One document matched: draft-turner-caclearanceconstraints-00.txt
Network Working Group Sean Turner
Internet Draft IECA
Intended Status: Standard Track Santosh Chokhani
Orion Security Solutions
Expires: June 5, 2008 December 5, 2007
Clearance and CA Clearance Constraints Certificate Extensions
draft-turner-caclearanceconstraints-00.txt
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document defines the syntax and semantics for the Clearance and
the Certification Authority (CA) Clearance Constraints X.509
certificate extensions. The Clearance certificate extension is used
to indicate the clearance held by the subject. The CA Clearance
Constraints certificate extension values in a Trust Anchor (TA) and
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the CAs 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
3. CA Clearance Constraints Certificate Extension.................4
4. Clearance and CA Clearance Constraints 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. Basic Certificate Processing...............7
4.1.1.2.2. Preparation for Certificate i+1............8
4.1.1.2.3. Wrap-up Procedure..........................8
4.1.1.2.4. Outputs....................................9
5. Security Considerations........................................9
6. IANA Considerations...........................................10
7. References....................................................10
7.1. Normative References.....................................10
7.2. Informative References...................................10
Appendix A. ASN.1 Module.........................................11
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 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 CAs, and these
organizations may wish to indicate to relying parties which clearance
values from a particular TA or CA 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 Clearance Constraints certificate extension would be included in
the CA's certificate.
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Cross-certified domains can also make use of the CA 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 certificate [RFC3280] extensions are defined using ASN.1
[X.680, X.690].
2. Clearance Certificate Extension
The Clearance certificate extension in a certificate indicates the
clearances held by the subject. It uses the clearance attribute
syntax from Section 4.4.6 of [RFC3281] 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. A certificate MUST include either
zero or one instance of the Clearance certificate extension.
The following object identifier identifies the Clearance certificate
extension:
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 is as
follows:
Clearance ::= SEQUENCE {
policyId [0] OBJECT IDENTIFIER,
classList [1] ClassList DEFAULT {unclassified},
securityCategories [2] SET OF SecurityCategory OPTIONAL
}
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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 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 Clearance Constraints Certificate Extension
The CA 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 or
the CA. It is only meaningful in trust anchor or CA certificates. A
trust anchor or CA certificate MUST include either zero or one
instance of the CA Clearance Constraints certificate extension. The
CA Clearance Constraints certificate extension MAY be critical or
non-critical.
Absence of this certificate extension in a CA certificate or in a TA
indicates that clearance of the subject of the last certificate in
the certification path containing the CA or the TA is not constrained
by the respective CA or TA.
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The following object identifier identifies the CA Clearance
Constraints certificate extension:
id-ce-caClearanceConstraints OBJECT IDENTIFIER ::= { id-TBSL }
The ASN.1 syntax for the CA Clearance Constraints certificate
extension is as follows:
CAClearanceConstraints ::= SEQUENCE SIZE (1..MAX) OF Clearance
The syntax for CA Clearance Constraints certificate extension
contains Clearance values that the CA asserts. The sequence MUST NOT
include more than one entry with the same policyId. This constraint
is enforced during Clearance and CA Clearance Constraints Processing
described below. If more than one entry with the same policyId is
present in CAClearanceConstraints certificate extension, the
certification path is rejected.
4. Clearance and CA Clearance Constraints Processing
CA Clearance Constraints certificate extension processing determines
the effective clearance (henceforth called effective-clearance) for
the end certificate. CA 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 certificate, each
path is processed independently. The process involves two steps:
1) collecting the CA Clearance Constraints; and
2) using CA Clearance Constraints in the certification path and the
Clearance in the end certificate to determine the 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 Clearance
Constraints, if present, in trust anchor and all CA Clearance
Constraints present in intermediate certificates. Any 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 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 Clearance Constraints certificate
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extension is not present in the trust anchor, otherwise this value is
initialized to CA Clearance Constraints associated with the trust
anchor. The permitted-clearances state variable is updated each time
an intermediate certificate that contains a CA 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 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
CA 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 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].
4.1.1.1. Inputs
Trust anchor information may include the CAClearanceConstraints
structure to specify CA Clearance Constraints for the trust anchor.
The trust anchor may be constrained or unconstrained.
4.1.1.2. Initialization
Examine the trust anchor and verify that it does not contain more
than one instance of CAClearanceConstraints extension. If the trust
anchor contains more than one instance of CAClearanceConstraints
extension, set 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 extension, then the initial
value of permitted-clearances is the CAClearanceConstraints extension
from the trust anchor.
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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..
If the trust anchor does not contain a CAClearanceConstraints
extension, the permitted-clearances variable is assigned the special
value all-clearances.
4.1.1.2.1. 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 extension. If the certificate
contains more than one instance of CAClearanceConstraints extension,
set effective-clearance to an empty list, set error code to "multiple
extension instances", and exit with failure.
If the CAClearanceConstraints certificate extension is not present in
the certificate, no action is taken, and the permitted-clearances
value is unchanged.
If the CAClearanceConstraints certificate extension is present in the
certificate, set the variable temp-clearances to
CAClearanceConstraints certificate extension. Examine the 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 certificate extension is present in the
certificate and permitted-clearances contains the all-clearances
special value, then assign permitted-clearances the value of the
temp-clearances.
If the CAClearanceConstraints 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.
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- 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. Preparation for Certificate i+1
No additional action associated with the Clearance or
CAClearanceConstraints certificate extensions is taken during this
phase of certification path validation as described in section 6 of
[RFC3280].
4.1.1.2.3. 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. If the certificate contains
more than one instance of Clearance extension, set effective-
clearance to an empty list, set error code to "multiple extension
instances", and exit with failure.
If the Clearance certificate extension 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 in the end certificate. Let us say policyID in effective-
clearance is X.
If permitted-clearance is an empty list, set effective-clearance to
an empty list and exit with success.
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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. 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. Security Considerations
Certificate issuers must recognize that absence of the
CAClearanceConstraints in a CA certificate means that in terms of the
clearance, the subject CA is not constrained.
Absence of Clearance extension 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 to be sensitive, then the
Clearance or CA Clearance Constraints should only be included if the
subject's and CA's certificate can be privacy protected. Also in
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this case, distribution of trust anchors and associated CA Clearance
Constraints extension or Clearance must also be privacy protected.
6. IANA Considerations
None. Please remove this section prior to publication as an RFC.
7. References
7.1. 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 D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and
Certification Revocation List (CRL) Profile", RFC 3280,
April 2002.
[RFC3281] Farrell, S., and Housley, R., "An Internet Attribute
Certificate Profile for Authorization", RFC 3281, April
2002.
[X.680] ITU-T Recommendation X.680: 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. Informative References
[RFC3114] Nicolls, W., "Implementing Company Classification Policy
with S/MIME Security Label", RFC3114, May 2002.
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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 { id-TBSL }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- EXPORTS ALL --
IMPORTS
-- IMPORTS from RFC3281
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)
}
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 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)
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-- 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 Clearance Constraints certificate extension OID and syntax
id-ce-caClearanceConstraints OBJECT IDENTIFIER ::= { id-TBSL }
caClearanceConstraints EXTENSION ::= {
SYNTAX CAClearanceConstraints
IDENTIFIED BY id-ce-caClearanceConstraints
}
CAClearanceConstraints ::= SEQUENCE SIZE (1..MAX) OF Clearance
END
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Author's Addresses
Sean Turner
IECA, Inc.
3057 Nutley Street, Suite 106
Fairfax, VA 22031
USA
EMail: turners@ieca.com
Santosh Chokhani
Orion Security Solutions, Inc.
Email: chokhani@orionsec.com
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