Clearance Attribute and Authority Clearance Constraints Certificate Extension
draft-ietf-pkix-authorityclearanceconstraints-03

Network Working Group                                 Sean Turner, IECA 
Internet Draft                     Santosh Chokhani, Cygnacom Solutions 
Intended Status: Standard Track                        October 19, 2009 
Expires: April 19, 2010 
 
 
                                      
          Clearance Attribute and Authority Clearance Constraints 
                           Certificate Extension 
           draft-ietf-pkix-authorityclearanceconstraints-03.txt 

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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), Certificate Authority (CA) public key 
   certificates, and an Attribute Authority (AA) public key certificate 
   in a public key certification path constrain the effective Clearance 
   of the subject. 

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. Clearance and Authority Clearance Constraints Processing in 
      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 Intersection of permitted-clearances and 
      AuthorityClearanceConstraints extension.......................12 
   7. Computing Intersection of securityCategories..................13 
   8. Recommended securityCategories................................15 
 
 
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   9. Security Considerations.......................................15 
   10. IANA Considerations..........................................16 
   11. References...................................................16 
      11.1. Normative References....................................16 
      11.2. Informative References..................................17 
   Appendix A. ASN.1 Module.........................................18 
   Authors' Addresses...............................................20 
    
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 [RFC3281bis]. 

   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 Clearance attribute in PKCs is desirable when the 
   credentials such as PKCs need to be revoked when the clearance 
   information changes or when clearance information is relatively 
   static, and clearance information can be verified as part of PKC 
   issuance process (e.g., using local databases).  The placement of 
   Clearance attribute in PKCs may also be made to simplify the 
   infrastructure, to reduce the infrastructure design cost, or to 
   reduce the infrastructure operations cost.  An example of placement 
   of 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 [RFC3739]. 

   The placement of Clearance attribute in ACs is desirable when the 
   clearance information is relatively dynamic and changes in the 
   clearance information does not require revocation of credentials such 
   as PKCs, or the clearance information can not be verified as part of 
   PKC issuance process. 

   Since [RFC3281bis] does not permit chain of ACs, the Authority 
   Clearance Constraints extension may only appear in the PKCs of 
   Certificate 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 
 
 
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   values from a particular TA, CA, or 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 
   Authority Clearance Constraints certificate extension would be 
   included in the CA's PKC. 

   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 [RFC5280] and ACs in [RFC3281bis].  

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 PKC [RFC5280] extensions are defined using ASN.1 [X.680].  
   All X.509 AC [RFC3281bis] extensions are defined using ASN.1 [X.680]. 

2. Clearance Attribute 

   The Clearance attribute in a certificate indicates the clearances 
   held by the subject.  It uses the clearance attribute syntax from 
   Section 4.4.6 of [RFC3281bis], which is included below for 
   convenience, 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 as follows [PKI-ASN]: 

     Clearance  ::=  SEQUENCE { 
       policyId            OBJECT IDENTIFIER, 
       classList           ClassList DEFAULT {unclassified}, 
 
 
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       securityCategories  SET OF SecurityCategory 
                             {{ SupportedSecurityCategories }} OPTIONAL 
     } 

     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 [PKI-ASN].  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 
   [RFC3281bis], 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 
 
 
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   subject of the AC or the subject of the last certificate in a PKC 
   certification path.  It is only meaningful in trust anchor, CA PKCs, 
   or AA PKCs.  A trust anchor, CA PKC, or AA PKC MUST include 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, in a CA PKC, or in 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 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 described below.  If more than one entry with 
   the same policyId is present in AuthorityClearanceConstraints 
   certificate extension, the certification path is rejected.   

4. Clearance and Authority Clearance Constraints Processing in PKC 

   This section describes the processing of certification path when 
   Clearance is asserted in PKC. 

   User input, Authority Clearance Constraints certificate extension, 
   and Clearance attribute processing determines the effective clearance 
   (henceforth called effective-clearance) for the end PKC.  User input, 
   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-entity PKC, each path is processed 
   independently.  The process involves two steps: 
 
 
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     1) collecting the Authority Clearance Constraints; and 

     2) using 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 
   Clearance attribute in the subject PKC, Authority Clearance 
   Constraints, if present, in trust anchor, user input, and all 
   Authority Clearance Constraints present in 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 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 extensions 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 was 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 extension 
   for the purposes of validating 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.  
 
 
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   The processing is presented as additions to the certification path 
   validation algorithm described in section 6 of [RFC5280].  Note that 
   this RFC is fully consistent with [RFC5280]; however, it augments 
   [RFC5280] with the following steps: 

     . Ability to provide and process Authority Clearance Constraints 
        as an additional input to the certification path processing 
        engine 

     . Requirement to process Authority Clearance Constraints present 
        with Trust anchor information. 

4.1.1.1. Inputs 

   User input may include AuthorityClearanceConstraints structure or 
   omit it. 

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

4.1.1.2. Initialization 

   If user input includes AuthorityClearanceConstraints, set the 
   permitted-clearances to the input value, otherwise, set the 
   permitted-clearances to 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 AuthorityClearanceConstraints 
   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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4.1.1.4. Preparation for Certificate i+1 

   No additional action associated with the Clearance attribute or 
   AuthorityClearanceConstraints certificate extensions is taken during 
   this phase of certification path validation as described in section 6 
   of [RFC5280]. 

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 Clearance attribute.  If the PKC contains more than one 
   instance of Clearance attribute, set effective-clearance to an empty 
   list, set 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 the permitted-clearances has special value of 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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   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 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 effective clearance for the subject of the 
   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 processing of certification path 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 determines the effective clearance 
   (henceforth called effective-clearance) for the AC.  User input, 
   Authority Clearance Constraints certificate extension 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 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 Clearance in the subject AC, Authority Clearance Constraints, if 
   present, in trust anchor, user input, and all Authority Clearance 
   Constraints present in 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. 
 
 
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   Authority Clearance Constraints is maintained in one state variable: 
   permitted-clearances.  When processing begins, permitted-clearances 
   is initialized to user input or 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 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 and 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. 

5.1. Collecting Constraints 

   Authority Clearance Constraints are collected from the user input, 
   the trust anchor and all the PKCs in a PKC certification path. 

5.1.1. Certification Path Processing 

   When processing Authority Clearance Constraints certificate extension 
   for the purposes of validating Clearance in the AC, 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 PKC certification path validation algorithm 
   described in section 6 of [RFC5280] for the AA PKC certification path 
   and the algorithm described in section 5 of [RFC3281bis] for the AC 
   validation.  Also see note related to [RFC5280] 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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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 Clearance attribute.  If the AC contains more than one 
   instance of Clearance attribute, set effective-clearance to an empty 
   list, set 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 
   [RFC3281bis]. 

6. Computing Intersection of permitted-clearances and 
   AuthorityClearanceConstraints extension 

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

   If the AuthorityClearanceConstraints certificate extension is not 
   present in the PKC, no action is taken, and the permitted-clearances 
   value is unchanged. 
 
 
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   If the AuthorityClearanceConstraints certificate extension is present 
   in the PKC, set the variable temp-clearances to 
   AuthorityClearanceConstraints 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 AuthorityClearanceConstraints certificate extension is present 
   in the PKC and permitted-clearances contains the all-clearances 
   special value, then assign permitted-clearances the value of the 
   temp-clearances. 

   If the AuthorityClearanceConstraints 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 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. 

       -- 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 Intersection of securityCategories 

   The algorithm described in here has the idempotency, associative, and 
   commutative properties, like the rest of the processing rules in this 
   document.      
 
 
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   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: 

 
 
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          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. 

          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 Do 

     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 include a recommended securityCategories 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 
   AuthorityClearanceConstraints in a CA or AA certificate means that in 
   terms of the clearance, the subject Authority is not constrained. 

   Absence of 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. 

 
 
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   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 
   included if the subject's and Authority's certificate 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. IANA Considerations 

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

11. References 

11.1. Normative References 

   [PKI-ASN]    Hoffman, P., and J. Schaad, "New ASN.1 Modules for 
                PKIX", draft-ietf-pkix-new-asn1-07, work-in-progress. 

   /*** RFC EDITOR: Please replace PKI-ASN with RFCXYZA when draft-ietf-
               pkix-new-asn1 is published. 

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

   [RFC3281bis] Farrell, S., Housley, R., and S. Turner, "An Internet 
                Attribute Certificate Profile for Authorization: 
                Update", draft-ietf-pkix-3281update-05, work-in-
                progress. 

   /*** RFC EDITOR: Please replace RFC3281bis with RFCXYZA when draft-
               ietf-pkix-3281update is published. 

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

   [X.680]      ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-
                1:2002. Information Technology - Abstract Syntax 
                Notation One. 

 
 
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11.2. Informative References 

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

   [RFC3739]    Santesson, S. et. al., "Internet X.509 Public Key 
                Infrastructure: Qualified Certificate Profile", RFC 
                3739, March 2004. 

 
 
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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. 

   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 [PKI-ASN] 

   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 [PKI-ASN] 

   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 '02 version for clearance. 
   -- It is included for convenience. 

   -- id-at-clearance OBJECT IDENTIFIER ::= 
   --  { joint-iso-ccitt(2) ds(5) attributeTypes(4) clearance (55) } 

 
 
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   -- Clearance  ::=  SEQUENCE { 
   --   policyId            OBJECT IDENTIFIER, 
   --   classList           ClassList DEFAULT {unclassified}, 
   --   securityCategories  SET OF SecurityCategory 
   --                          {{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 [PKI-ASN].  If Clearance was not imported 
   -- from [PKI-ASN] 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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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 

 
 
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