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.
Bonatti, et al. Informational [Page 1]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
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
Bonatti, et al. Informational [Page 9]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
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.
Bonatti, et al. Informational [Page 10]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
+---------------------------------------------+
| +-------------------------+ |
| 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.
Bonatti, et al. Informational [Page 11]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
+-----------------------------------------------+
| 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).
Bonatti, et al. Informational [Page 15]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
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].
Bonatti, et al. Informational [Page 17]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
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
Bonatti, et al. Informational [Page 18]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
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
Bonatti, et al. Informational [Page 19]
RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
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.
Bonatti, et al. Informational [Page 20]
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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).
Bonatti, et al. Informational [Page 21]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
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).
Bonatti, et al. Informational [Page 22]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
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
Bonatti, et al. Informational [Page 23]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
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).
Bonatti, et al. Informational [Page 24]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
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.
Bonatti, et al. Informational [Page 25]
RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
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.
Bonatti, et al. Informational [Page 26]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
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.
Bonatti, et al. Informational [Page 27]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
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.
Bonatti, et al. Informational [Page 28]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
+--------------+ +-----------------------+
| 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.
Bonatti, et al. Informational [Page 29]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
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
Bonatti, et al. Informational [Page 30]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
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.
Bonatti, et al. Informational [Page 31]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
+--------------+ +-----------------------+
| 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).
Bonatti, et al. Informational [Page 32]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
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.
Bonatti, et al. Informational [Page 33]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
- 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).
Bonatti, et al. Informational [Page 43]RFC 4809 Reqs for IPsec Certificate Mgmt Profile February 2007
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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contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
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Bonatti, et al. Informational [Page 45]
