wdiff draft-turner-caclearanceconstraints-00.txt draft-turner-caclearanceconstraints-01.txt

Network Working Group Sean Turner
Internet Draft IECA
Intended Status: Standard Track Santosh Chokhani
Orion Security
CygnaCom Solutions
Expires: June 5, January 14, 2009 July 14, 2008 December 5, 2007

Clearance and CA Clearance Constraints Certificate Extensions
draft-turner-caclearanceconstraints-00.txt
draft-turner-caclearanceconstraints-01.txt

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Abstract

This document defines the syntax and semantics for the Clearance
attribute and the Certification Authority (CA) Clearance Constraints extension in X.509
certificate extensions.
certificates. The Clearance certificate extension attribute is used to indicate the
clearance held by the subject. The CA Clearance attribute may appear in
the subject directory attributes extension of a public key
certificate or in the attributes field of an attribute certificate.
The Authority Clearance Constraints certificate extension values in a
Trust Anchor (TA) (TA), a CA public key certificate, and
the CAs an Attribute
Authority (AA) attribute certificate in a certification path
constrain the effective Clearance of the subject of the last
certificate in the certification path.

Table of Contents

1. Introduction...................................................2
1.1. Terminology...............................................3
1.2. ASN.1 Syntax Notation.....................................3
2. Clearance Certificate Extension................................3 Attribute............................................3
3. CA Authority Clearance Constraints Certificate Extension.................4 Extension..........4
4. Clearance and CA Authority Clearance Constraints Processing..............5 Processing.......5
4.1. Collecting Constraints....................................6
4.1.1. Certification Path Processing........................6
4.1.1.1. Inputs..........................................6
4.1.1.2. Initialization..................................6
4.1.1.2.1.
4.1.1.3. Basic Certificate Processing...............7
4.1.1.2.2. Processing....................7
4.1.1.4. Preparation for Certificate i+1............8
4.1.1.2.3. i+1.................8
4.1.1.5. Wrap-up Procedure..........................8
4.1.1.2.4. Outputs....................................9 Procedure...............................8
4.1.1.6. Outputs.........................................9
5. Security Considerations........................................9 Application of Algorithm to Attribute Certificates.............9
6. Security Considerations.......................................10
7. IANA Considerations...........................................10
7.
8. References....................................................10
7.1.
8.1. Normative References.....................................10
7.2.
8.2. Informative References...................................10 References...................................11
Appendix A. ASN.1 Module.........................................11 Module.........................................12

1. Introduction

Organizations that have implemented a security policy can issue
certificates that include an indication of the clearance values held
by the subject. The Clearance certificate extension attribute indicates the security
policy, the clearance levels held by the subject, and additional
authorization information held by the subject. This specification
makes use of the ASN.1 syntax for clearance from [RFC3281].

Some organizations have multiple TAs and/or TAs, CAs, and/or AAs and these
organizations may wish to indicate to relying parties which clearance
values from a particular TA TA, CA, or CA AA should be accepted. For
example, consider the security policies described in [RFC3114], where
a security policy has been defined for Amoco with three security
classification values (HIGHLY CONFIDENTIAL, CONFIDENTIAL, and
GENERAL). To constrain a CA for just one security classification, the
CA
Authority Clearance Constraints certificate extension would be
included in the CA's certificate.

Cross-certified domains can also make use of the CA Authority Clearance
Constraints certificate extension to indicate which clearance values
should be acceptable to relying parties.

1.1. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

1.2. ASN.1 Syntax Notation

All X.509 public key certificate [RFC3280] [RFC5280] extensions are defined
using ASN.1
[X.680, X.690]. [X.680]. All X.509 attribute certificate [RFC3281]
extensions are defined using ASN.1 [X.680].

2. Clearance Certificate Extension Attribute

The Clearance certificate extension attribute in a certificate indicates the clearances
held by the subject. It uses the clearance attribute syntax from
Section 4.4.6 of [RFC3281] [RFC3281], which is included below for convenience,
in the Subject Directory Attributes extension. The Clearance certificate extension MUST never
be marked critical. It is only meaningful if at least one of the
following key usage bits is set: digital signature, non-repudiation,
key transport, or key agreement. field. A certificate MUST include either zero or
one instance of the Clearance certificate extension. attribute.

The following object identifier identifies the Clearance attribute
(either in the subject directory attributes extension of a public key
certificate
extension: or in the Attributes field of an attribute certificate):

id-at-clearance OBJECT IDENTIFIER ::= { joint-iso-ccitt(2)
ds(5) module(1) selected-attribute-types(5) clearance(55) }

The ASN.1 syntax for the Clearance certificate extension attribute is as follows:

Clearance ::= SEQUENCE {
policyId [0] OBJECT IDENTIFIER,
classList [1] ClassList DEFAULT {unclassified},
securityCategories [2] SET OF SecurityCategory OPTIONAL
}
ClassList ::= BIT STRING {
unmarked (0),
unclassified (1),
restricted (2),
confidential (3),
secret (4),
topSecret (5)
}

SecurityCategory ::= SEQUENCE {
type [0] IMPLICIT OBJECT IDENTIFIER,
value [1] ANY DEFINED BY type
}

The fields in Clearance certificate extension take their attribute takes its meaning from Section 4.4.6 of
[RFC3281], which is repeated here for convenience:

- policyId identifies the security policy to which the clearance
relates. The policyId indicates the semantics of the classList
and securityCategory fields.

- classlist identifies the security classifications. Six basic
values are defined in bit positions 0 through 5 and more may be
defined by an organizational security policy.

- securityCategories provides additional authorization information.

If a trust anchor's public key is used directly, then the Clearance
associated with the trust anchor, if any, should be used as the
effective clearance (also defined as effective-clearance for a
certification path).

3. CA Authority Clearance Constraints Certificate Extension

The CA Authority Clearance Constraints certificate extension indicates
to the relying party what clearances should be acceptable for the
subject of the last certificate in the certification path containing
the TA TA, the CA, or the CA. AA. It is only meaningful in trust anchor or anchor, CA
certificates, or AA certificates. A trust anchor or anchor, CA certificate, or
AA certificate MUST include either zero or one instance of the CA
Authority Clearance Constraints certificate extension. The
CA Authority
Clearance Constraints certificate extension MAY be critical or
non-critical. non-
critical.

Absence of this certificate extension in a TA, in a CA certificate certificate,
or in a TA an AA certificate indicates that clearance of the subject of
the last certificate in the certification path containing the TA, the
CA or the TA AA is not constrained by the respective TA, CA or TA. AA.

The following object identifier identifies the CA Authority Clearance
Constraints certificate extension:

id-ce-caClearanceConstraints

id-ce-authorityClearanceConstraints OBJECT IDENTIFIER ::= {
id-TBSL }

The ASN.1 syntax for the CA Authority Clearance Constraints certificate
extension is as follows:

CAClearanceConstraints

AuthorityClearanceConstraints ::= SEQUENCE SIZE (1..MAX)
OF Clearance

The syntax for CA Authority Clearance Constraints certificate extension
contains Clearance values that the CA or the AA asserts. The
sequence MUST NOT include more than one entry with the same policyId.
This constraint is enforced during Clearance and CA Authority Clearance
Constraints Processing described below. If more than one entry with
the same policyId is present in CAClearanceConstraints AuthorityClearanceConstraints
certificate extension, the certification path is rejected.

4. Clearance and CA Authority Clearance Constraints Processing

Authority Clearance Constraints certificate extension processing
determines the effective clearance (henceforth called effective-clearance) effective-
clearance) for the end certificate. CA Authority Clearance Constraints
certificate extension in the TA and in each certificate up to but not
including the end certificate in a certification path impact the
effective-clearance. If there is more than one path to the end-entity end-
entity certificate, each path is processed independently. The
process involves two steps:

1) collecting the CA Authority Clearance Constraints; and

2) using CA Authority Clearance Constraints in the certification path
and the Clearance in the end certificate to determine the effective-
clearance
effective-clearance for the subject of the end certificate.

Assuming a certification path consisting of n certificates, the
effective-clearance for the subject of the end certificate is the
intersection of Clearance in the subject certificate, CA Authority
Clearance Constraints, if present, in trust anchor and all CA Authority
Clearance Constraints present in intermediate certificates. Any effective-
clearance
effective-clearance calculation algorithm that performs this
calculation and provides the same outcome as the one from the
algorithm described herein is considered compliant with the
requirements of this RFC.

When processing a certification path, CA Authority Clearance Constraints
are maintained in one state variable: permitted-clearances. When
processing begins, permitted-clearances is initialized to the special
value all-clearances if CA Authority Clearance Constraints certificate
extension is not present in the trust anchor, otherwise this value is
initialized to CA Authority Clearance Constraints associated with the
trust anchor. The permitted-clearances state variable is updated
each time an intermediate certificate that contains a CA an Authority
Clearance Constraints certificate extension in the path is processed.

When processing the end certificate, the value in the Clearance
certificate extension in the end certificate is intersected with the
permitted-clearances state variable.

The output of Clearance and CA Authority Clearance Constraint
certificate extensions processing is the effective-clearance, which
could also be an empty list; and success or failure with reason code
for failure.

4.1. Collecting Constraints

Authority Clearance Constraints are collected from the trust anchor
and the intermediate certificates in a certification path.

4.1.1. Certification Path Processing

When processing CA Authority Clearance Constraints certificate extension
for the purposes of validating Clearance in the end certificate, the
processing described in this section or an equivalent algorithm MUST
be included in the certification path validation. The processing is
presented as additions to the certification path validation algorithm
described in section 6 of [RFC3280]. [RFC5280].

4.1.1.1. Inputs

Trust anchor information may include the CAClearanceConstraints
AuthorityClearanceConstraints structure to specify CA Authority
Clearance Constraints for the trust anchor. The trust anchor may be
constrained or unconstrained.

4.1.1.2. Initialization

Examine the trust anchor information and verify that it does not
contain more than one instance of CAClearanceConstraints AuthorityClearanceConstraints
extension. If the trust anchor information contains more than one
instance of CAClearanceConstraints AuthorityClearanceConstraints extension, set effective-clearance effective-
clearance to an empty list, set error code to "multiple extension
instances", and exit with failure.

Create a state variable named permitted-clearances. If the trust
anchor contains a CAClearanceConstraints an AuthorityClearanceConstraints extension, then the
initial value of permitted-clearances is the CAClearanceConstraints
AuthorityClearanceConstraints extension from the trust anchor.

Examine the permitted-clearances for the same Policy ID appearing
more then once. If a policyID appears more than once in the
permitted-clearance state variable, set effective-clearance to an
empty list, set error code to "multiple instances of same clearance",
and exit with failure.. failure.

If the trust anchor does not contain a CAClearanceConstraints an AuthorityClearanceConstraints
extension, the permitted-clearances variable is assigned the special
value all-clearances.

4.1.1.2.1.

4.1.1.3. Basic Certificate Processing

If the certificate is the last certificate (i.e., certificate n),
skip the steps listed in this section.

Examine the certificate and verify that it does not contain more than
one instance of CAClearanceConstraints AuthorityClearanceConstraints extension. If the
certificate contains more than one instance of CAClearanceConstraints
AuthorityClearanceConstraints extension, set effective-clearance to
an empty list, set error code to "multiple extension instances", and
exit with failure.

If the CAClearanceConstraints AuthorityClearanceConstraints certificate extension is not
present in the certificate, no action is taken, and the permitted-clearances permitted-
clearances value is unchanged.

If the CAClearanceConstraints AuthorityClearanceConstraints certificate extension is present
in the certificate, set the variable temp-clearances to
CAClearanceConstraints
AuthorityClearanceConstraints certificate extension. Examine the temp-
clearances
temp-clearances for the same Policy ID appearing more then once. If
a policyID appears more than once in the temp-clearances state
variable, set effective-clearance to an empty list, set error code to
"multiple instances of same clearance", and exit with failure.

If the CAClearanceConstraints AuthorityClearanceConstraints certificate extension is present
in the certificate and permitted-clearances contains the all-clearances all-
clearances special value, then assign permitted-clearances the value
of the temp-clearances.

If the CAClearanceConstraints AuthorityClearanceConstraints certificate extension is present
in the certificate and permitted-clearances does not contain the all-
clearances special value, take the intersection of temp-clearances
and permitted-clearances by repeating the following steps for each
clearance in the permitted-clearances state variable:

- If the policyID associated with the clearance is absent in the
temp-clearances, delete the clearance structure associated with
the policyID from the permitted-clearances state variable.

- If the policyID is present in the temp-clearances:

-- For every classList bit, assign the classList bit a value of
one (1) for the policyID in permitted-clearances state
variable if the bit is one (1) in both the permitted-
clearances state variable and the temp-clearances for that
policyID; otherwise assign the bit a value of zero (0).

-- If no bits are one (1) for the classList, delete the clearance
structure associated with the policyID from the permitted-
clearances state variable and skip the next step of processing
securityCategories.

-- Calculate securityCategories intersection in accordance with
guidelines associated with the security policy represented by
the policyID.

4.1.1.2.2.

4.1.1.4. Preparation for Certificate i+1

No additional action associated with the Clearance attribute or
CAClearanceConstraints
AuthorityClearanceConstraints certificate extensions is taken during
this phase of certification path validation as described in section 6
of
[RFC3280].

4.1.1.2.3. [RFC5280].

4.1.1.5. Wrap-up Procedure

To complete the processing, perform the following steps for the last
certificate (i.e., certificate n).

Examine the certificate and verify that it does not contain more than
one instance of Clearance extension. attribute. If the certificate contains
more than one instance of Clearance extension, attribute, set effective-
clearance to an empty list, set error code to "multiple extension
instances", instances of
an attribute", and exit with failure.

If the Clearance certificate extension attribute is not present in the end certificate, set
effective-clearance to an empty list and exit with success.

Set effective-clearance to the value from the Clearance certificate
extension attribute in
the end certificate. Let us say policyID in effective-
clearance effective-clearance is
X.

If permitted-clearance is an empty list, set effective-clearance to
an empty list and exit with success.

If the permitted-clearance has special value of all-clearances, exit
with success.

If the policyID X in effective-clearance is absent from the
permitted-clearance, set effective-clearance to an empty list and
exit with success.

Assign those classList bits in effective-clearance a value of one (1)
that have a value of one (1) both in effective-clearance and in the
clearance structure in permitted-clearance associated with policyID
X. Assign all other classList bits in effective-clearance a value of
zero (0).

If none of the classList bits have a value of one (1) in effective-
clearance, set effective-clearance to an empty list and exit with
success.

Set securityCategories in effective-clearance as an intersection of
the securityCategories in the effective-clearance and
securityCategories in the permitted-clearances for policyID X as
defined by the policyID X.

Exit with Success

4.1.1.2.4.

4.1.1.6. Outputs

If certification path validation processing succeeds, effective-
clearance contains the effective clearance for the subject of the
certification path. Processing also returns success or failure
indication and reason for failure, if applicable.

5. Application of Algorithm to Attribute Certificates

The algorithm presented in Section 4 is public key certificate
centric. Its application to attribute certificates is
straightforward as described below.

If the current [RFC3281] constraint of not having chain of attribute
certificate chain is observed, the AC Issuer (i.e., AA) Authority
Clearance Constraints is used as the TA Authority Clearance
Constraints for the initialization step described in Section 4.1.1.2.
Since there is no intermediate steps, sections 4.1.1.3. and 4.1.1.4.
will not be executed.

If the current [RFC3281] constraint of not having chain of attribute
certificate chain is removed, the Source of Authority in the
Attribute Certificate chain becomes the TA for the purpose of Section
4.

6. Security Considerations

Certificate issuers must recognize that absence of the
CAClearanceConstraints
AuthorityClearanceConstraints in a CA or AA certificate means that in
terms of the clearance, the subject CA Authority is not constrained.

Absence of Clearance extension attribute in a certificate means that the
subject has not been assigned any clearance.

If there is no Clearance associated with a TA, it means that the TA
has not been assigned any clearance.

If the local security policy considers the clearance held by a
subject or those supported by a CA or AA to be sensitive, then the
Clearance attribute or CA Authority Clearance Constraints should only be
included if the subject's and CA's Authority's certificate can be privacy
protected. Also in this case, distribution of trust anchors and
associated CA Authority Clearance Constraints extension or Clearance
must also be privacy protected.

7. IANA Considerations

None. Please remove this section prior to publication as an RFC.

8. References

7.1.

8.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC3280] Housley, R., Polk, W., Ford, W., and

[RFC5280] Cooper, D. Solo, et. al., "Internet X.509 Public Key
Infrastructure Certificate and Certification Revocation
List (CRL) Profile", RFC 3280,
April 2002. 5280, May 2008.

[RFC3281] Farrell, S., and Housley, R., "An Internet Attribute
Certificate Profile for Authorization", RFC 3281, April
2002.

[X.680] ITU-T Recommendation X.680: X.680 (1997) | ISO/IEC 8824-1:1997.
Information Technology - Abstract Syntax Notation One, 1997.

[X.690] ITU-T Recommendation X.690 Information Technology - ASN.1
encoding rules: Specification of Basic Encoding Rules
(BER), Canonical Encoding Rules (CER) and Distinguished
Encoding Rules (DER), 1997.

7.2. One.

8.2. Informative References

[RFC3114] Nicolls, W., "Implementing Company Classification Policy
with S/MIME Security Label", RFC3114, May 2002.

Appendix A. ASN.1 Module

This appendix provides the normative ASN.1 definitions for
the structures described in this specification using ASN.1 as defined
in X.680.

Clearance-CAClearanceConstraints93

Clearance-AuthorityClearanceConstraints93 { id-TBSL }

DEFINITIONS IMPLICIT TAGS ::=

BEGIN

-- EXPORTS ALL --

IMPORTS

-- IMPORTS from RFC3281 [RFC3281]

id-at-clearance, Clearance
FROM PKIXAttributeCertificate
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-attribute-cert(12)
}

-- IMPORTS from [RFC5280]

EXTENSION
FROM PKIX1Explicit93
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-pkix1-explicit-93(3)
}
;

-- Clearance certificate extension attribute OID and syntax

clearance EXTENSION ::= {
SYNTAX Clearance
IDENTIFIED BY id-at-clearance
}

-- The following is a '93 version for clearance.
-- It is included for convenience.

-- id-at-clearance OBJECT IDENTIFIER ::=
-- { joint-iso-ccitt(2) ds(5) module(1) selected-attribute-types(5)
-- clearance (55)
-- }
-- Clearance ::= SEQUENCE {
-- policyId [0] OBJECT IDENTIFIER,
-- classList [1] ClassList DEFAULT {unclassified},
-- securityCategories [2] SET OF SecurityCategory OPTIONAL
-- }

-- ClassList ::= BIT STRING {
-- unmarked (0),
-- unclassified (1),
-- restricted (2),
-- confidential (3),
-- secret (4),
-- topSecret (5)
-- }

-- SECURITY-CATEGORY ::= TYPE-IDENTIFIER

-- SecurityCategory ::= SEQUENCE {
-- type [0]
-- IMPLICIT TYPE-IDENTIFIER.&id({SupportedSecurityCategories}),
-- value [1]
-- TYPE-IDENTIFIER.&Type({SupportedSecurityCategories}{@type})
-- }

-- CA Authority Clearance Constraints certificate extension OID
-- and syntax

id-ce-caClearanceConstraints

id-ce-AuthorityClearanceConstraints OBJECT IDENTIFIER ::= { id-TBSL }

caClearanceConstraints

AuthorityClearanceConstraints EXTENSION ::= {
SYNTAX CAClearanceConstraints AuthorityClearanceConstraints
IDENTIFIED BY id-ce-caClearanceConstraints id-ce-AuthorityClearanceConstraints
}
CAClearanceConstraints

AuthorityClearanceConstraints ::= SEQUENCE SIZE (1..MAX) OF Clearance

END

Author's Addresses

Sean Turner

IECA, Inc.
3057 Nutley Street, Suite 106
Fairfax, VA 22031
USA

EMail: turners@ieca.com

Santosh Chokhani
Orion Security
CygnaCom Solutions, Inc.

Email: chokhani@orionsec.com schokhani@ocygnacom.com

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