





Network Working Group                                    C. Bonatti, Ed.
Request for Comments: 4809                                S. Turner, Ed.
Category: Informational                                             IECA
                                                        G. Lebovitz, Ed.
                                                                 Juniper
                                                           February 2007


       Requirements for an IPsec Certificate Management Profile

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 IETF Trust (2007).

Abstract

   This informational document describes and identifies the requirements
   for transactions to handle Public Key Certificate (PKC) lifecycle
   transactions between Internet Protocol Security (IPsec) Virtual
   Private Network (VPN) Systems using Internet Key Exchange (IKE)
   (versions 1 and 2) and Public Key Infrastructure (PKI) Systems.
   These requirements are designed to meet the needs of enterprise-scale
   IPsec VPN deployments.  It is intended that a standards track profile
   of a management protocol will be created to address many of these
   requirements.




















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Table of Contents

   1. Introduction ....................................................4
      1.1. Scope ......................................................5
      1.2. Non-Goals ..................................................6
      1.3. Definitions ................................................6
      1.4. Requirements Terminology ...................................8
   2. Architecture ....................................................9
      2.1. VPN System .................................................9
           2.1.1. IPsec Peer(s) .......................................9
           2.1.2. VPN Administration Function (Admin) .................9
      2.2. PKI System ................................................10
      2.3. VPN-PKI Interaction .......................................11
   3. Requirements ...................................................13
      3.1. General Requirements ......................................13
           3.1.1. One Protocol .......................................13
           3.1.2. Secure Transactions ................................13
           3.1.3. Admin Availability .................................13
           3.1.4. PKI Availability ...................................14
           3.1.5. End-User Transparency ..............................14
           3.1.6. PKC Profile for PKI Interaction ....................14
                  3.1.6.1. Identity ..................................15
                  3.1.6.2. Key Usage .................................15
                  3.1.6.3. Extended Key Usage ........................15
                  3.1.6.4. Revocation Information Location ...........15
           3.1.7. Error Handling .....................................15
      3.2. Authorization .............................................15
           3.2.1. One Protocol .......................................15
           3.2.2. Bulk Authorization .................................16
           3.2.3. Authorization Scenario .............................16
           3.2.4. Authorization Request ..............................17
                  3.2.4.1. Specifying Fields within the PKC ..........17
                  3.2.4.2. Authorizations for Rekey, Renewal,
                           and Update ................................18
                  3.2.4.3. Other Authorization Elements ..............18
                  3.2.4.4. Cancel Capability .........................19
           3.2.5. Authorization Response .............................19
                  3.2.5.1. Error Handling for Authorization ..........20
      3.3. Generation ................................................20
           3.3.1. Generation Method 1: IPsec Peer Generates Key Pair,
                  Constructs PKC Request, and Signs PKC Request ......21
           3.3.2. Generation Method 2: IPsec Peer Generates Key Pair,
                  Admin Constructs PKS Request, Admin Signs PKC
                  Request ............................................22
           3.3.3. Generation Method 3: Admin Generates Key Pair,
                  Constructs PKC Request, and Signs PKC Request ......23
           3.3.4. Method 4: PKI Generates Key Pair ...................24
           3.3.5. Error Handling for Generation ......................25



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      3.4. Enrollment ................................................25
           3.4.1. One Protocol .......................................25
           3.4.2. On-line Protocol ...................................25
           3.4.3. Single Connection with Immediate Response ..........25
           3.4.4. Manual Approval Option .............................25
           3.4.5. Enrollment Method 1: Peer Enrolls to PKI Directly ..26
           3.4.6. Enrollment Method 2a: Peer Enrolls through Admin ...27
           3.4.7. Enrollment Method 2b: Peer Enrolls through Admin ...28
           3.4.8. Enrollment Method 3a: Admin Authorizes and
                  Enrolls Directly to PKI ............................30
           3.4.9. Enrollment Method 3b: Admin Requests and PKI
                  Generates and Sends PKC ............................31
           3.4.10. Confirmation Handshake ............................32
           3.4.11. Error Handling for Enrollment .....................33
      3.5. Lifecycle .................................................34
           3.5.1. One Protocol .......................................34
           3.5.2. PKC Rekeys, Renewals, and Updates ..................35
                  3.5.2.1. Rekey Request .............................36
                  3.5.2.2. Renew Request .............................36
                  3.5.2.3. Update Request ............................37
                  3.5.2.4. Error Handling for Rekey, Renewal,
                           and Update ................................38
                  3.5.2.5. Confirmation Handshakes ...................38
           3.5.3. Revocation .........................................38
      3.6. Repositories ..............................................39
           3.6.1. Lookups ............................................39
           3.6.2. Error Handling for Repository Lookups ..............40
      3.7. Trust .....................................................40
           3.7.1. Trust Anchor PKC Acquisition .......................40
           3.7.2. Certification Path Validation ......................41
           3.7.3. Revocation Checking and Status Information .........41
           3.7.4. Error Handling in Revocation Checking and
                  Certificate Path Validation ........................42
   4. Security Considerations ........................................42
   5. References .....................................................43
      5.1. Normative References ......................................43
      5.2. Informative References ....................................43
   6. Acknowledgements ...............................................43













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1.  Introduction

   This document describes and identifies the requirements for
   transactions to handle PKC lifecycle transactions between [IPsec] VPN
   Systems using IKE ([IKEv1] and [IKEv2]) and PKI Systems.  This
   document contains requirements for a transaction-based approach.
   Other models are conceivable, for example, a directory-centric
   approach, but their requirements are beyond the scope of this
   document.

   This document enumerates requirements for Public Key Certificate
   (PKC) lifecycle transactions between different VPN System and PKI
   System products in order to better enable large scale, PKI-enabled
   IPsec deployments with a common set of transactions.  Requirements
   for both the IPsec and the PKI products are discussed.  The
   requirements are carefully designed to achieve security without
   compromising ease of management and deployment, even where the
   deployment involves tens of thousands of IPsec users and devices.

   The requirements address transactions for the entire PKC lifecycle
   for PKI-enabled VPN System: authorization (of PKC issuance),
   generation (public-private key pair and PKC request), enrollment (PKC
   request, PKC response, and confirmation), maintenance (rekey, renew,
   update, revoke, and confirm), and repository lookups.  These
   transactions enable a VPN Operator to:

     - Use a VPN Administration function (Admin), which is introduced in
       this document, to manage PKC authorization and possibly act as
       the sole interface for the VPN System and the PKI System.

     - Authorize individual or batches of PKC issuances based on a pre-
       agreed template (i.e., both types of authorization requests refer
       to the pre-agreed template).  These authorizations can occur
       either prior to the enrollment or in the same transaction as the
       enrollment.

     - Provision PKI-based user or machine identity to IPsec Peers, on a
       large scale.

     - Set the corresponding gateway or client authorization policy for
       remote access and site-to-site connections.

     - Establish policies for automatic PKC rekeys, renewals, and
       updates.

     - Ensure timely revocation information is available for PKCs used
       in IKE exchanges.




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   These requirements are intended to be used to profile a certificate
   management protocol that the VPN System will use to communicate with
   the PKI System.  Note that this profile will be in another document.
   The certificate management profile will also clarify and constrain
   existing PKIX (PKI for X.509 Certificates) and IPsec standards to
   limit the complexity of deployment.  Some requirements may require
   either a new protocol, or changes or extensions to an existing
   protocol.

   The desired outcome of the requirements and profile documents is that
   both IPsec and PKI vendors create interoperable products to enable
   large-scale IPsec System deployments, and do so as quickly as
   possible.  For example, a VPN Operator should be able to use any
   conforming IPsec implementation (VPN Administration or IPsec Peer) of
   the certificate management profile with any conforming PKI vendor's
   implementation to perform the VPN rollout and management.

1.1.  Scope

   The document addresses requirements on transactions between the VPN
   Systems and the PKI Systems and between the VPN Administration and
   IPsec Peers.  The requirements strive to meet eighty percent of the
   market needs for large-scale deployments (i.e., VPNs including
   hundreds or thousands of managed VPN gateways or VPN remote access
   clients).  Environments will understandably exist in which large-
   scale deployment tools are desired, but local security policy
   stringency will not allow for the use of such commercial tools.  The
   solution will possibly miss the needs of the highest ten percent of
   stringency and the lowest ten percent of convenience requirements.
   Use cases will be considered or rejected based upon this eighty
   percent rule.  The needs of small deployments are a stated non-goal;
   however, service providers employing the scoped solution and applying
   it to many smaller deployments in aggregate may address them.

   Gateway-to-gateway access and end-user remote access (to a gateway)
   are both covered.  End-to-end communications are not necessarily
   excluded, but are intentionally not a focus.

   Only VPN-PKI transactions that ease and enable scalable PKI-enabled
   IPsec deployments are addressed.











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1.2.  Non-Goals

   The scenario for PKC cross-certification will not be addressed.

   The protocol specification for the VPN-PKI interactions will not be
   addressed.

   The protocol specification for the VPN Administrator to Peer
   transactions will not be addressed.  These interactions are
   considered vendor proprietary.  These interactions may be
   standardized later to enable interoperability between VPN
   Administration function stations and IPsec Peers from different
   vendors, but are far beyond the scope of this current effort, and
   will be described as opaque transactions in this document.

   The protocol specification for Registration Authority - Certificate
   Authority (RA-CA), CA-Repository, and RA-Repository interactions will
   not be addressed.

1.3.  Definitions

   VPN System
   The VPN System is comprised of the VPN Administration function
   (defined below), the IPsec Peers, and the communication mechanism
   between the VPN Administration and the IPsec Peers.  VPN System is
   defined in more detail in Section 2.1.

   PKI System
   The PKI System, or simply PKI, is the set of functions needed to
   authorize, issue, and manage PKCs.  PKI System is defined in more
   detail in Section 2.2.

   (VPN) Operator
   The Operator is the person or group of people that define security
   policy and configure the VPN System to enforce that policy, with the
   VPN Administration function.

   IPsec Peer (Gateway or Client)
   For the purposes of this document, an IPsec Peer, or simply "Peer",
   is any VPN System component that communicates IKE and IPsec to
   another Peer in order to create an IPsec Security Association for
   communications.  It can be either a traditional security gateway
   (with two network interfaces, one for the protected network and one
   for the unprotected network) or an IPsec client (with a single
   network interface).  In both cases, the Peer can pass traffic with no
   IPsec protection, and can add IPsec protection to chosen traffic
   streams.  See Section 2.1.1 for more details.




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   (VPN) Admin
   The Admin is the VPN System function that interacts with the PKI
   System to establish PKC provisioning for the VPN connections.  See
   Section 2.1.2 for more details.

   End Entity
   An end entity is the entity or subject that is identified in a PKC.
   The end entity is the one entity that will finally use a private key
   associated with a PKC to digitally sign data.  In this document, an
   IPsec Peer is certainly an end entity, but the VPN Admin can also
   constitute an end entity.  Note that end entities can have different
   PKCs for different purposes (e.g., signature vs. key exchange,
   Admin-functions vs. Peer-functions).

   PKC Rekey
   The routine procedure for replacement of a PKC with a new PKC with a
   new public key for the same subject name.  A rekey process can rely
   on the existing key pair to bootstrap authentication for the new
   enrollment.

   PKC Renewal
   The acquisition of a new PKC with the same public key due to the
   expiration of an existing PKC.  Renewal occurs prior to the
   expiration of the existing PKC to avoid any connection outages.  A
   renewal process can rely on the existing key pair to bootstrap
   authentication for the new enrollment.

   PKC Update
   A special case of a renewal-like occurrence where a PKC needs to be
   changed prior to expiration due to some change in its subject's
   information.  Examples might include change in the address, telephone
   number, or name change due to marriage of the end entity.  An update
   process can rely on the existing key pair to bootstrap authentication
   for the new enrollment.

   Registration Authority (RA)
   An optional entity in a PKI System given responsibility for
   performing some of the administrative tasks necessary in the
   registration of end entities, such as confirming the subject's
   identity and verifying that the subject has possession of the private
   key associated with the public key requested for a PKC.

   Certificate Authority (CA)
   An authority in a PKI System that is trusted by one or more users to
   create and sign PKCs.  It is important to note that the CA is
   responsible for the PKCs during their whole lifetime, not just for
   issuing them.




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   Repository
   An Internet-accessible server in a PKI System that stores and makes
   available for retrieval PKCs and Certificate Revocation Lists (CRLs).

   Root CA/Trust Anchor
   A CA that is directly trusted by an end entity; that is, securely
   acquiring the value of a Root CA public key requires some out-of-band
   step(s).  This term is not meant to imply that a Root CA is
   necessarily at the top of any hierarchy, simply that the CA in
   question is trusted directly.

   Certificate Revocation List (CRL)
   A CRL is a CA-signed, timestamped list identifying revoked PKCs and
   made freely available in a repository.  Peers retrieve the CRL to
   verify that a PKC being presented to them as the identity in an IKE
   transaction has not been revoked.

   CRL Distribution Point (CDP)
   The CDP is a PKC extension that identifies the location from which
   end entities should retrieve CRLs to check status information.

   Authority Info Access (AIA)
   The AIA is a PKC extension that indicates how to access CA
   information and services for the issuer of the PKC in which the
   extension appears.  Information and services may include on-line
   validation services and Certificate Policy (CP) data.

1.4.  Requirements 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 [MUSTSHOULD].



















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2.  Architecture

   This section describes the overall architecture for a PKI-supported
   IPsec VPN deployment.  First, an explanation of the VPN System is
   presented.  Second, key points about the PKI System are stated.
   Third, the VPN-PKI architecture is presented.

2.1.  VPN System

   The VPN System consists of the IPsec Peers and the VPN Administration
   function, as depicted in Figure 1.

            +---------------------------------------------------+
            |                                                   |
            |                      +----------+                 |
            |                      |   VPN    |                 |
            |          +---------->|  Admin   |<-------+        |
            |          |           | Function |        |        |
            |          |           +----------+        |        |
            |          v                               v        |
            |  +---------+                         +---------+  |
            |  |  IPsec  |                         |  IPsec  |  |
            |  |  Peer 1 |<=======================>|  Peer 2 |  |
            |  +---------+                         +---------+  |
            |                                                   |
            |                     VPN System                    |
            +---------------------------------------------------+

                             Figure 1: VPN System

2.1.1.  IPsec Peer(s)

   The Peers are two entities between which establishment of an IPsec
   Security Association is required.  Two Peers are shown in Figure 1,
   but implementations can support an actual number in the hundreds or
   thousands.  The Peers can be gateway-to-gateway, remote-access-host-
   to-gateway, or a mix of both.  The Peers authenticate themselves in
   the IKE negotiation using digital signatures generated with PKCs from
   a PKI System.

2.1.2.  VPN Administration Function (Admin)

   This document defines the notion of a VPN Administration function,
   hereafter referred to as Admin, and gives the Admin great
   responsibility within the VPN System.  The Admin is a centralized
   function used by the Operator to interact with the PKI System to
   establish PKI policy (e.g., algorithms, key lengths, lifecycle
   options, and PKC fields) for groups of IPsec Peers.  The Admin also



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   authorizes PKC issuance and can act as the Peer's PKI System
   interface, which allows the Admin to perform many RA-like functions.

   It is important to note that, within this document, the Admin is
   neither a device nor a person; rather, it is a function.  Every
   large-scale VPN deployment will contain the Admin function.  The
   function can be performed on a stand-alone workstation, on a gateway,
   or on an administration software component.  The Admin function can
   also be one and the same as the gateway, client device, or software.
   They are represented in the architectural diagram as different
   functions, but they need not be different physical entities.  As
   such, the Admin's architecture and the means by which it interacts
   with the participating IPsec Peers will vary widely from
   implementation to implementation.  However, some basic functions of
   the Admin are assumed.

     - It, and not the PKI, will define the Certificate Policy (CP)
       [FRAME] for use in a VPN System.  The PKC's characteristics and
       contents are a function of the CP.  In VPN Systems, the Operator
       chooses to strengthen the VPN by using PKI; PKI is a bolt-on to
       the VPN System.  The Operator will configure local security
       policy in part through the Admin and its authorized PKI-enabled
       Peers.

     - It will interact directly with the PKI System to initiate
       authorization for end entity PKCs by sending the parameters and
       contents for individual PKCs or batches of PKCs based on a pre-
       agreed template (i.e., both types of authorization requests refer
       to the pre-agreed template).  Templates will be agreed in an
       out-of-band mechanism by the VPN Operator and the PKI Operator.
       It will receive back from the PKI a unique tuple of authorization
       identifiers and one-time authorization tokens that will authorize
       Peers to request a PKC.

     - It will deliver instructions to the IPsec Peers, and the Peers
       will carry out those instructions (e.g., Admin passes Peer
       information necessary to generate keys and PKC request).

2.2.  PKI System

   The PKI System, as depicted in Figure 2, can be set up and operated
   by the Operator (in-house), be provided by third party PKI providers
   to which connectivity is available at the time of provisioning
   (managed PKI service), or be integrated with the VPN product.







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               +---------------------------------------------+
               |        +-------------------------+          |
               |        v                         |          |
               |   +--------------+               v          |
               |   |  Repository  |    +----+   +----+       |
               |   | Certs & CRLs |<-> | CA |<->| RA |       |
               |   +--------------+    +----+   +----+       |
               |                                             |
               +---------------------------------------------+

                              Figure 2: PKI System

   This framework assumes that all components of the VPN obtain PKCs
   from a single PKI community.  An IPsec Peer can accept a PKC from a
   Peer that is from a CA outside of the PKI community, but the auto
   provision and life cycle management for such a PKC or its trust
   anchor PKC fall out of scope.

   The PKI System contains a mechanism for handling Admin's
   authorization requests and PKC enrollments.  This mechanism is
   referred to as the Registration Authority (RA).  The PKI System
   contains a Repository for Peers to retrieve each other's PKCs and
   revocation information.  Last, the PKI System contains the core
   function of a CA that uses a public and private key pair and signs
   PKCs.

2.3.  VPN-PKI Interaction

   The interaction between the VPN System and the PKI System is the key
   focus of this requirements document, as shown in Figure 3.
   Therefore, it is sensible to consider the steps necessary to set up,
   use, and manage PKCs for one Peer to establish an association with
   another Peer.


















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          +-----------------------------------------------+
          |                  PKI System                   |
          |                                               |
          |   +--------------+                            |
          |   |  Repository  |     +----+    +----+       |
          |   | Certs & CRLs |     | CA |    | RA |       |
          |   +--------------+     +----+    +----+       |
          |                                               |
          +-----------------------------------------------+
               ^                  ^                   ^
               |[G]               |[A]                |[G]
               |[E]               |[G]                |[E]
               |[L]               |[E]                |[L]
               |[R]               |[R]                |[R]
               |                  |[L]                |
         +-----+------------------+-------------------+-------+
         |     |                  v                   |       |
         |     |             +----------+             |       |
         |     | [G][E][L][R]|   VPN    |[G][E][L][R] |       |
         |     | +---------->|  Admin   |<----------+ |       |
         |     | |           | Function |           | |       |
         |     | |           +----------+           | |       |
         |     v v                                  v v       |
         |  +---------+                          +---------+  |
         |  |  IPsec  |          [I]             |  IPsec  |  |
         |  |  Peer 1 |<========================>|  Peer 2 |  |
         |  +---------+                          +---------+  |
         |                                                    |
         |                     VPN System                     |
         +----------------------------------------------------+

   [A] = Authorization: PKC issuance
   [G] = Generation: Public key, private key, and PKC request
   [E] = Enrollment: Sending PKC request, verifying PKC response, and
         confirming PKC response
   [I] = IKE and IPsec communication
   [L] = Lifecycle: Rekey, renewal, update, revocation, and confirmation
   [R] = Repository: Posting and lookups

        Figure 3.  Architectural Framework for VPN-PKI Interaction

   Requirements for each of the interactions, [A], [G], [E], [L], and
   [R], are addressed in Sections 3.2 through 3.6.  However, only
   requirements for [A], [E], [L], and [R] will be addressed by the
   certificate management profile.  Requirements for [I] transactions
   are beyond the scope of this document.  Additionally, the act of
   certification (i.e., binding the public key to the name) is performed
   at the CA and is not shown in the figure.



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3.  Requirements

3.1.  General Requirements

3.1.1.  One Protocol

   The target profile, to be based on this requirements document, MUST
   call for ONE PROTOCOL or ONE USE PROFILE for each main element of the
   [A], [E], [L], and [R] interactions.  In order to reduce complexity
   and improve interoperability, having multiple competing protocols or
   profiles to solve the same requirement should be avoided whenever
   possible.

   Meeting some of the requirements may necessitate the creation of a
   new protocol or new extension for an existing protocol; however, the
   latter is much preferred.

3.1.2.  Secure Transactions

   The target certificate management profile MUST specify the [A], [E],
   [L], and [R] transactions between VPN and PKI Systems.  To support
   these transactions, the Admin and PKI MUST exchange policy details,
   identities, and keys.  As such, the method of communication for [A],
   [E], and [L] transactions MUST be secured in a manner that ensures
   privacy, authentication, and message data integrity.  The
   communication method MUST require that mutual trust be established
   between the PKI and the Admin (see Section 3.7.1).  [R] transactions
   do not require authentication or message data integrity because the
   responses (i.e., PKCs and CRLs) are already digitally signed.
   Whether [R] transactions require privacy is determined by the local
   security policy.

   The target certificate management profile will not specify [G]
   transactions.  However, these transactions MUST be secured in a
   manner that ensures privacy, authentication, and message data
   integrity because these transactions are the basis for the other
   transactions.

3.1.3.  Admin Availability

   The Admin MUST be reachable by the Peers.  Most implementations will
   meet this requirement by ensuring Peers can connect to the Admin from
   anywhere on the network or Internet.  However, communication between
   the Admin and Peers can be "off-line".  It can, in some environments,
   be "moving media" (i.e., the configuration or data is loaded on to a
   floppy disk or other media and physically moved to the IPsec Peers).
   Likewise, it can be entered directly on the IPsec Peer via a User
   Interface (UI).  In this case, the Admin function is co-located on



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   the Peer device itself.  Most requirements and scenarios in this
   document assume on-line availability of the Admin for the life of the
   VPN System.

3.1.4.  PKI Availability

   Availability is REQUIRED initially for authorization transactions
   between the PKI and Admin.  Further availability is required in most
   cases, but the extent of this availability is a decision point for
   the Operator.  Most requirements and scenarios in this document
   assume on-line availability of the PKI for the life of the VPN
   System.

   Off-line interaction between the VPN and PKI Systems (i.e., where
   physical media is used as the transport method) is beyond the scope
   of this document.

3.1.5.  End-User Transparency

   PKI interactions are to be transparent to the user.  Users SHOULD NOT
   even be aware that PKI is in use.  First time connections SHOULD
   consist of no more than a prompt for some identification and pass
   phrase, and a status bar notifying the user that setup is in
   progress.

3.1.6.  PKC Profile for PKI Interaction

   A PKC used for identity in VPN-PKI transactions MUST include all the
   [CERTPROFILE] mandatory fields.  It MUST also contain contents
   necessary to support path validation and certificate status checking.

   It is preferable that the PKC profiles for IPsec transactions
   [IKECERTPROFILE] and VPN-PKI transactions (in the certificate
   management profile) are the same so that one PKC could be used for
   both transaction sets.  If the profiles are inconsistent, then
   different PKCs (and perhaps different processing requirements) might
   be required.  However, the authors urge that progress continue on
   other aspects of this standardization effort regardless of the status
   of efforts to achieve PKC profile consensus.












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3.1.6.1.  Identity

   PKCs MUST support identifying (i.e., naming) Peers and Admins.  The
   following name forms MUST be supported:

     - Fully-Qualified Domain Name (FQDN)
     - RFC 822 (also called USER FQDN)
     - IPv4 Address
     - IPv6 Address

3.1.6.2.  Key Usage

   PKCs MUST support indicating the purposes for which the key (i.e.,
   digital signature) can be used.  Further, PKCs MUST always indicate
   that relying parties (i.e., Peers) need to understand the indication.

3.1.6.3.  Extended Key Usage

   Extended Key Usage (EKU) indications are not required.  The presence
   or lack of an EKU MUST NOT cause an implementation to fail an IKE
   connection.

3.1.6.4.  Revocation Information Location

   PKCs MUST indicate the location of CRL such that any Peer who holds
   the PKC locally will know exactly where to go and how to request the
   CRL.

3.1.7.  Error Handling

   The protocol for the VPN-PKI transactions MUST specify error handling
   for each transaction.  Thorough error condition descriptions and
   handling instructions will greatly aid interoperability efforts
   between the PKI and VPN System products.

3.2.  Authorization

   This section refers to the [A] elements labeled in Figure 3.

3.2.1.  One Protocol

   One protocol MUST be specified for the Admin to PKI (RA/CA)
   interactions.  This protocol MUST support privacy, authorization,
   authentication, and integrity.  PKCs for authorization of the Admin
   can be initialized through an out-of-band mechanism.

   The transport used to carry the authorization SHOULD be reliable
   (TCP).



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   The protocol SHOULD be as lightweight as possible.

3.2.2.  Bulk Authorization

   Bulk authorization MUST be supported by the certificate management
   profile.  Bulk authorization occurs when the Admin requests of the
   PKI that authorization be established for several different subjects
   with almost the same contents.  A minimum of one value (more is also
   acceptable) differs per subject.  Because the authorizations may
   occur before any keys have been generated, the only way to ensure
   unique authorization identifiers are issued is to have at least one
   value differ per subject.

   Authorization can occur prior to a PKC enrollment request, or the
   authorization and the PKC enrollment request can be presented to the
   PKI at the same time.  Both of these authorization scenarios MUST be
   supported.

   A bulk authorization SHOULD occur in one single connection to the PKI
   (RA/CA), with the number of subjects being one or greater.
   Implementations SHOULD be able to handle one thousand subjects in a
   batch authorization.

3.2.3  Authorization Scenario

   The authorization scenario for VPN-PKI transactions involves a two-
   step process: an authorization request and an authorization response.
   Figure 4 shows the salient interactions to perform authorization
   transactions.






















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       +--------------+     +-----------------------+
       |  Repository  |     |         CA/RA         |
       +--------------+     +-----------------------+
                                        ^
                                        | 1
                                      2 |
                                        v
                                     +-------+
                                     | Admin |
                                     +-------+


                +--------------------+          +--------+
                |       IPsec        |          | IPsec  |
                |      Peer 1        |          | Peer 2 |
                +--------------------+          +--------+

                  Figure 4.  Authorization Transactions

   1) Authorization Request [A].  Admin sends a list of identities and
      PKC contents for the PKI System to authorize enrollment.  See
      Section 3.2.4.

   2) Authorization Response [A].  The PKI returns a list of unique
      authorization identifiers and one-time authorization tokens to be
      used for the enrollment of each PKC (1).  Response may indicate
      success, failure, or errors for any particular authorization.  See
      Section 3.2.5.

3.2.4.  Authorization Request

3.2.4.1.  Specifying Fields within the PKC

   The Admin authorizes individual PKCs or batches of PKC issuances
   based on a pre-agreed template.  This template is agreed by the VPN
   Operator and PKI Operator and is referred to in each authorization
   request.  This allows the authorization requests to include the
   minimal amount of information necessary to support a VPN System.

   The Admin can send the PKI System the set of PKC contents that it
   wants the PKI to issue to a group of IPsec Peers.  In other words, it
   tells the PKI System, "if you see a PKC request that looks like this,
   from this person, process it and issue the PKC."

   Requirements for PKC fields used in IPsec transactions are specified
   in [IKECERTPROFILE].





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   Requirements for PKC fields used in VPN-PKI transactions are
   specified in Section 3.1.6.

3.2.4.2.  Authorizations for Rekey, Renewal, and Update

   When the VPN Operator and PKI Operator pre-agree on a template, they
   MUST also agree on the local policy regarding PKC renewal and PKC
   update.  These are:

     - Admin MUST specify if automatic renewals are allowed, that is,
       the Admin authorizes the PKI to process a future renewal for the
       specified Peer PKC.

     - Admin MUST specify if PKC update is allowed, that is, the Admin
       authorizes the PKI to accept a future request for a new PKC with
       changes to non-key-related fields.

       If a PKC renewal is authorized, the Admin MUST further specify:

     - Who can renew, that is, can only the Admin send a renewal request
       or can the Peer send a request directly to the PKI, or either.

     - How long before the PKC expiration date the PKI will accept and
       process a renewal (i.e., N% of validity period, or the UTC time
       after which renewal is permitted).

   If a PKC update is authorized, the Admin MUST further specify:

     - The aspects of non-key-related fields that are changeable.

     - The entity that can send the PKC Update request, that is, only
       the Admin, only the Peer, or either.

     - How long before the PKC expiration date the PKI will accept and
       process an update (i.e., N% of validity period, or the UTC time
       after which update is permitted).

   A new authorization by the Admin is REQUIRED for PKC rekey.  No
   parameters of prior authorizations need be considered.

3.2.4.3.  Other Authorization Elements

   The Admin MUST have the ability to specify the format for the
   authorization ID and one-time authorization token.  The one-time
   authorization token SHOULD be unique per authorization ID.  The more
   randomness that can be achieved in the relationship between an
   authorization ID and its one-time authorization token, the better.
   The one-time authorization token MUST be in UTF-8 format to avoid



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   incompatibilities that may occur due to international characters.  It
   MUST support normalization as in [CERTPROFILE].  The Admin MUST have
   the ability to constrain the UTF-8 character set.

   There MUST be an option to specify a validation period for the
   authorization ID and its one-time authorization token.  If such a
   validation period is set, any PKC requests using the authorization ID
   and one-time authorization token that arrive at the PKI outside of
   the validation period MUST be dropped, and the event logged.

   The Protocol SHOULD consider what happens when Admin-requested
   information conflicts with PKI settings such that the Admin request
   cannot be issued as requested (e.g., Admin requests validation period
   = 3 weeks and CA is configured to only allow validation periods = 1
   week).  Proper conflict handling MUST be specified.

3.2.4.4.  Cancel Capability

   Either the Admin or the Peer can send a cancel authorization message
   to PKI.  The canceling entity MUST provide the authorization ID and
   one-time authorization token in order to cancel the authorization.
   At that point, the authorization will be erased from the PKI, and a
   log entry of the event written.

   After the cancellation has been verified (a Cancel, Cancel ACK, ACK
   type of a process is REQUIRED to cover a lost connections scenario),
   the PKI will accept a new authorization request with the exact same
   contents as the canceled one, except that the identifier MUST be new.
   The PKI MUST NOT process duplicate authorization requests.

   Note that if the PKI has already issued a PKC associated with an
   authorization, then cancellation of the authorization is not possible
   and the authorization request SHOULD be refused by the PKI.  Once a
   PKC has been issued it MUST be revoked in accordance with Section
   3.6.

3.2.5.  Authorization Response

   If the authorization request is acceptable, the PKI will respond to
   the Admin with a unique authorization identifier per subject
   authorization requested and a one-time authorization token per
   authorization ID.  See Section 3.2.4.3 for additional authorization
   ID and one-time authorization token requirements.

   The PKI can alter parameters of the authorization request submitted
   by the Admin.  In that event, the PKI MUST return all the contents of
   the authorization request (as modified) to the Admin with the
   confirmation of authorization success.  This will allow the Admin to



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   perform an "operational test" to verify that the issued PKCs will
   meet its requirements.  If the Admin determines that the modified
   parameters are unacceptable, then the authorization should be
   cancelled in accordance with Section 3.2.4.4.

   After receiving a bulk authorization request from the Admin, the PKI
   MUST be able to reply YES to those individual PKC authorizations that
   it has satisfied and NO or FAILED for those requests that cannot be
   satisfied, along with sufficient reason or error codes.

   A method is REQUIRED to identify if there is a change in PKI settings
   between the time the authorization is granted and the PKC request
   occurs, and what to do about the discrepancy.

3.2.5.1.  Error Handling for Authorization

   Thorough error condition descriptions and handling instructions MUST
   be provided to the Admin for each transaction in the authorization
   process.  Providing such error codes will greatly aid
   interoperability efforts between the PKI and IPsec products.

3.3.  Generation

   This section refers to the [G] elements labeled in Figure 3.

   Once the PKI System has responded with authorization identifiers and
   authorization tokens (see Section 3.2), and this information is
   received at the Admin, the next step is to generate public and
   private key pairs and to construct PKC requests using those key
   pairs.  The key generations can occur at one of three places,
   depending on local requirements: at the IPsec Peer, at the Admin, or
   at the PKI.  The PKC request can come from either the IPsec Peer, a
   combination of the Peer and the Admin, or not at all.


















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3.3.1.  Generation Method 1: IPsec Peer Generates Key Pair, Constructs
        PKC Request, and Signs PKC Request

   This option will be used most often in the field.  This is the most
   secure method for keying, as the keys are generated on the end entity
   and the private key never leaves the end entity.  However, it is the
   most computationally intensive for the Peer, as it must be "ASN.1
   aware" to support generating and digitally signing the PKC request.

       +--------------+     +-----------------------+
       |  Repository  |     |         CA/RA         |
       +--------------+     +-----------------------+




                                     +-------+
                             +------>| Admin |
                             |       +-------+
                             |
                             | 1
                             V
                +--------------------+          +--------+
              2 |       IPsec        |          | IPsec  |
                |      Peer 1        |          | Peer 2 |
                +--------------------+          +--------+

                  Figure 5.  Generation Interactions:
      IPsec Peer Generates Key Pair and Constructs PKC Request

   1) Opaque transaction [G].  Admin sends authorization identifier,
      one-time authorization token, and any other parameters needed by
      the Peer to generate the PKC request, including key type and size.

   2) Generation [G].  Peer receives authorization identifier, one-time
      authorization token, and any parameters.  Peer generates key pair
      and constructs PKC request.

   Steps prior to these can be found in Section 3.2.  The next step,
   enrollment, can occur either directly between the Peer and PKI (see
   Section 3.4.5) or through the Admin (see Section 3.4.6).










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3.3.2.  Generation Method 2: IPsec Peer Generates Key Pair, Admin
        Constructs PKC Request, Admin Signs PKC Request

   This option also supports IPsec Peer generation of a key pair, but
   removes the requirement for the Peer to be ASN.1 aware because it
   does not have to construct or digitally sign the PKC request.  The
   drawback is that the key pair does need to be provided to the Admin.
   In the most probable cases where the Admin function is remotely
   located from the peer, this means that the private key will leave the
   cryptographic boundary of the peer, which is a significant security
   trade-off consideration.  Whenever possible, it is always better to
   have private keys generated and never leave the cryptographic
   boundary of the generating system.

       +--------------+     +-----------------------+
       |  Repository  |     |         CA/RA         |
       +--------------+     +-----------------------+




                                   3 +-------+
                             +------>| Admin | 4
                             |       +-------+
                             |
                             | 1
                             V
                +--------------------+          +--------+
              2 |       IPsec        |          | IPsec  |
                |      Peer 1        |          | Peer 2 |
                +--------------------+          +--------+

                  Figure 6.  Generation Interactions:
      IPsec Peer Generates Key Pair, Admin Constructs PKC Request

   1) Opaque transaction [G].  Admin sends command to Peer to generate
      key pair, based on parameters provided in the command.

   2) Generation [G].  Peer generates key pair.

   3) Opaque transaction [G].  Peer returns key pair to Admin.

   4) Generation [G].  Admin constructs and digitally signs PKC request.

   Steps prior to these can be found in Section 3.2.  The next step,
   enrollment, occurs through the Admin (see Section 3.4.7).





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3.3.3.  Generation Method 3: Admin Generates Key Pair, Constructs PKC
        Request, and Signs PKC Request

   This option exists for deployments where Peers cannot generate their
   own key pairs.  Some examples are for PDAs and handsets where to
   generate an RSA key would be operationally impossible due to
   processing and battery constraints.  Another case covers key recovery
   requirements, where the same PKCs are used for other functions in
   addition to IPsec, and key recovery is required (e.g., local data
   encryption), therefore key escrow is needed from the Peer.  If key
   escrow is performed then the exact requirements and procedures for it
   are beyond the scope of this document.

       +--------------+     +-----------------------+
       |  Repository  |     |         CA/RA         |
       +--------------+     +-----------------------+




                                     +-------+
                                     | Admin | 1
                                     +-------+



                +--------------------+          +--------+
                |       IPsec        |          | IPsec  |
                |      Peer 1        |          | Peer 2 |
                +--------------------+          +--------+

                  Figure 7.  Generation Interactions:
         Admin Generates Key Pair and Constructs PKC Request

   1) Generation [G].  Admin generates key pair, constructs PKC request,
      and digitally signs PKC request.

   Steps prior to these can be found in Section 3.2.  The next step,
   enrollment, occurs through the Admin (see Section 3.4.8).

   Note that separate authorizations steps are still of value even
   though the Admin is also performing the key generation.  The PKC
   template, Subject fields, SubjectAltName fields, and more are part of
   the request, and must be communicated in some way from the Admin to
   the PKI.  Instead of creating a new mechanism, the authorization
   schema can be reused.  This also allows for the feature of role-based





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   administration, where Operator 1 is the only one allowed to have the
   Admin function pre-authorize PKCs, but Operator 2 is the one doing
   batch enrollments and VPN device configurations.

3.3.4.  Method 4: PKI Generates Key Pair

   This option exists for deployments where end entities cannot generate
   their own key pairs and the Admin function is a minimal
   implementation.  The PKI and Admin pre-agree to have the PKI generate
   key pairs and PKCs.  This is, in all likelihood, the easiest way to
   deploy PKCs, though it sacrifices some security since both the CA and
   the Admin have access to the private key.  However, in cases where
   key escrow is required, this may be acceptable.  The Admin
   effectively acts as a proxy for the Peer in the PKC enrollment
   process.

       +--------------+     +-----------------------+
       |  Repository  |     |         CA/RA         | 1
       +--------------+     +-----------------------+




                                     +-------+
                                     | Admin |
                                     +-------+



                +--------------------+          +--------+
                |       IPsec        |          | IPsec  |
                |      Peer 1        |          | Peer 2 |
                +--------------------+          +--------+

                  Figure 8.  Generation Interactions:
      IPsec Peer Generates Key Pair, Admin Constructs PKC Request

   1) Generation [G] The PKI generates the key pair.

   Steps prior to these can be found in Section 3.2.  The next step,
   enrollment, occurs through the Admin (see Section 3.4.9).










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3.3.5.  Error Handling for Generation

   Thorough error condition descriptions and handling instructions MUST
   be provided for each transaction in the key generation and PKC
   request construction process.  Providing such error codes will
   greatly aid interoperability efforts between the PKI and IPsec
   products.

   Error conditions MUST be communicated to the Admin regardless of who
   generated the key or PKC request.

3.4.  Enrollment

   This section refers to the [E] elements labeled in Figure 3.

   Regardless of where the keys were generated and the PKC request
   constructed, an enrollment process will need to occur to request that
   the PKI issue a PKC and the corresponding PKC be returned.

   The protocol MUST be exactly the same regardless of whether the
   enrollment occurs from the Peer to the PKI or from the Admin to the
   PKI.

3.4.1.  One Protocol

   One protocol MUST be specified for enrollment requests, responses,
   and confirmations.

3.4.2.  On-line Protocol

   The protocol MUST support enrollment that occurs over the Internet
   and without the need for manual intervention.

3.4.3.  Single Connection with Immediate Response

   Enrollment requests and responses MUST be able to occur in one on-
   line connection between the Admin on behalf of the Peer or the Peer
   itself and the PKI (RA/CA).

3.4.4.  Manual Approval Option

   Manual approval of PKC enrollments is too time consuming for large
   scale implementations, and is therefore not required.








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3.4.5.  Enrollment Method 1: Peer Enrolls to PKI Directly

   In this case, the IPsec Peer only communicates with the PKI after
   being commanded to do so by the Admin.  This enrollment mode is
   depicted in Figure 9 and the letters in the following description
   refer to Figure 3.  Prior authorization (Section 3.2) and generation
   (Section 3.3.1) steps are not shown.

   Most IPsec Systems have enough CPU power to generate a public and
   private key pair of sufficient strength for secure IPsec.  In this
   case, the end entity needs to prove to the PKI that it has such a key
   pair; this is normally done by the PKI sending the end entity a
   nonce, which the end entity signs and returns to the Admin along with
   the end entity's public key.

       +--------------+     +-----------------------+
       |  Repository  |     |         CA/RA         |
       +--------------+     +-----------------------+
                               ^
                           1,3 |
                               |
                               |
                               |     +-------+
                               |     | Admin |
                               |     +-------+
                               |
                           2,4 |
                               v
                +--------------------+          +--------+
                |       IPsec        |          | IPsec  |
                |      Peer 1        |          | Peer 2 |
                +--------------------+          +--------+

                  Figure 9.  VPN-PKI Interaction Steps:
                IPsec Peer Generates Keys and PKC Request,
                         Enrolls Directly with PKI

   1) Enrollment Request [E].  The IPsec Peer sends PKC requests to the
      PKI, providing the generated public key.

   2) Enrollment Response [E].  The PKI responds to the enrollment
      request, providing either the new PKC that was generated or a
      suitable error indication.

   3) Enrollment Confirmation [E].  Peer positively acknowledges receipt
      of new PKC back to the Admin.





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   4) Enrollment Confirmation Receipt [E].  PKI sends enrollment
      confirmation receipt back to the Peer.

3.4.6  Enrollment Method 2a: Peer Enrolls through Admin

   In this case, the IPsec Peer has generated the key pair and the PKC
   request, but does not enroll directly to the PKI System.  Instead, it
   automatically sends its request to the Admin, and the Admin redirects
   the enrollment to the PKI System.  The PKI System does not care where
   the enrollment comes from, as long as it is a valid enrollment.  Once
   the Admin receives the PKC response, it automatically forwards it to
   the IPsec Peer.

   Most IPsec Systems have enough CPU power to generate a public and
   private key pair of sufficient strength for secure IPsec.  In this
   case, the end entity needs to prove to the Admin that it has such a
   key pair; this is normally done by the Admin sending the end entity a
   nonce, which the end entity signs and returns to the Admin along with
   the end entity's public key.

   This enrollment mode is depicted in Figure 10 and the letters in the
   following description refer to Figure 3.  Prior authorization
   (Section 3.2) and generation (Section 3.3.1) steps are not shown.

       +--------------+     +-----------------------+
       |  Repository  |     |         CA/RA         |
       +--------------+     +-----------------------+
                                        ^ 2,6
                                        |
                                        |
                                        v 3,7
                                1,5  +-------+
                                  +> | Admin |
                                  |  +-------+
                                  |
                                  |
                              4,8 v
                +--------------------+          +--------+
                |       IPsec        |          | IPsec  |
                |      Peer 1        |          | Peer 2 |
                +--------------------+          +--------+

                  Figure 10.  VPN-PKI Interaction Steps:
                IPsec Peer Generates Keys and PKC Request,
                         Enrolls Through Admin

   1) Opaque Transaction [E].  The IPsec Peer requests a PKC from the
      Admin, providing the generated public key.



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   2) Enrollment Request [E].  The Admin forwards the enrollment request
      to the PKI.

   3) Enrollment Response [E].  The PKI responds to the enrollment
      request, providing either the new PKC that was generated or a
      suitable error indication.

   4) Opaque Transaction [E].  The Admin forwards the enrollment
      response back to the IPsec Peer.

   5) Opaque Transaction [E].  Peer positively acknowledges receipt of
      new PKC back to the Admin.

   6) Enrollment Confirmation [E].  Admin forwards enrollment
      confirmation back to the PKI.

   7) Enrollment Confirmation Receipt [E].  PKI sends enrollment
      confirmation receipt back to the Admin.

   8) Opaque Transaction [E].  Admin forwards PKI's enrollment
      confirmation receipt back to the Peer.

3.4.7.  Enrollment Method 2b: Peer Enrolls through Admin

   In this case, the IPsec Peer has generated the key pair, but the PKC
   request is constructed and signed by the Admin.  The PKI System does
   not care where the enrollment comes from, as long as it is a valid
   enrollment.  Once the Admin retrieves the PKC, it then automatically
   forwards it to the IPsec Peer along with the key pair.

   Some IPsec Systems do not have enough CPU power to generate a public
   and private key pair of sufficient strength for secure IPsec.  In
   this case, the Admin needs to prove to the PKI that it has such a key
   pair; this is normally done by the PKI sending the Admin a nonce,
   which the Admin signs and returns to the PKI along with the end
   entity's public key.  A drawback to this case is that the private key
   will eventually be sent over the wire (though hopefully securely so)
   from Admin to the IPsec Peer; whenever possible, it is preferred to
   keep a key within its cryptographic boundary of origin.  Failing to
   do so opens the system to risk of the private keys being sniffed and
   discerned.

   This enrollment mode is depicted in Figure 11 and the letters in the
   following description refer to Figure 3.  Prior authorization
   (Section 3.2) and generation (Section 3.3.2) steps are not shown.






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       +--------------+     +-----------------------+
       |  Repository  |     |         CA/RA         |
       +--------------+     +-----------------------+
                                        ^ 1,5
                                        |
                                        |
                                        v 2,6
                                  4  +-------+
                                  +->| Admin |
                                  |  +-------+
                                  |
                                  |
                              3,7 v
                +--------------------+          +--------+
                |       IPsec        |          | IPsec  |
                |      Peer 1        |          | Peer 2 |
                +--------------------+          +--------+

                  Figure 11.  VPN-PKI Interaction Steps:
           IPsec Peer Generates Keys, Admin Constructs and
               Signs PKC Request, Enrolls through Admin

   1) Enrollment Request [E].  The Admin requests a PKC from the PKI,
      providing the generated public key.

   2) Enrollment Response [E].  The PKI responds to the enrollment
      request, providing either the new PKC that was generated or a
      suitable error indication.

   3) Opaque Transaction [E].  The Admin forwards the enrollment
      response back to the IPsec Peer.

   4) Opaque Transaction [E].  Peer positively acknowledges receipt of
      new PKC back to the Admin.

   5) Enrollment Confirmation [E].  Admin forwards enrollment
      confirmation back to the PKI.

   6) Enrollment Confirmation Receipt [E].  PKI sends enrollment
      confirmation receipt back to the Admin.

   7) Opaque Transaction [E].  Admin forwards PKI's enrollment
      confirmation receipt back to the Peer.








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3.4.8.  Enrollment Method 3a: Admin Authorizes and Enrolls Directly to
        PKI

   In this case, the Admin generates the key pair, PKC request, and
   digitally signs the PKC request.  The PKI System does not care where
   the enrollment comes from, as long as it is a valid enrollment.  Once
   the Admin retrieves the PKC, it then automatically forwards it to the
   IPsec Peer along with the key pair.

   Some IPsec Systems do not have enough CPU power to generate a public
   and private key pair of sufficient strength for secure IPsec.  In
   this case, the Admin needs to prove to the PKI that it has such a key
   pair; this is normally done by the PKI sending the Admin a nonce,
   which the Admin signs and returns to the PKI along with the end
   entity's public key.  A drawback to this case is that the private key
   will eventually be sent over the wire (though hopefully securely so)
   from Admin to the IPsec Peer; whenever possible, it is preferred to
   keep a key within its cryptographic boundary of origin.  Failing to
   do so opens the system to risk of the private keys being sniffed and
   discerned.

   This enrollment mode is depicted in Figure 12 and the letters in the
   following description refer to Figure 3.  Prior authorization
   (Section 3.2) and generation (Section 3.3.3) steps are not shown.

       +--------------+     +-----------------------+
       |  Repository  |     |         CA/RA         |
       +--------------+     +-----------------------+
                                        ^ 1,5
                                        |
                                        |
                                        v 2,6
                                  4  +-------+
                                  +->| Admin |
                                  |  +-------+
                                  |
                                  |
                              3,7 v
                +--------------------+          +--------+
                |       IPsec        |          | IPsec  |
                |      Peer 1        |          | Peer 2 |
                +--------------------+          +--------+

                  Figure 12.  VPN-PKI Interaction Steps:
        Admin Generates Keys and PKC Request, and Enrolls Directly
                              with PKI





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   1) Enrollment Request [E].  The Admin requests a PKC from the PKI,
      providing the generated public key.

   2) Enrollment Response [E].  The PKI responds to the enrollment
      request, providing either the new PKC that was generated or a
      suitable error indication.

   3) Opaque Transaction [E].  The Admin forwards the enrollment
      response back to the IPsec Peer, along with the keys.

   4) Opaque Transaction [E].  Peer positively acknowledges receipt of
      new PKC back to the Admin.

   5) Enrollment Confirmation [E].  Admin forwards enrollment
      confirmation back to the PKI.

   6) Enrollment Confirmation Receipt [E].  PKI sends enrollment
      confirmation receipt back to the Admin.

   7) Opaque Transaction [E].  Admin forwards PKI's enrollment
      confirmation receipt back to the Peer.

3.4.9.  Enrollment Method 3b: Admin Requests and PKI Generates and
        Sends PKC

   In this instance, the PKI and Admin have previously agreed to have
   the PKI generate keys and certificates when the PKI receives an
   authorization request.  The PKI returns to the IPsec Peer through the
   Admin, the final product of a key pair and PKC.  Again, the mechanism
   for the Peer to Admin communication is opaque.

   A drawback to this case is that the private key will eventually be
   sent over the wire (though hopefully securely so) from Admin to the
   IPsec Peer; whenever possible, it is preferred to keep a key within
   its cryptographic boundary of origin.  Failing to do so opens the
   system to risk of the private keys being sniffed and discerned.

   This enrollment mode is depicted in Figure 13 and the letters in the
   following description refer to Figure 3.  Prior authorization
   (Section 3.2) and generation (Section 3.3.4) steps are not shown.











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       +--------------+     +-----------------------+
       |  Repository  |     |         CA/RA         |
       +--------------+     +-----------------------+
                                        ^ 4
                                        |
                                        |
                                        v 1,5
                                  3  +-------+
                                  +->| Admin |
                                  |  +-------+
                                  |
                                  |
                              2,6 v
                +--------------------+        +--------+
                |       IPsec        |        | IPsec  |
                |      Peer 1        |        | Peer 2 |
                +--------------------+        +--------+

                  Figure 13.  VPN-PKI Interaction Steps:
               PKI Generates Keys, PKC Request, and Enrolls
                             Directly with PKI

   1) Enrollment Response [E].  The PKI responds to the authorization
      request sent, providing either the new PKC and public-private key
      pair that were generated or a suitable error indication.

   2) Opaque Transaction [E].  The Admin forwards the enrollment
      response back to the IPsec Peer, along with the keys.

   3) Opaque Transaction [E].  Peer positively acknowledge receipt of
      new PKC back to the Admin.

   4) Enrollment Confirmation [E].  Admin forwards enrollment
      confirmation back to the PKI.

   5) Enrollment Confirmation Receipt [E].  PKI sends enrollment
      confirmation receipt back to the Admin.

   6) Opaque Transaction [E].  Admin forwards PKI's enrollment
      confirmation receipt back to the Peer.

3.4.10.  Confirmation Handshake

   Any time a new PKC is issued by the PKI, a confirmation of PKC
   receipt MUST be sent back to the PKI by the Peer or the Admin
   (forwarding the Peer's confirmation).





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   Operationally, the Peer MUST send a confirmation to the PKI verifying
   that it has received the PKC, loaded it, and can use it effectively
   in an IKE exchange.  This requirement exists so that:

     - The PKI does not publish the new PKC in the repository for others
       until that PKC is able to be used effectively by the Peer, and

     - A revocation may be invoked if the PKC is not received and
       operational within an allowable window of time.

   To assert such proof, the Peer MUST sign a portion of data with the
   new key.  The result MUST be sent to the PKI.  The entity that
   actually sends the result to the PKI MAY be either the Peer (sending
   it directly to the PKI) or Admin (the Peer would send it to Admin,
   and Admin can, in turn, send it to the PKI).

   The Admin MUST acknowledge the successful receipt of the
   confirmation, thus signaling to the Peer that it may proceed using
   this PKC in IKE connections.  The PKI MUST complete all the
   processing necessary to enable the Peer's operational use of the new
   PKC (for example, writing the PKC to the repository) before sending
   the confirmation acknowledgement.  The Peer MUST NOT begin using the
   PKC until the PKI's confirmation acknowledgement has been received.

3.4.11.  Error Handling for Enrollment

   Thorough error condition descriptions and handling instructions are
   REQUIRED for each transaction in the enrollment process.  Providing
   such error codes will greatly aid interoperability efforts between
   the PKI and IPsec products.

   The profile will clarify what happens if the request and retrieval
   fails for some reason.  The following cases MUST be covered:

     - Admin or Peer cannot send the request.

     - Admin or Peer sent the request, but the PKI did not receive the
       request.

     - PKI received the request, but could not read it effectively.

     - PKI received and read the request, but some contents of the
       request violated the PKI's configured policy such that the PKI
       was unable to generate the PKC.

     - The PKI System generated the PKC, but could not send it.





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     - The PKI sent the PKC, but the requestor (Admin or Peer) did not
       receive it.

     - The Requestor (Admin or Peer) received the PKC, but could not
       process it due to incorrect contents, or other PKC-construction-
       related problem.

     - The Requestor failed trying to generate the confirmation.

     - The Requestor failed trying to send the confirmation.

     - The Requestor sent the confirmation, but the PKI did not receive
       it.

     - The PKI received the confirmation but could not process it.

   In each case the following questions MUST be addressed:

     - What does Peer do?
     - What does Admin do?
     - What does PKI do?
     - Is Authorization used?

   If a failure occurs after the PKI sends the PKC and before the Peer
   receives it, then the Peer MUST re-request with the same
   authorization ID and one-time authorization token.  The PKI, seeing
   the authorization ID and authorization token, MUST send the PKC
   again.

   Enrollment errors MUST be sent to the Admin regardless of the entity
   that generated the enrollment request.

3.5.  Lifecycle

   This section refers to the [L] elements labeled in Figure 3.

   Once the PKI has issued a PKC for the end entity Peer, the Peer MUST
   be able to either contact the PKI directly or through the Admin for
   any subsequent rekeys, renewals, updates, or revocations.  The PKI
   MUST support either case for renewals, updates, and revocations.
   Rekeys are Admin initiated; therefore, Peer initiated rekeys MUST be
   transferred via the Admin.

3.5.1.  One Protocol

   One protocol MUST be specified for rekey, renew, and update requests,
   responses, and confirmations.  It MUST be the same protocol as is
   specified in Section 3.4.



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   Revocation requests MAY use the same protocol as rekey, renew, and
   update operations.  Revocation requests MAY also occur via email,
   telephone, Instant Messaging, etc.

3.5.2.  PKC Rekeys, Renewals, and Updates

   Rekeys, renewals, and updates are variants of a PKC enrollment
   request scenario with unique operational and management requirements.

     - A PKC rekey replaces an end entity's PKC with a new PKC that has
       a new public key for the same SubjectName and SubjectAltName
       contents before the end entity's currently held PKC expires.

     - A PKC renewal replaces an end entity's PKC with the same public
       key for the same SubjectName and SubjectAlternativeName contents
       as an existing PKC before that PKC expires.

     - A PKC update is defined as a new PKC issuance with the same
       public key for an altered SubjectName or SubjectAlternativeName
       before expiration of the end entity's current PKC.

   When sending rekey, renew, or update requests, the entire contents of
   the PKC request needs to be sent to the PKI, not just the changed
   elements.

   The rekey, renew, and update requests MUST be signed by the private
   key of the old PKC.  This will allow the PKI to verify the identity
   of the requestor, and ensure that an attacker does not submit a
   request and receive a PKC with another end entity's identity.

   Whether or not a new key is used for the new PKC in a renew or update
   scenario is a matter of local security policy, and MUST be specified
   by the Admin to the PKI in the original authorization request.
   Reusing the same key is permitted, but not encouraged.  If a new key
   is used, the update or renew request must be signed by both the old
   key -- to prove the right to make the request -- and the new key --
   to use for the new PKC.

   The new PKC resulting from a rekey, renew, or update will be
   retrieved in-band, using the same mechanism as a new PKC request.

   For the duration of time after a rekey, renew, or update has been
   processed and before PKI has received confirmation of the Peer's
   successful receipt of the new PKC, both PKCs (the old and the new)
   for the end entity will be valid.  This will allow the Peer to
   continue with uninterrupted IKE connections with the previous PKC
   while the rekey, renewal, or update process occurs.




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   After the rekey, renewal, or update occurs, the question now exists
   for the PKI of what to do about the old PKC.  If the old PKC is to be
   made unusable, the PKI will need to add it to the revocation list,
   removed from the repository; however this should only occur once all
   connections that used the old PKC have expired.  The decision about
   if the old PKC should be made unusable is determined by local policy.
   Either the PKI or the Admin MUST specify this parameter during the
   authorization phase.  In this case, the PKI or the Admin MUST also
   specify the length of time from when the PKI receives the end entity
   Peer's confirmation (of receipt of the PKC) until when the old PKC is
   made unusable.

   In the case where the new keys were generated for a renew or update
   request and for rekey requests, once the Peer receives the
   confirmation acknowledgement from the PKI, it is good practice for
   the old key pair to be destroyed as soon as possible.  Deletion can
   occur once all connections that used the old PKC have expired.

   If a PKC has been revoked, it MUST NOT be allowed a rekey, renewal,
   or update.

   Should the PKC expire without rekey, renewal, or update, an entirely
   new request MUST be made.

3.5.2.1.  Rekey Request

   Admins manage rekeys to ensure uninterrupted use of the VPN by Peers
   with new keys.  Rekeys can occur automatically if the Admin is
   configured to initiate a new authorization for the rekey.

   Scenarios for rekey are omitted as they use the same scenarios used
   in the original PKC enrollment from Sections 3.2, 3.3, and 3.4.

3.5.2.2.  Renew Request

   Admins manage renewals to ensure uninterrupted use of the VPN by
   Peers with the same key pair.

   At the time of authorization, certain details about renewal
   acceptance will be conveyed by the Admin to the PKI, as stated in
   Section 3.2.4.2.  The renewal request MUST match the conditions that
   were specified in the original authorization for:

     - Keys: New, existing, or either.
     - Requestor: End entity Peer, Admin, or either.
     - Period: How soon before PKC expiry.
     - Time: Length of time before making the old PKC unusable.




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   If any of these conditions are not met, the PKI must reject the
   renewal and log the event.

   Scenarios for renewal are omitted as they use the same scenarios used
   in the original PKC enrollment from Sections 3.2, 3.3, and 3.4.

3.5.2.3.  Update Request

   An update to the contents of a PKC will be necessary when details
   about an end entity Peer's identity change, but the Operator does not
   want to generate a new PKC from scratch, requiring a whole new
   authorization.  For example, a gateway device may be moved from one
   site to another.  Its IPv4 Address will change in the SubjectAltName
   extension, but all other information could stay the same.  Another
   example is an end user who gets married and changes the last name or
   moves from one department to another.  In either case, only one field
   (the Surname or Organizational Unit (OU) in the DN) need change.

   An update differs from a rekey or a renewal in a few ways:

     - A new key is not necessary

     - The timing of the update event is not predictable, as is the case
       with a scheduled rekey or renewal.

     - The update request may occur at any time during a PKC's period of
       validity.

     - Once the update is completed, and the new PKC is confirmed, the
       old PKC should cease to be usable, as its contents no longer
       accurately describe the subject.

   At the time of authorization, certain details about update acceptance
   can be conveyed by the Admin to the PKI, as stated in Section
   3.2.4.2.  The update request MUST match the conditions that were
   specified in the original authorization for:

     - Keys: new, existing, or either.
     - Requestor: End entity Peer, Admin, or either.
     - The fields in the Subject and SubjectAltName that are changeable.
     - Time: Length of time before making the old PKC unusable.

   If any of these conditions are not met, the PKI MUST reject the
   update and log the event.

   If an update authorization was not made at the time of original
   authorization, one can be made from Admin to the PKI at any time
   during the PKC's valid life.  When such an update is desired, Admin



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   must notify the PKI System that an update is authorized for the end
   entity and must specify the new contents.  Admin then initiates the
   update request with the given contents in whichever mechanism the VPN
   System employs (direct from end entity to PKI, from end entity
   through Admin, or directly from Admin).

   Scenarios for update are omitted as they use the same scenarios used
   in the original PKC enrollment from Sections 3.2, 3.3, and 3.4.

3.5.2.4.  Error Handling for Rekey, Renewal, and Update

   Thorough error condition descriptions and handling instructions are
   required for each transaction in the rekey, renewal, or update
   process.  Providing such error codes will greatly aid
   interoperability efforts between the PKI and IPsec products.

3.5.2.5.  Confirmation Handshakes

   The confirmation handshake requirements are the same as in Sections
   3.2, 3.3, and 3.4 except that depending on the Administrative policy
   the PKI MUST also issue a revocation on the original PKC before
   sending the confirmation response.

3.5.3.  Revocation

   The Peer MUST be able to initiate revocation for its own PKC.  In
   this case the revocation request MUST be signed by the Peer's current
   key pair for the PKC it wishes to revoke.  Whether the actual
   revocation request transaction occurs directly with the PKI or is
   first sent to Admin (who proxies or forwards the request to the PKI)
   is a matter of implementation.

   The Admin MUST be able to initiate revocation for any PKC issued
   under a template it controls.  The Admin will identify itself to the
   PKI by use of its own PKC; it MUST sign any revocation request to the
   PKI with the private key from its own PKC.  The PKI MUST have the
   ability to configure Admin(s) with revocation authority, as
   identified by its PKC.  Any PKC authorizations must specify if said
   PKC may be revoked by the Admin (see Section 3.2.3.2 for more
   details).

   The profile MUST identify the one protocol or transaction within a
   protocol to be used for both Peer and Admin initiated revocations.

   The profile MUST identify the size of CRL the client will be prepared
   to support.





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   Below are guidelines for revocation in specific transactions:

     - AFTER RENEW, BEFORE EXPIRATION: The PKI MUST be responsible for
       the PKC revocation during a renew transaction.  PKI MUST revoke
       the PKC after receiving the confirm notification from the Peer,
       and before sending the confirm-ack to the Peer.  The Peer MUST
       NOT revoke its own PKC in this case.

     - AFTER UPDATE, BEFORE EXPIRATION: The PKI MUST be responsible for
       the PKC revocation during an update transaction.  PKI MUST revoke
       the PKC after receiving the confirm notification from the Peer,
       and before sending the confirm-ack to the Peer.  The Peer MUST
       NOT revoke its own PKC in this case.

3.6.  Repositories

   This section refers to the [R] elements labeled in Figure 3.

3.6.1.  Lookups

   The PKI System SHOULD be built so that lookups resolve directly and
   completely at the URL indicated in a CDP or AIA.  The PKI SHOULD be
   built such that URL contents do not contain referrals to other hosts
   or URLs, as such referral lookups will increase the time to complete
   the IKE negotiation, and can cause implementations to timeout.

   CDP MUST be flagged as required in the authorization request.  The
   method MUST also be specified: the HTTP method MUST be method; the
   Lightweight Directory Access Protocol (LDAP) method MAY be supported.

   The complete hierarchical PKC chain (except the trust anchor) MUST be
   able to be searched in their respective repositories.  The
   information to accomplish these searches MUST be adequately
   communicated in the PKCs sent during the IKE transaction.

   All PKCs must be retrievable through a single protocol.  The final
   specification will identify one protocol as a "MUST", others MAY be
   listed as "OPTIONAL".

   The general requirements for the retrieval protocol include:

     - The protocol can be easily firewalled (including Network Address
       Translation (NAT) or Port Address Translation (PAT)).

     - The protocol can easily perform some query against a remote
       repository on a specific ID element that was given to it in a
       standard PKC field.




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   Other considerations include:

     - Relative speed
     - Relative ease of administration
     - Scalability

   Intermediate PKCs will be needed for the case of re-keying of the CA,
   or a PKI System where multiple CAs exist.

   PKCs MAY have extendedKeyusage to help identify the proper PKC for
   IPsec, though the default behavior is to not use them (see 3.1.5.3).

   IPsec Peers MUST be able to resolve Internet domain names and support
   the mandatory repository access protocol at the time of starting up
   so they can perform the PKC lookups.

   IPsec Peers should cache PKCs to reduce latency in setting up Phase
   1.  Note that this is an operational issue, not an interoperability
   issue.

   The use case for accomplishing lookups when PKCs are not sent in IKE
   is a stated non-goal of the profile at this time.

3.6.2.  Error Handling for Repository Lookups

   Thorough error condition descriptions and handling instructions are
   required for each transaction in the repository lookup process.
   Providing such error codes will greatly aid interoperability efforts
   between the PKI and IPsec products.

3.7.  Trust

3.7.1.  Trust Anchor PKC Acquisition

   The root PKC MUST arrive on the Peer via one of two methods:

   (a) Peer can get the root PKC via its secure communication with
       Admin.  This requires the Peer to know less about interaction
       with the PKI.

   (b) Admin can command Peer to retrieve the root cert directly from
       the PKI.  How retrieval of the root cert takes place is beyond
       the scope of this document, but is assumed to occur via an
       unauthenticated but confidential enrollment protocol.







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3.7.2.  Certification Path Validation

   The IPsec Peer MUST perform identity verification based on the fields
   of the PKC and parameters applicable to the VPN Security Association.
   The fields of the PKC used for verification MAY include either the
   X.500 Distinguished Name (DN) within the Subject Name, or a specific
   field within the Extension SubjectAltName (per [DOI] 4.6.2.1
   Identification Type Values).  Usage descriptions for each follow.

   The Peers or a Simple Certificate Validation Protocol (SCVP) server
   MUST validate the certification path, as per RFC 3280.  The contents
   necessary in the PKC to allow this will be enumerated in the profile
   document.

   The Peer MAY have the ability to construct the certification path
   itself; however, Admin MUST be able to supply Peers with the trust
   anchor and any chaining PKCs necessary.  The Admin MAY ensure the
   template uses the AIA extension in PKCs as a means of facilitating
   path validation.

   DNS MUST be supported by the Peers in order to support resolving URLs
   present in CDPs and AIA extensions.

3.7.3.  Revocation Checking and Status Information

   The PKI System MUST provide a mechanism whereby Peers can check the
   revocation status of PKCs that are presented to it for IKE identity.
   The mechanism should allow for access to extremely fresh revocation
   information.  CRLs have been chosen as the mechanism for
   communicating this information.  Operators are RECOMMENDED to refresh
   CRLs as often as logistically possible.

   A single mandatory protocol mechanism for performing CRL lookups MUST
   be specified by the final specification.

   All PKCs used in IKE MUST have cRLDistributionPoint and
   authorityInfoAccess fields populated with valid URLs.  This will
   allow all recipients of the PKC to know immediately how revocation is
   to be accomplished, and where to find the revocation information.
   The AIA is needed in an environment where multiple layers of CAs
   exist and for the case of a CA key roll-over.

   IPsec Systems have an OPTION to turn off revocation checking.  Such
   may be desired when the two Peers are communicating over a network
   without access to the CRL service, such as at a trade show, in a lab,
   or in a demo environment.  If revocation checking is OFF, the
   implementation MUST proceed to use the PKC as valid identity in the
   exchange and need not perform any check.



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   If the revocation of a PKC is used as the only means of deactivation
   of access authorization for the Peer (or user), then the speed of
   deactivation will be as rapid as the refresh rate of the CRL issued
   and published by the PKI.  If more immediate deactivation of access
   is required than the CRL refreshing can provide, then another
   mechanism for authorization that provides more immediate access
   deactivation should be layered into the VPN deployment.  Such a
   second mechanism is out of the scope of this profile.  (Examples are
   Xauth, L2TP's authentication, etc.)

3.7.4.  Error Handling in Revocation Checking and Certificate Path
        Validation

   Thorough error condition descriptions and handling instructions are
   required for each transaction in the revocation checking and path
   validation process.  Providing such error codes will greatly aid
   interoperability efforts between the PKI and IPsec products.

4.  Security Considerations

   This requirements document does not specify a concrete solution, and
   as such has no system-related security considerations per se.
   However, the intent of the PKI4IPSEC WG was to profile and use
   concrete protocols for certificate management (e.g., Cryptographic
   Message Syntax (CMS), Certificate Management over CMS (CMC),
   Certificate Request Message Format (CRMF)).  The individual security
   considerations of these protocols should be carefully considered in
   the profiling effort.

   In addition, this document allows significant flexibility in the
   allocation of functions between the roles of Peer and Admin.  This
   functional allocation is crucial both to achieving successful
   deployment, and to maintaining the integrity of the PKI enrollment
   and management processes.  However, much of the responsibility for
   this allocation necessarily falls to product implementers and system
   operators through the selection of applicable use cases and
   development of security policy constraints.  These factors must be
   carefully considered to ensure the security of PKI4IPSEC certificate
   management.












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5.  References

5.1.  Normative References

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

5.2.  Informative References

   [CERTPROFILE]    Housley, R., Polk, W., Ford, W., and D. Solo,
                    "Internet X.509 Public Key Infrastructure
                    Certificate and Certificate Revocation List (CRL)
                    Profile", RFC 3280, April 2002.

   [DOI]            Piper, D., "The Internet IP Security Domain of
                    Interpretation for ISAKMP", RFC 2407, November 1998.

   [FRAME]          Chokhani, S., Ford, W., Sabett, R., Merrill, C., and
                    S. Wu, "Internet X.509 Public Key Infrastructure
                    Certificate Policy and Certification Practices
                    Framework", RFC 3647, November 2003.

   [IKECERTPROFILE] Korver, B., "The Internet IP Security PKI Profile of
                    IKEv1/ISAKMP, IKEv2, and PKIX", Work in Progress,
                    February 2007.

   [IKEv1]          Harkins, D. and D. Carrel, "The Internet Key
                    Exchange (IKE)", RFC 2409, November 1998.

   [IKEv2]          Kaufman, C., "Internet Key Exchange (IKEv2)
                    Protocol", RFC 4306, December 2005.

   [IPsec]          Kent, S. and K. Seo, "Security Architecture for the
                    Internet Protocol", RFC 4301, December 2005.

6.  Acknowledgements

   This RFC is substantially based on a prior document developed by
   Project Dploy.  The principle editor of that document was Gregory M.
   Lebovitz (NetScreen/Juniper).  Contributing authors included
   Lebovitz, Paul Hoffman (VPN Consortium), Hank Mauldin (Cisco
   Systems), and Jussi Kukkonen (SSH Communications Security).
   Substantial editorial contributions were made by Leo Pluswick (ICSA),
   Tim Polk (NIST), Chris Wells (SafeNet), Thomas Hardjono (VeriSign),
   Carlisle Adams (Entrust), and Michael Shieh (NetScreen/Juniper).






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   Once brought to the IETF's PKI4IPSEC WG, the following people made
   substantial contributions: Jim Schaad and Stefan Santesson.

Editors' Addresses

   Chris Bonatti
   IECA, Inc.
   EMail: Bonattic@ieca.com

   Sean Turner
   IECA, Inc.
   EMail: Turners@ieca.com

   Gregory M. Lebovitz
   Juniper
   EMail: gregory.ietf@gmail.com



































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Full Copyright Statement

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Bonatti, et al.             Informational                      [Page 45]

