Network Working Group Sean Turner Internet Draft IECA Intended Status: Standard Track Santosh Chokhani CygnaCom Solutions Expires: January 14, 2009 July 14, 2008 Clearance and CA Clearance Constraints Certificate Extensions draft-turner-caclearanceconstraints-01.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on January 14, 2009. Copyright Notice Copyright (C) The IETF Trust (2008). 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 Turner & Chokhani Expires January 14, 2009 [Page 1] Internet-Draft Clearance and CA Clearance Constraints July 2008 certificate or in the attributes field of an attribute certificate. The Authority Clearance Constraints certificate extension values in a Trust Anchor (TA), a CA public key certificate, and an Attribute Authority (AA) attribute certificate in a certification path constrain the effective Clearance of the subject of the last certificate in the certification path. Table of Contents 1. Introduction...................................................2 1.1. Terminology...............................................3 1.2. ASN.1 Syntax Notation.....................................3 2. Clearance Attribute............................................3 3. Authority Clearance Constraints Certificate Extension..........4 4. Clearance and Authority 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 4.1.1.3. Basic Certificate Processing....................7 4.1.1.4. Preparation for Certificate i+1.................8 4.1.1.5. Wrap-up Procedure...............................8 4.1.1.6. Outputs.........................................9 5. Application of Algorithm to Attribute Certificates.............9 6. Security Considerations.......................................10 7. IANA Considerations...........................................10 8. References....................................................10 8.1. Normative References.....................................10 8.2. Informative References...................................11 Appendix A. ASN.1 Module.........................................12 1. Introduction Organizations that have implemented a security policy can issue certificates that include an indication of the clearance values held by the subject. The Clearance attribute indicates the security policy, the clearance levels held by the subject, and additional authorization information held by the subject. This specification makes use of the ASN.1 syntax for clearance from [RFC3281]. Some organizations have multiple TAs, 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 [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 Turner & Chokhani Expires January 14, 2009 [Page 2] Internet-Draft Clearance and CA Clearance Constraints July 2008 Authority Clearance Constraints certificate extension would be included in the CA's certificate. 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. 1.1. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 1.2. ASN.1 Syntax Notation All X.509 public key certificate [RFC5280] extensions are defined using ASN.1 [X.680]. All X.509 attribute certificate [RFC3281] 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 [RFC3281], which is included below for convenience, in the Attributes field. A certificate MUST include either zero or one instance of the Clearance attribute. The following object identifier identifies the Clearance attribute (either in the subject directory attributes extension of a public key certificate or in the Attributes field of an attribute certificate): id-at-clearance OBJECT IDENTIFIER ::= { joint-iso-ccitt(2) ds(5) module(1) selected-attribute-types(5) clearance(55) } The ASN.1 syntax for the Clearance attribute is as follows: Clearance ::= SEQUENCE { policyId [0] OBJECT IDENTIFIER, classList [1] ClassList DEFAULT {unclassified}, securityCategories [2] SET OF SecurityCategory OPTIONAL } Turner & Chokhani Expires January 14, 2009 [Page 3] Internet-Draft Clearance and CA Clearance Constraints July 2008 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 Clearance attribute takes its meaning from Section 4.4.6 of [RFC3281], which is repeated here for convenience: - policyId identifies the security policy to which the clearance relates. The policyId indicates the semantics of the classList and securityCategory fields. - classlist identifies the security classifications. Six basic values are defined in bit positions 0 through 5 and more may be defined by an organizational security policy. - securityCategories provides additional authorization information. If a trust anchor's public key is used directly, then the Clearance associated with the trust anchor, if any, should be used as the effective clearance (also defined as effective-clearance for a certification path). 3. 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 last certificate in the certification path containing the TA, the CA, or the AA. It is only meaningful in trust anchor, CA certificates, or AA certificates. A trust anchor, CA certificate, or AA certificate 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 certificate, or in an AA certificate indicates that clearance of the subject of Turner & Chokhani Expires January 14, 2009 [Page 4] Internet-Draft Clearance and CA Clearance Constraints July 2008 the last certificate in the 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-ce-authorityClearanceConstraints OBJECT IDENTIFIER ::= { id-TBSL } 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 Clearance values that the CA or the AA asserts. The sequence MUST NOT include more than one entry with the same policyId. This constraint is enforced during Clearance and 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 Authority Clearance Constraints certificate extension processing determines the effective clearance (henceforth called effective- clearance) for the end certificate. Authority Clearance Constraints certificate extension in the TA and in each certificate up to but not including the end certificate in a certification path impact the effective-clearance. If there is more than one path to the end- entity certificate, each path is processed independently. The process involves two steps: 1) collecting the Authority Clearance Constraints; and 2) using Authority 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, Authority Clearance Constraints, if present, in trust anchor and all Authority 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 Turner & Chokhani Expires January 14, 2009 [Page 5] Internet-Draft Clearance and CA Clearance Constraints July 2008 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 special value all-clearances if Authority Clearance Constraints certificate extension is not present in the trust anchor, otherwise this value is initialized to Authority Clearance Constraints associated with the trust anchor. The permitted-clearances state variable is updated each time an intermediate certificate that contains an Authority Clearance Constraints certificate extension in the path is processed. When processing the end certificate, the value in the Clearance certificate extension in the end certificate is intersected with the permitted-clearances state variable. The output of Clearance and Authority Clearance Constraint certificate extensions processing is the effective-clearance, which could also be an empty list; and success or failure with reason code for failure. 4.1. Collecting Constraints Authority Clearance Constraints are collected from the trust anchor and the intermediate certificates in a certification path. 4.1.1. Certification Path Processing When processing Authority Clearance Constraints certificate extension for the purposes of validating Clearance in the end certificate, the processing described in this section or an equivalent algorithm MUST be included in the certification path validation. The processing is presented as additions to the certification path validation algorithm described in section 6 of [RFC5280]. 4.1.1.1. Inputs 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 Examine the trust anchor information and verify that it does not contain more than one instance of AuthorityClearanceConstraints Turner & Chokhani Expires January 14, 2009 [Page 6] Internet-Draft Clearance and CA Clearance Constraints July 2008 extension. If the trust anchor information 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. Create a state variable named permitted-clearances. If the trust anchor contains an AuthorityClearanceConstraints extension, then the initial value of permitted-clearances is the AuthorityClearanceConstraints extension from the trust anchor. Examine the permitted-clearances for the same Policy ID appearing more then once. If a policyID appears more than once in the permitted-clearance state variable, set effective-clearance to an empty list, set error code to "multiple instances of same clearance", and exit with failure. If the trust anchor does not contain an AuthorityClearanceConstraints extension, the permitted-clearances variable is assigned the special value all-clearances. 4.1.1.3. Basic Certificate Processing If the certificate is the last certificate (i.e., certificate n), skip the steps listed in this section. Examine the certificate and verify that it does not contain more than one instance of AuthorityClearanceConstraints extension. If the certificate 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 certificate, no action is taken, and the permitted- clearances value is unchanged. If the AuthorityClearanceConstraints certificate extension is present in the certificate, 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 certificate and permitted-clearances contains the all- Turner & Chokhani Expires January 14, 2009 [Page 7] Internet-Draft Clearance and CA Clearance Constraints July 2008 clearances special value, then assign permitted-clearances the value of the temp-clearances. If the AuthorityClearanceConstraints certificate extension is present in the certificate and permitted-clearances does not contain the all- clearances special value, take the intersection of temp-clearances and permitted-clearances by repeating the following steps for each clearance in the permitted-clearances state variable: - If the policyID associated with the clearance is absent in the temp-clearances, delete the clearance structure associated with the policyID from the permitted-clearances state variable. - If the policyID is present in the temp-clearances: -- For every classList bit, assign the classList bit a value of one (1) for the policyID in permitted-clearances state variable if the bit is one (1) in both the permitted- clearances state variable and the temp-clearances for that policyID; otherwise assign the bit a value of zero (0). -- If no bits are one (1) for the classList, delete the clearance structure associated with the policyID from the permitted- clearances state variable and skip the next step of processing securityCategories. -- Calculate securityCategories intersection in accordance with guidelines associated with the security policy represented by the policyID. 4.1.1.4. 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 certificate (i.e., certificate n). Examine the certificate and verify that it does not contain more than one instance of Clearance attribute. If the certificate 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. Turner & Chokhani Expires January 14, 2009 [Page 8] Internet-Draft Clearance and CA Clearance Constraints July 2008 If the Clearance attribute is not present in the end certificate, set effective-clearance to an empty list and exit with success. Set effective-clearance to the value from the Clearance attribute 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. 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 4.1.1.6. Outputs If certification path validation processing succeeds, effective- clearance contains the effective clearance for the subject of the certification path. Processing also returns success or failure indication and reason for failure, if applicable. 5. Application of Algorithm to Attribute Certificates The algorithm presented in Section 4 is public key certificate centric. Its application to attribute certificates is straightforward as described below. Turner & Chokhani Expires January 14, 2009 [Page 9] Internet-Draft Clearance and CA Clearance Constraints July 2008 If the current [RFC3281] constraint of not having chain of attribute certificate chain is observed, the AC Issuer (i.e., AA) Authority Clearance Constraints is used as the TA Authority Clearance Constraints for the initialization step described in Section 4.1.1.2. Since there is no intermediate steps, sections 4.1.1.3. and 4.1.1.4. will not be executed. If the current [RFC3281] constraint of not having chain of attribute certificate chain is removed, the Source of Authority in the Attribute Certificate chain becomes the TA for the purpose of Section 4. 6. Security Considerations Certificate issuers must recognize that absence of the 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. 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. 7. IANA Considerations None. Please remove this section prior to publication as an RFC. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5280] Cooper, D. et. al., "Internet X.509 Public Key Infrastructure Certificate and Certification Revocation List (CRL) Profile", RFC 5280, May 2008. Turner & Chokhani Expires January 14, 2009 [Page 10] Internet-Draft Clearance and CA Clearance Constraints July 2008 [RFC3281] Farrell, S., and Housley, R., "An Internet Attribute Certificate Profile for Authorization", RFC 3281, April 2002. [X.680] ITU-T Recommendation X.680 (1997) | ISO/IEC 8824-1:1997. Information Technology - Abstract Syntax Notation One. 8.2. Informative References [RFC3114] Nicolls, W., "Implementing Company Classification Policy with S/MIME Security Label", RFC3114, May 2002. Turner & Chokhani Expires January 14, 2009 [Page 11] Internet-Draft Clearance and CA Clearance Constraints July 2008 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-AuthorityClearanceConstraints93 { id-TBSL } DEFINITIONS IMPLICIT TAGS ::= BEGIN -- EXPORTS ALL -- IMPORTS -- IMPORTS from [RFC3281] id-at-clearance, Clearance FROM PKIXAttributeCertificate { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-attribute-cert(12) } -- IMPORTS from [RFC5280] EXTENSION FROM PKIX1Explicit93 { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-explicit-93(3) } ; -- Clearance attribute OID and syntax -- The following is a '93 version for clearance. -- It is included for convenience. -- id-at-clearance OBJECT IDENTIFIER ::= -- { joint-iso-ccitt(2) ds(5) module(1) selected-attribute-types(5) -- clearance (55) -- } Turner & Chokhani Expires January 14, 2009 [Page 12] Internet-Draft Clearance and CA Clearance Constraints July 2008 -- 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}) -- } -- Authority Clearance Constraints certificate extension OID -- and syntax id-ce-AuthorityClearanceConstraints OBJECT IDENTIFIER ::= { id-TBSL } AuthorityClearanceConstraints EXTENSION ::= { SYNTAX AuthorityClearanceConstraints IDENTIFIED BY id-ce-AuthorityClearanceConstraints } AuthorityClearanceConstraints ::= SEQUENCE SIZE (1..MAX) OF Clearance END Turner & Chokhani Expires January 14, 2009 [Page 13] Internet-Draft Clearance and CA Clearance Constraints July 2008 Author's 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@ocygnacom.com Turner & Chokhani Expires January 14, 2009 [Page 14] Internet-Draft Clearance and CA Clearance Constraints July 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 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