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IETF RFC 5913
Clearance Attribute and Authority Clearance Constraints Certificate Extension
Last modified on Saturday, June 5th, 2010
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Internet Engineering Task Force (IETF) S. Turner
Request for Comments: 5913 IECA
Category: Standards Track S. Chokhani
ISSN: 2070-1721 Cygnacom Solutions
June 2010
Clearance Attribute and Authority Clearance Constraints
Certificate Extension
 Abstract
This document defines the syntax and semantics for the Clearance
attribute and the Authority Clearance Constraints extension in X.509
certificates. The Clearance attribute is used to indicate the
clearance held by the subject. The 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), in Certification Authority (CA) public key
certificates, and in an Attribute Authority (AA) public key
certificate in a certification path for a given subject constrain the
effective Clearance of the subject.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/RFC 5913.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
Turner & Chokhani Standards Track PAGE 1 
RFC 5913 Clearance and Authority Clearance Constraints June 2010
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................3
1.1. Terminology ................................................4
1.2. ASN.1 Syntax Notation ......................................4
2. Clearance Attribute .............................................4
3. Authority Clearance Constraints Certificate Extension ...........5
4. Processing Clearance and Authority Clearance Constraints
in a PKC ........................................................6
4.1. Collecting Constraints .....................................7
4.1.1. Certification Path Processing .......................7
4.1.1.1. Inputs .....................................8
4.1.1.2. Initialization .............................8
4.1.1.3. Basic Certificate Processing ...............8
4.1.1.4. Preparation for Certificate i+1 ............9
4.1.1.5. Wrap-up Procedure ..........................9
4.1.1.5.1. Wrap Up Clearance ...............9
4.1.1.6. Outputs ...................................10
5. Clearance and Authority Clearance Constraints
Processing in AC ...............................................10
5.1. Collecting Constraints ....................................11
5.1.1. Certification Path Processing ......................11
5.1.1.1. Inputs ....................................11
5.1.1.2. Initialization ............................11
5.1.1.3. Basic PKC Processing ......................12
5.1.1.4. Preparation for Certificate i+1 ...........12
5.1.1.5. Wrap-up Procedure .........................12
5.1.1.5.1. Wrap Up Clearance ..............12
5.1.1.6. Outputs ...................................12
6. Computing the Intersection of permitted-clearances and
Authority Clearance Constraints Extension ......................12
7. Computing the Intersection of securityCategories ...............13
8. Recommended securityCategories .................................15
9. Security Considerations ........................................15
10. References ....................................................16
10.1. Normative References .....................................16
10.2. Informative References ...................................16
Appendix A. ASN.1 Module ..........................................17
Acknowledgments ...................................................19
Turner & Chokhani Standards Track PAGE 2
RFC 5913 Clearance and Authority Clearance Constraints June 2010
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 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 [RFC 5912].
The Clearance attribute may be placed in the subject directory
attributes extension of a Public Key Certificate (PKC) or may be
placed in a separate attribute certificate (AC).
The placement of the Clearance attribute in PKCs is suitable 1) when
the clearance information is relatively static and can be verified as
part of the PKC issuance process (e.g., using local databases) or 2)
when the credentials such as PKCs need to be revoked when the
clearance information changes. The Clearance attribute may also be
included to simplify the infrastructure, to reduce the infrastructure
design cost, or to reduce the infrastructure operations cost. An
example of placement of the Clearance attribute in PKCs in
operational Public Key Infrastructure (PKI) is the Defense Messaging
Service. An example of placement of attributes in PKCs is Qualified
Certificates [RFC 3739].
The placement of Clearance attributes in ACs is desirable when the
clearance information is relatively dynamic and changes in the
clearance information do not require revocation of credentials such
as PKCs, or the clearance information cannot be verified as part of
the PKC issuance process.
Since [RFC 5755] does not permit a chain of ACs, the Authority
Clearance Constraints extension may only appear in the PKCs of a
Certification Authority (CA) or Attribute Authority (AA). The
Authority Clearance Constraints extension may also appear in a trust
anchor (TA) or may be associated with a TA.
Some organizations have multiple TAs, CAs, and/or AAs, and these
organizations may wish to indicate to relying parties which clearance
values from a particular TA, CA, or AA should be accepted. For
example, consider the security policies described in [RFC 3114], 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 Authority Clearance Constraints certificate extension would be
included in the CA's PKC.
Turner & Chokhani Standards Track PAGE 3
RFC 5913 Clearance and Authority Clearance Constraints June 2010
Cross-certified domains can also make use of the Authority Clearance
Constraints certificate extension to indicate which clearance values
should be acceptable to relying parties.
This document augments the certification path validation rules for
PKCs (in [RFC 5280]) and ACs (in [RFC 5755]).
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 [RFC 2119].
1.2. ASN.1 Syntax Notation
All X.509 PKC [RFC 5280] extensions are defined using ASN.1 [X.680].
All X.509 AC [RFC 5755] extensions are defined using ASN.1 [X.680].
Note that [X.680] is the 2002 version of ASN.1, which is the most
recent version with freeware compiler support.
2. Clearance Attribute
The Clearance attribute in a certificate indicates the clearances
held by the subject. It uses the clearance attribute syntax, whose
semantics are defined in [RFC 5755], in the Attributes field. A
certificate MUST include either zero or one instance of the Clearance
attribute. If the Clearance attribute is present, it MUST contain a
single value.
The following object identifier identifies the Clearance attribute
(either in the subject directory attributes extension of a PKC or in
the Attributes field of an AC):
id-at-clearance OBJECT IDENTIFIER ::= { joint-iso-ccitt(2)
ds(5) attributeTypes(4) clearance(55) }
The ASN.1 syntax for the Clearance attribute is defined in [RFC 5912]
and that RFC provides the normative definition. The ASN.1 syntax for
Clearance attribute is as follows:
Clearance ::= SEQUENCE {
policyId OBJECT IDENTIFIER,
classList ClassList DEFAULT {unclassified},
securityCategories SET OF SecurityCategory
{{ SupportedSecurityCategories }} OPTIONAL
}
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RFC 5913 Clearance and Authority Clearance Constraints June 2010
ClassList ::= BIT STRING {
unmarked (0),
unclassified (1),
restricted (2),
confidential (3),
secret (4),
topSecret (5)
}
SECURITY-CATEGORY ::= TYPE-IDENTIFIER
SecurityCategory { SECURITY-CATEGORY:Supported }::= SEQUENCE {
type [0] IMPLICIT SECURITY-CATEGORY.&id({Supported}),
value [1] EXPLICIT SECURITY-CATEGORY.&Type
({Supported}{@type})
}
NOTE: SecurityCategory is shown exactly as it is in [RFC 5912]. That
module is an EXPLICIT tagged module, whereas the module contained in
this document is an IMPLICIT tagged module.
The Clearance attribute takes its meaning from Section 4.4.6 of
[RFC 5755], 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 securityCategories 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. Authority Clearance Constraints Certificate Extension
The Authority Clearance Constraints certificate extension indicates
to the relying party what clearances should be acceptable for the
subject of the AC or the subject of the last certificate in a PKC
certification path. It is only meaningful in a trust anchor, a CA
PKC, or an AA PKC. A trust anchor, CA PKC, or AA PKC MUST include
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RFC 5913 Clearance and Authority Clearance Constraints June 2010
either zero or one instance of the Authority Clearance Constraints
certificate extension. The Authority Clearance Constraints
certificate extension MAY be critical or non-critical.
Absence of this certificate extension in a TA, a CA PKC, or an AA PKC
indicates that clearance of the subject of the AC or the subject of
the last certificate in a PKC certification path containing the TA,
the CA, or the AA is not constrained by the respective TA, CA, or AA.
The following object identifier identifies the Authority Clearance
Constraints certificate extension:
id-pe-authorityClearanceConstraints OBJECT IDENTIFIER ::= {
iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) pe(1) 21 }
The ASN.1 syntax for the Authority Clearance Constraints certificate
extension is as follows:
AuthorityClearanceConstraints ::= SEQUENCE SIZE (1..MAX) OF
Clearance
The syntax for the Authority Clearance Constraints certificate
extension contains Clearances 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 Authority Clearance
Constraints Processing as described below. If more than one entry
with the same policyId is present in the Authority Clearance
Constraints certificate extension, the certification path is
rejected.
4. Processing of Clearance and Authority Clearance Constraints in a PKC
This section describes the certification path processing when
Clearance is asserted in the PKC under consideration.
User input, the Authority Clearance Constraints certificate
extension, and Clearance attribute processing determines the
effective clearance (henceforth called effective-clearance) for the
end PKC. User input and the Authority Clearance Constraints
certificate extension in the TA and in each PKC (up to but not
including the end PKC) in a PKC certification path impact the
effective-clearance. If there is more than one path to the end PKC,
each path is processed independently. The process involves two
steps:
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RFC 5913 Clearance and Authority Clearance Constraints June 2010
1) collecting the Authority Clearance Constraints; and
2) using the Authority Clearance Constraints in the certification
path and the Clearance in the end PKC to determine the
effective-clearance for the subject of the end PKC.
Assuming a certification path consisting of n PKCs, the effective-
clearance for the subject of the end PKC is the intersection of 1)
the Clearance attribute in the subject PKC, 2) the Authority
Clearance Constraints, if present, in the trust anchor, 3) user
input, and 4) all Authority Clearance Constraints present in n-1
intermediate PKCs. 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, Authority Clearance Constraints
are maintained in one state variable: permitted-clearances. When
processing begins, permitted-clearances is initialized to the user
input value or the special value all-clearances if Authority
Clearance Constraints user input is not provided. The permitted-
clearances state variable is updated by first processing Authority
Clearance Constraints associated with the trust anchor, and then each
time an intermediate PKC that contains an Authority Clearance
Constraints certificate extension in the path is processed.
When processing the end PKC, the value in the Clearance attribute in
the end PKC is intersected with the permitted-clearances state
variable.
The output of Clearance attribute and Authority Clearance Constraint
certificate extension processing is the effective-clearance (which
could also be an empty list), and a status indicator of either
success or failure. If the status indicator is failure, then the
process also returns a reason code.
4.1. Collecting Constraints
Authority Clearance Constraints are collected from the user input,
the trust anchor, and the intermediate PKCs in a certification path.
4.1.1. Certification Path Processing
When processing Authority Clearance Constraints certificate
extensions for the purposes of validating a Clearance attribute in
the end PKC, the processing described in this section or an
equivalent algorithm MUST be performed in addition to the
certification path validation.
Turner & Chokhani Standards Track PAGE 7
RFC 5913 Clearance and Authority Clearance Constraints June 2010
The processing is presented as an addition to the certification path
validation algorithm described in Section 6 of [RFC 5280]. Note that
this RFC is fully consistent with [RFC 5280]; however, it augments
[RFC 5280] with the following steps:
o Ability to provide and process Authority Clearance Constraints
as an additional input to the certification path processing
engine with Trust anchor information.
o Requirement to process Authority Clearance Constraints present
with trust anchor information.
4.1.1.1. Inputs
User input may include an Authority Clearance Constraints structure
or omit it.
Trust anchor information may include the Authority Clearance
Constraints structure to specify Authority Clearance Constraints for
the trust anchor. In other words, the trust anchor may be
constrained or unconstrained.
4.1.1.2. Initialization
If the user input includes Authority Clearance Constraints, set
permitted-clearances to the input value; otherwise, set permitted-
clearances to the special value all-clearances.
Examine the permitted-clearances for the same Policy ID appearing
more then once. If a policyId appears more than once in the
permitted-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 trust anchor does not contain an Authority Clearance
Constraints extension, continue at Section 4.1.1.3. Otherwise,
execute the procedure described in Section 6 as an in-line macro by
treating the trust anchor as a PKC.
4.1.1.3. Basic Certificate Processing
If the PKC is the last PKC (i.e., certificate n), skip the steps
listed in this section. Otherwise, execute the procedure described
in Section 6 as an in-line macro.
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RFC 5913 Clearance and Authority Clearance Constraints June 2010
4.1.1.4. Preparation for Certificate i+1
No additional action associated with the Clearance attribute or the
Authority Clearance Constraints certificate extensions is taken
during this phase of certification path validation as described in
Section 6 of [RFC 5280].
4.1.1.5. Wrap-up Procedure
To complete the processing, perform the following steps for the last
PKC (i.e., certificate n).
Examine the PKC and verify that it does not contain more than one
instance of the Clearance attribute. If the PKC contains more than
one instance of the Clearance attribute, set effective-clearance to
an empty list, set the error code to "multiple instances of an
attribute", and exit with failure.
If the Clearance attribute is not present in the end PKC, set
effective-clearance to an empty list and exit with success.
Set effective-clearance to the Clearance attribute in the end PKC.
4.1.1.5.1. Wrap Up Clearance
Examine effective-clearance and verify that it does not contain more
than one value. If effective-clearance contains more than one value,
set effective-clearance to an empty list, set error code to "multiple
values", and exit with failure.
If permitted-clearances is an empty list, set effective-clearance to
an empty list and exit with success.
If permitted-clearances has the special value all-clearances, exit
with success.
Let us say policyId in effective-clearance is X.
If the policyId X in effective-clearance is absent from the
permitted-clearances, 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-clearances associated with policyId
X. Assign all other classList bits in effective-clearance a value of
zero (0).
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RFC 5913 Clearance and Authority Clearance Constraints June 2010
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 the securityCategories in effective-clearance to the intersection
of securityCategories in effective-clearance and securityCategories
for policyId X in permitted-clearances using the algorithm described
in Section 7. Note that an empty SET is represented by simply
omitting the SET.
Exit with success.
4.1.1.6. Outputs
If certification path validation processing succeeds, effective-
clearance contains the subject's effective clearance for this
certification path. Processing also returns success or failure
indication and reason for failure, if applicable.
5. Clearance and Authority Clearance Constraints Processing in AC
This section describes the certification path processing when
Clearance is asserted in an AC. Relevant to processing are: one TA;
0 or more CA PKCs; 0 or 1 AA PKC; and 1 AC.
User input, Authority Clearance Constraints certificate extension,
and Clearance attribute processing determine the effective clearance
(henceforth called effective-clearance) for the subject of the AC.
User input and the Authority Clearance Constraints certificate
extensions in the TA and in each PKC (up to and including the AA PKC)
in a certification path impact the effective-clearance. If there is
more than one path to the AA PKC, each path is processed
independently. The process involves two steps:
1) collecting the Authority Clearance Constraints; and
2) using the Authority Clearance Constraints in the PKC
certification path and the Clearance in the AC to determine the
effective-clearance for the subject of the AC.
The effective-clearance for the subject of the AC is the intersection
of 1) the Clearance attribute in the subject AC, 2) the Authority
Clearance Constraints, if present, in trust anchor, 3) user input,
and 4) all Authority Clearance Constraints present in the PKC
certification path from the TA to the AA. 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.
Turner & Chokhani Standards Track PAGE 10
RFC 5913 Clearance and Authority Clearance Constraints June 2010
The Authority Clearance Constraints are maintained in one state
variable: permitted-clearances. When processing begins, permitted-
clearances is initialized to user input or the special value all-
clearances if Authority Clearance Constraints user input is not
provided. The permitted-clearances state variable is updated by
first processing the Authority Clearance Constraints associated with
the trust anchor, and then each time a PKC (other than AC holder PKC)
that contains an Authority Clearance Constraints certificate
extension in the path is processed.
When processing the AC, the value in the Clearance attribute in the
AC is intersected with the permitted-clearances state variable.
The output of Clearance attribute and Authority Clearance Constraint
certificate extension processing is the effective-clearance, which
could also be an empty list; and success or failure with a reason
code for failure.
5.1. Collecting Constraints
Authority Clearance Constraints are collected from the user input,
the trust anchor, and all the PKCs in the AA PKC certification path.
5.1.1. Certification Path Processing
When processing Authority Clearance Constraints certificate
extensions for the purpose of validating a Clearance attribute in the
AC, the processing described in this section or an equivalent
algorithm MUST be performed in addition to the certification path
validation. The processing is presented as an addition to the PKC
certification path validation algorithm described in Section 6 of
[RFC 5280] for the AA PKC certification path and the algorithm
described in Section 5 of [RFC 5755] for the AC validation. Also see
the note related to [RFC 5280] augmentation in Section 4.1.1.
5.1.1.1. Inputs
Same as Section 4.1.1.1.
In addition, let us assume that the PKC certification path for the AA
consists of n certificates.
5.1.1.2. Initialization
Same as Section 4.1.1.2.
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RFC 5913 Clearance and Authority Clearance Constraints June 2010
5.1.1.3. Basic PKC Processing
Same as Section 4.1.1.3 except that the logic is applied to all n
PKCs.
5.1.1.4. Preparation for Certificate i+1
Same as Section 4.1.1.4.
5.1.1.5. Wrap-up Procedure
To complete the processing, perform the following steps for the AC.
Examine the AC and verify that it does not contain more than one
instance of the Clearance attribute. If the AC contains more than
one instance of the Clearance attribute, set effective-clearance to
an empty list, set the error code to "multiple instances of an
attribute", and exit with failure.
If the Clearance attribute is not present in the AC, set effective-
clearance to an empty list and exit with success.
Set effective-clearance to the Clearance attribute in the AC.
5.1.1.5.1. Wrap Up Clearance
Same as Section 4.1.1.5.1.
5.1.1.6. Outputs
Same as Section 4.1.1.6.
In addition, apply AC processing rules described in Section 5 of
[RFC 5755].
6. Computing the Intersection of permitted-clearances and Authority
Clearance Constraints Extension
Examine the PKC and verify that it does not contain more than one
instance of the Authority Clearance Constraints extension. If the
PKC contains more than one instance of Authority Clearance
Constraints extension, set effective-clearance to an empty list, set
error code to "multiple extension instances", and exit with failure.
If the Authority Clearance Constraints certificate extension is not
present in the PKC, no action is taken, and the permitted-clearances
value is unchanged.
Turner & Chokhani Standards Track PAGE 12
RFC 5913 Clearance and Authority Clearance Constraints June 2010
If the Authority Clearance Constraints certificate extension is
present in the PKC, set the variable temp-clearances to the value of
the Authority Clearance Constraints 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 Authority Clearance Constraints certificate extension is
present in the PKC and permitted-clearances contains the all-
clearances special value, then assign permitted-clearances the value
of temp-clearances.
If the Authority Clearance Constraints certificate extension is
present in the PKC 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 temp-clearances:
-- For every classList bit, assign the classList bit a value of
one (1) for the policyId in the 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.
-- For the policyId in permitted-clearances, set the
securityCategories to the intersection of securityCategories
for the policyId in permitted-clearances and in temp-
clearances using the algorithm described in Section 7. Note
that an empty SET is represented by simply omitting the SET.
7. Computing the Intersection of securityCategories
The algorithm described here has the idempotent, associative, and
commutative properties.
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RFC 5913 Clearance and Authority Clearance Constraints June 2010
This section describes how to compute the intersection of
securityCategories A and B. It uses the state variable temp-set. It
also uses temporary variables X and Y.
Set the SET temp-set to empty.
Set X = A and Y = B.
If SET X is empty (i.e., securityCategories is absent), return temp-
set.
If SET Y is empty (i.e., securityCategories is absent), return temp-
set.
For each type OID in X, if all the elements for the type OID in X and
if and only if all the elements for that type OID in Y are identical,
add those elements to temp-set and delete those elements from X and
Y. Note: identical means that if the element with the type OID and
given value is present in X, it is also present in Y with the same
type OID and given value and vice versa. Delete the elements from X
and from Y.
If SET X is empty (i.e., securityCategories is absent), return temp-
set.
If SET Y is empty (i.e., securityCategories is absent), return temp-
set.
For every element (i.e., SecurityCategory) in the SET X, carry out
the following steps:
1. If there is no element in SET Y with the same type OID as the
type OID in the element from SET X, go to step 5.
2. If there is an element in SET Y with the same type OID and value
as in the element in SET X, carry out the following steps:
a) If the element is not present in the SET temp-set, add an
element containing the type OID and the value to the SET
temp-set.
3. If the processing semantics of type OID in the element in SET X
is not known, go to step 5.
4. For each element in SET Y, do the following:
a) If the type OID of the element in SET Y is not the same as
the element in SET X being processed, go to step 4.d.
Turner & Chokhani Standards Track PAGE 14
RFC 5913 Clearance and Authority Clearance Constraints June 2010
b) Perform type-OID-specific intersection of the value in the
element in SET X with the value in the element in SET Y.
c) If the intersection is not empty, and the element
representing the type OID and intersection value is not
already present in temp-set, add the element containing the
type OID and intersection value as an element to temp-set.
d) Continue to the next element in SET Y.
5. If more elements remain in SET X, process the next element
starting with step 1.
Return temp-set.
8. Recommended securityCategories
This RFC also includes a recommended securityCategories object as
follows:
recommended-category SECURITY-CATEGORY ::=
{ BIT STRING IDENTIFIED BY OID }
The above structure is provided as an example. To use this
structure, the object identifier (OID) needs to be registered and the
semantics of the bits in the bit string need to be enumerated.
Note that type-specific intersection of two values for this type will
be simply setting the bits that are set in both values. If the
resulting intersection has none of the bits set, the intersection is
considered empty.
9. Security Considerations
Certificate issuers must recognize that absence of the Authority
Clearance Constraints in a TA, in a CA certificate, or in an AA
certificate means that in terms of the clearance, the subject
Authority is not constrained.
Absence of the Clearance 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 Authority Clearance Constraints should only be
Turner & Chokhani Standards Track PAGE 15
RFC 5913 Clearance and Authority Clearance Constraints June 2010
included if the subject's and Authority's certificates can be privacy
protected. Also in this case, distribution of trust anchors and
associated Authority Clearance Constraints extension or Clearance
must also be privacy protected.
10. References
10.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 5280] Cooper, D. et. al., "Internet X.509 Public Key
Infrastructure Certificate and Certification Revocation
List (CRL) Profile", RFC 5280, May 2008.
[RFC 5755] Farrell, S., Housley, R., and S. Turner, "An Internet
Attribute Certificate Profile for Authorization", RFC
5755, January 2010.
[RFC 5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the
Public Key Infrastructure Using X.509 (PKIX) RFC 5912,
June 2010.
[X.680] ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-1:2002.
Information Technology - Abstract Syntax Notation One.
10.2. Informative References
[RFC 3114] Nicolls, W., "Implementing Company Classification Policy
with the S/MIME Security Label", RFC 3114, May 2002.
[RFC 3739] Santesson, S., Nystrom, M., and T. Polk, "Internet X.509
Public Key Infrastructure: Qualified Certificates
Profile", RFC 3739, March 2004.
Turner & Chokhani Standards Track PAGE 16
RFC 5913 Clearance and Authority Clearance Constraints June 2010
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.
ClearanceConstraints { iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) mod(0) 46 }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- EXPORTS ALL --
IMPORTS
-- IMPORTS from [RFC 5912]
id-at-clearance, Clearance
FROM PKIXAttributeCertificate-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-attribute-cert-02(47)
}
-- IMPORTS from [RFC 5912]
EXTENSION, SECURITY-CATEGORY
FROM PKIX-CommonTypes-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkixCommon-02(57)
}
;
-- Clearance attribute OID and syntax
-- The following is a 2002 ASN.1 version for clearance.
-- It is included for convenience.
-- id-at-clearance OBJECT IDENTIFIER ::=
-- { joint-iso-ccitt(2) ds(5) attributeTypes(4) clearance (55) }
-- Clearance ::= SEQUENCE {
-- policyId OBJECT IDENTIFIER,
-- classList ClassList DEFAULT {unclassified},
-- securityCategories SET OF SecurityCategory
Turner & Chokhani Standards Track PAGE 17
RFC 5913 Clearance and Authority Clearance Constraints June 2010
-- {{SupportSecurityCategories }} OPTIONAL
-- }
-- ClassList ::= BIT STRING {
-- unmarked (0),
-- unclassified (1),
-- restricted (2),
-- confidential (3),
-- secret (4),
-- topSecret (5)
-- }
-- SECURITY-CATEGORY ::= TYPE-IDENTIFIER
-- NOTE that the module SecurityCategory is taken from a module
-- that uses EXPLICIT tags [RFC 5912]. If Clearance was not imported
-- from [RFC 5912] and the comments were removed from the ASN.1
-- contained herein, then the IMPLICIT in type could also be removed
-- with no impact on the encoding.
-- SecurityCategory { SECURITY-CATEGORY:Supported } ::= SEQUENCE {
-- type [0] IMPLICIT SECURITY-CATEGORY.&id({Supported}),
-- value [1] EXPLICIT SECURITY-CATEGORY.&Type
-- ({Supported}{@type})
-- }
-- Authority Clearance Constraints certificate extension OID
-- and syntax
id-pe-clearanceConstraints OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) pe(1) 21 }
authorityClearanceConstraints EXTENSION ::= {
SYNTAX AuthorityClearanceConstraints
IDENTIFIED BY id-pe-clearanceConstraints
}
AuthorityClearanceConstraints ::= SEQUENCE SIZE (1..MAX) OF Clearance
END
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RFC 5913 Clearance and Authority Clearance Constraints June 2010
Acknowledgments
Many thanks go out to Mark Saaltink for his valuable contributions to
this document.
We would also like to thank Francis Dupont, Pasi Eronen, Adrian
Farrel, Dan Romascanu, and Stefan Santesson for their reviews and
comments.
Authors' Addresses
Sean Turner
IECA, Inc.
3057 Nutley Street, Suite 106
Fairfax, VA 22031
USA
EMail: turners@ieca.com
Santosh Chokhani
CygnaCom Solutions, Inc.
EMail: SChokhani@cygnacom.com
Turner & Chokhani Standards Track PAGE 19
Clearance Attribute and Authority Clearance Constraints Certificate Extension
RFC TOTAL SIZE: 39650 bytes
PUBLICATION DATE: Saturday, June 5th, 2010
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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