Network Working Group S. Chokhani Request for Comments: 3647 Orion Security Solutions, Inc. Obsoletes: 2527 W. Ford Category: Informational VeriSign, Inc. R. Sabett Cooley Godward LLP C. Merrill McCarter & English, LLP S. Wu Infoliance, Inc. November 2003 Internet X.509 Public Key Infrastructure Certificate Policy and Certification Practices Framework Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract This document presents a framework to assist the writers of certificate policies or certification practice statements for participants within public key infrastructures, such as certification authorities, policy authorities, and communities of interest that wish to rely on certificates. In particular, the framework provides a comprehensive list of topics that potentially (at the writer's discretion) need to be covered in a certificate policy or a certification practice statement. This document supersedes RFC 2527. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Background . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Purpose. . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3. Scope. . . . . . . . . . . . . . . . . . . . . . . . . . 6 2. Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.1. Certificate Policy . . . . . . . . . . . . . . . . . . . 9 3.2. Certificate Policy Examples. . . . . . . . . . . . . . . 11 3.3. X.509 Certificate Fields . . . . . . . . . . . . . . . . 12
3.3.1. Certificate Policies Extension . . . . . . . . . 12 3.3.2. Policy Mappings Extension. . . . . . . . . . . . 13 3.3.3. Policy Constraints Extension . . . . . . . . . . 13 3.3.4. Policy Qualifiers. . . . . . . . . . . . . . . . 14 3.4. Certification Practice Statement . . . . . . . . . . . . 15 3.5. Relationship Between CP and CPS. . . . . . . . . . . . . 16 3.6. Relationship Among CPs, CPSs, Agreements, and Other Documents. . . . . . . . . . . . . . . . . . . . . 17 3.7. Set of Provisions. . . . . . . . . . . . . . . . . . . . 20 4. Contents of a Set of Provisions. . . . . . . . . . . . . . . . 21 4.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 22 4.1.1. Overview . . . . . . . . . . . . . . . . . . . . 22 4.1.2. Document Name and Identification . . . . . . . . 22 4.1.3. PKI Participants . . . . . . . . . . . . . . . . 23 4.1.4. Certificate Usage. . . . . . . . . . . . . . . . 24 4.1.5. Policy Administration. . . . . . . . . . . . . . 24 4.1.6. Definitions and Acronyms . . . . . . . . . . . . 24 4.2. Publication and Repository Responsibilities. . . . . . . 25 4.3. Identification and Authentication (I&A). . . . . . . . . 25 4.3.1. Naming . . . . . . . . . . . . . . . . . . . . . 25 4.3.2. Initial Identity Validation. . . . . . . . . . . 26 4.3.3. Identification and Authentication for Re-key Requests. . . . . . . . . . . . . . . . . 27 4.3.4. Identification and Authentication for Revocation Requests. . . . . . . . . . . . . . . 27 4.4. Certificate Life-Cycle Operational Requirements. . . . . 27 4.4.1. Certificate Application. . . . . . . . . . . . . 28 4.4.2. Certificate Application Processing . . . . . . . 28 4.4.3. Certificate Issuance . . . . . . . . . . . . . . 28 4.4.4. Certificate Acceptance . . . . . . . . . . . . . 29 4.4.5. Key Pair and Certificate Usage . . . . . . . . . 29 4.4.6. Certificate Renewal. . . . . . . . . . . . . . . 30 4.4.7. Certificate Re-key . . . . . . . . . . . . . . . 30 4.4.8. Certificate Modification . . . . . . . . . . . . 31 4.4.9. Certificate Revocation and Suspension. . . . . . 31 4.4.10. Certificate Status Services. . . . . . . . . . . 33 4.4.11. End of Subscription. . . . . . . . . . . . . . . 33 4.4.12. Key Escrow and Recovery. . . . . . . . . . . . . 33 4.5. Management, Operational, and Physical Controls . . . . . 33 4.5.1. Physical Security Controls . . . . . . . . . . . 34 4.5.2. Procedural Controls. . . . . . . . . . . . . . . 35 4.5.3. Personnel Controls . . . . . . . . . . . . . . . 35 4.5.4. Audit Logging Procedures . . . . . . . . . . . . 36 4.5.5. Records Archival . . . . . . . . . . . . . . . . 37 4.5.6. Key Changeover . . . . . . . . . . . . . . . . . 38 4.5.7. Compromise and Disaster Recovery . . . . . . . . 38 4.5.8. CA or RA Termination . . . . . . . . . . . . . . 38 4.6. Technical Security Controls. . . . . . . . . . . . . . . 39 4.6.1. Key Pair Generation and Installation . . . . . . 39 4.6.2. Private Key Protection and Cryptographic
Module Engineering Controls. . . . . . . . . . . 40 4.6.3. Other Aspects of Key Pair Management . . . . . . 42 4.6.4. Activation Data. . . . . . . . . . . . . . . . . 42 4.6.5. Computer Security Controls . . . . . . . . . . . 42 4.6.6. Life Cycle Security Controls . . . . . . . . . . 43 4.6.7. Network Security Controls. . . . . . . . . . . . 43 4.6.8. Time-stamping. . . . . . . . . . . . . . . . . . 43 4.7. Certificate, CRL, and OCSP Profiles. . . . . . . . . . . 44 4.7.1. Certificate Profile. . . . . . . . . . . . . . . 44 4.7.2. CRL Profile. . . . . . . . . . . . . . . . . . . 44 4.7.3. OCSP Profile . . . . . . . . . . . . . . . . . . 44 4.8. Compliance Audit and Other Assessment. . . . . . . . . . 45 4.9. Other Business and Legal Matters . . . . . . . . . . . . 45 4.9.1. Fees . . . . . . . . . . . . . . . . . . . . . . 46 4.9.2. Financial Responsibility . . . . . . . . . . . . 47 4.9.3. Confidentiality of Business Information. . . . . 47 4.9.4. Privacy of Personal Information. . . . . . . . . 48 4.9.5. Intellectual Property Rights . . . . . . . . . . 48 4.9.6. Representations and Warranties . . . . . . . . . 48 4.9.7. Disclaimers of Warranties. . . . . . . . . . . . 49 4.9.8. Limitations of Liability . . . . . . . . . . . . 49 4.9.9. Indemnities. . . . . . . . . . . . . . . . . . . 49 4.9.10. Term and Termination . . . . . . . . . . . . . . 50 4.9.11. Individual notices and communications with participants. . . . . . . . . . . . . . . . 50 4.9.12. Amendments . . . . . . . . . . . . . . . . . . . 50 4.9.13. Dispute Resolution Procedures. . . . . . . . . . 51 4.9.14. Governing Law. . . . . . . . . . . . . . . . . . 51 4.9.15. Compliance with Applicable Law . . . . . . . . . 51 4.9.16. Miscellaneous Provisions . . . . . . . . . . . . 51 4.9.17. Other Provisions . . . . . . . . . . . . . . . . 53 5. Security Considerations. . . . . . . . . . . . . . . . . . . . 53 6. Outline of a Set of Provisions . . . . . . . . . . . . . . . . 53 7. Comparison to RFC 2527 . . . . . . . . . . . . . . . . . . . . 60 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 88 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 88 10. Notes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 11. List of Acronyms . . . . . . . . . . . . . . . . . . . . . . . 91 12. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 92 13. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 94
1. Introduction 1.1. Background In general, a public-key certificate (hereinafter "certificate") binds a public key held by an entity (such as person, organization, account, device, or site) to a set of information that identifies the entity associated with use of the corresponding private key. In most cases involving identity certificates, this entity is known as the "subject" or "subscriber" of the certificate. Two exceptions, however, include devices (in which the subscriber is usually the individual or organization controlling the device) and anonymous certificates (in which the identity of the individual or organization is not available from the certificate itself). Other types of certificates bind public keys to attributes of an entity other than the entity's identity, such as a role, a title, or creditworthiness information. A certificate is used by a "certificate user" or "relying party" that needs to use, and rely upon the accuracy of, the binding between the subject public key distributed via that certificate and the identity and/or other attributes of the subject contained in that certificate. A relying party is frequently an entity that verifies a digital signature from the certificate's subject where the digital signature is associated with an email, web form, electronic document, or other data. Other examples of relying parties can include a sender of encrypted email to the subscriber, a user of a web browser relying on a server certificate during a secure sockets layer (SSL) session, and an entity operating a server that controls access to online information using client certificates as an access control mechanism. In summary, a relying party is an entity that uses a public key in a certificate (for signature verification and/or encryption). The degree to which a relying party can trust the binding embodied in a certificate depends on several factors. These factors can include the practices followed by the certification authority (CA) in authenticating the subject; the CA's operating policy, procedures, and security controls; the scope of the subscriber's responsibilities (for example, in protecting the private key); and the stated responsibilities and liability terms and conditions of the CA (for example, warranties, disclaimers of warranties, and limitations of liability). A Version 3 X.509 certificate may contain a field declaring that one or more specific certificate policies apply to that certificate [ISO1]. According to X.509, a certificate policy (CP) is "a named set of rules that indicates the applicability of a certificate to a particular community and/or class of applications with common security requirements." A CP may be used by a relying party to help
in deciding whether a certificate, and the binding therein, are sufficiently trustworthy and otherwise appropriate for a particular application. The CP concept is an outgrowth of the policy statement concept developed for Internet Privacy Enhanced Mail [PEM1] and expanded upon in [BAU1]. The legal and liability aspects presented in Section 4.9 are outcomes of a collaborative effort between IETF PKIX working group and the American Bar Association (ABA) members who have worked on legal acceptance of digital signature and role of PKI in that acceptance. A more detailed description of the practices followed by a CA in issuing and otherwise managing certificates may be contained in a certification practice statement (CPS) published by or referenced by the CA. According to the American Bar Association Information Security Committee's Digital Signature Guidelines (hereinafter "DSG")(1) and the Information Security Committee's PKI Assessment Guidelines (hereinafter "PAG")(2), "a CPS is a statement of the practices which a certification authority employs in issuing certificates." [ABA1, ABA2] In general, CPSs also describe practices relating to all certificate lifecycle services (e.g., issuance, management, revocation, and renewal or re-keying), and CPSs provide details concerning other business, legal, and technical matters. The terms contained in a CP or CPS may or may not be binding upon a PKI's participants as a contract. A CP or CPS may itself purport to be a contract. More commonly, however, an agreement may incorporate a CP or CPS by reference and therefore attempt to bind the parties of the agreement to some or all of its terms. For example, some PKIs may utilize a CP or (more commonly) a CPS that is incorporated by reference in the agreement between a subscriber and a CA or RA (called a "subscriber agreement") or the agreement between a relying party and a CA (called a "relying party agreement" or "RPA"). In other cases, however, a CP or CPS has no contractual significance at all. A PKI may intend these CPs and CPSs to be strictly informational or disclosure documents. 1.2. Purpose The purpose of this document is twofold. First, the document aims to explain the concepts of a CP and a CPS, describe the differences between these two concepts, and describe their relationship to subscriber and relying party agreements. Second, this document aims to present a framework to assist the writers and users of certificate policies or CPSs in drafting and understanding these documents. In particular, the framework identifies the elements that may need to be considered in formulating a CP or a CPS. The purpose is not to define particular certificate policies or CPSs, per se. Moreover, this document does not aim to provide legal advice or recommendations
as to particular requirements or practices that should be contained within CPs or CPSs. (Such recommendations, however, appear in [ABA2].) 1.3. Scope The scope of this document is limited to discussion of the topics that can be covered in a CP (as defined in X.509) or CPS (as defined in the DSG and PAG). In particular, this document describes the types of information that should be considered for inclusion in a CP or a CPS. While the framework as presented generally assumes use of the X.509 version 3 certificate format for the purpose of providing assurances of identity, it is not intended that the material be restricted to use of that certificate format or identity certificates. Rather, it is intended that this framework be adaptable to other certificate formats and to certificates providing assurances other than identity that may come into use. The scope does not extend to defining security policies generally (such as organization security policy, system security policy, or data labeling policy). Further, this document does not define a specific CP or CPS. Moreover, in presenting a framework, this document should be viewed and used as a flexible tool presenting topics that should be considered of particular relevance to CPs or CPSs, and not as a rigid formula for producing CPs or CPSs. This document assumes that the reader is familiar with the general concepts of digital signatures, certificates, and public-key infrastructure (PKI), as used in X.509, the DSG, and the PAG. 2. Definitions This document makes use of the following defined terms: Activation data - Data values, other than keys, that are required to operate cryptographic modules and that need to be protected (e.g., a PIN, a passphrase, or a manually-held key share). Authentication - The process of establishing that individuals, organizations, or things are who or what they claim to be. In the context of a PKI, authentication can be the process of establishing that an individual or organization applying for or seeking access to something under a certain name is, in fact, the proper individual or organization. This corresponds to the second process involved with identification, as shown in the definition of "identification" below. Authentication can also refer to a security service that provides assurances that individuals, organizations, or things are who or what
they claim to be or that a message or other data originated from a specific individual, organization, or device. Thus, it is said that a digital signature of a message authenticates the message's sender. CA-certificate - A certificate for one CA's public key issued by another CA. Certificate policy (CP) - A named set of rules that indicates the applicability of a certificate to a particular community and/or class of application with common security requirements. For example, a particular CP might indicate applicability of a type of certificate to the authentication of parties engaging in business-to-business transactions for the trading of goods or services within a given price range. Certification path - An ordered sequence of certificates that, together with the public key of the initial object in the path, can be processed to obtain that of the final object in the path. Certification Practice Statement (CPS) - A statement of the practices that a certification authority employs in issuing, managing, revoking, and renewing or re-keying certificates. CPS Summary (or CPS Abstract) - A subset of the provisions of a complete CPS that is made public by a CA. Identification - The process of establishing the identity of an individual or organization, i.e., to show that an individual or organization is a specific individual or organization. In the context of a PKI, identification refers to two processes: (1) establishing that a given name of an individual or organization corresponds to a real-world identity of an individual or organization, and (2) establishing that an individual or organization applying for or seeking access to something under that name is, in fact, the named individual or organization. A person seeking identification may be a certificate applicant, an applicant for employment in a trusted position within a PKI participant, or a person seeking access to a network or software application, such as a CA administrator seeking access to CA systems. Issuing certification authority (issuing CA) - In the context of a particular certificate, the issuing CA is the CA that issued the certificate (see also Subject certification authority).
Participant - An individual or organization that plays a role within a given PKI as a subscriber, relying party, CA, RA, certificate manufacturing authority, repository service provider, or similar entity. PKI Disclosure Statement (PDS) - An instrument that supplements a CP or CPS by disclosing critical information about the policies and practices of a CA/PKI. A PDS is a vehicle for disclosing and emphasizing information normally covered in detail by associated CP and/or CPS documents. Consequently, a PDS is not intended to replace a CP or CPS. Policy qualifier - Policy-dependent information that may accompany a CP identifier in an X.509 certificate. Such information can include a pointer to the URL of the applicable CPS or relying party agreement. It may also include text (or number causing the appearance of text) that contains terms of the use of the certificate or other legal information. Registration authority (RA) - An entity that is responsible for one or more of the following functions: the identification and authentication of certificate applicants, the approval or rejection of certificate applications, initiating certificate revocations or suspensions under certain circumstances, processing subscriber requests to revoke or suspend their certificates, and approving or rejecting requests by subscribers to renew or re-key their certificates. RAs, however, do not sign or issue certificates (i.e., an RA is delegated certain tasks on behalf of a CA). [Note: The term Local Registration Authority (LRA) is sometimes used in other documents for the same concept.] Relying party - A recipient of a certificate who acts in reliance on that certificate and/or any digital signatures verified using that certificate. In this document, the terms "certificate user" and "relying party" are used interchangeably. Relying party agreement (RPA) - An agreement between a certification authority and relying party that typically establishes the rights and responsibilities between those parties regarding the verification of digital signatures or other uses of certificates. Set of provisions - A collection of practice and/or policy statements, spanning a range of standard topics, for use in expressing a CP or CPS employing the approach described in this framework.
Subject certification authority (subject CA) - In the context of a particular CA-certificate, the subject CA is the CA whose public key is certified in the certificate (see also Issuing certification authority). Subscriber - A subject of a certificate who is issued a certificate. Subscriber Agreement - An agreement between a CA and a subscriber that establishes the right and responsibilities of the parties regarding the issuance and management of certificates. Validation - The process of identification of certificate applicants. "Validation" is a subset of "identification" and refers to identification in the context of establishing the identity of certificate applicants. 3. Concepts This section explains the concepts of CP and CPS, and describes their relationship with other PKI documents, such as subscriber agreements and relying party agreements. Other related concepts are also described. Some of the material covered in this section and in some other sections is specific to certificate policies extensions as defined X.509 version 3. Except for those sections, this framework is intended to be adaptable to other certificate formats that may come into use. 3.1. Certificate Policy When a certification authority issues a certificate, it is providing a statement to a certificate user (i.e., a relying party) that a particular public key is bound to the identity and/or other attributes of a particular entity (the certificate subject, which is usually also the subscriber). The extent to which the relying party should rely on that statement by the CA, however, needs to be assessed by the relying party or entity controlling or coordinating the way relying parties or relying party applications use certificates. Different certificates are issued following different practices and procedures, and may be suitable for different applications and/or purposes. The X.509 standard defines a CP as "a named set of rules that indicates the applicability of a certificate to a particular community and/or class of application with common security requirements" [ISO1]. An X.509 Version 3 certificate may identify a specific applicable CP, which may be used by a relying party to
decide whether or not to trust a certificate, associated public key, or any digital signatures verified using the public key for a particular purpose. CPs typically fall into two major categories. First, some CPs "indicate the applicability of a certificate to a particular community" [ISO1]. These CPs set forth requirements for certificate usage and requirements on members of a community. For instance, a CP may focus on the needs of a geographical community, such as the ETSI policy requirements for CAs issuing qualified certificates [ETS]. Also, a CP of this kind may focus on the needs of a specific vertical-market community, such as financial services [IDT]. The second category of typical CPs "indicate the applicability of a certificate to a . . . class of application with common security requirements." These CPs identify a set of applications or uses for certificates and say that these applications or uses require a certain level of security. They then set forth PKI requirements that are appropriate for these applications or uses. A CP within this category often makes sets requirements appropriate for a certain "level of assurance" provided by certificates, relative to certificates issued pursuant to related CPs. These levels of assurance may correspond to "classes" or "types" of certificates. For instance, the Government of Canada PKI Policy Management Authority (GOC PMA) has established eight certificate policies in a single document [GOC], four policies for certificates used for digital signatures and four policies for certificates used for confidentiality encryption. For each of these applications, the document establishes four levels of assurances: rudimentary, basic, medium, and high. The GOC PMA described certain types of digital signature and confidentiality uses in the document, each with a certain set of security requirements, and grouped them into eight categories. The GOC PMA then established PKI requirements for each of these categories, thereby creating eight types of certificates, each providing rudimentary, basic, medium, or high levels of assurance. The progression from rudimentary to high levels corresponds to increasing security requirements and corresponding increasing levels of assurance. A CP is represented in a certificate by a unique number called an "Object Identifier" (OID). That OID, or at least an "arc", can be registered. An "arc" is the beginning of the numerical sequence of an OID and is assigned to a particular organization. The registration process follows the procedures specified in ISO/IEC and ITU standards. The party that registers the OID or arc also can publish the text of the CP, for examination by relying parties. Any one certificate will typically declare a single CP or, possibly, be
issued consistent with a small number of different policies. Such declaration appears in the Certificate Policies extension of a X.509 Version 3 certificate. When a CA places multiple CPs within a certificate's Certificate Policies extension, the CA is asserting that the certificate is appropriate for use in accordance with any of the listed CPs. CPs also constitute a basis for an audit, accreditation, or another assessment of a CA. Each CA can be assessed against one or more certificate policies or CPSs that it is recognized as implementing. When one CA issues a CA-certificate for another CA, the issuing CA must assess the set of certificate policies for which it trusts the subject CA (such assessment may be based upon an assessment with respect to the certificate policies involved). The assessed set of certificate policies is then indicated by the issuing CA in the CA- certificate. The X.509 certification path processing logic employs these CP indications in its well-defined trust model. 3.2. Certificate Policy Examples For example purposes, suppose that the International Air Transport Association (IATA) undertakes to define some certificate policies for use throughout the airline industry, in a PKI operated by IATA in combination with PKIs operated by individual airlines. Two CPs might be defined - the IATA General-Purpose CP, and the IATA Commercial- Grade CP. The IATA General-Purpose CP could be used by industry personnel for protecting routine information (e.g., casual electronic mail) and for authenticating connections from World Wide Web browsers to servers for general information retrieval purposes. The key pairs may be generated, stored, and managed using low-cost, software-based systems, such as commercial browsers. Under this policy, a certificate may be automatically issued to anybody listed as an employee in the corporate directory of IATA or any member airline who submits a signed certificate request form to a network administrator in his or her organization. The IATA Commercial-Grade CP could be used to protect financial transactions or binding contractual exchanges between airlines. Under this policy, IATA could require that certified key pairs be generated and stored in approved cryptographic hardware tokens. Certificates and tokens could be provided to airline employees with disbursement authority. These authorized individuals might then be required to present themselves to the corporate security office, show a valid identification badge, and sign a subscriber agreement requiring them to protect the token and use it only for authorized purposes, as a condition of being issued a token and a certificate.
3.3. X.509 Certificate Fields The following extension fields in an X.509 certificate are used to support CPs: * Certificate Policies extension; * Policy Mappings extension; and * Policy Constraints extension. 3.3.1. Certificate Policies Extension A Certificate Policies field lists CPs that the certification authority declares are applicable. Using the example of the IATA General-Purpose and Commercial-Grade policies defined in Section 3.2, the certificates issued to regular airline employees would contain the object identifier for General-Purpose policy. The certificates issued to the employees with disbursement authority would contain the object identifiers for both the General-Purpose policy and the Commercial-Grade policy. The inclusion of both object identifiers in the certificates means that they would be appropriate for either the General-Purpose or Commercial-Grade policies. The Certificate Policies field may also optionally convey qualifier values for each identified policy; the use of qualifiers is discussed in Section 3.4. When processing a certification path, a CP that is acceptable to the relying party application must be present in every certificate in the path, i.e., in CA-certificates as well as end entity certificates. If the Certificate Policies field is flagged critical, it serves the same purpose as described above but also has an additional role. Specifically, it indicates that the use of the certificate is restricted to one of the identified policies, i.e., the certification authority is declaring that the certificate must only be used in accordance with the provisions of at least one of the listed CPs. This field is intended to protect the certification authority against claims for damages asserted by a relying party who has used the certificate for an inappropriate purpose or in an inappropriate manner, as stipulated in the applicable CP. For example, the Internal Revenue Service might issue certificates to taxpayers for the purpose of protecting tax filings. The Internal Revenue Service understands and can accommodate the risks of erroneously issuing a bad certificate, e.g., to an imposter. Suppose, however, that someone used an Internal Revenue Service tax- filing certificate as the basis for encrypting multi-million-dollar- value proprietary trade secrets, which subsequently fell into the wrong hands because of a cryptanalytic attack by an attacker who is able to decrypt the message. The Internal Revenue Service may want
to defend itself against claims for damages in such circumstances by pointing to the criticality of the Certificate Policies extension to show that the subscriber and relying party misused the certificate. The critical-flagged Certificate Policies extension is intended to mitigate the risk to the CA in such situations. 3.3.2. Policy Mappings Extension The Policy Mappings extension may only be used in CA-certificates. This field allows a certification authority to indicate that certain policies in its own domain can be considered equivalent to certain other policies in the subject certification authority's domain. For example, suppose that for purposes of facilitating interoperability, the ACE Corporation establishes an agreement with the ABC Corporation to cross-certify the public keys of each others' certification authorities for the purposes of mutually securing their respective business-to-business exchanges. Further, suppose that both companies have pre-existing financial transaction protection policies called ace-e-commerce and abc-e-commerce, respectively. One can see that simply generating cross-certificates between the two domains will not provide the necessary interoperability, as the two companies' applications are configured with, and employee certificates are populated with, their respective certificate policies. One possible solution is to reconfigure all of the financial applications to require either policy and to reissue all the certificates with both policies appearing in their Certificate Policies extensions. Another solution, which may be easier to administer, uses the Policy Mapping field. If this field is included in a cross-certificate for the ABC Corporation certification authority issued by the ACE Corporation certification authority, it can provide a statement that the ABC's financial transaction protection policy (i.e., abc-e-commerce) can be considered equivalent to that of the ACE Corporation (i.e., ace-e-commerce). With such a statement included in the cross-certificate issued to ABC, relying party applications in the ACE domain requiring the presence of the object identifier for the ace-e-commerce CP can also accept, process, and rely upon certificates issued within the ABC domain containing the object identifier for the abc-e-commerce CP. 3.3.3. Policy Constraints Extension The Policy Constraints extension supports two optional features. The first is the ability for a certification authority to require that explicit CP indications be present in all subsequent certificates in a certification path. Certificates at the start of a certification path may be considered by a relying party to be part of a trusted domain, i.e., certification authorities are trusted for all purposes
so no particular CP is needed in the Certificate Policies extension. Such certificates need not contain explicit indications of CP. When a certification authority in the trusted domain, however, certifies outside the domain, it can activate the requirement that a specific CP's object identifier appear in subsequent certificates in the certification path. The other optional feature in the Policy Constraints field is the ability for a certification authority to disable policy mapping by subsequent certification authorities in a certification path. It may be prudent to disable policy mapping when certifying outside the domain. This can assist in controlling risks due to transitive trust, e.g., a domain A trusts domain B, domain B trusts domain C, but domain A does not want to be forced to trust domain C. 3.3.4. Policy Qualifiers The Certificate Policies extension field has a provision for conveying, along with each CP identifier, additional policy-dependent information in a qualifier field. The X.509 standard does not mandate the purpose for which this field is to be used, nor does it prescribe the syntax for this field. Policy qualifier types can be registered by any organization. The following policy qualifier types are defined in PKIX RFC 3280 [PKI1]: (a) The CPS Pointer qualifier contains a pointer to a CPS, CPS Summary, RPA, or PDS published by the CA. The pointer is in the form of a uniform resource identifier (URI). (b) The User Notice qualifier contains a text string that is to be displayed to subscribers and relying parties prior to the use of the certificate. The text string may be an IA5String or a BMPString - a subset of the ISO 100646-1 multiple octet coded character set. A CA may invoke a procedure that requires that the relying party acknowledge that the applicable terms and conditions have been disclosed and/or accepted. Policy qualifiers can be used to support the definition of generic, or parameterized, CPs. Provided the base CP so provides, policy qualifier types can be defined to convey, on a per-certificate basis, additional specific policy details that fill in the generic definition.
3.4. Certification Practice Statement The term certification practice statement (CPS) is defined by the DSG and PAG as: "A statement of the practices which a certification authority employs in issuing certificates." [ABA1, ABA2] As stated above, a CPS establishes practices concerning lifecycle services in addition to issuance, such as certificate management (including publication and archiving), revocation, and renewal or re-keying. In the DSG, the ABA expands this definition with the following comments: "A certification practice statement may take the form of a declaration by the certification authority of the details of its trustworthy system and the practices it employs in its operations and in support of issuance of a certificate . . . ." This form of CPS is the most common type, and can vary in length and level of detail. Some PKIs may not have the need to create a thorough and detailed statement of practices. For example, the CA may itself be the relying party and would already be aware of the nature and trustworthiness of its services. In other cases, a PKI may provide certificates providing only a very low level of assurances where the applications being secured may pose only marginal risks if compromised. In these cases, an organization establishing a PKI may only want to write or have CAs use a subscriber agreement, relying party agreement, or agreement combining subscriber and relying party terms, depending on the role of the different PKI participants. In such a PKI, that agreement may serve as the only "statement of practices" used by one or more CAs within that PKI. Consequently, that agreement may also be considered a CPS and can be entitled or subtitled as such. Likewise, since a detailed CPS may contain sensitive details of its system, a CA may elect not to publish its entire CPS. It may instead opt to publish a CPS Summary (or CPS Abstract). The CPS Summary would contain only those provisions from the CPS that the CA considers to be relevant to the participants in the PKI (such as the responsibilities of the parties or the stages of the certificate lifecycle). A CPS Summary, however, would not contain those sensitive provisions of the full CPS that might provide an attacker with useful information about the CA's operations. Throughout this document, the use of "CPS" includes both a detailed CPS and a CPS Summary (unless otherwise specified). CPSs do not automatically constitute contracts and do not automatically bind PKI participants as a contract would. Where a document serves the dual purpose of being a subscriber or relying party agreement and CPS, the document is intended to be a contract and constitutes a binding contract to the extent that a subscriber or
relying party agreement would ordinarily be considered as such. Most CPSs, however, do not serve such a dual purpose. Therefore, in most cases, a CPS's terms have a binding effect as contract terms only if a separate document creates a contractual relationship between the parties and that document incorporates part or all of the CPS by reference. Further, if a particular PKI employs a CPS Summary (as opposed to the entire CPS), the CPS Summary could be incorporated into any applicable subscriber or relying party agreement. In the future, a court or applicable statutory or regulatory law may declare that a certificate itself is a document that is capable of creating a contractual relationship, to the extent its mechanisms designed for incorporation by reference (such as the Certificate Policies extension and its qualifiers) indicate that terms of its use appear in certain documents. In the meantime, however, some subscriber agreements and relying party agreements may incorporate a CPS by reference and therefore make its terms binding on the parties to such agreements. 3.5. Relationship Between Certificate Policy and Certification Practice Statement The CP and CPS address the same set of topics that are of interest to the relying party in terms of the degree to and purpose for which a public key certificate should be trusted. Their primary difference is in the focus of their provisions. A CP sets forth the requirements and standards imposed by the PKI with respect to the various topics. In other words, the purpose of the CP is to establish what participants must do. A CPS, by contrast, states how a CA and other participants in a given domain implement procedures and controls to meet the requirements stated in the CP. In other words, the purpose of the CPS is to disclose how the participants perform their functions and implement controls. An additional difference between a CP and CPS relates the scope of coverage of the two kinds of documents. Since a CP is a statement of requirements, it best serves as the vehicle for communicating minimum operating guidelines that must be met by interoperating PKIs. Thus, a CP generally applies to multiple CAs, multiple organizations, or multiple domains. By contrast, a CPS applies only to a single CA or single organization and is not generally a vehicle to facilitate interoperation. A CA with a single CPS may support multiple CPs (used for different application purposes and/or by different relying party communities). Also, multiple CAs, with non-identical CPSs, may support the same CP.
For example, the Federal Government might define a government-wide CP for handling confidential human resources information. The CP will be a broad statement of the general requirements for participants within the Government's PKI, and an indication of the types of applications for which it is suitable for use. Each department or agency wishing to operate a certification authority in this PKI may be required to write its own certification practice statement to support this CP by explaining how it meets the requirements of the CP. At the same time, a department's or agency's CPS may support other certificate policies. An additional difference between a CP and CPS concerns the level of detail of the provisions in each. Although the level of detail may vary among CPSs, a CPS will generally be more detailed than a CP. A CPS provides a detailed description of procedures and controls in place to meet the CP requirements, while a CP is more general. The main differences between CPs and CPSs can therefore be summarized as follows: (a) A PKI uses a CP to establish requirements that state what participants within it must do. A single CA or organization can use a CPS to disclose how it meets the requirements of a CP or how it implements its practices and controls. (b) A CP facilitates interoperation through cross-certification, unilateral certification, or other means. Therefore, it is intended to cover multiple CAs. By contrast, a CPS is a statement of a single CA or organization. Its purpose is not to facilitate interoperation (since doing so is the function of a CP). (c) A CPS is generally more detailed than a CP and specifies how the CA meets the requirements specified in the one or more CPs under which it issues certificates. In addition to populating the certificate policies extension with the applicable CP object identifier, a certification authority may include, in certificates it issues, a reference to its certification practice statement. A standard way to do this, using a CP qualifier, is described in Section 3.4. 3.6. Relationship Among CPs, CPSs, Agreements, and Other Documents CPs and CPSs play a central role in documenting the requirements and practices of a PKI. Nonetheless, they are not the only documents relevant to a PKI. For instance, subscriber agreements and relying party agreements play a critical role in allocating responsibilities
to subscribers and relying parties relating to the use of certificates and key pairs. They establish the terms and conditions under which certificates are issued, managed, and used. The term subscriber agreement is defined by the PAG as: "An agreement between a CA and a subscriber that establishes the right and obligations of the parties regarding the issuance and management of certificates." [ABA2] The PAG defines a relying party agreement as: "An agreement between a certification authority and relying party that typically establishes the rights and obligations between those parties regarding the verification of digital signatures or other uses of certificates." [ABA2] As mentioned in Section 3.5, a subscriber agreement, relying party agreement, or an agreement that combines subscriber and relying party terms may also serve as a CPS. In other PKIs, however, a subscriber or relying party agreement may incorporate some or all of the terms of a CP or CPS by reference. Yet other PKIs may distill from a CP and/or CPS the terms that are applicable to a subscriber and place such terms in a self-contained subscriber agreement, without incorporating a CP or CPS by reference. They may use the same method to distill relying party terms from a CP and/or CPS and place such terms in a self-contained relying party agreement. Creating such self-contained agreements has the advantage of creating documents that are easier for consumers to review. In some cases, subscribers or relying parties may be deemed to be "consumers" under applicable law, who are subject to certain statutory or regulatory protections. Under the legal systems of civil law countries, incorporating a CP or CPS by reference may not be effective to bind consumers to the terms of an incorporated CP or CPS. CPs and CPSs may be incorporated by reference in other documents, including: * Interoperability agreements (including agreements between CAs for cross-certification, unilateral certification, or other forms of interoperation), * Vendor agreements (under which a PKI vendor agrees to meet standards set forth in a CP or CPS), or * A PDS. See [ABA2] A PDS serves a similar function to a CPS Summary. It is a relatively short document containing only a subset of critical details about a PKI or CA. It may differ from a CPS Summary, however, in that its purpose is to act as a summary of information about the overall nature of the PKI, as opposed to simply a condensed form of the CPS.
Moreover, its purpose is to distill information about the PKI, as opposed to protecting security sensitive information contained in an unpublished CPS, although a PDS could also serve that function. Just as writers may wish to refer to a CP or CPS or incorporate it by reference in an agreement or PDS, a CP or CPS may refer to other documents when establishing requirements or making disclosures. For instance, a CP may set requirements for certificate content by referring to an external document setting forth a standard certificate profile. Referencing external documents permits a CP or CPS to impose detailed requirements or make detailed disclosures without having to reprint lengthy provisions from other documents within the CP or CPS. Moreover, referencing a document in a CP or CPS is another useful way of dividing disclosures between public information and security sensitive confidential information (in addition to or as an alternative to publishing a CPS Summary). For example, a PKI may want to publish a CP or CPS, but maintain site construction parameters for CA high security zones as confidential information. In that case, the CP or CPS could reference an external manual or document containing the detailed site construction parameters. Documents that a PKI may wish to refer to in a CP or CPS include: * A security policy, * Training, operational, installation, and user manuals (which may contain operational requirements), * Standards documents that apply to particular aspects of the PKI (such as standards specifying the level of protection offered by any hardware tokens used in the PKI or standards applicable to the site construction), * Key management plans, * Human resource guides and employment manuals (which may describe some aspects of personnel security practices), and * E-mail policies (which may discuss subscriber and relying party responsibilities, as well as the implications of key management, if applicable). See [ABA2]
3.7. Set of Provisions A set of provisions is a collection of practice and/or policy statements, spanning a range of standard topics for use in expressing a CP or CPS employing the approach described in this framework by covering the topic appearing in Section 5 below. They are also described in detail in Section 4 below. A CP can be expressed as a single set of provisions. A CPS can be expressed as a single set of provisions with each component addressing the requirements of one or more certificate policies, or, alternatively, as an organized collection of sets of provisions. For example, a CPS could be expressed as a combination of the following: (a) a list of certificate policies supported by the CPS; (b) for each CP in (a), a set of provisions that contains statements responding to that CP by filling in details not stipulated in that policy or expressly left to the discretion of the CA (in its CPS) ; such statements serve to state how this particular CPS implements the requirements of the particular CP; or (c) a set of provisions that contains statements regarding the certification practices on the CA, regardless of CP. The statements provided in (b) and (c) may augment or refine the stipulations of the applicable CP, but generally must not conflict with any of the stipulations of such CP. In certain cases, however, a policy authority may permit exceptions to the requirements in a CP, because certain compensating controls of the CA are disclosed in its CPS that allow the CA to provide assurances that are equivalent to the assurances provided by CAs that are in full compliance with the CP. This framework outlines the contents of a set of provisions, in terms of nine primary components, as follows: 1. Introduction 2. Publication and Repository 3. Identification and Authentication 4. Certificate Life-Cycle Operational Requirements 5. Facilities, Management, and Operational Controls 6. Technical Security Controls 7. Certificate, CRL, and OCSP Profile 8. Compliance audit 9. Other Business and Legal Matters
PKIs can use this simple framework of nine primary components to write a simple CP or CPS. Moreover, a CA can use this same framework to write a subscriber agreement, relying party agreement, or agreement containing subscriber and relying party terms. If a CA uses this simple framework to construct an agreement, it can use paragraph 1 as an introduction or recitals, it can set forth the responsibilities of the parties in paragraphs 2-8, and it can use paragraph 9 to cover the business and legal issues described in more detail, using the ordering of Section 4.9 below (such as representations and warranties, disclaimers, and liability limitations). The ordering of topics in this simple framework and the business and legal matters Section 4.9 is the same as (or similar to) the ordering of topics in a typical software or other technology agreement. Therefore, a PKI can establish a set of core documents (with a CP, CPS, subscriber agreement, and relying party agreement) all having the same structure and ordering of topics, thereby facilitating comparisons and mappings among these documents and among the corresponding documents of other PKIs. This simple framework may also be useful for agreements other than subscriber agreements and relying party agreements. For instance, a CA wishing to outsource certain services to an RA or certificate manufacturing authority (CMA) may find it useful to use this framework as a checklist to write a registration authority agreement or outsourcing agreement. Similarly, two CAs may wish to use this simple framework for the purpose of drafting a cross-certification, unilateral certification, or other interoperability agreement. In short, the primary components of the simple framework (specified above) may meet the needs of drafters of short CPs, CPSs, subscriber agreements, and relying party agreements. Nonetheless, this framework is extensible, and its coverage of the nine components is flexible enough to meet the needs of drafters of comprehensive CPs and CPSs. Specifically, components appearing above can be further divided into subcomponents, and a subcomponent may comprise multiple elements. Section 4 provides a more detailed description of the contents of the above components, and their subcomponents. Drafters of CPs and CPSs are permitted to add additional levels of subcomponents below the subcomponents described in Section 4 for the purpose of meeting the needs of the drafter's particular PKI.