Movatterモバイル変換

Network Working Group                                          D. PinkasRequest for Comments: 3379                                          BullCategory: Informational                                       R. Housley                                                        RSA Laboratories                                                          September 2002Delegated Path Validation and Delegated Path DiscoveryProtocol RequirementsStatus 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 (2002).  All Rights Reserved.Abstract   This document specifies the requirements for Delegated Path   Validation (DPV) and Delegated Path Discovery (DPD) for Public Key   Certificates. It also specifies the requirements for DPV and DPD   policy management.1. Introduction   This document specifies the requirements for Delegated Path   Validation (DPV) and Delegated Path Discovery (DPD) for Public Key   Certificates, using two main request/response pairs.   Delegated processing provides two primary services: DPV and DPD.   Some clients require a server to perform certification path   validation and have no need for data acquisition, while some other   clients require only path discovery in support of local path   validation.   The DPV request/response pair, can be used to fully delegate path   validation processing to an DPV server, according to a set of rules,   called a validation policy.   The DPD request/response pair can be used to obtain from a DPD server   all the information needed (e.g., the end-entity certificate, the CA   certificates, full CRLs, delta-CRLs, OCSP responses) to locally   validate a certificate.  The DPD server uses a set of rules, called a   path discovery policy, to determine which information to return.Pinkas & Housley             Informational                      [Page 1]

RFC 3379           DPV and DPD Protocol Requirements      September 2002   A third request/response pair allows clients to obtain references for   the policies supported by a DPV or DPD server.1.1. Terminology   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document (in uppercase, as shown) are to be interpreted as described   in [RFC2119].2. Rationale and Benefits for DPV (Delegated Path Validation)   DPV allows a server to perform a real time certificate validation for   a validation time T, where T may be the current time or a time in the   recent past.   In order to validate a certificate, a chain of multiple certificates,   called a certification path, may be needed, comprising a certificate   of the public key owner (the end entity) signed by one CA, and zero   or more additional certificates of CAs signed by other CAs.   Offloading path validation to a server may be required by a client   that lacks the processing, and/or communication capabilities to fetch   the necessary certificates and revocation information, perform   certification path construction, and perform local path validation.   In constrained execution environments, such as telephones and PDAs,   memory and processing limitations may preclude local implementation   of complete, PKIX-compliant certification path validation [PKIX-1].   In applications where minimum latency is critical, delegating   validation to a trusted server can offer significant advantages. The   time required to send the target certificate to the validation   server, receive the response, and authenticate the response, can be   considerably less than the time required for the client to perform   certification path discovery and validation.  Even if a certification   path were readily available to the client, the processing time   associated with signature verification for each certificate in the   path might (especially when validating very long paths or using a   limited processor) be greater than the delay associated with use of a   validation server.Pinkas & Housley             Informational                      [Page 2]

RFC 3379           DPV and DPD Protocol Requirements      September 2002   Another motivation for offloading path validation is that it allows   validation against management-defined validation policies in a   consistent fashion across an enterprise.  Clients that are able to do   their own path validation may rely on a trusted server to do path   validation if centralized management of validation policies is   needed, or the clients rely on a trusted server to maintain   centralized records of such activities.   When a client uses this service, it inherently trusts the server as   much as it would its own path validation software (if it contained   such software).  Clients can direct the server to perform path   validation in accordance with a particular validation policy.3. Rationale and Benefits for DPD (Delegated Path Discovery)   DPD is valuable for clients that do much of the PKI processing   themselves and simply want a server to collect information for them.   The server is trusted to return the most current information that is   available to it (which may not be the most current information that   has been issued).  The client will ultimately perform certification   path validation.   A client that performs path validation for itself may get benefit in   several ways from using a server to acquire certificates, CRLs, and   OCSP responses [OCSP] as inputs to the validation process.  In this   context, the client is relying on the server to interact with   repositories to acquire the data that the client would otherwise have   to acquire using LDAP, HTTP, FTP [LDAP, FTP&HTTP] or another   repository access protocol.  Since these data items are digitally   signed, the client need not trust the server any more than the client   would trust the repositories.   DPD provides several benefits.  For example, a single query to a   server can replace multiple repository queries, and caching by the   server can reduce latency.  Another benefit to the client system is   that it need not incorporate a diverse set of software to interact   with various forms of repositories, perhaps via different protocols,   nor to perform the graph processing necessary to discover   certification paths, separate from making the queries to acquire path   validation data.4. Delegated Path Validation Protocol Requirements4.1. Basic Protocol   The Delegated Path Validation (DPV) protocol allows a server to   validate one or more public key certificates on behalf of a client   according to a validation policy.Pinkas & Housley             Informational                      [Page 3]

RFC 3379           DPV and DPD Protocol Requirements      September 2002   If the DPV server does not support the client requested validation   policy, then the DPV server MUST return an error.   If the DPV request does not specify a validation policy, the server   response MUST indicate the validation policy that was used.   Policy definitions can be quite long and complex, and some policies   may allow for the setting of a few parameters (such as root self-   signed certificates).  The protocol MUST allow the client to include   these policy dependent parameters in the DPV request; however, it is   expected that most clients will simply reference a validation policy   for a given application or accept the DPV server's default validation   policy.   The client can request that the server determines the certificate   validity at a time other than the current time.  The DPV server MUST   obtain revocation status information for the validation time in the   client request.   In order to obtain the revocation status information of any   certificate from the certification path, the DPV server might use, in   accordance with the validation policy, different sources of   revocation information.  For example, a combination of OCSP   responses, CRLs, and delta CRLs could be used.  Alternatively, a   response from another DPV server could be used.   If the revocation status information for the requested validation   time is unavailable, then the DPV server MUST return a status   indicating that the certificate is invalid.  Additional information   about the reason for invalidity MAY also be provided.   The certificate to be validated MUST either be directly provided in   the request or unambiguously referenced, such as the CA distinguished   name, certificate serial number, and the hash of the certificate,   like ESSCertID as defined in [ESS] or OtherSigningCertificate as   defined in [ES-F].   The DPV client MUST be able to provide to the validation server,   associated with each certificate to be validated, useful   certificates, as well as useful revocation information.  Revocation   information includes OCSP responses, CRLs, and delta CRLs.  As an   example, an S/MIME message might include such information, and the   client can simply copy that information into the DPV request.Pinkas & Housley             Informational                      [Page 4]

RFC 3379           DPV and DPD Protocol Requirements      September 2002   The DPV server MUST have the certificate to be validated.  When the   certificate is not provided in the request, the server MUST obtain   the certificate and then verify that the certificate is indeed the   one being unambiguous referenced by the client.  The DPV server MUST   include either the certificate or an unambiguous reference to the   certificate (in case of a CA key compromise) in the DPV response.   The DPV response MUST indicate one of the following status   alternatives:   1) the certificate is valid according to the validation policy.   2) the certificate is not valid according to the validation policy.   3) the validity of the certificate is unknown according to the      validation policy.   4) the validity could not be determined due to an error.   When the certificate is not valid according to the validation policy,   then the reason MUST also be indicated.  Invalidity reasons include:   a) the DPV server cannot determine the validity of the certificate      because a certification path cannot be constructed.   b) the DPV server successfully constructed a certification path, but      it was not valid according to the validation algorithm in      [PKIX-1].   c) the certificate is not valid at this time.  If another request      could be made later on, the certificate could possibly be      determined as valid.  This condition may occur before a      certificate validity period has begun or while a certificate is      suspended.   The protocol MUST prevent replay attacks, and the replay prevention   mechanism employed by the protocol MUST NOT rely on synchronized   clocks.   The DPV request MUST allow the client to request that the server   include in its response additional information which will allow   relying parties not trusting the DPV server to be confident that the   certificate validation has correctly been performed.  Such   information may (not necessarily exclusively) consist of a   certification path, revocation status information from authorized CRL   issuers or authorized OCSP responders, revocation status information   from CRL issuers or OCSP responders trusted under the validationPinkas & Housley             Informational                      [Page 5]

RFC 3379           DPV and DPD Protocol Requirements      September 2002   policy, time-stamp tokens from TSAs responders trusted under the   validation policy, or a DPV response from a DPV server that is   trusted under the validation policy.  When the certificate is valid   according to the validation policy, the server MUST, upon request,   include that information in the response.  However, the server MAY   omit that information when the certificate is invalid or when it   cannot determine the validity.   The DPV server MUST be able, upon request, copy a text field provided   by the client into the DPV response.  As an example, this field may   relate to the nature or reason for the DPV query.   The DPV response MUST be bound to the DPV request so that the client   can be sure that all the parameters from the request have been taken   into consideration by the DPV server to build the response.  This can   be accomplished by including a one-way hash of the request in the   response.   In some environments it may be necessary to present only a DPV   response to another relying party without the corresponding request.   In this case the response MUST be self contained.  This can be   accomplished by repeating only the important components from the   request in the response.   For the client to be confident that the certificate validation was   handled by the expected DPV server, the DPV response MUST be   authenticated, unless an error is reported (such as a badly formatted   request or unknown validation policy).   For the client to be able prove to a third party that trusts the same   DPV server that the certificate validation was handled correctly, the   DPV response MUST be digitally signed, unless an error is reported.   The DPV server's certificate MUST authenticate the DPV server.   The DPV server MAY require client authentication, therefore, the DPV   request MUST be able to be authenticated.   When the DPV request is authenticated, the client SHOULD be able to   include a client identifier in the request for the DPV server to copy   into the response.  Mechanisms for matching this identifier with the   authenticated identity depends on local DPV server conditions and/or   the validation policy.  The DPV server MAY choose to blindly copy the   identifier, omit the identifier, or return an error response.   There are no specific confidentiality requirements within this   application layer protocol.  However, when confidentiality is needed,   it can be achieved with a lower-layer security protocol.Pinkas & Housley             Informational                      [Page 6]

RFC 3379           DPV and DPD Protocol Requirements      September 20024.2. Relaying, Re-direction and Multicasting   In some network environments, especially ones that include firewalls,   a DPV server might not be able to obtain all of the information that   it needs to process a request.  However, the DPV server might be   configured to use the services of one or more other DPV servers to   fulfill all requests.  In such cases, the client is unaware that the   queried DPV server is using the services of other DPV servers, and   the client-queried DPV server acts as a DPV client to another DPV   server.  Unlike the original client, the DPV server is expected to   have moderate computing and memory resources, enabling the use of   relay, re-direct or multicasting mechanisms.  The requirements in   this section support DPV server-to-DPV server exchanges without   imposing them on DPV client-to-DPV server exchanges.   Protocols designed to satisfy these requirements MAY include optional   fields and/or extensions to support relaying, re-direction or   multicasting.  However, DPV clients are not expected to support   relay, re-direct or multicast.  If the protocol supports such   features, the protocol MUST include provisions for DPV clients and   DPV servers that do not support such features, allowing them to   conform to the basic set of requirements.   - When a server supports a relay mechanism, a mechanism to detect     loops or repetition MUST be provided.   - When a protocol provides the capability for a DPV server to re-     direct a request to another DPV server (that is, the protocol     chooses to provide a referral mechanism), a mechanism to provide     information to be used for the re-direction SHOULD be supported.     If such re-direction information is sent back to clients, then the     protocol MUST allow conforming clients to ignore it.   - Optional parameters in the protocol request and/or response MAY be     provide support for relaying, re-direction or multicasting.  DPV     clients that ignore any such optional parameters MUST be able to     use the DPV service.  DPV servers that ignore any such optional     parameters MUST still be able to offer the DPV service, although     they might not be able to overcome the limitations imposed by the     network topology.  In this way, protocol implementers do not need     to understand the syntax or semantics of any such optional     parameters.5. Delegated Path Discovery Protocol Requirements   The Delegated Path Discovery (DPD) protocol allows the client to use   a single request to collect at one time from a single server the data   elements available at the current time that might be collected usingPinkas & Housley             Informational                      [Page 7]

RFC 3379           DPV and DPD Protocol Requirements      September 2002   different protocols (such as LDAP, HTTP, FTP, or OCSP) or by querying   multiple servers, to locally validate a public key certificate   according to a single path discovery policy.  The returned   information can be used to locally validate one or more certificates   for the current time.   Clients MUST be able to specify whether they want, in addition to the   certification path, the revocation information associated with the   path, for the end-entity certificate, for the CA certificates, or for   both.   If the DPD server does not support the client requested path   discovery policy, the DPD server MUST return an error.  Some forms of   path discovery policy can be simple.  In that case it is acceptable   to pass the parameters from the path discovery policy with each   individual request.  For example, the client might provide a set of   trust anchors and separate revocation status conditions for the end-   entity certificate and for the other certificates.  The DPD request   MUST allow more elaborated path discovery policies to be referenced.   However, it is expected that most of the time clients will only be   aware of the referenced path discovery policy for a given   application.   The DPD server response includes zero, one, or several certification   paths.  Each path consists of a sequence of certificates, starting   with the certificate to be validated and ending with a trust anchor.   If the trust anchor is a self-signed certificate, that self-signed   certificate MUST NOT be included.  In addition, if requested, the   revocation information associated with each certificate in the path   MUST also be returned.   By default, the DPD server MUST return a single certification path   for each end-entity certificate in the DPD request.  However, the   returned path may need to match some additional local criteria known   only to the client.  For example, the client might require the   presence of a particular certificate extension or a particular name   form.  Therefore, the DPD client MUST have a means of obtaining more   than one certification path for each end-entity certificate in the   DPD request.  At the same time, the mechanism for obtaining   additional certification paths MUST NOT impose protocol state on the   DPD server.  Avoiding the maintenance of state information associated   with previous requests minimizes potential denial of service attacks   and other problems associated with server crashes.   Path discovery MUST be performed according to the path discovery   policy.  The DPD response MUST indicate one of the following status   alternatives:Pinkas & Housley             Informational                      [Page 8]

RFC 3379           DPV and DPD Protocol Requirements      September 2002   1) one or more certification paths was found according to the path      discovery policy, with all of the requested revocation information      present.   2) one or more certification paths was found according to the path      discovery policy, with a subset of the requested revocation      information present.   3) one or more certification paths was found according to the path      discovery policy, with none of the requested revocation      information present.   4) no certification path was found according to the path discovery      policy.   5) path construction could not be performed due to an error.   When no errors are detected, the information that is returned   consists of one or more certification paths and, if requested, its   associated revocation status information for each certificate in the   path.   For the client to be confident that all of the elements from the   response originate from the expected DPD server, an authenticated   response MAY be required.  For example, the server might sign the   response or data authentication might also be achieved using a   lower-layer security protocol.   The DPD server MAY require client authentication, allowing the DPD   request MUST to be authenticated.   There are no specific confidentiality requirement within the   application layer protocol.  However, when confidentiality is needed,   it can be achieved with a lower-layer security protocol.6. DPV and DPD Policy Query   Using a separate request/response pair, the DPV or DPD client MUST be   able to obtain references for the default policy or for all of the   policies supported by the server.  The response can include   references to previously defined policies or to a priori known   policies.7. Validation Policy   A validation policy is a set of rules against which the validation of   the certificate is performed.Pinkas & Housley             Informational                      [Page 9]

RFC 3379           DPV and DPD Protocol Requirements      September 2002   A validation policy MAY include several trust anchors.  A trust   anchor is defined as one public key, a CA name, and a validity time   interval; a trust anchor optionally includes additional constraints.   The use of a self-signed certificate is one way to specify the public   key to be used, the issuer name, and the validity period of the   public key.   Additional constraints for each trust anchor MAY be defined.  These   constraints might include a set of certification policy constraints   or a set of naming constraints.  These constraints MAY also be   included in self-signed certificates.   Additional conditions that apply to the certificates in the path MAY   also be specified in the validation policy.  For example, specific   values could be provided for the inputs to the certification path   validation algorithm in [PKIX-1], such as user-initial-policy-set,   initial-policy-mapping-inhibit, initial-explicit-policy, or initial-   any-policy-inhibit.   Additional conditions that apply to the end-entity certificate MAY   also be specified in the validation policy.  For example, a specific   name form might be required.   In order to succeed, one valid certification path (none of the   certificates in the path are expired or revoked) MUST be found   between an end-entity certificate and a trust anchor and all   constraints that apply to the certification path MUST be verified.7.1. Components for a Validation Policy   A validation policy is built from three components:   1. Certification path requirements,   2. Revocation requirements, and   3. End-entity certificate specific requirements.   Note:  [ES-P] defines ASN.1 data elements that may be useful while   defining the components of a validation policy.7.2. Certificate Path Requirements   The path requirements identify a sequence of trust anchors used to   start certification path processing and initial conditions for   certification path validation as defined in [PKIX-1].Pinkas & Housley             Informational                     [Page 10]

RFC 3379           DPV and DPD Protocol Requirements      September 20027.3. Revocation Requirements   Revocation information might be obtained through CRLs, delta CRLs or   OCSP responses.  Certificate revocation requirements are specified in   terms of checks required on the end-entity certificate and CA   certificates.   Revocation requirements for the end-entity certificate may not be the   same as the requirements for the CA certificates.  For example, an   OCSP response may be needed for the end-entity certificate while CRLs   may be sufficient for the CA certificates.   The validation policy MUST specify the source of revocation   information:   - full CRLs (or full Authority Revocation Lists) have to be     collected.   - OCSP responses, using [OCSP], have to be collected.   - delta CRLs and the relevant associated full CRLs (or full Authority     Revocation Lists) are to be collected.   - any available revocation information has to be collected.   - no revocation information need be collected.7.4. End-entity Certificate Specific Requirements   The validation policy might require the end-entity certificate to   contain specific extensions with specific types or values (it does   not matter whether they are critical or non-critical).  For example,   the validation policy might require an end-entity certificate that   contains an electronic mail address (either in therfc822 subject alt   name or in the emailAddress naming attribute in the subject name).8. Path Discovery Policy   A path discovery policy is a set of rules against which the discovery   of a certification path is performed.  A path discovery policy is a   subset of a validation policy.  A path discovery policy MAY either be   a reference to a validation policy or contain only some major   elements from a validation policy, such as the trust anchors.   Since the DPD client is "PKI aware", it can locally apply additional   selection criteria to the certification paths returned by the server.   Thus, a simpler policy can be defined and used for path discovery.Pinkas & Housley             Informational                     [Page 11]

RFC 3379           DPV and DPD Protocol Requirements      September 20028.1. Components for a Path Discovery Policy   The path discovery policy includes certification path requirements,   revocation requirements, and end-entity certificate specific   requirements.  These requirements are the same as those specified in   sections7.2,7.3, and7.4, respectively.9. Security Considerations   A DPV client must trust a DPV server to provide the correct answer.   However, this does not mean that all DPV clients will trust the same   DPV servers.  While a positive answer might be sufficient for one DPV   client, that same positive answer will not necessarily convince   another DPV client.   Other clients may trust their own DPV servers, or they might perform   certification path validation themselves.  DPV clients operating   under an organizational validation policy must ensure that each of   the DPV servers they trust is operating under that organizational   validation policy.   When no policy reference is present in the DPV request, the DPV   client ought to verify that the policy selected by the DPV server is   appropriate.   The revocation status information is obtained for the validation   time.  In case of a digital signature, it is not necessarily   identical to the time when the private key was used.  The validation   time ought to be adjusted by the DPV client to compensate for:   1) time for the end-entity to realize that its private key has been      or could possibly be compromised, and/or   2) time for the end-entity to report the key compromise, and/or   3) time for the revocation authority to process the revocation      request from the end-entity, and/or   4) time for the revocation authority to update and distribute the      revocation status information.10. Acknowledgments   These requirements have been refined after some valuable inputs from   Trevor Freeman, Paul Hoffman, Ambarish Malpani, Mike Myers, Tim Polk,   and Peter Sylvester.Pinkas & Housley             Informational                     [Page 12]

RFC 3379           DPV and DPD Protocol Requirements      September 200211. References11.1. Normative References   [PKIX-1]   Housley, R., Ford, W., Polk, W. and D. Solo, "Internet              X.509 Public Key Infrastructure Certificate and CRL              Profile",RFC 3280, April 2002.   [OCSP]     Myers, M., Ankney, R., Malpani, A., Galperin, S. and C.              Adams, "X.509 Internet Public Key Infrastructure Online              Certificate Status Protocol - OCSP",RFC 2560, June 1999.11.2. Informative References   [ES-F]     Pinkas, D., Ross, J. and N. Pope, "Electronic Signature              Formats for long term electronic signatures",RFC 3126,              September 2001.   [ES-P]     Pinkas, D., Ross, J. and N. Pope, "Electronic Signature              Policies",RFC 3125, September 2001.   [ESS]      Hoffman, P., "Enhanced Security Services for S/MIME",RFC2634, June 1999.   [ISO-X509] ISO/IEC 9594-8/ITU-T Recommendation X.509, "Information              Technology - Open Systems Interconnection: The Directory:              Authentication Framework," 1997 edition.   [FTP&HTTP] Housley, R. and P. Hoffman, "Internet X.509 Public Key              Infrastructure. Operational Protocols: FTP and HTTP",RFC2585, May 1999.   [LDAP]     Boeyen, S., Howes, T. and P. Richard, "Internet X.509              Public Key Infrastructure Operational Protocols LDAPv2",RFC 2559, April 1999.Pinkas & Housley             Informational                     [Page 13]

RFC 3379           DPV and DPD Protocol Requirements      September 200212. Authors' Addresses   Denis Pinkas   Bull   Rue Jean-Jaures - BP 68   78340 Les Clayes-sous-Bois   FRANCE   EMail: Denis.Pinkas@bull.net   Russell Housley   RSA Laboratories   918 Spring Knoll Drive   Herndon, VA 20170   USA   EMail: rhousley@rsasecurity.comPinkas & Housley             Informational                     [Page 14]

RFC 3379           DPV and DPD Protocol Requirements      September 200213.  Full Copyright Statement   Copyright (C) The Internet Society (2002).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS 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.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Pinkas & Housley             Informational                     [Page 15]