Lightweight Certificate Management Protocol (CMP) Profile
draft-ietf-lamps-lightweight-cmp-profile-06
The information below is for an old version of the document.
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This is an older version of an Internet-Draft that was ultimately published as RFC 9483.
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| Authors | Hendrik Brockhaus , Steffen Fries , David von Oheimb | ||
| Last updated | 2021-07-09 (Latest revision 2021-02-22) | ||
| Replaces | draft-brockhaus-lamps-lightweight-cmp-profile | ||
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draft-ietf-lamps-lightweight-cmp-profile-06
LAMPS Working Group H. Brockhaus, Ed.
Internet-Draft S. Fries
Intended status: Standards Track D. von Oheimb
Expires: 10 January 2022 Siemens
9 July 2021
Lightweight Certificate Management Protocol (CMP) Profile
draft-ietf-lamps-lightweight-cmp-profile-06
Abstract
This document aims at simple, interoperable, and automated PKI
management operations covering typical use cases of industrial and
IoT scenarios. This is achieved by profiling the Certificate
Management Protocol (CMP), the related Certificate Request Message
Format (CRMF), and HTTP-based or CoAP-based transport in a succinct
but sufficiently detailed and self-contained way. To make secure
certificate management for simple scenarios and constrained devices
as lightweight as possible, only the most crucial types of operations
and options are specified as mandatory. More special and complex use
cases are supported as well, by features specified as recommended or
optional.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 10 January 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. How to Read This Document . . . . . . . . . . . . . . . . 4
1.2. Motivation for a lightweight profile of CMP . . . . . . . 4
1.3. Special requirements of industrial and IoT scenarios . . 5
1.4. Existing CMP profiles . . . . . . . . . . . . . . . . . . 6
1.5. Compatibility with existing CMP profiles . . . . . . . . 7
1.6. Scope of this document . . . . . . . . . . . . . . . . . 8
1.7. Structure of this document . . . . . . . . . . . . . . . 9
1.8. Convention and Terminology . . . . . . . . . . . . . . . 10
2. Architecture and use cases . . . . . . . . . . . . . . . . . 11
2.1. Solution architecture . . . . . . . . . . . . . . . . . . 11
2.2. Supported PKI management operations . . . . . . . . . . . 13
2.2.1. Mandatory PKI management operations . . . . . . . . . 13
2.2.2. Recommended PKI management operations . . . . . . . . 13
2.2.3. Optional PKI management operations . . . . . . . . . 14
2.3. CMP message transport . . . . . . . . . . . . . . . . . . 16
3. Generic aspects of the PKI message . . . . . . . . . . . . . 16
3.1. General description of the CMP message header . . . . . . 17
3.2. General description of the CMP message protection . . . . 19
3.3. General description of CMP message extraCerts . . . . . . 20
3.4. Generic PKI management operation prerequisites . . . . . 20
3.5. Generic validation of a PKI message . . . . . . . . . . . 22
3.6. Error handling . . . . . . . . . . . . . . . . . . . . . 24
3.6.1. Reporting error conditions upstream . . . . . . . . . 24
3.6.2. Reporting error conditions downstream . . . . . . . . 25
3.6.3. Handling error conditions on nested messages used for
batching . . . . . . . . . . . . . . . . . . . . . . 25
3.6.4. Reporting error conditions . . . . . . . . . . . . . 25
4. End Entity PKI management operations . . . . . . . . . . . . 27
4.1. Requesting a new certificate from a PKI . . . . . . . . . 30
4.1.1. Requesting a certificate from a new PKI with
signature-based protection . . . . . . . . . . . . . 31
4.1.2. Requesting an additional certificate with
signature-based protection . . . . . . . . . . . . . 37
4.1.3. Updating an existing certificate with signature
protection . . . . . . . . . . . . . . . . . . . . . 38
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4.1.4. Requesting a certificate from a PKI with MAC-based
protection . . . . . . . . . . . . . . . . . . . . . 39
4.1.5. Requesting a certificate from a legacy PKI using a
PKCS#10 request . . . . . . . . . . . . . . . . . . . 40
4.1.6. Adding central key pair generation to a certificate
request . . . . . . . . . . . . . . . . . . . . . . . 42
4.1.6.1. Using key agreement key management technique . . 47
4.1.6.2. Using key transport key management technique . . 48
4.1.6.3. Using password-based key management technique . . 49
4.1.7. Handling delayed enrollment . . . . . . . . . . . . . 50
4.2. Revoking a certificate . . . . . . . . . . . . . . . . . 55
4.3. Support messages . . . . . . . . . . . . . . . . . . . . 57
4.3.1. Get CA certificates . . . . . . . . . . . . . . . . . 59
4.3.2. Get root CA certificate update . . . . . . . . . . . 60
4.3.3. Get certificate request template . . . . . . . . . . 61
5. PKI management entity operations . . . . . . . . . . . . . . 63
5.1. Responding to requests . . . . . . . . . . . . . . . . . 64
5.1.1. Responding to a certificate request . . . . . . . . . 64
5.1.2. Initiating delayed enrollment . . . . . . . . . . . . 65
5.1.3. Responding to a confirmation message . . . . . . . . 66
5.1.4. Responding to a revocation request . . . . . . . . . 66
5.1.5. Responding to a support message . . . . . . . . . . . 66
5.2. Forwarding messages . . . . . . . . . . . . . . . . . . . 66
5.2.1. Not changing protection . . . . . . . . . . . . . . . 68
5.2.2. Adding protection and batching of messages . . . . . 69
5.2.2.1. Adding protection to a request message . . . . . 69
5.2.2.2. Batching messages . . . . . . . . . . . . . . . . 71
5.2.3. Replacing protection . . . . . . . . . . . . . . . . 72
5.2.3.1. Not changing any included proof-of-possession . . 73
5.2.3.2. Breaking proof-of-possession . . . . . . . . . . 73
5.3. Acting on behalf of other PKI entities . . . . . . . . . 74
5.3.1. Requesting certificates . . . . . . . . . . . . . . . 74
5.3.2. Revoking a certificate . . . . . . . . . . . . . . . 75
6. CMP message transport mechanisms . . . . . . . . . . . . . . 75
6.1. HTTP transport . . . . . . . . . . . . . . . . . . . . . 76
6.2. CoAP transport . . . . . . . . . . . . . . . . . . . . . 78
6.3. Piggybacking on other reliable transport . . . . . . . . 80
6.4. Offline transport . . . . . . . . . . . . . . . . . . . . 80
6.4.1. File-based transport . . . . . . . . . . . . . . . . 80
6.4.2. Other asynchronous transport protocols . . . . . . . 81
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 81
8. Security Considerations . . . . . . . . . . . . . . . . . . . 81
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 82
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 82
10.1. Normative References . . . . . . . . . . . . . . . . . . 82
10.2. Informative References . . . . . . . . . . . . . . . . . 83
Appendix A. Example CertReqTemplate . . . . . . . . . . . . . . 85
Appendix B. History of changes . . . . . . . . . . . . . . . . . 87
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 91
1. Introduction
[RFC Editor: please delete]: The labels "RFC-CMP-Updates" and "RFC-
CMP-Alg" in ASN.1 Syntax needs to be replaced with the RFC numbers of
CMP Updates [I-D.ietf-lamps-cmp-updates] and CMP Algorithms
[I-D.ietf-lamps-cmp-algorithms], when available.
This document specifies PKI management operations supporting machine-
to-machine and IoT use cases. Its focus is to maximize automation
and interoperability between all involved PKI entities, ranging from
end entities (EE) over any number of intermediate PKI management
entities such as Registration Authorities (RA) to the CMP endpoints
of Certification Authority (CA) systems. This profile makes use of
the concepts and syntax specified in CMP [RFC4210], CRMF [RFC4211],
CMS [RFC5652], HTTP transfer for CMP [RFC6712], CoAP transfer for CMP
[I-D.ietf-ace-cmpv2-coap-transport], CRMF Algorithm Requirements
Update [RFC9045], CMP Updates [I-D.ietf-lamps-cmp-updates], and CMP
Algorithms [I-D.ietf-lamps-cmp-algorithms]. Especially CMP, CRMF,
and CMS are very feature-rich standards, while in most application
scenarios only a limited subset of the specified functionality is
needed. Additionally, the standards are not always precise enough on
how to interpret and implement the described concepts. Therefore,
this document aims at tailoring the available options and specifying
at an adequate detail how to use them to make the implementation of
interoperable automated certificate management as straightforward and
lightweight as possible.
1.1. How to Read This Document
This document has become longer than the authors would have liked it
to be. Yet apart from studying Section 3, which contains general
requirements, the reader does not have to work through the whole
document but can use the guidance in Section 1.7, Section 2.2, and
Section 2.3 to figure out which parts of Section 4 to Section 6 are
relevant, depending on the PKI management operations and options of
interest.
1.2. Motivation for a lightweight profile of CMP
CMP was standardized in 1999 and is implemented in several PKI
products. In 2005, a completely reworked and enhanced version 2 of
CMP [RFC4210] and CRMF [RFC4211] has been published, followed by a
document specifying a transfer mechanism for CMP messages using HTTP
[RFC6712] in 2012.
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Though CMP is a solid and very capable protocol it is so far not used
very widely. The most important reason appears to be that the
protocol offers a too large set of features and options. On the one
hand, this makes CMP applicable to a very wide range of scenarios,
but on the other hand, a full implementation supporting all options
is not realistic because this would take undue effort.
Moreover, many details of the CMP protocol have been left open or
have not been specified in full preciseness. The profiles specified
in Appendix D and E of [RFC4210] define some more detailed PKI
management operations. Yet the specific needs of highly automated
scenarios for a machine-to-machine communication are not covered
sufficiently.
As also 3GPP and UNISIG already put across, profiling is a way of
coping with the challenges mentioned above. To profile means to take
advantage of the strengths of the given protocol, while explicitly
narrowing down the options it provides to those needed for the
purpose(s) at hand and eliminating all identified ambiguities. In
this way all the general and applicable aspects of the general
protocol are taken over and only the peculiarities of the target
scenarios need to be dealt with specifically.
Defining a profile for a new target environment takes high effort
because the range of available options needs to be well understood
and the selected options need to be consistent with each other and
suitably cover the intended application scenario. Since most
industrial PKI management use cases typically have much in common it
is worth sharing this effort, which is the aim of this document.
Other standardization bodies can reference this document and do not
need to come up with individual profiles from scratch.
1.3. Special requirements of industrial and IoT scenarios
The profiles specified in Appendix D and E of RFC 4210 [RFC4210] have
been developed particularly for managing certificates of human end
entities. With the evolution of distributed systems and client-
server architectures, certificates for machines and applications on
them have become widely used. This trend has strengthened even more
in emerging industrial and IoT scenarios. CMP is sufficiently
flexible to support them well.
Today's IT security architectures for industrial solutions typically
use certificates for endpoint authentication within protocols like
IPSec, TLS, or SSH. Therefore, the security of these architectures
highly relies upon the security and availability of the implemented
certificate management operations.
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Due to increasing security needs in operational networks as well as
availability requirements, especially on critical infrastructures and
systems with a high number of certificates, a state-of-the-art
certificate management system must be constantly available and cost-
efficient, which calls for high automation and reliability.
Consequently, the NIST Framework for Improving Critical
Infrastructure Cybersecurity [NIST.CSWP.04162018] refers to proper
processes for issuance, management, verification, revocation, and
audit for authorized devices, users, and processes involving identity
and credential management. Such PKI management operations according
to commonly accepted best practices are also required in
IEC 62443-3-3 [IEC.62443-3-3] for security level 2 and higher.
Further challenges in many industrial systems are network
segmentation and asynchronous communication, while PKI management
entities like Certification Authorities (CA) typically are not
deployed on-site but in a more protected environment of a data center
or trust center. Certificate management must be able to cope with
such network architectures. CMP offers the required flexibility and
functionality, namely self-contained messages, efficient polling, and
support for asynchronous message transfer while retaining end-to-end
security.
1.4. Existing CMP profiles
As already stated, RFC 4210 [RFC4210] contains profiles with
mandatory and optional PKI management operations in Appendix D and E.
Those profiles focus on management of human user certificates and
only partly address the specific needs of certificate management
automation for unattended devices or machine-to-machine application
scenarios.
Both Appendixes D and E focus on EE-to-RA/CA PKI management
operations and do not address further profiling of RA-to-CA
communication as typically needed for full backend automation. All
requirements regarding algorithm support for RFC 4210 Appendix D and
E [RFC4210] have been updated by CMP Algorithms Section 7.1
[I-D.ietf-lamps-cmp-algorithms].
3GPP makes use of CMP [RFC4210] in its Technical Specification 33.310
[ETSI-3GPP.33.310] for automatic management of IPSec certificates in
3G, LTE, and 5G backbone networks. Since 2010, a dedicated CMP
profile for initial certificate enrollment and certificate update
operations between EE and RA/CA is specified in that document.
UNISIG has included a CMP profile for enrollment of TLS certificates
in the Subset-137 specifying the ETRAM/ETCS on-line key management
for train control systems [UNISIG.Subset-137] in 2015.
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Both standardization bodies tailor CMP [RFC4210], CRMF [RFC4211], and
HTTP transfer for CMP [RFC6712] for highly automated and reliable PKI
management operations for unattended devices and services.
1.5. Compatibility with existing CMP profiles
The profile specified in this document is compatible with RFC 4210
Appendixes D and E (PKI Management Message Profiles) [RFC4210], with
the following exceptions:
* signature-based protection is the default protection; an initial
PKI management operation may also use MAC-based protection,
* certification of a second key pair within the same PKI management
operation is not supported,
* proof-of-possession (POPO) with self-signature of the certTemplate
according to RFC 4211 Section 4.1 [RFC4211] clause 3 is the
recommended default POPO method (deviations are possible for EEs
when requesting central key generation, for RAs when using
raVerified, and if the newly generated keypair is technically not
capable to generate digital signatures),
* confirmation of newly enrolled certificates may be omitted, and
* all PKI management operations consist of request-response message
pairs originating at the EE, i.e., announcement messages
(requiring the push model, a CMP server on the EE) are excluded in
favor of a lightweight implementation on the EE.
The profile specified in this document is compatible with the CMP
profile for 3G, LTE, and 5G network domain security and
authentication framework [ETSI-3GPP.33.310], except that:
* protection of initial PKI management operations may be MAC-based,
* the subject field is mandatory in certificate templates, and
* confirmation of newly enrolled certificates may be omitted.
The profile specified in this document is compatible with the CMP
profile for on-line key management in rail networks as specified in
UNISIG Subset-137 [UNISIG.Subset-137], except that:
* A certificate enrollment request message consists of only one
certificate request (CertReqMsg).
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* RFC 4210 [RFC4210] requires that the messageTime is Greenwich Mean
Time coded as generalizedTime.
Note: As UNISIG Subset-137 Table 5 [UNISIG.Subset-137] explicitly
states that the messageTime in required to be "UTC time", it is
not clear if this means a coding as UTCTime or generalizedTime and
if other time zones than Greenwich Mean Time shall be allowed.
Both time formats are described in RFC 5280 Section 4.1.2.5
[RFC5280].
* The same type of protection is required to be used for all
messages of one PKI management operation. This means, in case the
request message protection is MAC-based, also the response,
certConf, and pkiConf messages must have a MAC-based protection.
* Use of caPubs is not required but typically allowed in combination
with MAC-based protected PKI management operations. On the other
hand UNISIG Subset-137 Table 12 [UNISIG.Subset-137] requires using
caPubs.
Note: In case of UNISIG Subset-137 the response to a MAC-protected
request shall be signature-based. The signature-based protection
uses a certificate issued under the same root CA that is to be
transported in the caPubs field. This is not a secure delivery of
the root CA certificate.
* This profile requires that the certConf message has one CertStatus
element where the statusInfo field is recommended.
Note: In contrast, UNISIG Subset-137 Table 18 [UNISIG.Subset-137]
requires that the certConf message has one CertStatus element
where the statusInfo field must be absent. This precludes sending
a negative certConf message in case the EE rejects the newly
enrolled certificate. This results in violating the general rule
that a certificate request transaction must include a certConf
message (since moreover, using implicitConfirm is not allowed
there, neither).
1.6. Scope of this document
To minimize ambiguity and complexity through needless variety, this
document specifies exhaustive requirements on generating PKI
management messages on the sender side. On the other hand, it gives
only minimal requirements on checks by the receiving side and how to
handle error cases.
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Especially on the EE side this profile aims at a lightweight
implementation. This means that the number of PKI management
operations implementations are reduced to a reasonable minimum to
support typical certificate management use cases in industrial
machine-to-machine environments. On the EE side only limited
resources are expected, while on the side of the PKI management
entities the profile accepts higher requirements.
For the sake of interoperability and robustness, implementations
should, as far as security is not affected, adhere to Postel's law:
"Be conservative in what you do, be liberal in what you accept from
others" (often reworded as: "Be conservative in what you send, be
liberal in what you receive").
When in Section 3, Section 4, and Section 5 a field of the ASN.1
syntax as defined in CMP [RFC4210], CRMF [RFC4211], CMS [RFC5652],
and CMP Updates [I-D.ietf-lamps-cmp-updates] is not explicitly
specified, it SHOULD not be used by the sending entity. The
receiving entity MUST NOT require its absence and if present MUST
gracefully handle its presence.
1.7. Structure of this document
Section 2 introduces the general PKI architecture and approach to
certificate management that is assumed in this document. Then it
lists the PKI management operations specified in this document,
partitioning them into mandatory, recommended, and optional ones.
Section 3 profiles the generic aspects of the PKI management
operations specified in detail in Section 4 and Section 5 to minimize
redundancy in the description and to ease implementation. This
covers the general structure and protection of messages, as well as
generic prerequisites, validation, and error handling.
Section 4 profiles the exchange of CMP messages between an EE and the
PKI management entity. There are various flavors of certificate
enrollment requests, optionally with polling, central key generation,
revocation, and general support PKI management operations.
Section 5 profiles responding to requests, exchange between PKI
management entities, and operations on behalf of other PKI entities.
This may include delayed delivery of messages, which involves polling
for certificate responses, and nesting of messages.
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Section 6 outlines several mechanisms for CMP message transfer,
including HTTP-based transfer as already specified in RFC 6712
[RFC6712] optionally using TLS, and offline file-based transport.
CoAP-based transport as specified in
[I-D.ietf-ace-cmpv2-coap-transport] and piggybacking CMP messages are
also briefly addressed.
1.8. Convention and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Technical terminology is used in conformance with RFC 4210 [RFC4210],
RFC 4211 [RFC4211], RFC 5280 [RFC5280], and IEEE 802.1AR
[IEEE.802.1AR_2018]. The following key words are used:
CA: Certification authority, which issues certificates.
RA: Registration authority, an optional PKI component to which a CA
delegates certificate management functions such as end entity
authentication and authorization checks for incoming requests.
An RA can also provide conversion between various certificate
management protocols and other protocols providing some
operations related to certificate management.
LRA: Local registration authority, a specific form of RA with
proximity to the end entities.
Note: For ease of reading, this document uses the term "RA"
also for LRAs in all cases where the difference is not
relevant.
KGA: Key generation authority, an optional system component,
typically co-located with an RA or CA, that offers key
generation services to end entities.
EE: End entity, typically a device or service that holds public-
private key pair for which it manages a public-key certificate.
An identifier for the EE is given as the subject of its
certificate.
The following terminology is reused from RFC 4210 [RFC4210], as
follows:
PKI management operation: All CMP messages belonging to a single
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transaction. The transaction is
identified by the transactionID field of
the message headers.
PKI management entity: A non-EE PKI entity, i.e., RA or CA.
PKI entity: An EE or PKI management entity.
2. Architecture and use cases
2.1. Solution architecture
To facilitate secure automatic certificate enrollment, the device
hosting an EE is typically equipped with a manufacturer-issued device
certificate. Such a certificate is typically installed during
production and is meant to identify the device throughout its
lifetime. This certificate can be used to protect the initial
enrollment of operational certificates after installation of the EE
in its operational environment. In contrast to the manufacturer-
issued device certificate, operational certificates are issued by the
owner or operator of the device to identify the device or one of its
components for operational use, e.g., in a security protocol like
IPSec, TLS, or SSH. In IEEE 802.1AR [IEEE.802.1AR_2018] a
manufacturer-issued device certificate is called IDevID certificate
and an operational certificate is called LDevID certificate.
Note: According to IEEE 802.1AR [IEEE.802.1AR_2018] a DevID comprises
the triple of the certificate, the corresponding private key, and the
certificate chain.
All certificate management operations specified in this document
follow the pull model, i.e., are initiated by an EE (or by an RA
acting as an EE). The EE creates a CMP request message, protects it
using some asymmetric credential or shared secret information and
sends it to its locally reachable PKI management entity. This PKI
management entity may be a CA or more typically an RA, which checks
the request, responds to it itself, or forwards the request upstream
to the next PKI management entity. In case an RA changes the CMP
request message header or body or wants to demonstrate successful
verification or authorization, it can apply a protection of its own.
Especially the communication between an LRA and RA can be performed
synchronously or asynchronously. Synchronous communication describes
a timely uninterrupted communication between two communication
partners, while asynchronous communication is not performed in a
timely consistent manner, e.g., because of a delayed message
delivery.
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+-----+ +-----+ +-----+ +-----+
| | | | | | | |
| EE |<---------->| LRA |<-------------->| RA |<---------->| CA |
| | | | | | | |
+-----+ +-----+ +-----+ +-----+
synchronous (a)synchronous (a)synchronous
+----connection----+------connection------+----connection----+
operators service partner
+---------on site--------+----back-end services-----+-trust center-+
Figure 1: Certificate management architecture example
In operational environments the certificate management architecture
can have multiple LRAs bundling requests from multiple EEs at
dedicated locations and one (or more than one) central RA aggregating
the requests from the LRAs. Every LRA in this scenario has shared
secret information (one per EE) for MAC-based protection or a CMP
protection key and certificate allowing it to (re-)protect CMP
messages it processes. The figure above shows an architecture
example with at least one LRA, RA, and CA. It is also possible not
to have an RA or LRA or that there is no CA with a CMP interface.
Depending on the network infrastructure, the message transfer between
PKI management entities may be based on synchronous online
connections, delayed asynchronous connections, or even offline (e.g.,
file-based) transfer.
Note: CMP response messages could also be used proactively to
implement the push model towards the EE. In this case the EE acts as
receiver, not initiating the interaction with the PKI. Also, when
using a commissioning tool or a registrar agent as described in:
Support of asynchronous Enrollment in Bootstrapping Remote Secure Key
Infrastructures (BRSKI) [I-D.ietf-anima-brski-async-enroll],
certificate enrollment in a push model is needed. CMP in general and
the messages specified in this profile offer all required
capabilities, but the message flow and state machine as described in
Section 4 must be adapted to implement a push model.
Third-party CAs may implement other variants of CMP, different
standardized protocols, or even proprietary interfaces for
certificate management. Therefore, the RA may need to adapt the
exchanged CMP messages to the flavor of certificate management
interaction required by the CA.
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2.2. Supported PKI management operations
Following the scope outlined in Section 1.6, this section gives a
brief overview of the PKI management operations specified in
Section 4 and Section 5 and states whether implementation by
compliant EEs or PKI management entities is mandatory, recommended,
or optional.
2.2.1. Mandatory PKI management operations
The set of mandatory PKI management operations in this document is
intentionally lean to help for keeping development effort low and to
enable use in memory-constrained devices.
+=====================================+=========+
| PKI management operations | Section |
+=====================================+=========+
| Requesting a certificate from a new | Section |
| PKI with signature-based protection | 4.1.1 |
+-------------------------------------+---------+
| Updating an existing certificate | Section |
| with signature-based protection | 4.1.3 |
+-------------------------------------+---------+
Table 1: Mandatory End Entity PKI management
operations
+===============================================+=================+
| PKI management operations | Section |
+===============================================+=================+
| Responding to a certificate request | Section 5.1 |
+-----------------------------------------------+-----------------+
| Responding to a confirmation message | Section 5.1.3 |
+-----------------------------------------------+-----------------+
| Forwarding messages - not changing protection | Section 5.2.1 |
+-----------------------------------------------+-----------------+
| Adding protection to a request message | Section 5.2.2.1 |
+-----------------------------------------------+-----------------+
Table 2: Mandatory PKI management entity operations
2.2.2. Recommended PKI management operations
Additional recommended PKI management operations support some more
complex scenarios, that are considered beneficial for environments
with more specific demand or boundary conditions.
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+=================================+=========+
| PKI management operations | Section |
+=================================+=========+
| Requesting a certificate from a | Section |
| PKI with MAC-based protection | 4.1.4 |
+---------------------------------+---------+
| Revoking a certificate | Section |
| | 4.2 |
+---------------------------------+---------+
Table 3: Recommended End Entity PKI
management operations
+====================================+===============+
| PKI management operations | Section |
+====================================+===============+
| Responding to a revocation request | Section 5.1.4 |
+------------------------------------+---------------+
| Acting on behalf of other PKI | Section 5.3.2 |
| entities - revoking a certificate | |
+------------------------------------+---------------+
Table 4: Recommended PKI management entity operations
2.2.3. Optional PKI management operations
The optional PKI management operations support specific scenarios
seen only in some environments with special requirements.
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+========================================================+=========+
| PKI management operations | Section |
+========================================================+=========+
| Requesting an additional certificate with signature- | Section |
| based protection | 4.1.2 |
+--------------------------------------------------------+---------+
| Requesting a certificate from a legacy PKI using a | Section |
| PKCS#10 request | 4.1.5 |
+--------------------------------------------------------+---------+
| Adding central key generation to a certificate | Section |
| request. (If central key generation is supported, the | 4.1.6 |
| key agreement key management technique is REQUIRED to | |
| be supported, and the key transport and password-based | |
| key management techniques are OPTIONAL.) | |
+--------------------------------------------------------+---------+
| Handling delayed enrollment | Section |
| | 4.1.7 |
+--------------------------------------------------------+---------+
| Support messages - get CA certificates, get a trust | Section |
| anchor updates, e.g., root CA certificate updates, and | 4.3 |
| get a certificate request template | |
+--------------------------------------------------------+---------+
| Acting on behalf of other PKI entities - requesting | Section |
| certificates | 5.3.1 |
+--------------------------------------------------------+---------+
Table 5: Optional End Entity PKI management operations
+===============================================+=========+
| PKI management operations | Section |
+===============================================+=========+
| Forwarding messages - replacing protection, | Section |
| not changing any included proof-of-possession | 5.2.3.1 |
+-----------------------------------------------+---------+
| Forwarding messages - replacing protection, | Section |
| breaking proof-of-possession | 5.2.3.2 |
+-----------------------------------------------+---------+
| Batching messages | Section |
| | 5.2.2.2 |
+-----------------------------------------------+---------+
| Initiating delayed enrollment | Section |
| | 5.1.2 |
+-----------------------------------------------+---------+
Table 6: Optional PKI management entity operations
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2.3. CMP message transport
On different links between PKI entities, e.g., EE-RA and RA-CA,
different transport MAY be used. As CMP does not have specific needs
regarding message transport, virtually any reliable transport
mechanism can be used, e.g., HTTP, CoAP, and offline file-based
transport. Therefore, this document does not require any specific
transport protocol to be supported by conforming implementations.
HTTP transfer is RECOMMENDED to use for all PKI entities, yet full
flexibility is retained to choose whatever transport is suitable, for
instance for devices and system architectures with special
constraints.
+================+=============+
| Transport | Section |
+================+=============+
| HTTP transport | Section 6.1 |
+----------------+-------------+
Table 7: Recommended
transport mechanisms
+==========================================+=============+
| Transport | Section |
+==========================================+=============+
| Offline transport | Section 6.4 |
+------------------------------------------+-------------+
| CoAP transport | Section 6.2 |
+------------------------------------------+-------------+
| Piggybacking on other reliable transport | Section 6.3 |
+------------------------------------------+-------------+
Table 8: Optional transport mechanisms
3. Generic aspects of the PKI message
This section covers the generic aspects of the PKI management
operations specified in Section 4 and Section 5 as upfront general
requirements to minimize redundancy in the description and to ease
implementation.
As described in Section 5.1 of RFC 4210 [RFC4210], all CMP messages
have the following general structure:
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+--------------------------------------------+
| PKIMessage |
| +----------------------------------------+ |
| | header | |
| +----------------------------------------+ |
| +----------------------------------------+ |
| | body | |
| +----------------------------------------+ |
| +----------------------------------------+ |
| | protection (OPTIONAL) | |
| +----------------------------------------+ |
| +----------------------------------------+ |
| | extraCerts (OPTIONAL) | |
| +----------------------------------------+ |
+--------------------------------------------+
Figure 2: CMP message structure
The general contents of the message header, protection, and
extraCerts fields are specified in the following three subsections.
In case a specific PKI management operation needs different contents
in the header, protection, or extraCerts fields, the differences are
described in the respective subsections.
The CMP message body contains the PKI management operation-specific
information. It is described in Section 4 and Section 5.
The generic prerequisites needed by the PKI entities in order to be
able to perform PKI management operations are described in
Section 3.4.
The generic validation steps to be performed by PKI entities on
receiving a CMP message are described in Section 3.5.
The generic aspects of handling and reporting errors are described in
Section 3.6.
3.1. General description of the CMP message header
This section describes the generic header fields of all CMP messages
with signature-based protection.
In case a message has MAC-based protection the changes are described
in Section 4.1.4. The variations will affect the fields sender,
protectionAlg, and senderKID.
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Any PKI management operation-specific fields or variations are
described in Section 4 and 5.
header
pvno REQUIRED
-- MUST be 3 to indicate CMP v3 in all cases where EnvelopedData
-- is supported and expected to be used in the current
-- PKI management operation
-- MUST be 3 to indicate CMP v3 in certConf messages when using
-- the hashAlg field
-- MUST be 2 to indicate CMP v2 in all other cases
-- For details on version negotiation see RFC-CMP-Updates
sender REQUIRED
-- SHOULD contain a name representing the originator of the
-- message; otherwise, the NULL-DN (a zero-length
-- SEQUENCE OF RelativeDistinguishedNames) MUST be used
-- SHOULD be the subject of the CMP protection certificate, i.e.,
-- the certificate for the private key used to sign the message
-- In a multi-hop scenario, the receiving entity SHOULD not rely
-- on the correctness of the sender field.
recipient REQUIRED
-- SHOULD be the name of the intended recipient; otherwise, the
-- NULL-DN MUST be used
-- In the first message of a PKI management operation:
-- SHOULD be the subject DN of the CA the PKI management
-- operation is requested from
-- In all other messages:
-- SHOULD contain the value of the sender field of the previous
-- message in the same PKI management operation
-- The recipient field SHALL be handled gracefully by the
-- receiving entity, because in a multi-hop scenario its
-- correctness cannot be guaranteed.
messageTime RECOMMENDED
-- MUST be the time at which the message was produced, if present
protectionAlg REQUIRED
-- MUST be an algorithm identifier indicating the algorithm
-- used for calculating the protection bits
-- If it is a signature algorithm its type MUST be a
-- MSG_SIG_ALG as specified in [RFC-CMP-Alg] Section 3 and
-- MUST be consistent with the subjectPublicKeyInfo field of
-- the protection certificate
-- If it is a MAC algorithm its type MUST be a MSG_MAC_ALG as
-- specified in [RFC-CMP-Alg] Section 6.1
senderKID RECOMMENDED
-- MUST be the SubjectKeyIdentifier of the CMP protection
-- certificate
transactionID REQUIRED
-- In the first message of a PKI management operation:
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-- MUST be 128 bits of random data, to minimize the probability
-- of having the transactionID already in use at the server
-- In all other messages:
-- MUST be the value from the previous message in the same
-- PKI management operation
senderNonce REQUIRED
-- MUST be cryptographically secure and fresh 128 random bits
recipNonce RECOMMENDED
-- If this is the first message of a transaction: SHOULD be
-- absent
-- In all other messages: MUST be present and contain the value
-- of the senderNonce of the previous message in the same
-- transaction
generalInfo OPTIONAL
implicitConfirm OPTIONAL
-- The extension is optional in ir/cr/kur/p10cr requests and
-- ip/cp/kup response messages and PROHIBTED in other types of
-- messages
-- Added to request messages to request omission of the certConf
-- message
-- Added to response messages to grant omission of the certConf
-- message
-- See [RFC4210] Section 5.1.1.1.
ImplicitConfirmValue REQUIRED
-- ImplicitConfirmValue MUST be NULL
rootCaCert OPTIONAL
-- MAY be present in genm messages of type id-it-rootCaKeyUpdate
-- MUST be omitted in all other messages
-- See [RFC-CMP-Updates]
RootCaCertValue REQUIRED
-- contains the root CA certificate for which an update is
-- requested
certProfile OPTIONAL
-- MAY be present in ir/cr/kur/p10cr and in genm messages of type
-- id-it-certReqTemplate
-- MUST be omitted in all other messages
-- See [RFC-CMP-Updates]
CertProfileValue REQUIRED
-- MUST contain exactly one UTF8String element
-- MUST contain the name of a certificate profile
3.2. General description of the CMP message protection
This section describes the generic protection field contents of all
CMP messages with signature-based protection. The private key used
to sign a CMP message is called "protection key" and the related
certificate is called "protection certificate". Any included
keyUsage extension SHOULD allow digitalSignature.
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protection RECOMMENDED
-- MUST contain the signature calculated using the private key
-- of the entity protecting the message. The signature
-- algorithm used MUST be given in the protectionAlg field.
Generally, CMP message protection is required for CMP messages, but
there are cases where protection of error messages specified in
Section 3.6 is not possible and therefore MAY be omitted.
For MAC-based protection as specified in Section 4.1.4 major
differences apply as described there.
The CMP message protection provides, if available, message origin
authentication and integrity protection for the header and body. The
CMP message extraCerts field is not covered by this protection.
Note: The extended key usages described in CMP Updates
[I-D.ietf-lamps-cmp-updates] can be used for authorization of a
sending PKI management entity.
3.3. General description of CMP message extraCerts
This section describes the generic extraCerts field of all CMP
messages with signature-based protection. Any specific requirements
on the extraCerts are specified in the respective PKI management
operation.
extraCerts
-- SHOULD contain the CMP protection certificate together with
-- its chain, if needed
-- If present, the first certificate in this field MUST be
-- the CMP protection certificate followed by its chain
-- where each element SHOULD directly certify the one
-- immediately preceding it.
-- Self-signed certificates SHOULD be omitted from extraCerts,
-- unless they are the same as the protection certificate and
-- MUST NOT be trusted based on their inclusion in any case
Note: For maximum compatibility, all implementations SHOULD be
prepared to handle potentially additional certificates and arbitrary
orderings of the certificates.
3.4. Generic PKI management operation prerequisites
This subsection describes what is generally needed by the PKI
entities to be able to perform PKI management operations.
Identification of PKI entities:
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* Each EE SHOULD know its own identity to fill the sender field.
* Each EE SHOULD know the intended recipient of its requests to fill
the recipient field, e.g., the name of the addressed CA.
Note: This name may be established using an enrollment voucher,
e.g., [RFC8366], the issuer field from a CertReqTemplate response
message content, or by other configuration means.
Routing of CMP messages:
* Each PKI entity sending messages upstream MUST know the address
needed for transporting messages to the next PKI management
entity.
Note: This address may depend on the recipient, the certificate
profile, and on the used transport mechanism.
Authentication of PKI entities:
* Each PKI entity MUST have credentials to authenticate itself. For
signature-based protection it MUST have a private key and the
corresponding certificate along with its chain.
* Each PKI entity MUST be able to establish trust in PKI it receives
responses from. When signature-based protection is used, it MUST
have the trust anchor(s) and any certificate status information
needed to perform path validation of CMP protection certificates
used for signature-based protection.
Note: A trust anchor usually is a root certificate of the PKI
addressed by the requesting EE. It may be established by
configuration or in an out-of-band manner. For an EE it may be
established using an enrollment voucher [RFC8366] or in-band of
CMP by the caPubs field in a certificate response message.
Authorization of PKI management operations:
* Each EE or RA MUST have sufficient information to be able to
authorize the PKI management entity for performing the upstream
PKI management operation.
Note: This may be achieved for example by using the cmcRA extended
key usage in server certificates, by local configuration such as
specific name patterns for subject DN or SAN portions that may
identify an RA, and/or by having a dedicated PKI Infrastructure
root CA usable only for authenticating PKI management entities.
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* Each PKI management entity MUST have sufficient information to be
able to authorize the downstream PKI entity requesting the PKI
management operation.
Note: For authorizing an RA the same examples apply as above. The
authorization of EEs can be very specific to the application
domain and may involve information from configuration or inventory
database. It may involve, e.g., the issuer information of the EE
certificate, specific contents of the CMP protection certificate
used by the EE such as name patterns of subject DN or SAN
portions, shared secret information, and other types of
credentials and evidence potentially communicated out-of-band.
3.5. Generic validation of a PKI message
This section describes generic validation steps of each PKI entity
receiving a PKI request or response message before any further
processing or forwarding. If a PKI management entity decides to
terminate a PKI management operation because a check failed, it MUST
send a negative response or an error message as described in
Section 3.6. The PKIFailureInfo bits given below in parentheses MAY
be used in the failInfo field of the PKIStatusInfo as described in
Section 3.6.4, see also RFC 4210 Appendix F [RFC4210].
All PKI message header fields not mentioned in this section like the
recipient and generalInfo fields SHOULD be handled gracefully on
reception.
The following list describes the basic set of message input
validation steps. Without these checks the protocol becomes
dysfunctional.
* The formal ASN.1 syntax of the whole message MUST be compliant
with the definitions given in CMP [RFC4210], CRMF [RFC4211],
RFC 5652 [RFC5652], and CMP Updates [I-D.ietf-lamps-cmp-updates].
(failInfo: badDataFormat)
* The pvno MUST be cmp2000(2) or cmp2021(3). (failInfo bit:
unsupportedVersion)
* The transactionID MUST be present. (failInfo bit: badDataFormat)
* The PKI message body type MUST be one of the message types
supported by the receiving PKI entity and MUST be allowed in the
current state of the PKI management operation identified by the
given transactionID. (failInfo bit: badRequest)
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The following list describes the set of message input validation
steps required to ensure secure protocol operation:
* The senderNonce MUST be present and MUST contain at least 128 bits
of data. (failInfo bit: badSenderNonce)
* Unless the PKI message is the first message of a PKI management
operation,
- the recipNonce MUST be present and MUST equal the senderNonce
of the previous message. (failInfo bit: badRecipientNonce)
* The message protection MUST be validated:
- The protection MUST be signature-based except if MAC-based
protection is used as described in Section 4.1.4and for some
error messages as described in Section 3.6.4. (failInfo bit:
wrongIntegrity)
- The senderKID SHOULD identify the key material used for
verifying the message protection. (failInfo bit:
badMessageCheck)
- The protection, if present, MUST be validated successfully. If
signature-based protection is used, the CMP protection
certificate MUST be successfully validated including path
validation using a trust anchor and MUST be authorized
according to local policies. If the keyUsage extension is
present in the CMP protection certificate the digitalSignature
bit SHOULD be set. (failInfo bit: badAlg, badMessageCheck, or
signerNotTrusted)
- The sender of a request message MUST be authorized for
requesting the operation according to PKI policies. (failInfo
bit: notAuthorized)
Note: The requirements for checking certificates given in RFC 5280
[RFC5280] MUST be followed for signature-based CMP message
protection. Unless the message is a positive ip/cp/kup where the
issuing CA certificate of the newly enrolled certificate is the same
as the CMP protection certificate of that message, certificate status
checking SHOULD be performed on the CMP protection certificates.
Depending on local policies, one or more of the input validation
checks described below need to be implemented:
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* If signature-based protection is used, the sender field SHOULD
match the subject of the CMP protection certificate. (failInfo
bit: badMessageCheck)
* If the messageTime is present, it SHOULD be close to the current
time. (failInfo bit: badTime)
3.6. Error handling
This section describes how a PKI entity handles error conditions on
messages it receives. Each error condition SHOULD be logged
appropriately.
3.6.1. Reporting error conditions upstream
An EE SHALL NOT send error messages. PKI management entities SHALL
NOT send error messages in upstream direction, either.
In case an EE rejects a newly issued certificate contained in an ip,
cp, or kup message and implicit confirmation has not been granted,
the EE MUST report this using a certConf message with "rejection"
status and await the pkiConf response as described in Section 4.1.1.
On all other error conditions regarding response messages, the EE or
PKI management entity MUST regard the current PKI management
operation as terminated with failure. The error conditions include
* invalid response message header, body type, protection, or
extraCerts according to the checks described in Section 3.5,
* any issue detected with response message contents,
* receipt of an error message from upstream,
* timeout occurred while waiting for a response,
* rejection of a newly issued certificate while implicit
confirmation has been granted.
Upstream PKI management entities will not receive any CMP message to
learn that the PKI management operation has been terminated. In case
they expect a further message from the EE, a connection interruption
or timeout will occur. Then they also MUST regard the current PKI
management operation as terminated with failure and MUST not attempt
to send an error message downstream.
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3.6.2. Reporting error conditions downstream
In case the PKI management entity detects an error condition, e.g.,
rejecting the request due to policy decision, in the body of an ir,
cr, p10cr, kur, or rr message received from downstream, it SHOULD
report the error in the specific response message, i.e., an ip, cp,
kup, or rp with "rejection" status, as described in Section 4.1.1 and
Section 4.2. This can also happen in case of polling.
In case the PKI management entity detects any other error condition
on requests, including pollReq, certConf, genm, and nested messages,
received from downstream and on responses received from upstream,
such as invalid message header, body type, protection, or extraCerts
according to the checks described in Section 3.5 it MUST report them
downstream in the form of an error message as described in
Section 3.6.4.
3.6.3. Handling error conditions on nested messages used for batching
Batching of messages using nested messages as described in
Section 5.2.2.2 requires special error handling.
If the error condition is on an upstream nested message containing
batched requests, it MUST not attempt to respond to the individual
requests included in it.
In case a PKI management entity receives an error message in response
to a nested message, it must propagate the error by responding with
an error message to each of the request messages contained in the
nested message.
In case a PKI management entity detects an error condition on the
downstream nested message received in response to a nested message
sent before, it MAY ignore this error condition and handle the
response as described in Section 5.2.2.2. Otherwise, it MUST
propagate the error by responding with an error message to each of
the requests contained in the nested message it sent originally.
3.6.4. Reporting error conditions
When sending any kind of negative response, including error messages,
a PKI entity MUST indicate the error condition in the PKIStatusInfo
structure of the respective message as described below. It then MUST
regard the current PKI management operation as terminated with
failure.
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The PKIStatusInfo structure is used to report errors. It may be part
of various message types, in particular: certConf, ip, cp, kup, and
error. The PKIStatusInfo structure consists of the following fields:
* status: Here the PKIStatus value "rejection" MUST be used.
* statusString: Here any human-readable valid value for logging or
to display via a user interface SHOULD be added.
* failInfo: Here the PKIFailureInfo bits MAY be used in the way
explained in Appendix F of RFC 4210 [RFC4210]. PKIFailureInfo
bits regarding the validation described in Section 3.5 are
referenced there. The PKIFailureInfo bits referenced in
Section 5.1 and Section 6 are described here:
- badCertId: A kur, certConf, or rr message references an unknown
certificate
- badPOP: An ir/cr/p10cr/kur contains an invalid proof-of-
possession
- certRevoked: Revocation requested for a certificate already
revoked
- badCertTemplate: The contents of a certificate request are not
accepted, e.g., a field is missing or has a non-acceptable
value or the given public key is already in use in some other
certificate (depending on policy).
- transactionIdInUse: This is sent by a PKI management entity in
case the received request contains a transaction ID that has
already been used for another transaction. An EE receiving
such error message SHOULD resend the request in a new
transaction using a different transaction ID.
- notAuthorized: The sender of a request message is not
authorized for requesting the operation.
- systemUnavail: This is sent by a PKI management entity in case
a back-end system is not available.
- systemFailure: This is sent by a PKI management entity in case
a back-end system is currently not functioning correctly.
An EE receiving a systemUnavail or systemFailure failInfo SHOULD
resend the request in a new transaction after some time.
Detailed error message description:
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Error Message -- error
Field Value
header
-- As described in Section 3.1
body
-- The message sent by an PKI management entity error that
-- occurred
error REQUIRED
pKIStatusInfo REQUIRED
status REQUIRED
-- MUST have the value "rejection"
statusString RECOMMENDED
-- SHOULD be any human-readable text for debugging, logging
-- or to display in a GUI
failInfo OPTIONAL
-- MAY be present and contain the relevant PKIFailureInfo bits
protection REQUIRED
-- As described in Section 3.2
extraCerts OPTIONAL
-- As described in Section 3.3
4. End Entity PKI management operations
This chapter focuses on the communication of an EE with the PKI
management entity it directly talks to. Depending on the network and
PKI solution, this can be an RA or directly a CA. Handling of a
message by a PKI management entity is described in Section 5.
The PKI management operations specified in this section cover the
following:
* Requesting a certificate with variations like initial enrollment,
certificate updates, central key generation, and MAC-based
protection
* Revoking a certificate
* Support messages
These operations mainly specify the message body of the CMP messages
and utilize the specification of the message header, protection and
extraCerts as specified in Section 3.
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The following diagram shows the EE state machine covering all PKI
management operations described in this section including negative
responses, while no generic error messages are shown.
On receiving messages from upstream, the EE MUST perform the general
validation checks described in Section 3.5. The behavior in case an
error occurs is described in Section 3.6.
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State machine:
Start
|
+---------+--------------------+
| |
| send ir/cr/p10cr/kur | send
| | rr/genm
v v
Waiting for ip/cp/kup Waiting for rp/genp
| |
| ip/cp/kup received | rp/genp
+-------------------+------------------+ | received
| | \ \
| with status | with status \ \
| "accepted" or | "waiting" \ \
| "grantedWithMods" | \ \
| and certificate | \ \
| v | \
| +---------> Polling | \
| | | | |
| | pollRep | send | with status |
| | received | pollReq | "rejection" |
| | v | |
| | Waiting for pollRep/ip/cp/kup | |
| | | | | | |
| +---+ | ip/cp/kup | ip/cp/kup | |
| | with certificate | with status | |
| | received | "rejection" | |
v v | received | |
certificate received | | |
| | | |
+-----------+-----+ | | |
| | | | |
| implicitConfirm | implicitConfirm | | |
| granted | not granted | | |
| | | | |
| | send certConf | | |
| v | | |
| Waiting for pkiConf | | |
| | | | |
| | pkiConf | | |
| | received | | |
+-----------------+--------------------+-------------+-------------+
|
v
End
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Note: All CMP messages belonging to the same PKI management operation
MUST have the same transactionID because the message receiver
identifies the elements of the operation in this way.
This section is aligned with CMP [RFC4210], CMP Updates
[I-D.ietf-lamps-cmp-updates], and CMP Algorithms
[I-D.ietf-lamps-cmp-algorithms].
Guidelines as well as an algorithm use profile for this document are
available in CMP Algorithms [I-D.ietf-lamps-cmp-algorithms].
4.1. Requesting a new certificate from a PKI
There are various approaches for requesting a certificate from a PKI.
These approaches differ in the way the EE authenticates itself to the
PKI, in the form of the request being used, and how the key pair to
be certified is generated. The authentication mechanisms may be as
follows:
* Using a certificate from an external PKI, e.g., a manufacturer-
issued device certificate, and the corresponding private key
* Using a private key and certificate issued from the same PKI that
is addressed for requesting a certificate
* Using the certificate to be updated and the corresponding private
key
* Using shared secret information known to the EE and the PKI
management entity
An EE requests a certificate indirectly or directly from a CA. When
the PKI management entity handles the request as described in
Section 5.1.1 and responds with a message containing the requested
certificate, the EE MUST reply with a confirmation message unless
implicitConfirm was granted. The PKI management entity then MUST
handle it as described in Section 5.1.3 and respond with a
confirmation, closing the PKI management operation.
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The message sequences described in this section allow the EE to
request certification of a locally or centrally generated public-
private key pair. Typically, the EE provides a signature-based
proof-of-possession of the private key associated with the public key
contained in the certificate request as defined by RFC 4211
Section 4.1 [RFC4211] case 3. To this end it is assumed that the
private key can technically be used for signing. This is the case
for the most common algorithms RSA and ECDSA, regardless of
potentially intended restrictions of the key usage.
Note: In conformance with NIST SP 800-57 Part 1 Section 8.1.5.1.1.2
[NIST.SP.800-57p1r5] the newly generated private key MAY be used for
self-signature, if technically possible, even if the keyUsage
extension requested in the certificate request prohibits generation
of digital signatures.
The requesting EE provides the binding of the proof-of-possession to
its identity by signature-based or MAC-based protection of the CMP
request message containing that POP. As detailed in Section 5.1.1
and Section 5.1.2, an upstream PKI management entity should verify
whether this EE is authorized to obtain a certificate with the
requested subject and other fields and extensions.
The EE MAY indicate the certificate profile to use in the certProfile
extension of the generalInfo field in the PKIHeader of the
certificate request message as described in Section 3.1.
In case a new trust anchor, e.g., a root CA certificate, is to be
installed that has been received in the caPubs field of an ip or cp
message, the EE MUST properly authenticate the message and authorize
its sender as trusted source of the new trust anchor certificate.
This authorization is typically indicated by using shared secret
information, but it can also be indicated by using a private key with
a certificate issued by another PKI explicitly authorized for this
purpose, for the CMP message protection.
4.1.1. Requesting a certificate from a new PKI with signature-based
protection
This PKI management operation should be used by an EE to request a
certificate from a new PKI using an existing certificate from an
external PKI, e.g., a manufacturer-issued IDevID certificate
[IEEE.802.1AR_2018], to authenticate itself to the new PKI.
Specific prerequisites augmenting the prerequisites in Section 3.4:
* The certificate of the EE MUST have been enrolled by an external
PKI, e.g., a manufacturer-issued device certificate.
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* The PKI management entity MUST have the trust anchor of the
external PKI.
* When using the generalInfo field certProfile, the EE MUST know the
identifier needed to indicate the requested certificate profile.
Message flow:
Step# EE PKI management entity
1 format ir
2 -> ir ->
3 handle or
forward ir
4 format or receive ip
5 possibly grant
implicitConfirm
6 <- ip <-
7 handle ip
----------------- if implicitConfirm not granted -----------------
8 format certConf
9 -> certConf ->
10 handle or
forward certConf
11 format or receive pkiConf
12 <- pkiConf <-
13 handle pkiConf
For this PKI management operation, the EE MUST include exactly one
CertReqMsg in the ir. If more certificates are required, further
requests MUST be sent using separate PKI management operation. If
the EE wants to omit sending a certificate confirmation message after
receiving the ip, e.g., to reduce the number of protocol messages
exchanged in this PKI management operation, it MUST request this by
including the implicitConfirm extension in the header of the ir
message, see Section 3.1.
If the EE did not request implicit confirmation or the request was
not granted by the PKI management entity, certificate confirmation
MUST be performed as follows. If the EE successfully received the
certificate, it MUST send a certConf message in due time. On
receiving a certConf message, the PKI management entity MUST respond
with a pkiConf message. If the PKI management entity does not
receive the expected certConf message in time it MUST handle this
like a rejection by the EE. In case of rejection the PKI management
entity SHALL terminate the PKI management operation, and the PKI MAY
revoke the newly issued certificate.
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If the EE did not request implicit confirmation or the request was
not granted by the PKI management entity, certificate confirmation
MUST be performed as follows. If the EE successfully received the
certificate and accepts it, the EE MUST send a certConf message,
which the PKI management entity must respond using a pkiConf message.
If the PKI management entity does not receive the expected certConf
message in time it MUST handle this like a rejection by the EE. In
this case the PKI management entity SHALL terminate the PKI
management operation. The PKI MAY revoke the newly issued
certificates depending on the local policy.
If the certificate request was rejected by the CA, the PKI management
entity must return an ip message containing the status code
"rejection" as described in Section 3.6 and no certifiedKeyPair
field. The EE MUST NOT react to such an ip message with a certConf
message and the PKI management operation MUST be terminated.
Detailed message description:
Initialization Request -- ir
Field Value
header
-- As described in Section 3.1
body
-- The request of the EE for a new certificate
ir REQUIRED
-- MUST contain exactly one CertReqMsg
-- If more certificates are required, further PKI management
-- operations MUST be initiated
certReq REQUIRED
certReqId REQUIRED
-- MUST be 0
certTemplate REQUIRED
version OPTIONAL
-- MUST be 2 if supplied
subject REQUIRED
-- The EE subject name MUST be carried in the subject field
-- and/or the subjectAltName extension.
-- If subject name is present only in the subjectAltName
-- extension, then the subject field MUST be a NULL-DN
publicKey REQUIRED
algorithm REQUIRED
-- MUST include the subject public key algorithm identifier
subjectPublicKey REQUIRED
-- MUST contain the public key to be certified in case of local
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-- key generation
extensions OPTIONAL
-- MAY include end-entity-specific X.509 extensions of the
-- requested certificate like subject alternative name, key
-- usage, and extended key usage
-- The subjectAltName extension MUST be present if the EE subject
-- name includes a subject alternative name.
popo OPTIONAL
-- MUST be present if local key generation is used
-- MUST be absent if central key generation is requested
signature RECOMMENDED
-- MUST be used by an EE if the key can be used for signing and
-- has the type POPOSigningKey
poposkInput PROHIBITED
-- MUST NOT be used; it is not needed because subject and
-- publicKey are both present in the certTemplate
algorithmIdentifier REQUIRED
-- The signature algorithm MUST be consistent with the publicKey
-- algorithm field of the certTemplate
signature REQUIRED
-- MUST contain the signature value computed over the DER-encoded
-- certTemplate
raVerified OPTIONAL
-- MAY be used by an RA after verifying the proof-of-possession
-- provided by the EE
protection REQUIRED
-- As described in Section 3.2
extraCerts REQUIRED
-- As described in Section 3.3
Initialization Response -- ip
Field Value
header
-- As described in Section 3.1
body
-- The response of the CA to the request as appropriate
ip REQUIRED
caPubs OPTIONAL
-- MAY be used if the certifiedKeyPair field is present
-- If used it MUST contain only a trust anchor, e.g. root
-- certificate, of the certificate contained in certOrEncCert
response REQUIRED
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-- MUST contain exactly one CertResponse
certReqId REQUIRED
-- MUST be 0
status REQUIRED
-- PKIStatusInfo structure MUST be present
status REQUIRED
-- positive values allowed: "accepted", "grantedWithMods"
-- negative values allowed: "rejection"
statusString OPTIONAL
-- MAY be any human-readable text for debugging, logging or to
-- display in a GUI
failInfo OPTIONAL
-- MAY be present if status is "rejection"
-- MUST be absent if status is "accepted" or "grantedWithMods"
certifiedKeyPair OPTIONAL
-- MUST be present if status is "accepted" or "grantedWithMods"
-- MUST be absent if status is "rejection"
certOrEncCert REQUIRED
-- MUST be present if status is "accepted" or "grantedWithMods"
certificate REQUIRED
-- MUST be present when certifiedKeyPair is present
-- MUST contain the newly enrolled X.509 certificate
privateKey OPTIONAL
-- MUST be absent in case of local key generation or "rejection"
-- MUST contain the encrypted private key in an EnvelopedData
-- structure as specified in Section 4.1.6 in case the private
-- key was generated centrally
protection REQUIRED
-- As described in Section 3.2
extraCerts REQUIRED
-- As described in Section 3.3
-- MUST contain the chain of the certificate present in
-- certOrEncCert
-- Self-signed certificates SHOULD be omitted
-- Duplicate certificates MAY be omitted
Certificate Confirmation -- certConf
Field Value
header
-- As described in Section 3.1
body
-- The message of the EE sends confirmation to the PKI
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-- management entity to accept or reject the issued certificates
certConf REQUIRED
-- MUST contain exactly one CertStatus
CertStatus REQUIRED
hashAlg OPTIONAL
-- The hash algorithm to use for calculating certHash
-- SHOULD NOT be used in all cases where the AlgorithmIdentifier
-- of the certificate signature specifies a hash algorithm
-- If used, the pvno field in the header MUST be cmp2021 (3)
certHash REQUIRED
-- MUST be the hash of the certificate, using the hash algorithm
-- indicated in hashAlg or the same one as used to create the
-- certificate signature
certReqId REQUIRED
-- MUST be 0
statusInfo RECOMMENDED
-- PKIStatusInfo structure SHOULD be present
-- Omission indicates acceptance of the indicated certificate
status REQUIRED
-- positive values allowed: "accepted"
-- negative values allowed: "rejection"
statusString OPTIONAL
-- MAY be any human-readable text for debugging, logging, or to
-- display in a GUI
failInfo OPTIONAL
-- MAY be present if status is "rejection"
-- MUST be absent if status is "accepted"
protection REQUIRED
-- As described in Section 3.2
-- MUST use the same credentials as in the first request message
-- of this PKI management operation
extraCerts RECOMMENDED
-- As described in Section 3.3
-- MAY be omitted if the message size is critical and
-- the PKI management entity caches the extraCerts from the
-- first request message of this PKI management operation
PKI Confirmation -- pkiConf
Field Value
header
-- As described in Section 3.1
body
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pkiconf REQUIRED
-- The content of this field MUST be NULL
protection REQUIRED
-- As described in Section 3.2
-- MUST use the same credentials as in the first response
-- message of this PKI management operation
extraCerts RECOMMENDED
-- As described in Section 3.3
-- MAY be omitted if the message size is critical and the EE has
-- cached the extraCerts from the first response message of
-- this PKI management operation
4.1.2. Requesting an additional certificate with signature-based
protection
This PKI management operation should be used by an EE to request an
additional certificate of the same PKI it already has certificates
from. The EE uses one of these existing certificates to authenticate
itself by signing its request messages using the respective private
key.
Specific prerequisites augmenting the prerequisites in Section 3.4:
* The certificate used by the EE MUST have been enrolled by the PKI
it requests another certificate from.
* When using the generalInfo field certProfile, the EE MUST know the
identifier needed to indicate the requested certificate profile.
The message sequence for this PKI management operation is identical
to that given in Section 4.1.1, with the following changes:
1 The body of the first request and response SHOULD be cr and cp,
respectively.
Note: Since the difference between ir/ip and cr/cp is
syntactically not essential, an ir/ip MAY be used in this PKI
management operation.
2 The caPubs field in the certificate response message SHOULD be
absent.
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4.1.3. Updating an existing certificate with signature protection
This PKI management operation should be used by an EE to request an
update for one of its certificates that is still valid. The EE uses
the certificate it wishes to update as the protection certificate.
Both for authenticating itself and for proving ownership of the
certificate to be updated, it signs the request messages with the
corresponding private key.
Specific prerequisites augmenting the prerequisites in Section 3.4:
* The certificate the EE wishes to update MUST NOT be expired or
revoked and MUST have been issued by the addressed CA.
* A new public-private key pair SHOULD be used.
* When using the generalInfo field certProfile, the EE MUST know the
identifier needed to indicate the requested certificate profile.
The message sequence for this PKI management operation is identical
to that given in Section 4.1.1, with the following changes:
1 The body of the first request and response MUST be kur and kup,
respectively.
2 Protection of the kur MUST be performed using the certificate to
be updated.
3 The subject field and/or the subjectAltName extension of the
certTemplate MUST contain the EE subject name of the existing
certificate to be updated, without modifications.
4 The certTemplate SHOULD contain the subject and/or subjectAltName
extension and publicKey of the EE only.
5 The oldCertId control MAY be used to make clear which certificate
is to be updated.
6 The caPubs field in the kup message MUST be absent.
As part of the certReq structure of the kur the oldCertId control is
added after the certTemplate field.
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controls
type RECOMMENDED
-- MUST be the value id-regCtrl-oldCertID, if present
value
issuer REQUIRED
serialNumber REQUIRED
-- MUST contain the issuer and serialNumber of the certificate
-- to be updated
4.1.4. Requesting a certificate from a PKI with MAC-based protection
This PKI management operation should be used by an EE to request a
certificate of a new PKI in case it does not have a certificate to
prove its identity to the target PKI, but has some secret information
shared with the PKI management entity. Therefore, the request and
response messages are MAC-protected using this shared secret
information. The PKI management entity checking the MAC-based
protection SHOULD replace this protection according to Section 5.2.3
in case the next hop does not know the shared secret information.
Note: The entropy of the shared secret information is crucial for the
level of protection when using MAC-based protection. Further
guidance is available in Section 8.
Specific prerequisites augmenting the prerequisites in Section 3.4:
* Rather than using private keys, certificates, and trust anchors,
the EE and the PKI management entity MUST share secret
information.
Note: The shared secret information MUST be established out-of-
band, e.g., by a service technician during initial local
configuration.
* When using the generalInfo field certProfile, the EE MUST know the
identifier needed to indicate the requested certificate profile.
The message sequence for this PKI management operation is identical
to that given in Section 4.1.1, with the following changes:
1 The protection of all messages MUST be MAC-based.
2 The senderKID MUST contain a reference the recipient can use to
identify the shared secret information used for the protection,
e.g., the username of the EE.
3 The extraCerts of all messages does not contain CMP protection
certs and associated chains.
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See Section 6 of CMP Algorithms [I-D.ietf-lamps-cmp-algorithms] for
details on message authentication code algorithms (MSG_MAC_ALG) to
use. Typically, parameters are part of the protectionAlg field,
e.g., used for key derivation, like a salt and an iteration count.
Such fields SHOULD remain constant for message protection throughout
this PKI management operation to reduce the computational overhead.
4.1.5. Requesting a certificate from a legacy PKI using a PKCS#10
request
This PKI management operation can be used by an EE to request a
certificate using a legacy PKCS#10 [RFC2986] request instead of CRMF
[RFC4211]. This offers a variation of the PKI management operations
specified in Section 4.1.1 to Section 4.1.4.
In this PKI management operation the public key and all further
certificate template data MUST be contained in the subjectPKInfo and
other certificationRequestInfo fields of the PKCS#10 structure.
The prerequisites are the same as given in Section 4.1.1,
Section 4.1.2, Section 4.1.3, or Section 4.1.4.
The message sequence for this PKI management operation is identical
to that given in Section 4.1.1 to Section 4.1.4, with the following
changes:
1 The body of the first request and response MUST be p10cr and cp,
respectively.
2 The certReqId in the cp message MUST be 0.
3 The caPubs field in the cp message SHOULD be absent.
Detailed description of the p10cr message:
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Certification Request -- p10cr
Field Value
header
-- As described in Section 3.1
body
-- The request of the EE for a new certificate using a PKCS#10
-- certificate request
p10cr REQUIRED
certificationRequestInfo REQUIRED
version REQUIRED
-- MUST be 0 to indicate PKCS#10 V1.7
subject REQUIRED
-- The EE subject name MUST be carried in the subject field
-- and/or the subjectAltName extension.
-- If subject name is present only in the subjectAltName
-- extension, then the subject field MUST be a NULL-DN
subjectPKInfo REQUIRED
algorithm REQUIRED
-- MUST include the subject public key algorithm identifier
subjectPublicKey REQUIRED
-- MUST include the public key to be certified
attributes OPTIONAL
-- MAY include end-entity-specific X.509 extensions of the
-- requested certificate like subject alternative name,
-- key usage, and extended key usage
-- The subjectAltName extension MUST be present if the EE
-- subject name includes a subject alternative name.
signatureAlgorithm REQUIRED
-- The signature algorithm MUST be consistent with the
-- subjectPKInfo field.
signature REQUIRED
-- MUST contain the self-signature for proof-of-possession
protection REQUIRED
-- As described for the underlying PKI management operation
extraCerts REQUIRED
-- As described for the underlying PKI management operation
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4.1.6. Adding central key pair generation to a certificate request
This functional extension can combined with certificate enrollment as
described in Section 4.1.1 to Section 4.1.4. It needs to be used in
case an EE is not able to generate its new public-private key pair
itself or central generation of the EE key material is preferred. It
is a matter of the local implementation which PKI management entity
will act as Key Generation Authority (KGA) and perform the key
generation. This PKI management entity MUST use a certificate
containing the additional extended key usage extension id-kp-cmKGA in
order to be accepted by the EE as a legitimate key generation
authority.
As described in Section 5.3.1, the KGA can use one of the PKI
management operations described in the sections above to request the
certificate for this key pair on behalf of the EE.
Generally speaking, in machine-to-machine scenarios it is strongly
preferable to generate public-private key pairs locally at the EE.
Together with proof-of-possession of the private key in the
certificate request, this is advisable to make sure that the entity
identified in the newly issued certificate is the only entity that
knows the private key.
Reasons for central key generation may include the following:
* Lack of sufficient initial entropy.
Note: Good random numbers are needed not only for key generation
but also for session keys and nonces in any security protocol.
Therefore, a decent security architecture should anyways support
good random number generation on the EE side or provide enough
initial entropy for the RNG seed to guarantee good pseudo-random
number generation. Yet maybe this is not the case at the time of
requesting an initial certificate during manufacturing.
* Lack of computational resources, in particular for RSA key
generation.
Note: Since key generation could be performed in advance to the
certificate enrollment communication, it is often not time
critical.
Note: As mentioned in Section 2.1, central key generation may be
required in a push model, where the certificate response message is
transferred by the PKI management entity to the EE without a previous
request message.
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The EE requesting central key generation MUST omit the publicKey
field from the certTemplate or, in case it has a preference on the
key type to be generated, provide it in the algorithm sub-field and
fill the subjectPublicKey sub-field with a zero-length BIT STRING.
Both variants indicate to the PKI management entity that a new key
pair shall be generated centrally on behalf of the EE.
Note: As the protection of centrally generated keys in the response
message has been extended to EncryptedKey by CMP Updates
[I-D.ietf-lamps-cmp-updates], EnvelopedData is the preferred
alternative to EncryptedValue. In CRMF Section 2.1.9 [RFC4211] the
use of EncryptedValue has been deprecated in favor of the
EnvelopedData structure. Therefore, this profile requires using
EnvelopedData as specified in CMS Section 6 [RFC5652]. When
EnvelopedData is to be used in a PKI management operation, CMP v3
MUST be indicated in the message header already for the initial
request message, see Section 7 of CMP Updates
[I-D.ietf-lamps-cmp-updates].
+----------------------------------+
| EnvelopedData |
| [RFC5652] section 6 |
| +------------------------------+ |
| | SignedData | |
| | [RFC5652] section 5 | |
| | +--------------------------+ | |
| | | AsymmetricKeyPackage | | |
| | | [RFC5958] | | |
| | | +----------------------+ | | |
| | | | privateKey | | | |
| | | | OCTET STRING | | | |
| | | +----------------------+ | | |
| | +--------------------------+ | |
| +------------------------------+ |
+----------------------------------+
Figure 3: Encrypted private key container
The PKI management entity delivers the private key in the privateKey
field in the certifiedKeyPair structure of the response message also
containing the newly issued certificate.
The private key MUST be provided as an AsymmetricKeyPackage structure
as defined in RFC 5958 [RFC5958].
This AsymmetricKeyPackage structure MUST be wrapped in a SignedData
structure, as specified in CMS Section 5 [RFC5652], signed by the KGA
generating the key pair. The signature MUST be performed using a
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private key related to a certificate asserting the extended key usage
id-kp-cmKGA as described in CMP Updates [I-D.ietf-lamps-cmp-updates]
to demonstrate authorization to generate key pairs on behalf of an
EE. The EE SHOULD verify the presence of this extended key usage in
the SignedData structure.
Note: When using password-based key management technique as described
in Section 4.1.6.3 it may not be possible or meaningful to the EE to
validate the KGA signature in the SignedData structure since shared
secret information is used for initial authentication. In this case
the EE MAY omit this signature validation.
The SignedData structure MUST be wrapped in an EnvelopedData
structure, as specified in CMS Section 6 [RFC5652], encrypting it
using a newly generated symmetric content-encryption key.
This content-encryption key MUST be securely provided as part of the
EnvelopedData structure to the EE using one of three key management
techniques. The choice of the key management technique to be used by
the PKI management entity depends on the authentication mechanism the
EE chose to protect the request message. See CMP Updates section 2.8
[I-D.ietf-lamps-cmp-updates] for more details on which key management
technique to use.
* Signature-based protection of the request message:
- The content-encryption key SHALL be protected using the key
agreement key management technique, see Section 4.1.6.1, if the
certificate used by the EE for protecting the request message
allows the key usage keyAgreement. If the certificate also
allows the key usage keyEncipherment, the key transport key
management technique SHALL NOT be used.
- The content-encryption key SHALL be protected using the key
transport key management technique, see Section 4.1.6.2, if the
certificate used by the EE for protecting the respective
request message allows the key usage keyEncipherment but not
keyAgreement.
* MAC-based protected of the request message:
- The content-encryption key SHALL be protected using the
password-based key management technique, see Section 4.1.6.3,
if and only if the EE used MAC-based protection for the request
message.
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If central key generation is supported, support of the key agreement
key management technique is REQUIRED and support of key transport and
password-based key management techniques are OPTION, for two reasons:
The key agreement key management technique is supported by most
asymmetric algorithms, while the key transport key management
technique is supported only by a very few of them. The password-
based key management technique shall only be used in combination with
MAC-based protection, which is a sideline in this document.
Specific prerequisites augmenting those of the respective certificate
enrollment PKI management operations:
* If signature-based protection is used, the EE MUST be able to
authenticate and authorize the KGA, using suitable information,
which includes a trust anchor.
* If MAC-based protection is used, the KGA MUST also know the shared
secret information to protect the encrypted transport of the newly
generated key pair. Consequently, the EE can also authorize the
KGA.
* The PKI management entity MUST have a certificate containing the
additional extended key usage extension id-kp-cmKGA for signing
the SignedData structure containing the private key package.
* For encrypting the SignedData structure a fresh content-encryption
key to be used by the symmetric encryption algorithm MUST be
generated with sufficient entropy.
Note: The security strength of the protection of the generated
private key should be similar or higher than the security strength
of the generated private key.
The detailed description of the privateKey field as follows:
privateKey OPTIONAL
-- MUST be an EnvelopedData structure as specified in CMS
-- Section 6 [RFC5652]
version REQUIRED
-- MUST be 2 for recipientInfo type KeyAgreeRecipientInfo and
-- KeyTransRecipientInfo
-- MUST be 0 for recipientInfo type PasswordRecipientInfo
recipientInfos REQUIRED
-- MUST contain exactly one RecipientInfo, which MUST be
-- kari of type KeyAgreeRecipientInfo (see section 4.1.6.1),
-- ktri of type KeyTransRecipientInfo (see section 4.1.6.2), or
-- pwri of type PasswordRecipientInfo (see section 4.1.6.3)
encryptedContentInfo
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REQUIRED
contentType REQUIRED
-- MUST be id-signedData
contentEncryptionAlgorithm
REQUIRED
-- MUST be the algorithm identifier of the algorithm used for
-- content encryption
-- The algorithm type MUST be a PROT_SYM_ALG as specified in
-- RFC-CMP-Alg Section 5
encryptedContent REQUIRED
-- MUST be the SignedData structure as specified in CMS
-- Section 5 [RFC5652] in encrypted form
version REQUIRED
-- MUST be 3
digestAlgorithms
REQUIRED
-- MUST contain exactly one AlgorithmIdentifier element
-- MUST be the algorithm identifier of the digest algorithm
-- used for generating the signature and match the signature
-- algorithm specified in signatureAlgorithm
encapContentInfo
REQUIRED
-- MUST contain the content that is to be signed
eContentType REQUIRED
-- MUST be id-ct-KP-aKeyPackage as specified in [RFC5958]
eContent REQUIRED
-- MUST be of type AsymmetricKeyPackage and
-- MUST contain exactly one OneAsymmetricKey element
version REQUIRED
-- MUST be 1 (indicating v2)
privateKeyAlgorithm
REQUIRED
-- The privateKeyAlgorithm field MUST contain the algorithm
-- identifier of the asymmetric key pair algorithm
privateKey
REQUIRED
publicKey
REQUIRED
-- MUST contain the public key corresponding to the private key
-- for simplicity and consistency with v2 of OneAsymmetricKey
certificates REQUIRED
-- MUST contain the certificate for the private key used to sign
-- the signedData content, together with its chain
-- The first certificate in this field MUST be the KGA
-- certificate used for protecting this content
-- Self-signed certificates SHOULD NOT be included and MUST NOT
-- be trusted based on their inclusion in any case
signerInfos REQUIRED
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-- MUST contain exactly one SignerInfo element
version REQUIRED
-- MUST be 3
sid REQUIRED
subjectKeyIdentifier
REQUIRED
-- MUST be the subjectKeyIdentifier of the KGA certificate
digestAlgorithm
REQUIRED
-- MUST be the same as in digestAlgorithmIdentifier
signedAttrs REQUIRED
-- MUST contain an id-contentType attribute containing the value
-- id-ct-KP-aKeyPackage
-- MUST contain an id-messageDigest attribute containing the
-- message digest of eContent
-- MAY contain an id-signingTime attribute containing the time
-- of signature
-- For details on the signed attributes see CMS Section 5.3 and
-- Section 11 [RFC5652]
signatureAlgorithm
REQUIRED
-- MUST be the algorithm identifier of the signature algorithm
-- used for calculation of the signature bits
-- The signature algorithm type MUST be a MSG_SIG_ALG as
-- specified in RFC-CMP-Alg Section 3 and MUST be consistent
-- with the subjectPublicKeyInfo field of the KGA certificate
signature REQUIRED
-- MUST be the digital signature of the encapContentInfo
NOTE: As stated in Section 1.5, all fields of the ASN.1 syntax that
are defined in RFC 5652 [RFC5652] but are not explicitly specified
here SHOULD NOT be used.
4.1.6.1. Using key agreement key management technique
This variant can be applied in combination with the PKI management
operations specified in Section 4.1.1 to Section 4.1.3 using
signature-based protection of CMP messages. The EE certificate used
for the signature-based protection of the request message MUST allow
for the key usage "keyAgreement" and therefore, the related key pair
MUST be used for establishment of the content-encryption key. For
this key management technique the KeyAgreeRecipientInfo structure
MUST be used in the contentInfo field.
The KeyAgreeRecipientInfo structure included into the EnvelopedData
structure is specified in CMS Section 6.2.2 [RFC5652].
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The detailed description of the KeyAgreeRecipientInfo structure looks
like this:
kari REQUIRED
-- MUST be a KeyAgreeRecipientInfo as specified in CMS Section
-- 6.2.2 [RFC5652]
version REQUIRED
-- MUST be 3
originator REQUIRED
-- MUST contain the originatorKey choice
algorithm REQUIRED
-- MUST be the algorithm identifier of the key agreement
-- algorithm
-- The algorithm type MUST be a KM_KA_ALG as specified in
-- RFC-CMP-Alg Section 4.1
publicKey REQUIRED
-- MUST be the ephemeral public key of the sending party
ukm RECOMMENDED
-- MUST be used when 1-pass ECMQV is used
-- SHOULD be present to ensure uniqueness of the key
-- encryption key, see [RFC8419]
keyEncryptionAlgorithm
REQUIRED
-- MUST be the algorithm identifier of the key wrap algorithm
-- The algorithm type MUST be a KM_KW_ALG as specified in
-- RFC-CMP-Alg Section 4.3
recipientEncryptedKeys
REQUIRED
-- MUST contain exactly one RecipientEncryptedKey element
rid REQUIRED
-- MUST contain the rKeyId choice
rKeyId REQUIRED
subjectKeyIdentifier
REQUIRED
-- MUST contain the same value as the senderKID in the
-- respective request message header
encryptedKey
REQUIRED
-- MUST be the encrypted content-encryption key
4.1.6.2. Using key transport key management technique
This variant can be applied in combination with the PKI management
operations specified in Section 4.1.1 to Section 4.1.3 using
signature-based protection of CMP messages. The EE certificate used
for the signature-based protection of the request message MUST allow
for the key usage "keyEncipherment" and not for "keyAgreement".
Therefore, the related key pair MUST be used for encipherment of the
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content-encryption key. For this key management technique the
KeyTransRecipientInfo structure MUST be used in the contentInfo
field.
The KeyTransRecipientInfo structure included into the EnvelopedData
structure is specified in CMS Section 6.2.1 [RFC5652].
The detailed description of the KeyTransRecipientInfo structure looks
like this:
ktri REQUIRED
-- MUST be a KeyTransRecipientInfo as specified in CMS
-- Section 6.2.1 [RFC5652]
version REQUIRED
-- MUST be 2
rid REQUIRED
-- MUST contain the subjectKeyIdentifier choice
subjectKeyIdentifier
REQUIRED
-- MUST contain the same value as the senderKID in the
-- respective request message header
keyEncryptionAlgorithm
REQUIRED
-- MUST be the algorithm identifier of the key transport
-- algorithm
-- The algorithm type MUST be a KM_KT_ALG as specified in
-- RFC-CMP-Alg Section 4.2
encryptedKey REQUIRED
-- MUST be the encrypted content-encryption key
4.1.6.3. Using password-based key management technique
This variant can be applied in combination with the PKI management
operation specified in Section 4.1.4 using MAC-based protection of
CMP messages. The shared secret information used for the MAC-based
protection MUST also be used for the encryption of the content-
encryption key but with a different salt value applied in the key
derivation algorithm. For this key management technique the
PasswordRecipientInfo structure MUST be used in the contentInfo
field.
Note: The entropy of the shared secret information is crucial for the
level of protection when using a password-based key management
technique. For centrally generated key pairs, the entropy of the
shared secret information SHALL not be less than the security
strength of the centrally generated key pair. Further guidance is
available in Section 8.
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The PasswordRecipientInfo structure included into the EnvelopedData
structure is specified in CMS Section 6.2.4 [RFC5652].
The detailed description of the PasswordRecipientInfo structure looks
like this:
pwri REQUIRED
-- MUST be a PasswordRecipientInfo as specified in CMS
-- Section 6.2.4 [RFC5652]
version REQUIRED
-- MUST be 0
keyDerivationAlgorithm
REQUIRED
-- MUST be the algorithm identifier of the key derivation
-- algorithm
-- The algorithm type MUST be a KM_KD_ALG as specified in
-- RFC-CMP-Alg Section 4.4
keyEncryptionAlgorithm
REQUIRED
-- MUST be the algorithm identifier of the key wrap algorithm
-- The algorithm type MUST be a KM_KW_ALG as specified in
-- RFC-CMP-Alg Section 4.3
encryptedKey REQUIRED
-- MUST be the encrypted content-encryption key
4.1.7. Handling delayed enrollment
This functional extension can be applied in combination with
certificate enrollment as described in Section 4.1.1 to
Section 4.1.5, optionally including central key generation. The
functional extension can be used in case a PKI management entity
cannot respond to the certificate request in a timely manner, e.g.,
due to offline upstream communication or required human interaction.
Depending on the PKI architecture, the entity initiating delayed
enrollment (see also Section 5.1.2) is not necessarily the PKI
management entity addressed by the EE.
Note: According to CMP Updates [I-D.ietf-lamps-cmp-updates] delayed
enrollment is also possible for PKI management operations starting
with a p10cr request message.
The PKI management entity initiating the delayed enrollment MUST
respond with an ip/cp/kup message including the status "waiting".
When receiving a response with status "waiting" the EE MUST send a
poll request. The PKI management entity that initiated the delayed
enrollment MUST answer with a poll response containing a checkAfter
time. This value indicates the minimum number of seconds that SHOULD
elapse before the EE sends another poll request. This is repeated as
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long as no final response is available or any party involved gives up
on the current PKI management operation. When the PKI management
entity that initiated delayed enrollment can provide the final ip/cp/
kup message for the initial request of the EE, it MUST provide this
message in response to a poll request. After receiving this
response, the EE can continue the original PKI management operation
as described in the respective section of this document, i.e.,
sending a certConf message if required.
No specific prerequisites apply in addition to those of the
respective certificate enrollment.
Message flow:
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Step# EE PKI management entity
1 format ir/cr/p10cr/kur
2 ->ir/cr/p10cr/kur->
3 handle or forward request
4 in case no immediate final
response is possible,
format or receive ip/cp/
kup with status "waiting"
5 <- ip/cp/kup <-
6 handle ip/cp/kup with status "waiting"
-------------------------- start polling -------------------------
7 format pollReq
8 -> pollReq ->
9 handle or forward pollReq
10 in case the requested
certificate or a
corresponding response
message is available,
continue with step 14
otherwise, format or
receive pollRep with
checkAfter value
11 <- pollRep <-
12 handle pollRep
13 let checkAfter
time elapse and
continue with step 7
----------------- end polling, continue as usual -----------------
14 format or receive
ip/cp/kup
15 possibly grant implicit
confirm
16 <- ip/cp/kup <-
17 handle ip/cp/kup
----------------- if implicitConfirm not granted -----------------
18 format certConf
19 -> certConf ->
20 handle or forward certConf
21 format or receive pkiConf
22 <- pkiConf <-
23 handle pkiConf
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Detailed description of the first ip/cp/kup:
Response with status "waiting" -- ip/cp/kup
Field Value
header
-- MUST be as described for the first response message of the
-- respective PKI management operation
body
-- The response of the PKI management entity to the request in
-- case no immediate final response can be sent
ip/cp/kup REQUIRED
response REQUIRED
-- MUST contain exactly one CertResponse
certReqId REQUIRED
-- MUST be 0
status REQUIRED
-- PKIStatusInfo structure MUST be present
status REQUIRED
-- MUST be "waiting"
statusString OPTIONAL
-- MAY be any human-readable text for debugging, logging or to
-- display in a GUI
failInfo PROHIBITED
certifiedKeyPair PROHIBITED
protection REQUIRED
-- MUST be as described for the first response message of the
-- respective PKI management operation, except that the PKI
-- management entity that initiated the delayed enrollment and
-- created this response MUST apply its own protection
extraCerts REQUIRED
-- MUST be as described for the first response message of the
-- respective PKI management operation. Yet since no newly
-- enrolled certificate is available yet, no respective
-- certificate chain is included
Polling Request -- pollReq
Field Value
header
-- MUST contain a header as described for the certConf message
-- of the respective PKI management operation
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body
-- The message of the EE asks for the final response or for a
-- time to check again
pollReq REQUIRED
-- MUST contain exactly one PollReqContent element
certReqId REQUIRED
-- MUST be 0
protection REQUIRED
-- MUST be as described for the certConf message of the
-- respective PKI management operation
extraCerts OPTIONAL
-- MUST be as described for the certConf message of the
-- respective PKI management operation
Polling Response -- pollRep
Field Value
header
-- MUST contain a header as described for the pkiConf message
-- of the respective PKI management operation
body
-- The message indicates the delay after which the EE SHOULD
-- send another pollReq message for this transaction
pollRep REQUIRED
-- MUST contain exactly one PollRepContent entry
certReqId REQUIRED
-- MUST be 0
checkAfter REQUIRED
-- time in seconds to elapse before a new pollReq SHOULD be sent
reason OPTIONAL
-- MAY be any human-readable text for debugging, logging or to
-- display in a GUI
protection REQUIRED
-- MUST be as described for the pkiConf message of the
-- respectiveprofile, except that the PKI management entity that
-- initiated the delayed enrollment and created this response
-- MUST apply its own protection
extraCerts OPTIONAL
-- If present, it MUST be as described for the pkiConf message
-- of the respective PKI management operation.
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Final response -- ip/cp/kup
Field Value
header
-- MUST be as described for the first response except that the
-- PKI management entity that initiated the delayed enrollment
-- MUST use as recipNonce the senderNonce of the last pollReq
-- message
body
-- The response of the PKI management entity to the initial
-- request as described in the respective PKI management
-- operation
protection REQUIRED
-- MUST be as described for the first response message of this
-- PKI management operation, except that the PKI management
-- entity that initiated the delayed enrollment MUST re-protect
-- the response message
extraCerts REQUIRED
-- MUST be as described for the first response message of the
-- respective PKI management operation
4.2. Revoking a certificate
This PKI management operation should be used by an entity to request
revocation of a certificate. Here the revocation request is used by
an EE to revoke one of its own certificates.
The revocation request message MUST be signed using the certificate
that is to be revoked to prove the authorization to revoke. The
revocation request message is signature-protected using this
certificate.
An EE requests the revocation of an own certificate at the CA that
issued this certificate. The PKI management entity handles the
request as described in Section 5.1.4 and responds with a message
that contains the status of the revocation from the CA.
Specific prerequisites augmenting the prerequisites in Section 3.4:
* The certificate the EE wishes to revoke is not yet expired or
revoked.
Message flow:
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Step# EE PKI management entity
1 format rr
2 -> rr ->
3 handle or forward rr
4 format or receive rp
5 <- rp <-
6 handle rp
For this PKI management operation, the EE MUST include exactly one
RevDetails structure in the rr message body. In case no generic
error occurred the response to the rr MUST be an rp message
containing a single status field.
Detailed message description:
Revocation Request -- rr
Field Value
header
-- As described in Section 3.1
body
-- The request of the EE to revoke its certificate
rr REQUIRED
-- MUST contain exactly one element of type RevDetails
-- If more revocations are desired, further PKI management
-- operations MUST be initiated
certDetails REQUIRED
-- MUST be present and is of type CertTemplate
serialNumber REQUIRED
-- MUST contain the certificate serialNumber attribute of the
-- certificate to be revoked
issuer REQUIRED
-- MUST contain the issuer attribute of the certificate to be
-- revoked
crlEntryDetails REQUIRED
-- MUST contain exactly one reasonCode of type CRLReason (see
-- [RFC5280] section 5.3.1)
-- If the reason for this revocation is not known or shall not
-- be published the reasonCode MUST be 0 = unspecified
protection REQUIRED
-- As described in Section 3.2 and using the private key related
-- to the certificate to be revoked
extraCerts REQUIRED
-- As described in Section 3.3
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Revocation Response -- rp
Field Value
header
-- As described in Section 3.1
body
-- The responds of the PKI management entity to the request as
-- appropriate
rp REQUIRED
status REQUIRED
-- MUST contain exactly one element of type PKIStatusInfo
status REQUIRED
-- positive value allowed: "accepted"
-- negative value allowed: "rejection"
statusString OPTIONAL
-- MAY be any human-readable text for debugging, logging or to
-- display in a GUI
failInfo OPTIONAL
-- MAY be present if status is "rejection"
-- MUST be absent if the status is "accepted"
protection REQUIRED
-- As described in section 3.2
extraCerts REQUIRED
-- As described in section 3.3
4.3. Support messages
The following support messages offer on demand in-band transport of
content relevant to the EE that may be provided by the PKI management
entity. CMP general messages and general response are used for this
purpose. Depending on the environment, these requests may be
answered by an RA or CA (see also Section 5.1.5).
The general messages and general response messages transport
InfoTypeAndValue structures. In addition to those infoType values
defined in RFC 4210 [RFC4210] and CMP Updates
[I-D.ietf-lamps-cmp-updates] further OIDs MAY be used to define new
PKI management operations or new general-purpose support messages as
needed in specific environments.
The following contents are specified in this document:
* Get CA certificates
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* Get root CA certificate update
* Get certificate request template
In the following the aspects common to all general messages (genm)
and general response (genp) messages are described.
Message flow:
Step# EE PKI management entity
1 format genm
2 -> genm ->
3 handle or forward genm
4 format or receive genp
5 <- genp <-
6 handle genp
Detailed message description:
General Message -- genm
Field Value
header
-- As described in Section 3.1
body
-- A request by the EE to receive information
genm REQUIRED
-- MUST contain exactly one element of type InfoTypeAndValue
infoType REQUIRED
-- MUST be the OID identifying one of the specific PKI
-- management operations described below
infoValue OPTIONAL
-- MUST be as described in the specific PKI management
-- operation described below
protection REQUIRED
-- As described in Section 3.2
extraCerts REQUIRED
-- As described in Section 3.3
General Response -- genp
Field Value
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header
-- As described in Section 3.1
body
-- The response of the PKI management entity on an information
-- request
genp REQUIRED
-- MUST contain exactly one element of type InfoTypeAndValue
infoType REQUIRED
-- MUST be the OID identifying the specific PKI management
-- operation described below
infoValue OPTIONAL
-- MUST be as described in the specific PKI management operation
-- described below
protection REQUIRED
-- As described in Section 3.2
extraCerts REQUIRED
-- As described in Section 3.3
4.3.1. Get CA certificates
This PKI management operation can be used by an EE to request CA
certificates from the PKI management entity.
An EE requests CA certificates, e.g., for chain construction, from an
PKI management entity by sending a general message with OID id-it-
caCerts as specified in CMP Updates [I-D.ietf-lamps-cmp-updates].
The PKI management entity responds with a general response with the
same OID that either contains a SEQUENCE of certificates populated
with the available intermediate and issuing CA certificates or with
no content in case no CA certificate is available.
No specific prerequisites apply in addition to those specified in
Section 3.4.
The message sequence for this PKI management operation is as given
above, with the following specific content:
1 the infoType OID to use is id-it-caCerts
2 the infoValue of the request MUST be absent
3 if present, the infoValue of the response MUST contain a sequence
of certificates
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The infoValue field of the general response containing the id-it-
caCerts OID looks like this:
infoValue OPTIONAL
-- MUST be absent if no CA certificate is available
-- MUST be present if CA certificates are available
-- MUST be a sequence of CMPCertificate
4.3.2. Get root CA certificate update
This PKI management operation can be used by an EE to request an
updated root CA Certificate as described in Section 4.4 of RFC 4210
[RFC4210].
An EE requests a root CA certificate update from the PKI management
entity by sending a general message with OID id-it-rootCaKeyUpdate,
optionally including the certificate to be updated in the rootCaCert
generalInfo field, as specified in CMP Updates
[I-D.ietf-lamps-cmp-updates]. The PKI management entity responds
with a general response with the same OID that either contains the
update of the root CA certificate consisting of up to three
certificates, or with no content in case no update is available.
The newWithNew certificate is the new root CA certificate and is
REQUIRED to be present if available. The newWithOld certificate is
REQUIRED to be present in the response message because it is needed
for the receiving entity trusting the old root CA certificate to gain
trust in the new root CA certificate. The oldWithNew certificate is
OPTIONAL because it is only needed in rare scenarios where entities
do not already trust the old root CA.
No specific prerequisites apply in addition to those specified in
Section 3.4.
The message sequence for this PKI management operation is as given
above, with the following specific content:
1 the infoType OID to use is id-it-rootCaKeyUpdate
2 the rootCaCert general info field in the header of the request MAY
contain the root CA certificate the update is requested for
3 the infoValue of the request MUST be absent
4 if present, the infoValue of the response MUST be a
RootCaKeyUpdateContent structure
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The infoValue field of the general response containing the id-it-
rootCaKeyUpdate extension looks like this:
infoValue OPTIONAL
-- MUST be absent if no update of the root CA certificate is
-- available
-- MUST be present if an update of the root CA certificate
-- is available and MUST be of type RootCaKeyUpdate
newWithNew REQUIRED
-- MUST be present if infoValue is present
-- MUST contain the new root CA certificate
newWithOld REQUIRED
-- MUST be present if infoValue is present
-- MUST contain a certificate containing the new public
-- root CA key signed with the old private root CA key
oldWithNew OPTIONAL
-- MAY be present if infoValue is present
-- MUST contain a certificate containing the old public
-- root CA key signed with the new private root CA key
4.3.3. Get certificate request template
This PKI management operation can be used by an EE to request a
template with parameters for a future certificate requests.
An EE requests certificate request parameters from the PKI management
entity by sending a general message with OID id-it-certReqTemplate as
specified in CMP Updates [I-D.ietf-lamps-cmp-updates]. The EE MAY
indicate the certificate profile to use in the certProfile extension
of the generalInfo field in the PKIHeader of the general message as
described in Section 3.1. The PKI management entity responds with a
general response with the same OID that either contains requirements
on the certificate request template, or with no content in case no
specific requirements are imposed by the PKI. The
CertReqTemplateValue contains requirements on certificate fields and
extensions in a certTemplate. Optionally it contains a keySpec field
containing requirements on algorithms acceptable for key pair
generation.
The EE SHOULD follow the requirements from the received CertTemplate,
by including in the certificate requests all the fields requested,
taking over all the field values provided and filling in any
remaining fields values. The EE SHOULD NOT add further fields, name
components, and extensions or their (sub-)components.
Note: We deliberately do not use "MUST" or "MUST NOT" here in order
to allow more flexibility in case the rules given here are not
sufficient for specific scenarios. The EE can populate the
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certificate request as wanted and ignore any of the requirements
contained in the CertReqTemplateValue. On the other hand, a PKI
management entity is free to ignore or replace any parts of the
content of the certificate request provided by the EE. The
CertReqTemplate PKI management operation offers means to ease a joint
understanding which fields and/or which field values should be used.
An example is provided in Appendix A.
In case a field of type Name, e.g., subject, is present in the
CertTemplate but has the value NULL-DN (i.e., has an empty list of
RDN components), the field SHOULD be included in the certificate
request and filled with content provided by the EE. Similarly, in
case an X.509v3 extension is present but its extnValue is empty, this
means that the extension SHOULD be included and filled with content
provided by the EE. In case a Name component, for instance a common
name or serial number, is given but has an empty string value, the EE
SHOULD fill in a value. Similarly, in case an extension has sub-
components (e.g., an IP address in a SubjectAltName field) with empty
value, the EE SHOULD fill in a value.
The EE MUST ignore (i.e., not include and fill in) empty fields,
extensions, and sub-components that it does not understand or does
not know suitable values to be filled in.
The publicKey field of type SubjectPublicKeyInfo in the CertTemplate
of the CertReqTemplateValue MUST be omitted. In case the PKI
management entity wishes to make stipulation on algorithms the EE may
use for key generation, this MUST be specified using the keySpec
field as specified in CMP Updates [I-D.ietf-lamps-cmp-updates].
The keySpec field, if present, specifies the public key types
optionally with parameters, and/or RSA key lengths for which a
certificate may be requested.
The value of a keySpec element with the OID id-regCtrl-algId, as
specified in CMP Updates [I-D.ietf-lamps-cmp-updates], MUST be of
type AlgorithmIdentifier and give an algorithm other than RSA. For
EC keys the curve information MUST be specified as described in the
respective standard documents.
The value of a keySpec element with the OID id-regCtrl-rsaKeyLen, as
specified in CMP Updates [I-D.ietf-lamps-cmp-updates], MUST be of
type Integer and give an RSA key length.
In the CertTemplate of the CertReqTemplateValue the serialNumber,
signingAlg, issuerUID, and subjectUID fields MUST be omitted.
Specific prerequisites augmenting the prerequisites in Section 3.4:
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* When using the generalInfo field certProfile, the EE MUST know the
identifier needed to indicate the requested certificate profile.
The message sequence for this PKI management operation is as given
above, with the following specific content:
1 the infoType OID to use is id-it-certReqTemplate
2 the certProfile generalInfo field in the header of the request MAY
contain the name of the requested certificate request template
3 the infoValue of the request MUST be absent
4 if present, the infoValue of the response MUST be a
CertReqTemplateValue containing a CertTemplate structure and an
optional keySpec field
The infoValue field of the general response containing the id-it-
certReqTemplate OID looks like this:
InfoValue OPTIONAL
-- MUST be absent if no requirements are available
-- MUST be present if the PKI management entity has any
-- requirements on the contents of the certificate template
certTemplate REQUIRED
-- MUST be present if infoValue is present
-- MUST contain the required CertTemplate structure elements
-- The SubjectPublicKeyInfo field MUST be absent
keySpec OPTIONAL
-- MUST be absent if no requirements on the public key are
-- available
-- MUST be present if the PKI management entity has any
-- requirements on the keys generated
-- MUST contain one AttributeTypeAndValue per supported
-- algorithm with attribute id-regCtrl-algId or
-- id-regCtrl-rsaKeyLen
5. PKI management entity operations
This section focuses on request processing by a PKI management
entity. Depending on the network and PKI solution design, this can
be an RA or CA, any of which may include protocol conversion or
central key generation (i.e., acting as a KGA).
A PKI management entity may directly respond to request messages from
downstream and report errors. In case the PKI management entity is
an RA it typically forwards the received request messages upstream
after checking them and forwards respective response messages
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downstream. Besides responding to messages or forwarding them, a PKI
management entity may request or revoke certificates on behalf of
EEs. A PKI management entity may also need to manage its own
certificates and thus act as an EE using the PKI management
operations specified in Section 4.
5.1. Responding to requests
The PKI management entity terminating the PKI management operation at
CMP level MUST respond to all received requests by returning a
related CMP response message or an error. Any intermediate PKI
management entity MAY respond depending on the PKI configuration and
policy.
In addition to the checks described in Section 3.5, the responding
PKI management entity SHOULD check that a request that initiates a
new PKI management operation does not use a transactionID that is
currently in useThe failInfo bit value to use on reporting failure as
described in Section 3.6.4 is transactionIdInUse. If any of these
verification steps or any of the essential checks described in the
below subsections fails, the PKI management entity MUST proceed as
described in Section 3.6.
The responding PKI management entity SHOULD copy the sender field of
the request to the recipient field of the response, MUST copy the
senderNonce of the request to the recipNonce of the response, and
MUST use the same transactionID for the response.
5.1.1. Responding to a certificate request
An ir/cr/p10cr/kur message is used to request a certificate as
described in Section 4.1. The responding PKI management entity MUST
proceed as follows unless it initiates delayed enrollment as
described in Section 5.1.2.
The PKI management entity SHOULD check the message body according to
the applicable requirements from Section 4.1. Possible failInfo bit
values used for error reporting in case a check failed include
badCertId and badCertTemplate. It MUST verify the presence and value
of the proof-of-possession (failInfo bit: badPOP), unless central key
generation is requested. In case the special POP value "raVerified"
is given, it SHOULD check that the request message was signed using a
certificate containing the cmcRA extended key usage (failInfo bit:
notAuthorized). The PKI management entity SHOULD perform also any
further checks on the certTemplate contents (failInfo:
badCertTemplate) according to any applicable PKI policy and
certificate profile.
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If the requested certificate is available, the PKI management entity
MUST respond with a positive ip/cp/kup message as described in
Section 4.1.
Note: If central key generation is performed by the responding PKI
management entity, the responding PKI management entity MUST include
in the response the privateKey field as specified in Section 4.1.6.
It may have issued the certificate for the newly generated key pair
itself if it is a CA, or have requested the certificate on behalf of
the EE as described in Section 5.3.1, or have received it by other
means from a CA.
The prerequisites of the respective PKI management operation as
specified in Section 4.1 apply.
Note: If the EE requested omission of the certConf message, the PKI
management entity SHOULD handle it as described in Section 4.1.1 and
therfore MAY grant this by including the implicitConfirm extension in
the response header.
5.1.2. Initiating delayed enrollment
This functional extension can be used by a PKI management entity to
initiate delayed enrollment. In this case a PKI management entity
MUST use the status "waiting" in the response message as described in
Section 4.1.7 and then MUST reply to pollReq messages as described
there.
Typically, as stated in Section 5.2.3, an intermediate PKI management
entity SHOULD NOT change the sender and recipient nonces even in case
it modifies a request or a response message. In the special case of
delayed enrollment initiated by an intermediate PKI management
entity, for example by an LRA with offline transport to an upstream
RA, there is an exception. Between the EE and this PKI management
entity, pollReq and pollRep messages are exchanged handling the
nonces as usual. Yet when, after some pollRep, the final response
from upstream arrives at the PKI management entity, this response
contains the recipNonce copied (as usual) from the senderNonce in the
original request message. The PKI management entity that initiated
the delayed enrollment MUST replace the recipNonce in the response
message with the senderNonce of the last received pollReq because the
downstream entities, including the EE, will expect it in this way.
The prerequisites of the respective PKI management operation as
specified in Section 4.1.7 apply.
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5.1.3. Responding to a confirmation message
A PKI management entity MUST handle a certConf message if it has
responded before with a positive ip/cp/kup message not granting
implicit confirmation. It SHOULD check the message body according to
the requirements given in Section 4.1.1 (failInfo bit: badCertId) and
react as described there.
The prerequisites of the respective PKI management operation as
specified in Section 4.1 apply.
5.1.4. Responding to a revocation request
An rr message is used to request revocation of a certificate. The
responding PKI management entity SHOULD check the message body
according to the requirements in Section 4.2. It MUST make sure that
the referenced certificate exists (failInfo bit: badCertId), has been
issued by the addressed CA, and is not already expired or revoked
(failInfo bit: certRevoked). On success it MUST respond with a
positive rp message as described in Section 4.2.
No specific prerequisites apply in addition to those specified in
Section 3.4.
5.1.5. Responding to a support message
A genm message is used to retrieve extra content. The responding PKI
management entity SHOULD check the message body according to the
applicable requirements in Section 4.3 and perform any further checks
depending on the PKI policy. On success it MUST respond with a genp
message as described there.
No specific prerequisites apply in addition to those specified in
Section 3.4.
5.2. Forwarding messages
In case the PKI solution consists of intermediate PKI management
entities (i.e., LRA or RA), each CMP request message coming from an
EE or any other downstream PKI management entity SHOULD be forwarded
to the next (upstream) PKI management entity as described in this
section and otherwise MUST be answered as described in Section 5.1.
Any received response message or error message MUST be forwarded to
the next (downstream) PKI entity.
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In addition to the checks described in Section 3.5, the forwarding
PKI management entity MAY verify the proof-of-possession for
ir/cr/p10cr/kur messages. If one of these verification procedures
fails, the RA proceeds as described in Section 3.6.
A PKI management entity SHOULD NOT change the received message unless
necessary. The PKI management entity SHOULD only update the message
protection and the certificate template in a certificate request
message if this is technically necessary. Concrete PKI system
specifications may define in more detail when to do so.
This is particularly relevant in the upstream communication of a
request message.
Each forwarding PKI management entity has one or more
functionalities. It may
* verify the identities of EEs and make authorization decisions for
certification request processing based on specific knowledge of
the local setup, e.g., by consulting an inventory or asset
management system,
* add or modify fields of certificate request messages,
* store data from a message in a database for later usage or audit
purposes,
* provide traversal of a network boundary,
* replace a MAC-based protection by a signature-based protection
that can be verified also further upstream,
* double-check if the messages transferred back and forth are
properly protected and well-formed,
* provide an authentic indication that it has performed all required
checks,
* initiate a delayed enrollment due to offline upstream
communication or human interaction, or
* collect messages from multiple RAs and forward them jointly.
The decision if a message should be forwarded
* unchanged with the original protection,
* unchanged with a new protection, or
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* changed with a new protection
depends on the PKI solution design and the associated security policy
(CP/CPS [RFC3647]).
A PKI management entity MUST replace or add a protection of a message
if it
* needs to securely indicate that it has done checks or validations
on the message to one of the next (upstream) PKI management entity
or
* needs to protect the message using a key and certificate from a
different PKI.
A PKI management entity MUST replace a protection of a message if it
* performs changes to the header or the body of the message or
* needs to convert from or to a MAC-based protection.
This is particularly relevant in the upstream communication of
certificate request messages.
Note that the message protection covers only the header and the body
and not the extraCerts. The PKI management entity MAY change the
extraCerts in any of the following message adaptations, e.g., to
sort, add, or delete certificates to support subsequent PKI entities.
This may be particularly helpful to augment upstream messages with
additional certificates or to reduce the number of certificates in
downstream messages when forwarding to constrained devices.
5.2.1. Not changing protection
This variant means that a PKI management entity forwards a CMP
message without changing the header, body, or protection. In this
case the PKI management entity acts more like a proxy, e.g., on a
network boundary, implementing no specific RA-like security
functionality that requires an authentic indication to the PKI.
Still the PKI management entity might implement checks that result in
refusing to forward the request message and instead responding as
specified in Section 3.6.
This variant of forwarding a message or the one described in
Section 5.2.2.1 SHOULD be used for kur messages and for central key
generation.
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No specific prerequisites apply in addition to those specified in
Section 3.4.
5.2.2. Adding protection and batching of messages
This variant of forwarding a message means that a PKI management
entity adds another protection to PKI management messages before
forwarding them.
The nested message is a PKI management message containing a
PKIMessages sequence as its body containing one or more CMP messages.
As specified in the updated Section 5.1.3.4 of RFC4210 [RFC4210] (see
CMP Updates [I-D.ietf-lamps-cmp-updates]) there are various use cases
for adding another protection by a PKI management entity. Specific
procedures are described in more detail in the following sections.
Detailed message description:
Nested Message - nested
Field Value
header
-- As described in Section 3.1
body
-- Container to provide additional protection to original
-- messages and to bundle request messages or alternatively
-- response messages
PKIMessages REQUIRED
-- MUST be a sequence of one or more CMP messages
protection REQUIRED
-- As described in Section 3.2 using the CMP protection key of
-- the PKI management entity
extraCerts REQUIRED
-- As described in Section 3.3
5.2.2.1. Adding protection to a request message
A PKI management entity may authentically indicate successful
validation and approval of a request message by adding an extra
signature to the original message.
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By adding a protection using its own CMP protecting key the PKI
management entity provides a proof of verifying and approving the
message as described above. Thus, the PKI management entity acts as
an actual Registration Authority (RA), which implements important
security functionality of the PKI. Applying an additional protection
is specifically relevant when forwarding a message that requests a
certificate update or central key generation. This is because the
original protection of the EE must be preserved while adding an
indication of approval by the PKI management entity.
The PKI management entity wrapping the original request message in a
nested message structure MUST take over the recipient, recipNonce,
and transactionID of the original message to the nested message and
apply signature-based protection. The additional signature serves as
proof of verification and authorization by this PKI management
entity.
The PKI management entity receiving such a nested message that
contains a single request message MUST validate the additional
protection signature on the nested message and check the
authorization for the approval it implies.
The PKI management entity responding to the request contained in the
nested message sends the response message as described in
Section 5.1, without wrapping it in a nested message.
Note: This form of nesting messages is characterized by the fact that
the transactionID in the header of the nested message is the same as
the one used in the included message.
Specific prerequisites augmenting the prerequisites in Section 3.4:
* The PKI management entity MUST have the authorization to perform
the validation and approval of the respective request according to
the PKI policies.
Message flow:
Step# PKI management entity PKI management entity
1 format nested
2 -> nested ->
3 handle or forward nested
4 format or receive response
5 <- response <-
6 forward response
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5.2.2.2. Batching messages
A PKI management entity MAY bundle any number of PKI management
messages for batch processing or to transfer a bulk of PKI management
messages using the nested message structure. In this use case,
nested messages are used both on the upstream interface towards the
next PKI management entity and on the downstream interface from the
PKI management entity towards the EE.
This PKI management operation is typically used on the interface
between an LRA and an RA to bundle several messages for offline
transport. In this case the LRA needs to initiate delayed enrollment
as described in Section 5.1.2. If the RA needs different routing
information per nested PKI management message a suitable mechanism
may need to be implemented. Since this mechanism strongly depends on
the requirements of the target architecture, it is out of scope of
this document.
A nested message containing requests is generated locally at the PKI
management entity. For the upstream nested message, the PKI
management entity acts as a protocol end point and therefore a fresh
transactionID and a fresh senderNonce MUST be used in the header of
the nested message. An upstream nested message may contain request
messages, e.g., ir, cr, p10cr, kur, pollReq, certConf, rr, or genm.
While building the upstream nested message the PKI management entity
SHOULD store the sender, transactionID, and senderNonce fields of all
bundled messages together with the transactionID of the upstream
nested message.
Such an upstream nested message is sent to the next PKI management
entity. The upstream PKI management entity that unbundles it MUST
handle each of the included request messages as usual. It MUST
answer with a downstream nested message. This downstream nested
message MUST use the transactionID of the upstream nested message and
return the senderNonce of the upstream nested message as the
recipNonce of the downstream nested message. The downstream nested
message SHOULD bundle the individual response messages (e.g., ip, cp,
kup, pollRep, pkiConf, rp, genp, error) for all original request
messages of the upstream nested message. While unbundling the
downstream nested message, the former PKI management entity can
determine lost and unexpected responses based on the previously
stored transactionIDs. When it forwards the unbundled responses, any
extra messages SHOULD be dropped, and any missing response message
(failInfo bit: systemUnavail) MUST be answered with an error message
to inform the respective requester about the failed certificate
management operation.
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Note: This form of nesting messages is characterized by the fact that
the transactionID in the header of the nested message is different to
those used in the included messages.
The protection of the nested messages SHOULD NOT be regarded as an
indication of verification or approval of the bundled PKI request
messages.
No specific prerequisites apply in addition to those specified in
Section 3.4.
Message flow:
Step# PKI management entity PKI management entity
1 format nested
2 -> nested ->
3 handle or forward nested
4 format or receive nested
5 <- nested <-
6 handle nested
5.2.3. Replacing protection
The following two alternatives can be used by any PKI management
entity forwarding a CMP message with or without changes while
providing its own protection and in this way asserting approval of
the message.
By replacing the existing protection using its own CMP protecting key
the PKI management entity provides a proof of verifying and approving
the message as described above. Thus, the PKI management entity acts
as an actual Registration Authority (RA), which implements important
security functionality of the PKI.
Before replacing the existing protection by a new protection, the PKI
management entity MUST verify the protection provided and approve its
content, including any modifications that it may perform. It MUST
also check that the sender, as authenticated by the message
protection, is authorized for the given operation.
These message adaptations MUST NOT be applied to kur messages
described in Section 4.1.3 since their original protection using the
key and certificate to be updated needs to be preserved, unless the
regCtrl OldCertId is used to strongly identify the certificate to be
updated.
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These message adaptations MUST NOT be applied to certificate request
messages described in for central key generation Section 4.1.6 since
their original protection needs to be preserved up to the Key
Generation Authority, which needs to use it for encrypting the new
private key for the EE.
In both the kur and central key generation cases, if a PKI management
entity needs to state its approval of the original request message it
MUST provide this using a nested message as specified in
Section 5.2.2.1.
When an intermediate PKI management entity modifies a message, it
SHOULD NOT change the transactionID nor the sender and recipient
nonces except as stated for delayed enrollment in Section 4.1.7 and
Section 5.1.2.
5.2.3.1. Not changing any included proof-of-possession
This variant of forwarding a message means that a PKI management
entity forwards a CMP message with or without modifying the message
header or body while preserving any included proof-of-possession.
In case the PKI management entity breaks an existing proof-of-
possession, the message adaptation described in Section 5.2.3.2 needs
to be applied instead.
Specific prerequisites augmenting the prerequisites in Section 3.4:
* The PKI management entity MUST have the authorization to perform
the validation and approval of the respective request according to
the PKI policies.
5.2.3.2. Breaking proof-of-possession
This variant of forwarding a message needs to be used if a PKI
management entity breaks a signature-based proof-of-possession in a
certificate request message, for instance because it forwards an ir
or cr message with modifications of the certTemplate, i.e.,
modification, addition, or removal of fields.
The PKI management entity MUST verify the proof-of-possession
contained in the original message using the included public key. If
successful, the PKI management entity MUST change the popo field
value to raVerified.
Specific prerequisites augmenting the prerequisites in Section 3.4:
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* The PKI management entity MUST have the authorization to verify
the proof-of-possession.
* The PKI management entity MUST have the authorization to perform
the validation and approval of the respective request according to
the PKI policies.
The new popo field MUST contain the raVerified choice in the certReq
structure of the modified message as follows:
popo
raVerified REQUIRED
-- MUST have the value NULL and indicates that the PKI
-- management entity verified the popo of the original message
5.3. Acting on behalf of other PKI entities
A PKI management entity may need to request a PKI management
operation on behalf of another PKI entity. In this case the PKI
management entity initiates the respective PKI management operation
as described in Section 4 acting in the role of the EE.
5.3.1. Requesting certificates
A PKI management entity may use on of the PKI management operations
described in Section 4.1 to request a certificate on behalf of
another PKI entity. It either generates the key pair itself and
inserts the new public key in the subjectPublicKey field of the
request certTemplate, or it uses a certificate request received from
downstream, e.g., by means of a different protocol. In the latter
case it SHOULD verify the received proof-of-possession.
No specific prerequisites apply in addition to those specified in
Section 4.1.
Note: An upstream PKI management entity will not be able to
differentiate this PKI management operation from the one described in
Section 5.2.3.
The message sequence for this PKI management operation is identical
to the respective PKI management operation given in Section 4.1, with
the following changes:
1 The request messages MUST be signed using the CMP protection key
of the PKI management entity taking the role of the EE in this
operation.
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2 If inclusion of a proper proof-of-possession is not possible the
PKI management entity MUST verify the POP provided from downstream
and use "raVerified" in its upstream request.
5.3.2. Revoking a certificate
A PKI management entity may use the PKI management operation
described in Section 4.2 to revoke a certificate of another PKI
entity. This revocation request message MUST be signed by the PKI
management entity using its own CMP protection key to prove to the
PKI authorization to revoke the certificate on behalf of that PKI
entity.
No specific prerequisites apply in addition to those specified in
Section 4.2.
Note: An upstream PKI management entity will not be able to
differentiate this PKI management operation from the ones described
in Section 5.2.3.
The message sequence for this PKI management operation is identical
to that given in Section 4.2, with the following changes:
1 The rr message MUST be signed using the CMP protection key of the
PKI management entity taking the role of the EE in this operation.
6. CMP message transport mechanisms
The CMP messages are designed to be self-contained, such that in
principle any transport can be used. HTTP SHOULD be used for online
transport while file-based transport MAY be used in case offline
transport is required. In case HTTP transport is not desired or
possible, CMP messages MAY also be piggybacked on any other reliable
transport protocol such as CoAP [RFC7252].
Independently of the means of transport, it can happen that messages
are lost or that a communication partner does not respond. To
prevent waiting indefinitely, each CMP client component SHOULD use a
configurable per-request timeout, and each CMP server component
SHOULD use a configurable per-response timeout in case a further
Request message is to be expected from the client side within the
same transaction. In this way a hanging transaction can be closed
cleanly with an error as described in Section 3.6 (failInfo bit:
systemUnavail) and related resources (for instance, any cached
extraCerts) can be freed.
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When conveying a CMP messages in HTTP, CoAP, or MIME-based transport
protocols, the internet media type "application/pkixcmp" MUST be set
for transport encoding as specified in Section 5.3 of RFC 2510
[RFC2510], Section 2.4 of CMP over CoAP
[I-D.ietf-ace-cmpv2-coap-transport], and Section 3.4 of CMP over HTTP
[RFC6712].
Note: When using TCP as reliable transport layer protocol, which is
typical in conjunction with HTTP, there is the option to keep the
connection open over the lifetime of the PKI management operation
containing multiple request-response message pairs. This may improve
efficiency but is not required from a security point of view.
6.1. HTTP transport
This transport mechanism can be used by a PKI entity to transfer CMP
messages over HTTP. If HTTP transport is used the specifications as
described in [RFC6712] and updated by CMP Updates
[I-D.ietf-lamps-cmp-updates] MUST be followed.
PKI management operations SHOULD use the following URI paths. When a
single request message is nested as described in Section 5.2.2.1, the
endpoint to use is the same as for the underlying request message.
For MAC-based protection the endpoint of the respective message body
SHALL be used, e.g, use /initialization for ir messages.
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+=================================+=====================+=========+
| PKI management operation | Path | Details |
+=================================+=====================+=========+
| Enroll client to new PKI | /initialization | Section |
| | | 4.1.1 |
+---------------------------------+---------------------+---------+
| Enroll client to existing PKI | /certification | Section |
| | | 4.1.2 |
+---------------------------------+---------------------+---------+
| Update client certificate | /keyupdate | Section |
| | | 4.1.3 |
+---------------------------------+---------------------+---------+
| Enroll client using PKCS#10 | /p10 | Section |
| | | 4.1.5 |
+---------------------------------+---------------------+---------+
| Enroll client using central key | /serverkeygen | Section |
| generation | | 4.1.6 |
| | | |
| Note: This path element MAY | | |
| also be appended to each of the | | |
| path elements listed above. | | |
+---------------------------------+---------------------+---------+
| Revoke client certificate | /revocation | Section |
| | | 4.2 |
+---------------------------------+---------------------+---------+
| Get CA certificates | /getcacert | Section |
| | | 4.3.1 |
+---------------------------------+---------------------+---------+
| Get root CA certificate update | /getrootupdate | Section |
| | | 4.3.2 |
+---------------------------------+---------------------+---------+
| Get certificate request | /getcertreqtemplate | Section |
| template | | 4.3.3 |
+---------------------------------+---------------------+---------+
| Batching messages | /nested | Section |
| | | 5.2.2.2 |
| Note: This path element is | | |
| applicable only between PKI | | |
| management entities. | | |
+---------------------------------+---------------------+---------+
Table 9: HTTP endpoints
Subsequent certConf and pollReq messages are sent to the URI of the
first request message of the respective PKI management operation.
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By sending a request to its preferred enrollment endpoint, the PKI
entity will recognize via the HTTP response status code whether a
configured URI is supported by the PKI management entity.
In case a PKI management entity receives an unexpected HTTP status
code from upstream, it MUST respond downstream with an error message
as described in Section 3.6 using a failInfo bit corresponding to the
status code, e.g., systemFailure.
For certificate management the major security goal is integrity and
data origin authentication. For delivery of centrally generated
keys, also confidentiality is a must. These goals are sufficiently
achieved by CMP itself, also in an end-to-end fashion. If a second
line of defense is required or general privacy concerns exist, TLS
can be used to provide confidentiality on a hop-by-hop basis.
TLS SHOULD be used with certificate-based authentication to further
protect the HTTP transport as described in [RFC2818]. The CMP
transport via HTTPS MUST use TLS server authentication and SHOULD use
TLS client authentication.
Note: The requirements for checking certificates given in [RFC5280],
[RFC5246], and [RFC8446] MUST be followed for the TLS layer.
Certificate status checking SHOULD be used for the TLS certificates
of all communication partners.
TLS with mutual authentication based on shared secret information MAY
be used in case no suitable certificates for certificate-based
authentication are available, e.g., a PKI management operation with
MAC-based protection is used.
Note: The entropy of the shared secret information is crucial for the
level of protection available using shard secret information-based
TLS authentication. A pre-shared key (PSK) mechanism is acceptable
using shared secret information with an entropy of at least 128 bits.
Otherwise a password-authenticated key exchange (PAKE) protocol is
RECOMMENDED.
6.2. CoAP transport
This transport mechanism can be used by a PKI entity to transfer CMP
messages over CoAP [RFC7252], e.g., in constrained environments. If
CoAP transport is used the specifications as described in CMP over
CoAP [I-D.ietf-ace-cmpv2-coap-transport] MUST be followed.
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PKI management operations SHOULD use the following URI paths. When a
single request message is nested as described in Section 5.2.2.1, the
path to use is the same as for the underlying request message. For
MAC-based protection the path of the respective message body SHALL be
used, e.g., use /ir for ir messages.
+==============================================+=======+=========+
| PKI management operation | Path | Details |
+==============================================+=======+=========+
| Enroll client to new PKI | /ir | Section |
| | | 4.1.1 |
+----------------------------------------------+-------+---------+
| Enroll client to existing PKI | /cr | Section |
| | | 4.1.2 |
+----------------------------------------------+-------+---------+
| Update client certificate | /kur | Section |
| | | 4.1.3 |
+----------------------------------------------+-------+---------+
| Enroll client using PKCS#10 | /p10 | Section |
| | | 4.1.5 |
+----------------------------------------------+-------+---------+
| Enroll client using central key generation | /ckg | Section |
| | | 4.1.6 |
| Note: This path element MAY also be appended | | |
| to each of the path elements listed above. | | |
+----------------------------------------------+-------+---------+
| Revoke client certificate | /rr | Section |
| | | 4.2 |
+----------------------------------------------+-------+---------+
| Get CA certificates | /crts | Section |
| | | 4.3.1 |
+----------------------------------------------+-------+---------+
| Get root CA certificate update | /rcu | Section |
| | | 4.3.2 |
+----------------------------------------------+-------+---------+
| Get certificate request template | /att | Section |
| | | 4.3.3 |
+----------------------------------------------+-------+---------+
| Batching messages | /nest | Section |
| | | 5.2.2.2 |
| Note: This path element is applicable only | | |
| between PKI management entities. | | |
+----------------------------------------------+-------+---------+
Table 10: CoAP endpoints
Subsequent certConf and pollReq messages are sent to the URI of the
first request message of the respective PKI management operation.
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By sending a request to its preferred enrollment endpoint, the PKI
entity will recognize via the CoAP response status code whether a
configured URI is supported by the PKI management entity. The CoAP-
inherent discovery mechanisms MAY also be used.
In case a PKI management entity receives an unexpected CoAP status
code from upstream, it MUST respond downstream with an error message
as described in Section 3.6 using a failInfo bit corresponding to the
status code, e.g., systemFailure.
Like for HTTP transport, to offer a second line of defense or to
provide hop-by-hop privacy protection, DTLS MAY be utilized as
described in CMP over CoAP [I-D.ietf-ace-cmpv2-coap-transport].
6.3. Piggybacking on other reliable transport
CMP messages MAY also be transported on some other reliable protocol.
Connection and error handling mechanisms similar to those specified
for HTTP in Section 6.1 need to be implemented.
A more detailed specification is out of scope of this document and
would need to be given for instance in the scope of the transport
protocol used.
6.4. Offline transport
For transporting CMP messages between PKI entities, any mechanism can
be used that is able to store and forward binary objects of
sufficient length and with sufficient reliability while preserving
the order of messages for each transaction.
The transport mechanism SHOULD be able to indicate message loss,
excessive delay, and possibly other transmission errors. In such
cases the PKI entities SHOULD report an error as specified in
Section 3.6 as far as possible.
6.4.1. File-based transport
CMP messages MAY be transferred between PKI entities using file-based
mechanisms, for instance when an offline EE or a PKI management
entity performs delayed enrollment. Each file MUST contain the ASN.1
DER encoding of one CMP message only, where the message may be
nested. There MUST be no extraneous header or trailer information in
the file. The file name extension ".PKI" MUST be used.
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6.4.2. Other asynchronous transport protocols
Other asynchronous transport protocols, e.g., email or website
up-/download, MAY transfer CMP messages between PKI entities. A MIME
wrapping is defined for those environments that are MIME-native. The
MIME wrapping in this section is specified in [RFC8551], section 3.1.
The ASN.1 DER encoding of the CMP messages MUST be transferred using
the "application/pkixcmp" content type and base64-encoded content
transfer encoding as specified in [RFC2510], section 5.3. A filename
MUST be included either in a "content-type" or a "content-
disposition" statement. The file name extension ".PKI" MUST be used.
7. IANA Considerations
8. Security Considerations
For requirements regarding proper random number and key generation
please refer to [RFC4086].
For the case of centrally generated key pairs, the entropy of the
shared secret information SHALL not be less than the security
strength of the centrally generated key pair; if the shared secret
information is re-used for different key pairs, the entropy and the
security of the underlying cryptographic mechanisms SHOULD exceed the
security strength of the key pairs.
For the case of a PKI management operation that delivers a new trust
anchor, e.g., a root CA certificate, using caPubs, (a) that is not
concluded in a timely manner or (b) where the shared secret
information is re-used for several key management operations, the
entropy of the shared secret information SHALL not be less than the
security strength of the key material being managed by the operation.
For other cases, it is recommended to (a) either use a shared secret
information of possibly low entropy (e.g., a password) only for a
single PKI management operation or (b) use a shared secret
information with an entropy that matches the security strength of the
key material being managed by the operation.
Further recommendations on algorithms to use with shared secret
information is available in CMP Algorithms
[I-D.ietf-lamps-cmp-algorithms].
For TLS using shared secret information-based authentication both PSK
and PAKE provide the same amount of protection against a real-time
authentication attack which is directly the amount of entropy in the
shared secret. The difference between a pre-shared key (PSK) and a
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password-authenticated key exchange (PAKE) protocols is in the level
of long-term confidentiality of the TLS messages against brute-force
decryption, where a PSK-based cipher suite only provides security
according to the entropy of the shared secret, while a PAKE-based
cipher suite provides full security independent of the entropy of the
shared secret.
< TBD: Add any security considerations >
9. Acknowledgements
We thank the various reviewers of this document.
10. References
10.1. Normative References
[I-D.ietf-ace-cmpv2-coap-transport]
Sahni, M. and S. Tripathi, "CoAP Transport for Certificate
Management Protocol", Work in Progress, Internet-Draft,
draft-ietf-ace-cmpv2-coap-transport-02, 25 May 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-ace-
cmpv2-coap-transport-02>.
[I-D.ietf-lamps-cmp-algorithms]
Brockhaus, H., Aschauer, H., Ounsworth, M., and J. Gray,
"Certificate Management Protocol (CMP) Algorithms", Work
in Progress, Internet-Draft, draft-ietf-lamps-cmp-
algorithms-05, 7 May 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
cmp-algorithms-05>.
[I-D.ietf-lamps-cmp-updates]
Brockhaus, H. and D. V. Oheimb, "Certificate Management
Protocol (CMP) Updates", Work in Progress, Internet-Draft,
draft-ietf-lamps-cmp-updates-10, 4 May 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
cmp-updates-10>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification
Request Syntax Specification Version 1.7", RFC 2986,
DOI 10.17487/RFC2986, November 2000,
<https://www.rfc-editor.org/info/rfc2986>.
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[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC4086, June 2005,
<https://www.rfc-editor.org/info/rfc4086>.
[RFC4210] Adams, C., Farrell, S., Kause, T., and T. Mononen,
"Internet X.509 Public Key Infrastructure Certificate
Management Protocol (CMP)", RFC 4210,
DOI 10.17487/RFC4210, September 2005,
<https://www.rfc-editor.org/info/rfc4210>.
[RFC4211] Schaad, J., "Internet X.509 Public Key Infrastructure
Certificate Request Message Format (CRMF)", RFC 4211,
DOI 10.17487/RFC4211, September 2005,
<https://www.rfc-editor.org/info/rfc4211>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>.
[RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958,
DOI 10.17487/RFC5958, August 2010,
<https://www.rfc-editor.org/info/rfc5958>.
[RFC6712] Kause, T. and M. Peylo, "Internet X.509 Public Key
Infrastructure -- HTTP Transfer for the Certificate
Management Protocol (CMP)", RFC 6712,
DOI 10.17487/RFC6712, September 2012,
<https://www.rfc-editor.org/info/rfc6712>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC9045] Housley, R., "Algorithm Requirements Update to the
Internet X.509 Public Key Infrastructure Certificate
Request Message Format (CRMF)", RFC 9045,
DOI 10.17487/RFC9045, June 2021,
<https://www.rfc-editor.org/info/rfc9045>.
10.2. Informative References
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[ETSI-3GPP.33.310]
3GPP, "Network Domain Security (NDS); Authentication
Framework (AF)", 3GPP TS 33.310 16.6.0, 16 December 2020.
[I-D.ietf-anima-brski-async-enroll]
Fries, S., Brockhaus, H., Lear, E., and T. Werner,
"Support of asynchronous Enrollment in BRSKI (BRSKI-AE)",
Work in Progress, Internet-Draft, draft-ietf-anima-brski-
async-enroll-03, 24 June 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-anima-
brski-async-enroll-03>.
[IEC.62443-3-3]
IEC, "Industrial communication networks - Network and
system security - Part 3-3: System security requirements
and security levels", IEC 62443-3-3, August 2013,
<https://webstore.iec.ch/publication/7033>.
[IEEE.802.1AR_2018]
IEEE, "IEEE Standard for Local and metropolitan area
networks - Secure Device Identity", IEEE 802.1AR-2018,
DOI 10.1109/IEEESTD.2018.8423794, 2 August 2018,
<https://ieeexplore.ieee.org/document/8423794>.
[NIST.CSWP.04162018]
National Institute of Standards and Technology (NIST),
"Framework for Improving Critical Infrastructure
Cybersecurity, Version 1.1", NIST NIST CSWP 04162018,
DOI 10.6028/NIST.CSWP.04162018, April 2018,
<http://nvlpubs.nist.gov/nistpubs/CSWP/
NIST.CSWP.04162018.pdf>.
[NIST.SP.800-57p1r5]
Barker, E B., "Recommendation for key management, part 1
:general", NIST NIST.SP.800-57pt1r5,
DOI 10.6028/NIST.SP.800-57pt1r5, 2020,
<https://doi.org/10.6028/NIST.SP.800-57pt1r5>.
[RFC2510] Adams, C. and S. Farrell, "Internet X.509 Public Key
Infrastructure Certificate Management Protocols",
RFC 2510, DOI 10.17487/RFC2510, March 1999,
<https://www.rfc-editor.org/info/rfc2510>.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<https://www.rfc-editor.org/info/rfc2818>.
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[RFC3647] 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,
DOI 10.17487/RFC3647, November 2003,
<https://www.rfc-editor.org/info/rfc3647>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC8366] Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
"A Voucher Artifact for Bootstrapping Protocols",
RFC 8366, DOI 10.17487/RFC8366, May 2018,
<https://www.rfc-editor.org/info/rfc8366>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC8551] Schaad, J., Ramsdell, B., and S. Turner, "Secure/
Multipurpose Internet Mail Extensions (S/MIME) Version 4.0
Message Specification", RFC 8551, DOI 10.17487/RFC8551,
April 2019, <https://www.rfc-editor.org/info/rfc8551>.
[UNISIG.Subset-137]
UNISIG, "Subset-137; ERTMS/ETCS On-line Key Management
FFFIS; V1.0.0", December 2015,
<https://www.era.europa.eu/filebrowser/download/542_en>.
Appendix A. Example CertReqTemplate
Suppose the server requires that the certTemplate contains
* the issuer field with a value to be filled in by the EE,
* the subject field with a common name to be filled in by the EE and
two organizational unit fields with given values "myDept" and
"myGroup",
* the publicKey field contains an ECC key on curve secp256r1 or an
RSA public key of length 2048,
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* the subjectAltName extension with DNS name "www.myServer.com" and
an IP address to be filled in,
* the keyUsage extension marked critical with the value
digitalSignature and keyAgreement, and
* the extKeyUsage extension with values to be filled in by the EE.
Then the infoValue with certTemplate and keySpec fields returned to
the EE will be encoded as follows:
SEQUENCE {
SEQUENCE {
[3] {
SEQUENCE {}
}
[5] {
SEQUENCE {
SET {
SEQUENCE {
OBJECT IDENTIFIER commonName (2 5 4 3)
UTF8String ""
}
}
SET {
SEQUENCE {
OBJECT IDENTIFIER organizationalUnitName (2 5 4 11)
UTF8String "myDept"
}
}
SET {
SEQUENCE {
OBJECT IDENTIFIER organizationalUnitName (2 5 4 11)
UTF8String "myGroup"
}
}
}
}
[9] {
SEQUENCE {
OBJECT IDENTIFIER subjectAltName (2 5 29 17)
OCTET STRING, encapsulates {
SEQUENCE {
[2] "www.myServer.com"
[7] ""
}
}
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}
SEQUENCE {
OBJECT IDENTIFIER keyUsage (2 5 29 15)
BOOLEAN TRUE
OCTET STRING, encapsulates {
BIT STRING 3 unused bits
"10001"B
}
}
SEQUENCE {
OBJECT IDENTIFIER extKeyUsage (2 5 29 37)
OCTET STRING, encapsulates {
SEQUENCE {}
}
}
}
}
SEQUENCE {
SEQUENCE {
OBJECT IDENTIFIER aldId (1 3 6 1 5 5 7 5 1 TBD3)
SEQUENCE {
OBJECT IDENTIFIER ecPublicKey (1 2 840 10045 2 1)
OBJECT IDENTIFIER secp256r1 (1 2 840 10045 3 1 7)
}
}
SEQUENCE {
OBJECT IDENTIFIER rsaKeyLen (1 3 6 1 5 5 7 5 1 TBD4)
INTEGER 2048
}
}
}
Appendix B. History of changes
Note: This appendix will be deleted in the final version of the
document.
From version 05 -> 06:
* Changed in Section 2.3 the normative requirement in of adding
protection to a single message to mandatory and replacing
protection to optional
* Added Section 3.4 specifying generic prerequisites to PKI
management operations
* Added Section 3.5 specifying generic message validation
* Added Section 3.6 on generic error reporting. This section
replaces the former error handling section from Section 4 and 5.
* Added reference to using hashAlg
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* Updates Section 4.3.2 and Section 4.3.3 to align with CMP Updates
* Added Section 5.1 specifying the behavior of PKI management
entities when responding to requests
* Reworked Section 5.2.3. on usage of nested messages
* Updates Section 5.3 on performing PKI management operation on
behalf of another entity
* Updates Section 6.2 on HTTPS transport of CMP messages as
discusses at IETF 110 and email thread "I-D Action: draft-ietf-
lamps-lightweight-cmp-profile-05.txt"
* Added CoAP endpoints to Section 6.4
* Added security considerations on usage of shared secret
information
* Updated the example in Appendix A
* Added newly registered OIDs to the example in Appendix A
* Updated new RFC numbers for I-D.ietf-lamps-crmf-update-algs
* Multiple language corrections, clarifications, and changes in
wording
From version 04 -> 05:
* Changed to XML V3
* Added algorithm names introduced in CMP Algorithms Section 7.3 to
Section 4 of this document
* Updates Syntax in Section 4.4.3 due to changes made in CMP Updates
* Deleted the text on HTTP-based discovery as discussed in
Section 6.1
* Updates Appendix A due to change syntax in Section 4.4.3
* Many clarifications and changes in wording thanks to David's
extensive review
From version 03 -> 04:
* Deleted normative text sections on algorithms and refer to CMP
Algorithms and CRMF Algorithm Requirements Update instead
* Some clarifications and changes in wording
From version 02 -> 03:
* Updated the interoperability with [UNISIG.Subset-137] in
Section 1.4.
* Changed Section 2.3 to a tabular layout to enhanced readability
* Added a ToDo to section 3.1 on aligning with the CMP Algorithms
draft that will be set up as decided in IETF 108
* Updated section 4.1.6 to add the AsymmetricKey Package structure
to transport a newly generated private key as decided in IETF 108
* Added a ToDo to section 4.1.7 on required review of the nonce
handling in case an offline LRA responds and not forwards the
pollReq messages
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* Updated Section 4 due to the definition of the new ITAV OIDs in
CMP Updates
* Updated Section 4.4.4 to utilize controls instead of rsaKeyLen
(see thread "dtaft-ietf-lamps-cmp-updates and rsaKeyLen")
* Deleted the section on definition and discovery of HTTP URIs and
copied the text to the HTTP transport section and to CMP Updates
section 3.2
* Added some explanation to Section 5.1.2 and Section 5.1.3 on using
nested messages when a protection by the RA is required.
* Deleted the section on HTTP URI definition and discovery as some
content was moved to CMP Updates. The rest of the content was
moved back to the HTTP transport section
* Deleted the ASN.1 module after moving the new OIDs id-it-caCerts,
id-it-rootCaKeyUpdate, and id-it-certReqTemplate to CMP Updates
* Minor changes in wording and addition of some open ToDos
From version 01 -> 02:
* Extend Section 1.5 with regard to conflicts with UNISIG Subset-
137.
* Minor clarifications on extraCerts in Section 3.3 and
Section 4.1.1.
* Complete specification of requesting a certificate from a trusted
PKI with signature protection in Section 4.1.2.
* Changed from symmetric key-encryption to password-based key
management technique in section Section 4.1.6.3 as discussed on
the mailing list (see thread "draft-ietf-lamps-lightweight-cmp-
profile-01, section 5.1.6.1")
* Changed delayed enrollment described in Section 4.1.7 from
recommended to optional as decided at IETF 107
* Introduced the new RootCAKeyUpdate structure for root CA
certificate update in Section 4.3.2 as decided at IETF 107 (also
see email thread "draft-ietf-lamps-lightweight-cmp-profile-01,
section 5.4.3")
* Extend the description of the CertReqTemplate PKI management
operation, including an example added in the Appendix. Keep
rsaKeyLen as a single integer value in Section 4.3.3 as discussed
on the mailing list (see thread "draft-ietf-lamps-lightweight-cmp-
profile-01, section 5.4.4")
* Deleted Sections "Get certificate management configuration" and
"Get enrollment voucher" as decided at IETF 107
* Complete specification of adding an additional protection by an
PKI management entity in Section 5.2.2.
* Added a section on HTTP URI definition and discovery and extended
Section 6.1 on definition and discovery of supported HTTP URIs and
content types, add a path for nested messages as specified in
Section 5.2.2 and delete the paths for /getCertMgtConfig and
/getVoucher
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* Changed Section 6.4 to address offline transport and added more
detailed specification file-based transport of CMP
* Added a reference to the new I-D of Mohit Sahni on "CoAP Transport
for CMPV2" in Section 6.2; thanks to Mohit supporting the effort
to ease utilization of CMP
* Moved the change history to the Appendix
* Minor changes in wording
From version 00 -> 01:
* Harmonize terminology with CMP [RFC4210], e.g.,
- transaction, message sequence, exchange, use case -> PKI
management operation
- PKI component, (L)RA/CA -> PKI management entity
* Minor changes in wording
From draft-brockhaus-lamps-lightweight-cmp-profile-03 -> draft-ietf-
lamps-lightweight-cmp-profile-00:
* Changes required to reflect WG adoption
* Minor changes in wording
From version 02 -> 03:
* Added a short summary of [RFC4210] Appendix D and E in
Section 1.4.
* Clarified some references to different sections and added some
clarification in response to feedback from Michael Richardson and
Tomas Gustavsson.
* Added an additional label to the operational path to address
multiple CAs or certificate profiles in Section 6.1.
From version 01 -> 02:
* Added some clarification on the key management techniques for
protection of centrally generated keys in Section 4.1.6.
* Added some clarifications on the certificates for root CA
certificate update in Section 4.3.2.
* Added a section to specify the usage of nested messages for RAs to
add an additional protection for further discussion, see
Section 5.2.2.
* Added a table containing endpoints for HTTP transport in
Section 6.1 to simplify addressing PKI management entities.
* Added some ToDos resulting from discussion with Tomas Gustavsson.
* Minor clarifications and changes in wording.
From version 00 -> 01:
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* Added a section to specify the enrollment with an already trusted
PKI for further discussion, see Section 4.1.2.
* Complete specification of requesting a certificate from a legacy
PKI using a PKCS#10 [RFC2986] request in Section 4.1.5.
* Complete specification of adding central generation of a key pair
on behalf of an end entity in Section 4.1.6.
* Complete specification of handling delayed enrollment due to
asynchronous message delivery in Section 4.1.7.
* Complete specification of additional support messages, e.g., to
update a Root CA certificate or to request an RFC 8366 [RFC8366]
voucher, in Section 4.3.
* Minor changes in wording.
From draft-brockhaus-lamps-industrial-cmp-profile-00 -> draft-
brockhaus-lamps-lightweight-cmp-profile-00:
* Change focus from industrial to more multi-purpose use cases and
lightweight CMP profile.
* Incorporate the omitted confirmation into the header specified in
Section 3.1 and described in the standard enrollment use case in
Section 4.1.1 due to discussion with Tomas Gustavsson.
* Change from OPTIONAL to RECOMMENDED for use case 'Revoke another's
entities certificate' in Section 5.3.2, because it is regarded as
important functionality in many environments to enable the
management station to revoke EE certificates.
* Complete the specification of the revocation message flow in
Section 4.2 and Section 5.3.2.
* The CoAP based transport mechanism and piggybacking of CMP
messages on top of other reliable transport protocols is out of
scope of this document and would need to be specified in another
document.
* Further minor changes in wording.
Authors' Addresses
Hendrik Brockhaus (editor)
Siemens AG
Email: hendrik.brockhaus@siemens.com
Steffen Fries
Siemens AG
Email: steffen.fries@siemens.com
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David von Oheimb
Siemens AG
Email: david.von.oheimb@siemens.com
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