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S/MIME Working Group                                           Weston Nicolls
INTERNET-DRAFT                                          Telenisus Corporation
Expires July, 2001                                               January 2001


                  Implementing Company Classification Policy
                        with the S/MIME Security Label
                      <draft-ietf-smime-seclabel-03.txt>

Status of this memo

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of [RFC2026].

Internet-Drafts are working documents of the Internet Engineering Task
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Copyright (C) The Internet Society (2001). All Rights Reserved.

1.   Introduction

This document discusses how company security policy for data classification
can be mapped to the S/MIME security label.  Actual policies from 3 companies
are used to provide worked examples.

Security labels are an optional security service for S/MIME. A security label
is a set of security information regarding the sensitivity of the content
that is protected by S/MIME encapsulation. A security label can be included
in the signed attributes of any SignedData object.  A security label attribute
may be included in either the inner signature, outer signature, or both.
The syntax and processing rules for security labels are described in [ESS].

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 [MUSTSHOULD].

This draft is being discussed on the 'ietf-smime' mailing list.  To join the
list, send a message to <ietf-smime-request@imc.org> with the single word
'subscribe' in the body of the message.  Also, there is a Web site for the
mailing list at <http://www.imc.org/ietf-smime>.

1.1 Information Classification Policies

Information is an asset, but not all information has the same value for a
business. Not all information needs to be protected as strongly as other
information.

Research and development plans, marketing strategies and manufacturing quality
specifications developed and used by a company provide competitive advantage.
This type of information needs stronger protective measures than other
information, which if disclosed or modified, would cause moderate to severe
damage to the company.

Other types of information such as internal organization charts, employee lists
and policies may need little and no protective measures based on value the
organization places on it.

A corporate information classification policy defines how its information assets
are to be protected.  It provides guidance to employees on how to classify
information assets.  It defines how to label and protect an asset based on its
classification and state (e.g. facsimile, electronic transfer, storage,
shipping, etc.).

1.2 Access Control and Security Labels

"Access control" is a means of enforcing authorizations. There are a variety of
access control methods that are based on different types of policies and rely on
different security mechanisms.

-  Rule based access control is based on policies that can be algorithmically
expressed.

-  Identity based access control is based on a policy which applies explicitly
to an individual person or host entity, or to a defined group of such entities.
Once identity has been authenticated, if the identity is verified to be on the
access list, then access is granted.

-  Rank base access control is based on a policy of hierarchical positions in an
organization.  It is based on who you are in the company structure. A rank-based
policy would define what information that the position of Partner or Senior
Consultant could access.

-  Role based access control is based on a policy of roles in an organization.
It may or may not be hierarchical.  It is based on who you are in the company.
The role-based policy would define what information that the role of Database
Administrator, Network Administrator, Mailroom Clerk or Purchaser could access.

Rule, rank and role-based access control methods can rely on a security label as
the security mechanism to convey the sensitivity or classification of the
information.  When processing an S/MIME encapsulated message, the sensitivity
information in the message's security label can be compared with the recipient's
authorizations to determine if the recipient is allowed to access the protected
content.

An S/MIME security label may be included as a signed attribute in the inner
(or only) signature or the outer signature.  In the case of a triple-wrapped
message as defined in RFC 2634, the inner signature would be used for access
control decisions related to the plaintext original content, while the outer
signature would be used for access control decisions related to the encrypted
message.

1.3 User Authorizations

Users need to be granted authorizations to access information that has been
classified by an authority.  The sending and receiving agents need to be able to
securely determine the user's authorizations for access control processing.

[X.509] and the Internet profile for X.509 certificates [CERTCRL] do not define
the means to represent and convey authorizations in a certificate.

[X.501] defines how to represent authorization in the form of a clearance
attribute.  The clearance attribute identifies the security policy in force to
which a list of possible classifications and security categories relates.

[X.501] also notes two means for binding the clearance to a named entity: an
Attribute Certificate and a Certificate extension field (e.g., within the
subjectDirectoryAttribute extension).

[AC509] defines a profile of X.509 Attribute Certificate (AC) suitable for use
with authorization information within Internet Protocols. One of the defined
attributes is Clearance, which carries clearance (security labeling) information
about the AC owner.  The syntax for Clearance is imported from [X.501].

2. Developed Examples

2.1 Classification Policies

The following describes the information classification policies in effect at 3
companies.

2.1.1 Amoco Corporation

The description for the Amoco information classification policy was taken from
the Amoco Computer Security Guidelines.  Amoco classifies its information assets
based on confidentiality and integrity and defines 3 hierarchical
classifications for each.  The confidentiality and integrity polices are
independent, so either or both may be applied to the information.  Amoco also
defines an availability classification for time critical information.

HIGHLY CONFIDENTIAL - Information whose unauthorized disclosure will cause the
company severe financial, legal or reputation damage. Examples:  Certain
acquisitions, bid economics, negotiation strategies.

CONFIDENTIAL - Information whose unauthorized disclosure may cause the company
financial, legal, or reputation damage. Examples:  Employee Personnel & Payroll
Files, some interpreted Exploration Data.

GENERAL - Information that, because of its personal, technical, or business
sensitivity is restricted for use within the company. Unless otherwise
classified, all information within Amoco is in this category.

MAXIMUM - Information whose unauthorized modification and destruction will cause
the company severe financial, legal, or reputation damage.

MEDIUM - Information whose unauthorized modification and destruction may cause
the company financial, legal, or reputation damage. Examples: Electronic Funds,
Transfer, Payroll, and Commercial Checks

MINIMUM - Although an error in this data would be of minimal consequence, this
is still important company information and therefore will require some minimal
controls to ensure a minimal level of assurance that the integrity of the data
is maintained. This applies to all data that is not placed in one of the above
classifications. Examples: Lease Production Data, Expense Data, Financial Data,
and Exploration Data.

CRITICAL - It is important to assess the availability requirements of data,
applications and systems. A business decision will be required to determine the
length of unavailability that can be tolerated prior to expending additional
resources to ensure the information availability that is required. Information
should be labeled "CRITICAL" if it is determined that special procedures should
be used to ensure its availability.

2.1.2 Caterpillar, Inc.

The description for the Caterpillar information classification policy is taken
from the Caterpillar Information Protection Guidelines.  Caterpillar classifies
its information assets based on confidentiality and defines 4 hierarchical
classifications.

Caterpillar Confidential Red - Provides a significant competitive advantage.
Disclosure would cause severe damage to operations. Relates to or describes a
long-term strategy or critical business plans. Disclosure would cause regulatory
or contractual liability. Disclosure would cause severe damage to our reputation
or the public image. Disclosure would cause a severe loss of market share or the
ability to be first to market. Disclosure would cause a loss of an important
customer, shareholder, or business partner. Disclosure would cause a long-term
or severe drop in stock value. Strong likelihood somebody is seeking to acquire
this information.

Caterpillar Confidential Yellow - Provides a competitive advantage. Disclosure
could cause moderate damage to the company or an individual. Relates to or
describes an important part of the operational direction of the company over
time. Important technical or financial aspects of a product line or a business
unit. Disclosure could cause a loss of Customer or Shareholder confidence.
Disclosure could cause a temporary drop in stock value. A likelihood that
somebody could seek to acquire this information.

Caterpillar Confidential Green - Might provide a business advantage over those
who do not have access to the same information. Might be useful to a competitor.
Not easily identifiable by inspection of a product. Not generally known outside
the company or available from public sources. Generally available internally.
Little competitive interest.

Caterpillar Public - Would not provide a business or competitive advantage.
Routinely made available to interested members of the General Public.  Little or
no competitive interest.

2.1.3 Whirlpool Corporation

The description for the Whirlpool information classification policy is taken
from the Whirlpool Information Protection Policy.  Whirlpool classifies its
information assets based on confidentiality and defines 2 hierarchical
classifications.  The policy states that:

"All information generated by or for Whirlpool, in whatever form, written,
verbal, or electronic, is to be treated as WHIRLPOOL INTERNAL or WHIRLPOOL
CONFIDENTIAL.  Classification of information in either category depends on its
value, the impact of unauthorized disclosure, legal requirements, and the manner
in which it needs to be used by the company.  Some WHIRLPOOL INTERNAL
information may be authorized for public release."

WHIRLPOOL CONFIDENTIAL - A subset of Whirlpool Internal information, the
unauthorized disclosure or compromise of which would likely have an adverse
impact on the company's competitive position, tarnish its reputation, or
embarrass an individual.  Examples: Customer, financial, pricing, or personnel
data; merger/acquisition, product, or marketing plans; new product designs,
proprietary processes and systems.

WHIRLPOOL INTERNAL - All forms of proprietary information originated or owned by
Whirlpool, or entrusted to it by others.  Examples: Organization charts,
policies, procedures, phone directories, some types of training materials.

WHIRLPOOL PUBLIC - Information officially released by Whirlpool for widespread
public disclosure. Example: Press releases, public marketing materials,
employment advertising, annual reports, product brochures, the public web site,
etc.

The policy also states that privacy markings are allowable. Specifically:

For WHIRLPOOL INTERNAL, additional markings or caveats are optional at the
discretion of the information owner.

For WHIRLPOOL CONFIDENTIAL, add additional marking or caveats as necessary to
comply with regulatory or heightened security requirements.  Examples:  MAKE NO
COPIES, THIRD PARTY CONFIDENTIAL, ATTORNEY-CLIENT PRIVILEGED DOCUMENT,
DISTRIBUTION LIMITED TO ____, COVERED BY A NON-ANALYSIS AGREEMENT.

2.2 S/MIME Classification Label Organizational Examples

[ESS] defines the ESSSecurityLabel syntax and processing rules.  This section
builds upon those definitions to define detailed example policies.

2.2.1 Security Label Components

The examples are detailed using the various components of the eSSSecurity Label
syntax.

2.2.1.1 Security Policy Identifier

A security policy is a set of criteria for the provision of security services.
The eSSSecurityLabel security-policy-identifier is used to identify the security
policy in force to which the security label relates. It indicates the semantics
of the other security label components.

For the example policies, the following security policy object identifiers are
defined:

-- S/MIME Working Group Object Identifier Registry
id-smime OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549)
                                        pkcs(1) pkcs-9(9) 16 }

-- S/MIME Test Security Policy Arc
id-tsp  OBJECT IDENTIFIER ::= { id-smime 7 }

-- Test Security Policies
id-tsp-TEST-Amoco          OBJECT IDENTIFIER ::= { id-tsp 1 }
id-tsp-TEST-Caterpillar    OBJECT IDENTIFIER ::= { id-tsp 2 }
id-tsp-TEST-Whirlpool      OBJECT IDENTIFIER ::= { id-tsp 3 }

2.2.1.2 Security Classification

The security classification values and meanings are defined by the governing
company policies. The security-classification values defined are hierarchical
and do not use integers 0 through 5.

Amoco-SecurityClassification ::= INTEGER {
  amoco-general (6),
  amoco-confidential (7),
  amoco-highly-confidential (8) }

Caterpillar-SecurityClassification ::= INTEGER {
  caterpillar-public (6),
  caterpillar-green (7),
  caterpillar-yellow (8),
  caterpillar-red (9) }

Whirlpool-SecurityClassification ::= INTEGER {
  whirlpool-public (6),
  whirlpool-internal (7),
  whirlpool-confidential (8) }

2.2.1.3 Privacy Mark

Privacy marks are specified the Whirlpool policy. The policy provides examples
of possible markings but others can be defined by users as necessary (though no
guidance is given).  The Whirlpool policy provides the following examples:
MAKE NO COPIES, THIRD PARTY CONFIDENTIAL, ATTORNEY-CLIENT PRIVILEGED DOCUMENT,
DISTRIBUTION LIMITED TO ____, and COVERED BY A NON-ANALYSIS AGREEMENT.

The Amoco policy does not identify any privacy marks but the classification
labels defined for availability and integrity would be most appropriately
displayed here.  The CRITICAL, MAXIMUM, MEDIUM, and MINIMUM labels are examples
of information classifications that are not used for access control.

In general, the privacy marks should provide brief but clear direction to the
user on how to handle the information.

2.2.1.4 Security Categories

Security categories or caveats are not specified in any of the sample policies.
However, they are used in at least 2 of the companies.  Though the security
categories are not defined formally in their security policies, once locally
defined they are formal and are to be enforced. The security categories are
defined when necessary to provide identifiable proprietary information more
granular access control.  A category can be based organizationally or by project
(i.e., Legal Only or Project Vallor).

2.2.1.4.1 Syntax

Security categories are represented in the RFC 2634 ESSSecurityLabel
(to specify the sensitivity of labeled data) and X.501 Clearance attribute
(to specify an entity's authorizations) using the following syntax.

SecurityCategories ::= SET SIZE (1..ub-security-categories) OF SecurityCategory

ub-security-categories INTEGER ::= 64

SecurityCategory ::= SEQUENCE {
  type  [0] OBJECT IDENTIFIER
  value [1] ANY DEFINED BY type -- defined by type

One example of a SecurityCategory syntax is SecurityCategoryValues, as follows.

When id-securityCategoryValues is present in the SecurityCategory type field,
then the SecurityCategory value field could take the form of:

SecurityCategoryValues ::= SEQUENCE OF UTF8String

2.2.1.4.2 Use

An organization will define a securityCategoryType OID representing the
syntax for representing a security category value within their security policy.

For the example security category syntax, a UTF8String is used to convey the
security category value that applies to the labeled message. Access MUST be
restricted to only those entities who are authorized to access every
SecurityCategoryValue.  Access is authorized if the ESSSecurity Label
SecurityCategoryValue EXACTLY matches the Clearance SecurityCategoryValue.

2.2.2 Attribute Owner Clearance

The security clearance and category authorizations for the user are defined in
the clearance attribute.

2.2.2.1 Amoco User

Clearance:
  policyId:  1 2 840 113549 1 9 16 7 1
  classList:  amoco-general              (6),
              amoco-confidential         (7),
              amoco-highly confidential  (8),

2.2.2.2 Caterpillar User

Clearance:
  policyId:  1 2 840 113549 1 9 16 7 2
  classList:  caterpillar-public              (6),
              caterpillar-confidential greeen (7),
              caterpillar-confidential yellow (8),
              caterpillar-confidential red    (9)

2.2.2.3 Whirlpool User

Clearance:
  policyId:  1 2 840 113549 1 9 16 7 3
  classList:  whirlpool-public        (6),
              whirlpool-internal      (7),
              whirlpool-confidential  (8),

2.2.3 Security Category Example

This section includes an example RFC 2634 ESSSecurityLabel including the example
Security Category syntax.  This section also includes example X.501
Clearance attributes.  One of the example Clearance attributes includes a
set of authorizations that pass the access control check for the example
ESSSecurityLabel.  The other example Clearance attributes each include a set
of authorizations that fail the access control check for the example
ESSSecurityLabel.

These examples use the id-tsp-TEST-Whirlpool OID defined
in section 2.2.1.1.  Assume that the security policy identified
by id-tsp-TEST-Whirlpool defines one securityCategoryType OIDs as follows:

  id-tsp-TEST-Whirlpool-Categories OBJECT IDENTIFIER ::= { id-tsp 4 }

Example ESSSecurityLabel:
 security-policy-identifier: id-tsp-3
 security-classification: 8
 privacy-mark: ATTORNEY-CLIENT PRIVILEGED INFORMATION
 security-categories: SEQUENCE OF SecurityCategory

   SecurityCategory #1
     type:  id-tsp-4
     value:  LAW DEPARTMENT USE ONLY

Example Clearance Attribute #1 (passes access control check):

Clearance:
  policyId: id-tsp-3
  classList BIT STRING: Bits 6, 7, 8 are set to TRUE
  securityCategories: SEQUENCE OF SecurityCategory

   SecurityCategory #1
     type:  id-tsp-4
     value:  LAW DEPARTMENT USE ONLY

Example Clearance Attribute #2 (fails access control check because
SecurityCategoryValues do not match):

Clearance:
  policyId: id-tsp-3
  classList BIT STRING: Bits 6, 7, 8 are set to TRUE
  securityCategories: SEQUENCE OF SecurityCategory

   SecurityCategory #1:
     type:  id-tsp-4
     value:  HUMAN RESOURCES USE ONLY

2.2.4 Additional ESSSecurityLabel Processing Guidance

An implementation issue can be the mapping of the security label values to
displayable characters.  This is an issue for users who want to develop and
retire their own classifications and categories a regular basis and when the
values are encoded in non-human readable form.  Applications
should provide a means for the enterprise to manage these changes.  The practice
of hard coding the mapping into the applications is discouraged.

This issue is viewed as local issue for the application vendor, as the solution
does not need to be interoperable between vendors.

An approach is the use of a Security Policy Information File (SPIF)[ ISO15816].
A SPIF is a construct that conveys domain-specific security policy information.
It is a signed object to protect it from unauthorized changes and to
authenticate the source of the policy information.  It contains critical display
information such as the text string for security classifications and security
categories to be displayed to the user, as well as additional security policy
information.

Another implementation issue can be obtaining the recipient's certificate when
sending a signed-only message with a security label. Normally the recipient's
certificate is only needed when sending an encrypted message. Applications will
need to be able to retrieve the recipient's certificate so that the recipient's
clearance information is available for the access control check.

3. Security Considerations

All security considerations from [CMS] and [ESS] apply to applications that use
procedures described in this document.

A. References

[AC509] Farrell, S., Housley, R., "An Internet Attribute Certificate Profile for
Authorization", draft-ietf-pkix-ac509prof-05.txt.

[CMS] Housley, R., "Cryptographic Message Syntax", RFC 2630.

[ESS] Hoffman, P., Editor, "Enhanced Security Services for S/MIME", RFC 2634.

[MUSTSHOULD] Bradner, S., "Key Words for Use in RFCs to Indicate Requirement
Levels", RFC 2119.

[X.501] "ITU-T Recommendation X.501: Information Technology - Open Systems
Interconnection - The Directory: Models", 1993.

[X.509] "ITU-T Recommendation X.509 (1997 E): Information
Technology - Open Systems Interconnection - The Directory: Authentication
Framework", June 1997.

[ISO15816] "Information Technology - Security Techniques - Security Information
Objects for Access Control", ISO/IEC FDIS 15816:2000.

B. Acknowledgements

I would like to thank Russ Housley for helping me through the process of
developing this document.  I would like to thank John Pawling for his technical
assistance and guidance.  I would also like to thank the good people at Amoco
(bp), Caterpillar and Whirlpool who allowed me to use their policies as the
real examples that make this document possible.

C. Author's Address

Weston Nicolls
Telenisus Corporation (formerly with Ernst & Young LLP)
1701 Golf Rd
Tower 3, Suite 600
Rolling Meadows, IL 60008
(847) 871-5086
wnicolls@telenisus.com


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