content consumers when
   access is granted by the PDEP to define when the DR MUST discard the
   message CEK and submit a new access request to the PDEP. The TTL
   value MUST be based on the message policy and optional attributes
   about the content consumer and it's environment.

   The PDEP MUST be stateless for processing policy requests from
   content creators and consumers with respect to any instance of
   protected content. It MUST be possible to have multiple instances of
   a PDEP service and load balance requests across all instances of the
   service transparently to the client and not require synchronization
   of state about requests between instances of the service.

   A PDEP MUST be capable of generating audit events associated with
   access to protected content using policy defined by the PAP.

5.1.1 Email Specific General Requirements

   It MUST be possible for domains to publish keys and attributes about
   the boundary inspection agents.  This allows senders to pre-authorize
   the inspection agents of recipients for access to messages.

   It MUST be possible for boundary inspection agents to request access
   to protected messages which have not been preauthorized by the
   sender.

   It MUST be possible for MTAs to request access to protected messages
   which have not been preauthorized by the sender (see section 3.5).

5.2.  Basic Policy Requirements

   The use of a Basic policy MUST be backwards compatible with existing



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   S/MIME.

   A sender's agent MAY discover some recipients' encryption
   certificates  and create recipient info structures using the existing
   S/MIME standard (unless specifically forbidden by the selected
   policy).

   A sender's agent MAY elect to use a Basic Policy mechanism for
   recipients for whom encryption certificates cannot be discovered.

   Four Basic policies are to be defined by this work.  These Basic
   policies MUST map to the LoA of NIST 800-63-1.  This does not
   preclude other Basic policies to be defined by other groups, trust
   frameworks, or even within the context of the IETF.

   When using a Basic policy defined by this work, the sending agent
   MUST define which Basic policy is required and the list of
   rfc5322[RFC5322] recipients.

   A sender using  Basic policy MUST be able to send protected messages
   without discovering a recipient's encryption key.

   A sender using Basic policy MUST NOT require a bilateral agreement
   between sender and recipients as a prerequisite to sending the
   message.

5.2.1 Email Specific Basic Policy Requirements

   The use of Basic Policy MUST be backwards compatible with existing
   S/MIME.

   A sender's agent MAY discover some recipient's certificates and
   create recipient info structures as per the existing S/MIME standard
   and elect to use the new mechanism for recipients it cannot discover
   keys for rather than remove the recipient's without certificates.

5.3.  Advanced Policy Requirements

   A Basic policy MAY be combined with Advanced policies

   It MUST be possible to apply one or more Advanced policies to
   content.

   Where two or more policies are applied to content, the logical
   relationship between the policies MUST also be expressed e.g., are
   the policies a logical AND or a logical OR. (See section 3.3)

   An advanced policy MAY require attributes about:



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   o  The content consumer
   o  The device the content consumer is using
   o  The environment of the device that is attempting to access the
        protected content
   o The content being accessed

   Advanced policy MUST support an extensible list of obligations on the
   DR or PDEP. where use of the policy requires some specific action on
   the part of the content creator e.g. signing content with two-factor
   smart card and/or that the signature is legally binding, or the
   message needs to be verified for an extended period.(see sections 3.3
   and 3.4.)

   Advanced policies MUST support the ability to verify the content for
   an extended period as required by policy. For example policy may
   require signatures to be verifiable for a period of 10 years.

   Advanced polices NUST support the ability to resign the data to
   support the verification over the extended period.
































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6.  IANA Considerations

   This document describes the requirements for message access control.
   As such no action by IANA is necessary for this document















































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7.  Security Considerations

   Authentication by itself is not a good trust indicator for users.
   Authentication raises the level of assurance the identity is correct
   but does not address whether the identity is trustworthy or
   noteworthy to the recipient.  Authentication should be coupled with
   some form of reputation e.g. the domain is on a white list or is not
   or a black list.  Malicious actors may attempt to "legitimize" a
   message if an indication of authentication is not coupled with some
   form of reputation.

   Malicious actors could attempt to use encrypted email as a way to
   bypass existing message pipeline controls or to mine information from
   a domain.  Domain should have sufficient granularity of policy to
   handle situations where their email pipeline agents have not been
   authorized to inspect the contents.

   It must be possible for a third party to, upon correctly presenting a
   legitimate legal justification, to recover the content of a message.
   This includes the Sender's and Recipient's companies for business
   continuity purposes, as well as Law Enforcement.  If the entity
   requesting the information and the entity controlling the access are
   in different jurisdictions, then the process would be subject to some
   form of rendition.

   The use of a security label type that requires the recipient of a
   message to query a PDEP in order to obtain the contents of a message
   opens an additional method for adversaries to confirm that an email
   address does or does not exist. Additionally it allows for a new
   channel for materials to be delivered to the recipient's mail
   processor that is not checked for malware or viruses by the standard
   mail scanning methods in place.  For these reasons recipient
   processing systems need to implement the following counter-measures:

     1)  The pointer to the PDEP MUST be checked against some policy
     before attempting to query the PDEP for a policy decision. 2)  Care
     MUST be taken when processing the responses from a PDEP check that
     they are well-formed and meet local policy before using the
     responses.












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Editorial Comments


















































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Appendix A.  References

A.1.  Normative References

 [RFC2119]     Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC3198]     Westerinen et. al., "Terminology for Policy Based
               Management", November 2001.
 [RFC5035]     Schaad, J., "Enhanced Security Services (ESS) Update",
               August 2007.
 [RFC5280]     Cooper, D, et al, "Internet X.509 Public Key
               Infrastructure Certificate and Certificate Revocation
               List (CRL) Profile", RFC5280, May 2008
 [RFC5322]     Resnick, P., "Internet Message Format", RFC5322, October
               2008.
 [RFC5652]     Housley, R., "Cryptographic Message Syntax (CMS)", RFC
               5652, September 2009.
 [RFC5750]     Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
               Mail Extensions (S/MIME) Version 3.2 Certificate
               Handling", RFC 5750, January 2010.
 [RFC5751]     Ramsdell B., Turner S., "Secure/Multipurpose Internet
               Mail Extensions (S/MIME) Version 3.2 Message
               Specification", January 2010
 [SAML-core]   OASIS, Assertions and Protocols for the Security
               Assertion Markup Language (SAML) Version 2.0, March 2005
 [sp800-63-1]  NIST SP 800-63-1 "Electronic Authentication Guideline",
               December 2008

A.2.  Informative References

 [bc-iaf]      Province of British Columbia; Electronic Credential And
               Authentication Standard, version 1.0
 [kan-iaf]     Kantara Initiative; Identity Assurance Framework: 4
               Assurance Levels, version 2.0
 [lib- iaf]    Liberty Alliance; Liberty Identity Assurance Framework,
               version 1.1
 [RFC3114]     Nicolls, W., "Implementing Company Classification Policy
               with the S/MIME Security Label", RFC 3114, May 2002.
 [RFC5408]     Appenzeller, G., "Identity-Based Encryption Architecture
               and Supporting Data Structures", RFC5408, January 2009.

 [SAML-over]   OASIS, Security Assertion Markup Language (SAML) Version
               2.0 Technical Overview
 [XACML-core]  OASIS, eXtensible Access Control Markup Language (XACML)
               Version 3.0 Core Specification






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Appendix B Authors' Addresses

   Trevor Freeman

          Microsoft Corp.

          Email: trevorf@microsoft.com


   Jim Schaad

          Soaring Hawk Consulting

          Email: ietf@augustcellars.com

   Patrick Patterson

          Carillon Information Security Inc

          Email: ppatterson@carillon.ca































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Appendix C Document Change History

   Added general data model (section 4) Added regulated industry Email
   scenario (section 3.4 Split requirements into general requirements
   and Email specific requirements Cleaned up scenarios to differentiate
   requirements and workflow Fixed multiple document nits from Jim
   Schaad Need a paRAGRAPH on namespaces to deal with SAML attributes of
   different names with same semantics Don't use a proxyf5 tls offload.
   Define a proxy in arch Made changes from XACML TC to better align
   terminology Cleaned up integrity scenario Merged the two vocabulary
   sections into a single section Added LOA for key exchange Added the
   forward proxy to the architecture addressed [anchor21] comment by
   clarifying text in paragraph 1.2  Addressed [anchor22] comment by
   clarifying text in paragraph 2.4 Addresses [anchor23] comments by
   clarifying text in section 4. Addresses [anchor24] comment by
   clarifying text in section 3. Completed the scalable policy decision
   making scenario (3.10) Added Email compliance scenario (3.7)


































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