Lightweight Certificate Management Protocol (CMP) Profile
draft-ietf-lamps-lightweight-cmp-profile-16
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 9483.
|
|
|---|---|---|---|
| Authors | Hendrik Brockhaus , David von Oheimb , Steffen Fries | ||
| Last updated | 2022-12-01 (Latest revision 2022-11-30) | ||
| Replaces | draft-brockhaus-lamps-lightweight-cmp-profile | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
INTDIR Telechat review
(of
-15)
by Sheng Jiang
Ready w/nits
IOTDIR Telechat review
(of
-15)
by Niklas Widell
Ready w/nits
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Russ Housley | ||
| Shepherd write-up | Show Last changed 2022-02-01 | ||
| IESG | IESG state | Became RFC 9483 (Proposed Standard) | |
| Consensus boilerplate | Yes | ||
| Telechat date |
(None)
Needs 8 more YES or NO OBJECTION positions to pass. |
||
| Responsible AD | Roman Danyliw | ||
| Send notices to | housley@vigilsec.com | ||
| IANA | IANA review state | IANA - Not OK | |
| IANA expert review state | Need IANA Expert(s) |
draft-ietf-lamps-lightweight-cmp-profile-16
LAMPS Working Group H. Brockhaus
Internet-Draft D. von Oheimb
Intended status: Standards Track S. Fries
Expires: 3 June 2023 Siemens
30 November 2022
Lightweight Certificate Management Protocol (CMP) Profile
draft-ietf-lamps-lightweight-cmp-profile-16
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 transfer 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 specialized or complex
use cases are supported with optional features.
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 3 June 2023.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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.
Brockhaus, et al. Expires 3 June 2023 [Page 1]
Internet-Draft Lightweight CMP Profile November 2022
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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. How to Read This Document . . . . . . . . . . . . . . . . 5
1.2. Motivation for a Lightweight Profile of CMP . . . . . . . 5
1.3. Special Requirements of Industrial and IoT Scenarios . . 6
1.4. Existing CMP Profiles . . . . . . . . . . . . . . . . . . 7
1.5. Use of CMP in SZTP and BRSKI Environments . . . . . . . . 8
1.6. Compatibility with Existing CMP Profiles . . . . . . . . 8
1.7. Scope of this Document . . . . . . . . . . . . . . . . . 10
1.8. Structure of this Document . . . . . . . . . . . . . . . 11
1.9. Convention and Terminology . . . . . . . . . . . . . . . 11
2. Solution Architecture . . . . . . . . . . . . . . . . . . . . 13
3. Generic Aspects of PKI Messages and PKI Management
Operations . . . . . . . . . . . . . . . . . . . . . . . 15
3.1. General Description of the CMP Message Header . . . . . . 16
3.2. General Description of the CMP Message Protection . . . . 18
3.3. General Description of CMP Message ExtraCerts . . . . . . 19
3.4. Generic PKI Management Operation Prerequisites . . . . . 19
3.5. Generic Validation of a PKI Message . . . . . . . . . . . 21
3.6. Error Handling . . . . . . . . . . . . . . . . . . . . . 23
3.6.1. Reporting Error Conditions Upstream . . . . . . . . . 23
3.6.2. Reporting Error Conditions Downstream . . . . . . . . 24
3.6.3. Handling Error Conditions on Nested Messages Used for
Batching . . . . . . . . . . . . . . . . . . . . . . 24
3.6.4. PKIStatusInfo and Error Messages . . . . . . . . . . 24
4. PKI Management Operations . . . . . . . . . . . . . . . . . . 26
4.1. Enrolling End Entities . . . . . . . . . . . . . . . . . 29
4.1.1. Enrolling an End Entity to a New PKI . . . . . . . . 30
4.1.2. Enrolling an End Entity to a Known PKI . . . . . . . 37
4.1.3. Updating a Valid Certificate . . . . . . . . . . . . 37
4.1.4. Enrolling an End Entity Using a PKCS#10 Request . . . 38
4.1.5. Using MAC-Based Protection for Enrollment . . . . . . 41
4.1.6. Adding Central Key Pair Generation to Enrollment . . 42
4.1.6.1. Using Key Agreement Key Management Technique . . 48
4.1.6.2. Using Key Transport Key Management Technique . . 49
4.1.6.3. Using Password-Based Key Management Technique . . 50
4.2. Revoking a Certificate . . . . . . . . . . . . . . . . . 51
4.3. Support Messages . . . . . . . . . . . . . . . . . . . . 53
4.3.1. Get CA Certificates . . . . . . . . . . . . . . . . . 55
4.3.2. Get Root CA Certificate Update . . . . . . . . . . . 56
4.3.3. Get Certificate Request Template . . . . . . . . . . 57
Brockhaus, et al. Expires 3 June 2023 [Page 2]
Internet-Draft Lightweight CMP Profile November 2022
4.3.4. CRL Update Retrieval . . . . . . . . . . . . . . . . 60
4.4. Handling Delayed Delivery . . . . . . . . . . . . . . . . 62
5. PKI Management Entity Operations . . . . . . . . . . . . . . 66
5.1. Responding to Requests . . . . . . . . . . . . . . . . . 66
5.1.1. Responding to a Certificate Request . . . . . . . . . 67
5.1.2. Responding to a Confirmation Message . . . . . . . . 67
5.1.3. Responding to a Revocation Request . . . . . . . . . 68
5.1.4. Responding to a Support Message . . . . . . . . . . . 68
5.1.5. Initiating Delayed Delivery . . . . . . . . . . . . . 68
5.2. Forwarding Messages . . . . . . . . . . . . . . . . . . . 69
5.2.1. Not Changing Protection . . . . . . . . . . . . . . . 71
5.2.2. Adding Protection and Batching of Messages . . . . . 71
5.2.2.1. Adding Protection to a Request Message . . . . . 72
5.2.2.2. Batching Messages . . . . . . . . . . . . . . . . 73
5.2.3. Replacing Protection . . . . . . . . . . . . . . . . 75
5.2.3.1. Not Changing Proof-of-Possession . . . . . . . . 76
5.2.3.2. Using raVerified . . . . . . . . . . . . . . . . 76
5.3. Acting on Behalf of other PKI Entities . . . . . . . . . 77
5.3.1. Requesting a Certificate . . . . . . . . . . . . . . 77
5.3.2. Revoking a Certificate . . . . . . . . . . . . . . . 77
6. CMP Message Transfer Mechanisms . . . . . . . . . . . . . . . 78
6.1. HTTP Transfer . . . . . . . . . . . . . . . . . . . . . . 79
6.2. CoAP Transfer . . . . . . . . . . . . . . . . . . . . . . 82
6.3. Piggybacking on Other Reliable Transfer . . . . . . . . . 84
6.4. Offline Transfer . . . . . . . . . . . . . . . . . . . . 84
6.4.1. File-Based Transfer . . . . . . . . . . . . . . . . . 85
6.4.2. Other Asynchronous Transfer Protocols . . . . . . . . 85
7. Conformance Requirements . . . . . . . . . . . . . . . . . . 85
7.1. PKI Management Operations . . . . . . . . . . . . . . . . 85
7.2. Message Transfer . . . . . . . . . . . . . . . . . . . . 88
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 89
9. Security Considerations . . . . . . . . . . . . . . . . . . . 91
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 91
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 91
11.1. Normative References . . . . . . . . . . . . . . . . . . 91
11.2. Informative References . . . . . . . . . . . . . . . . . 93
Appendix A. Example CertReqTemplate . . . . . . . . . . . . . . 97
Appendix B. History of Changes . . . . . . . . . . . . . . . . . 99
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 105
1. Introduction
[RFC Editor:
Please perform the following substitution.
* RFCXXXX --> the assigned numerical RFC value for this draft
Brockhaus, et al. Expires 3 June 2023 [Page 3]
Internet-Draft Lightweight CMP Profile November 2022
* RFCAAAA --> the assigned numerical RFC value for
[I-D.ietf-lamps-cmp-updates]
* RFCBBBB --> the assigned numerical RFC value for
[I-D.ietf-lamps-cmp-algorithms]
Please also update the following references to associated drafts in
progress to reflect their final RFC assignments, if available:
* [I-D.ietf-lamps-cmp-updates]
* [I-D.ietf-lamps-cmp-algorithms]
* [I-D.ietf-ace-cmpv2-coap-transport]
* [I-D.ietf-uta-rfc7525bis]
* [I-D.ietf-netconf-sztp-csr]
* [I-D.ietf-anima-brski-ae]
* [I-D.ietf-anima-brski-prm]
]
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],
[I-D.ietf-lamps-cmp-updates], and [I-D.ietf-lamps-cmp-algorithms],
CRMF [RFC4211] and [RFC9045], CMS [RFC5652] and [RFC8933], HTTP
transfer for CMP [RFC6712], and CoAP transfer for CMP
[I-D.ietf-ace-cmpv2-coap-transport]. CMP, CRMF and CMS are feature-
rich specifications, but most application scenarios use only a
limited subset of the same specified functionality. Additionally,
the standards are not always precise enough on how to interpret and
implement the described concepts. Therefore, this document aims to
tailor the available options and specify how to use them in adequate
detail to make the implementation of interoperable automated
certificate management as straightforward and lightweight as
possible.
Brockhaus, et al. Expires 3 June 2023 [Page 4]
Internet-Draft Lightweight CMP Profile November 2022
Note: In the meantime RFC4210bis [I-D.ietf-lamps-rfc4210bis] and
RFC6712bis [I-D.ietf-lamps-rfc6712bis] drafts were submitted
incorporating the changes listed in CMP Updates
[I-D.ietf-lamps-cmp-updates] into the original RFC text.
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. The guidance in Section 1.8 and Section 7 should be used
to figure out which parts of Section 4 to Section 6 are relevant for
the target certificate management solution depending on the PKI
management operations, their variants, and types of message transfer
needed.
Since conformity to this document can be achieved by implementing
only the functionality declared mandatory in Section 7, the profile
can still be called lightweight because in particular for end
entities the mandatory-to-implement set of features is rather
limited.
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.
Though CMP is a 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.
Brockhaus, et al. Expires 3 June 2023 [Page 5]
Internet-Draft Lightweight CMP Profile November 2022
In order to reduce complexity, the set of mandatory PKI management
operations and variants required by this specification has been kept
lean. This limits development effort and minimizes resource needs,
which is particularly important for memory-constrained devices. To
this end, when there was design flexibility to either have necessary
complexity on the EE or in the PKI management entity, this profile
chose to include it in the PKI management entities where typically
more computational resources are available. Additional recommended
PKI management operations and variants support some more complex
scenarios that are considered beneficial for environments with more
specific demands or boundary conditions. The optional PKI management
operations support less common scenarios and requirements.
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.
Profiling is a way to reduce feature richness and complexity of
standards to what is needed for specific use cases. 3GPP and UNISIG
already use profiling of CMP as a way to cope with these challenges.
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 the general aspects of the
protocol are utilized and only the special requirements of the target
scenarios need to be dealt with using distinct features the protocol
offers.
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
Brockhaus, et al. Expires 3 June 2023 [Page 6]
Internet-Draft Lightweight CMP Profile November 2022
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.
Due to increasing security and availability needs in operational
technology, especially when used for 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. Also, PKI management
entities like Certification Authorities (CA) typically are not
deployed on-site but in a highly protected data center environment,
e.g., operated according to ETSI Policy and security requirements for
Trust Service Providers issuing certificates [ETSI-EN.319411-1].
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].
Brockhaus, et al. Expires 3 June 2023 [Page 7]
Internet-Draft Lightweight CMP Profile November 2022
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.
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. Use of CMP in SZTP and BRSKI Environments
In Secure Zero Touch Provisioning (SZTP) [RFC8572] and other
environments using NETCONF/YANG modules, SZTP-CSR
[I-D.ietf-netconf-sztp-csr] offers a YANG module that includes
different types of certificate requests to obtain a public-key
certificate for a locally generated key pair. One option is using a
CMP p10cr message. Such a message is of the form ietf-ztp-types:cmp-
csr from module ietf-ztp-csr and offers both proof-of-possession and
proof-of-identity. To allow PKI management entities to also comply
with this profile, the p10cr message MUST be formatted by the EE as
described in Section 4.1.4 of this profile, and it MAY be forwarded
as specified in Section 5.2.
In Bootstrapping Remote Secure Key Infrastructure (BRSKI) [RFC8995]
environments, BRSKI-AE: Alternative Enrollment Protocols in BRSKI
[I-D.ietf-anima-brski-ae] describes a generalization regarding the
employed enrollment protocols to allow alternatives to EST [RFC7030].
For the use of CMP, it requires adherence to this profile.
1.6. 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,
Brockhaus, et al. Expires 3 June 2023 [Page 8]
Internet-Draft Lightweight CMP Profile November 2022
* 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 a 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).
* 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.
Brockhaus, et al. Expires 3 June 2023 [Page 9]
Internet-Draft Lightweight CMP Profile November 2022
* 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: It remains unclear from UNISIG Subset-137 for which
certificate(s) the caPubs field should be used. For security
reasons, it cannot be used for delivering the root CA certificate
needed for validating the signature-based protection of the given
response message (as stated indirectly also in its UNISIG
Subset-137 Section 6.3.1.5.2 b [UNISIG.Subset-137]).
* 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, either).
1.7. Scope of this Document
To minimize ambiguity and complexity through needless variety, this
document specifies exhaustive requirements for 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.
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").
Brockhaus, et al. Expires 3 June 2023 [Page 10]
Internet-Draft Lightweight CMP Profile November 2022
Fields used in ASN.1 syntax in Section 3, Section 4, or Section 5 are
specified in CMP [RFC4210] [I-D.ietf-lamps-cmp-updates], CRMF
[RFC4211], and CMS [RFC5652] [RFC8933]. When these sections do not
explicitly discuss a field, then the field SHOULD NOT be used by the
sending entity. The receiving entity MUST NOT require the absence of
such a field, and if the field is present, MUST handle it gracefully.
1.8. 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, exchanges between PKI
management entities, and operations on behalf of other PKI entities.
This may include delayed delivery of messages, which involves polling
for responses, and nesting of messages.
Section 6 outlines several mechanisms for CMP message transfer,
including HTTP-based [RFC6712] transfer optionally using TLS, and
[I-D.ietf-ace-cmpv2-coap-transport] transfer optionally using DTLS,
and offline file-based transport.
Section 7 defines which parts of the profile are mandatory,
recommended, optional, or not relevant to implement for which type of
entity.
1.9. 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.
Brockhaus, et al. Expires 3 June 2023 [Page 11]
Internet-Draft Lightweight CMP Profile November 2022
The key word "PROHIBITED" is to be interpreted to mean that the
respective ASN.1 field SHALL NOT be present or used.
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 a 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
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.
CMP messages are referred to by the names of PKIBody choices defined
in CMP Section 5.1.2 [RFC4210] and are further described in Section 4
of this document.
Brockhaus, et al. Expires 3 June 2023 [Page 12]
Internet-Draft Lightweight CMP Profile November 2022
2. 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: The owner or operator using the manufacturer-issued device
certificate for authenticating the device during initial enrollment
of operational certificates MUST trust the respective trust anchor
provided by the manufacturer.
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 a 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. The
communication between an LRA and RA can be performed synchronously or
asynchronously. Asynchronous communication typically leads to
delayed message delivery as described in Section 4.4.
Brockhaus, et al. Expires 3 June 2023 [Page 13]
Internet-Draft Lightweight CMP Profile November 2022
+-----+ +-----+ +-----+ +-----+
| | | | | | | |
| EE |<---------->| LRA |<-------------->| RA |<---------->| CA |
| | | | | | | |
+-----+ +-----+ +-----+ +-----+
synchronous (a)synchronous (a)synchronous
+----connection----+------connection------+----connection----+
operators service partner
+---------on site--------+----back-end services-----+-trust center-+
<--- downstream <--- | ---> upstream --->
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 architectural
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, asynchronous connections, or even offline (e.g., file-
based) transfer.
Note: In contrast to the pull model used in this document, other
specifications could use the messages specified in this document
implementing the push model. In this case the EE is pushed
(triggered) by the PKI management entity to provide the CMP request,
and therefore, EE acts as the receiver, not initiating the
interaction with the PKI. For example, when the device itself does
only act as a server as described in BRSKI with Pledge in Responder
Mode (BRSKI-PRM) [I-D.ietf-anima-brski-prm], support of certificate
enrollment in a push model is needed. While BRSKI-PRM currently
utilizes its own format for the exchanges, CMP in general and the
messages specified in this profile offer all required capabilities.
Nevertheless, the message flow and state machine as described in
Section 4 must be adapted to implement a push model.
Brockhaus, et al. Expires 3 June 2023 [Page 14]
Internet-Draft Lightweight CMP Profile November 2022
Note: Third-party CAs, not conforming to this document, may implement
other variants of CMP, different standardized protocols, or even
proprietary interfaces for certificate management. In such cases, an
RA needs to adapt the exchanged CMP messages to the flavor of
certificate management interaction required by such a non-conformant
CA.
3. Generic Aspects of PKI Messages and PKI Management Operations
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:
+--------------------------------------------+
| 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.
Note: In the description of CMP messages, the presence of some fields
is stated as OPTIONAL or RECOMMENDED. The following text may state
requirements on the same fields apply only if the field is present.
Brockhaus, et al. Expires 3 June 2023 [Page 15]
Internet-Draft Lightweight CMP Profile November 2022
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 4.1.5. The variations will affect the fields sender,
protectionAlg, and senderKID.
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 RFCAAAA
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 corresponding to 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
Brockhaus, et al. Expires 3 June 2023 [Page 16]
Internet-Draft Lightweight CMP Profile November 2022
-- 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 [RFCBBBB] 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 [RFCBBBB] Section 6.1
senderKID REQUIRED
-- MUST be set
-- MUST be the SubjectKeyIdentifier of the CMP protection
-- certificate in case of signature-based protection
transactionID REQUIRED
-- In the first message of a PKI management operation: 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: MUST be absent
-- If this is a delayed response message: MUST be present and
-- contain the value of the senderNonce of the respective
-- requestmessage in the same transaction
-- 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
-- RECOMMENDED in ir/cr/kur/p10cr messages,
-- OPTIONAL in ip/cp/kup response messages, and
-- PROHIBITED 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
confirmWaitTime OPTIONAL
Brockhaus, et al. Expires 3 June 2023 [Page 17]
Internet-Draft Lightweight CMP Profile November 2022
-- RECOMMENDED in ip/cp/kup messages if implicitConfirm is
-- not included
-- PROHIBITED if implicitConfirm is included
-- See [RFC4210] Section 5.1.1.2.
ConfirmWaitTimeValue REQUIRED
-- ConfirmWaitTimeValue MUST be a GeneralizedTime value
-- specifying the point in time up to which the PKI management
-- entity will wait for the certConf message. The accepted
-- length of the waiting period will vary by use case.
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 [RFCAAAA]
CertProfileValue REQUIRED
-- MUST contain a sequence of 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, which is the default
protection mechanism for all CMP messages described in this profile.
The private key used to sign a CMP message is called "protection key"
and the related certificate is called "protection certificate". If
the keyUsage extension is present, it MUST include digitalSignature.
protection
-- RECOMMENDED for error messages
-- REQUIRED for all other messages
-- 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.
All CMP messages but those carrying error messages MUST be protected.
CMP error messages SHOULD be protected when possible. See
Section 3.6.4 for use cases where this would not be possible.
For MAC-based protection as specified in Section 4.1.5 and
Section 4.1.6.3 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 Section 2.2
[I-D.ietf-lamps-cmp-updates] can be used for authorization of a
sending PKI management entity.
Brockhaus, et al. Expires 3 June 2023 [Page 18]
Internet-Draft Lightweight CMP Profile November 2022
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 and
-- MUST NOT be trusted based on their inclusion in any case
Note: One reason for adding a self-signed certificate to extraCerts
is if it is the protection certificate or a successor root CA self-
signed certificate as indicated in the HashOfRootKey extension of the
current root CA certificate, see [RFC8649]. Another reason for
including self-signed certificates in the extraCerts is, for instance
due to storage limitations, a receiving PKI entity may not have the
complete trust anchor as self-signed certificate available but just
unique identification of it, and thus needs the full self-signed
certificate for further processing (see also Security Considerations
Section 9).
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:
* 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.
Brockhaus, et al. Expires 3 June 2023 [Page 19]
Internet-Draft Lightweight CMP Profile November 2022
Routing of CMP messages:
* Each PKI entity sending messages upstream MUST know the address
needed for transferring messages to the next PKI management
entity.
Note: This address may depend on the recipient, the certificate
profile, and on the used transfer 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 root CA usable only
for authenticating PKI management entities.
* 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 based on local PKI policy.
Brockhaus, et al. Expires 3 June 2023 [Page 20]
Internet-Draft Lightweight CMP Profile November 2022
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] and
[I-D.ietf-lamps-cmp-updates], CRMF [RFC4211], and CMS [RFC5652]
and [RFC8933]. (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)
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 or equal the senderNonce of the most
recent request message for which the response was delayed, in
case of delayed delivery as specified in Section 4.4. (failInfo
bit: badRecipientNonce)
Brockhaus, et al. Expires 3 June 2023 [Page 21]
Internet-Draft Lightweight CMP Profile November 2022
* Messages without protection MUST be rejected except for error
messages as described in Section 3.6.4.
* The message protection MUST be validated when present and messages
with an invalid protection MUST be rejected.
- The protection MUST be signature-based except if MAC-based
protection is used as described in Section 4.1.5 and
Section 4.1.6.3. (failInfo bit: wrongIntegrity)
- If present, the senderKID MUST identify the key material needed
for verifying the message protection. (failInfo bit:
badMessageCheck)
- 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 MUST 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:
* 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 and
- the receiving system has a reliable system time, the
messageTime SHOULD be close to the current time of the
receiving system, where the threshold will vary by use case.
(failInfo bit: badTime)
Brockhaus, et al. Expires 3 June 2023 [Page 22]
Internet-Draft Lightweight CMP Profile November 2022
- the receiving system does not have a reliable system time, the
messageTime MAY be used for time synchronization.
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 the 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. The value set for such timeouts will vary by
use case. Then they also MUST regard the current PKI management
operation as terminated with failure and MUST NOT attempt to send an
error message downstream.
Brockhaus, et al. Expires 3 June 2023 [Page 23]
Internet-Draft Lightweight CMP Profile November 2022
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. PKIStatusInfo and Error Messages
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.
Brockhaus, et al. Expires 3 June 2023 [Page 24]
Internet-Draft Lightweight CMP Profile November 2022
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.
Note: When a PKI management entity indicates delayed delivery of a
CMP response message to the EE with an error message as described
in Section 4.4, the status "waiting" is used there.
* 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 transactionID 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 transactionID.
- 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.
Brockhaus, et al. Expires 3 June 2023 [Page 25]
Internet-Draft Lightweight CMP Profile November 2022
An EE receiving a systemUnavail or systemFailure failInfo SHOULD
resend the request in a new transaction after some time.
Detailed Message Description:
Error Message -- error
Field Value
header
-- As described in Section 3.1
body
-- The message indicating the 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 RECOMMENDED
-- As described in Section 3.2
-- MAY be omitted if protection is technically not feasible
extraCerts RECOMMENDED
-- As described in Section 3.3
Note: Protecting the error message may not be technically feasible if
it is not clear which credential the recipient will be able to use
when validating this protection, e.g., in case the request message
was fundamentally broken.
4. 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:
Brockhaus, et al. Expires 3 June 2023 [Page 26]
Internet-Draft Lightweight CMP Profile November 2022
* 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. The messages are named by the
respective field names in PKIBody like ir, ip, cr, cp, etc., see
RFC 4210 Section 5.1.2 [RFC4210].
The following diagram shows the EE state machine covering all PKI
management operations described in this section, including negative
responses, error messages described in Section 3.6.4, as well as
ip/cp/kup/error messages with status "waiting", pollReq, and pollRep
messages described in Section 4.4.
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.
Brockhaus, et al. Expires 3 June 2023 [Page 27]
Internet-Draft Lightweight CMP Profile November 2022
End Entity State Machine:
start
|
| send ir/cr/p10cr/kur/rr/genm
v
waiting for response
v
+--------------------------+--------------------------+
| | |
| receives ip/cp/kup with | received ip/cp/kup/error | received
| status "accepted" or | with status "waiting" | rp/genp or
| "grantedWithMods" | | ip/cp/kup/
| v | error
| +-------> polling | with status
| | | | "rejection"
| | received | send |
| | pollRep | pollReq |
| | v |
| | waiting for response |
| | v |
| +------------+--------+ |
| | | |
| received ip/cp/kup | | received |
| with status "accepted" | | rp/genp or |
| or "grantedWithMods" | | ip/cp/kup/error |
| | | with status |
+---------->+<-------------+ | "rejection" |
v | |
+-----------+-----+ | |
| | | |
| implicitConfirm | implicitConfirm | |
| granted | not granted | |
| | | |
| | send certConf | |
| v | |
| waiting for pkiConf*) | |
| | | |
| | received | |
| v pkiConf v |
+---------------->+------->+<-------+<----------------+
|
v
end
*) in case of a delayed delivery of pkiConf responses the same
polling mechanism is initiated as for rp or genp messages, by
sending an error message with status "waiting".
Brockhaus, et al. Expires 3 June 2023 [Page 28]
Internet-Draft Lightweight CMP Profile November 2022
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. Enrolling End Entities
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 5.1.2 and respond with a
confirmation, closing the PKI management operation.
Brockhaus, et al. Expires 3 June 2023 [Page 29]
Internet-Draft Lightweight CMP Profile November 2022
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: RFC 4211 Section 4 [RFC4211] allows for providing proof-of-
possession using any method that a key can be used for. 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. 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 the EE receives a CA certificate in the caPubs field for
installation as a new trust anchor, it MUST properly authenticate the
message and authorize the sender as trusted source of the new trust
anchor. This authorization is typically indicated using shared
secret information for protecting an initialization response (ir)
message. Authorization can also be signature-based using a
certificate issued by another PKI that is explicitly authorized for
this purpose. A certificate received in caPubs MUST NOT be accepted
as a trust anchor if it is the root CA certificate of the certificate
used for protecting the message.
4.1.1. Enrolling an End Entity to a New PKI
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.
Brockhaus, et al. Expires 3 June 2023 [Page 30]
Internet-Draft Lightweight CMP Profile November 2022
Note: In Bootstrapping Remote Secure Key Infrastructure (BRSKI)
[RFC8995] environments, BRSKI-AE: Alternative Enrollment Protocols in
BRSKI [I-D.ietf-anima-brski-ae] describes a generalization regarding
enrollment protocols alternative to EST [RFC7030]. As replacement of
EST simpleenroll, BRSKI-AE uses this PKI management operation for
bootstrapping LDevID certificates.
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.
* 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 a sequence of
one CertReqMsg in the ir. If more certificates are required, further
requests MUST be sent using separate PKI management operations.
The EE SHOULD include the implicitConfirm extension in the header of
the ir message as described in Section 3.1, unless it knows that
certificate confirmation is needed. This leaves the choice to the
Brockhaus, et al. Expires 3 June 2023 [Page 31]
Internet-Draft Lightweight CMP Profile November 2022
PKI management entities whether the EE must send a certConf message
on receiving a new certificate. Depending on the PKI policy and
requirements for managing EE certificates, it can be important for
PKI management entities to learn if the EE accepted the new
certificate. In such cases, when responding with an ip message, the
PKI management entity MUST NOT include the implicitConfirm extension.
In case the PKI management entity does not need any explicit
confirmation from the EE, it MUST include the generalInfo field
implicitConfirm. Otherwise, it SHOULD include confirmWaitTime as
described in Section 3.1. This prevents explicit certificate
confirmation and saves the overhead of a further message round-trip.
If the EE did not request implicit confirmation or implicit
confirmation 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 valid 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, depending on its policy the PKI management entity MAY
revoke the newly issued certificate, notify a monitoring system, or
log the event internally.
Note: Depending on PKI policy, a new certificate may be published by
a PKI management entity, and explicit confirmation may be required.
In this case it is advisable not to do the publication until a
positive certificate confirmation has been received. This way the
need to revoke the certificate on negative confirmation is avoided.
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
Brockhaus, et al. Expires 3 June 2023 [Page 32]
Internet-Draft Lightweight CMP Profile November 2022
-- MUST contain a sequence of 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 OPTIONAL
-- MUST be present if local key generation is used
-- MAY be absent if central key generation is requested
algorithm OPTIONAL
-- MUST be present if local key generation is used and MUST
-- include the subject public key algorithm identifier
-- MAY be present if central key generation is requested and
-- if present, informs the KGA of algorithm and parameter
-- preferences regarding the to-be-generated key pair
subjectPublicKey REQUIRED
-- MUST contain the public key to be certified in case of local
-- key generation
-- MUST be a zero-length BIT STRING if central key generation
-- is requested
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
Brockhaus, et al. Expires 3 June 2023 [Page 33]
Internet-Draft Lightweight CMP Profile November 2022
-- 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
-- MUST contain a sequence of 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"
-- "waiting" only allowed with polling use case as described in
-- Section 4.4
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"
Brockhaus, et al. Expires 3 June 2023 [Page 34]
Internet-Draft Lightweight CMP Profile November 2022
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 as confirmation to the PKI
-- management entity to accept or reject the issued
-- certificates
certConf REQUIRED
-- MUST contain a sequence of one CertStatus
CertStatus REQUIRED
certHash REQUIRED
-- MUST be the hash of the certificate, using the hash algorithm
-- indicated in hashAlg, see below, 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
Brockhaus, et al. Expires 3 June 2023 [Page 35]
Internet-Draft Lightweight CMP Profile November 2022
-- display in a GUI
failInfo OPTIONAL
-- MAY be present if status is "rejection"
-- MUST be absent if status is "accepted"
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)
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
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
Brockhaus, et al. Expires 3 June 2023 [Page 36]
Internet-Draft Lightweight CMP Profile November 2022
4.1.2. Enrolling an End Entity to a Known PKI
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.
4.1.3. Updating a Valid Certificate
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.
Brockhaus, et al. Expires 3 June 2023 [Page 37]
Internet-Draft Lightweight CMP Profile November 2022
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.
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. Enrolling an End Entity Using a PKCS#10 Request
This PKI management operation can be used by an EE to request a
certificate using PKCS#10 [RFC2986] format to interoperate with CAs
not supporting CRMF [RFC4211]. This offers a variation of the PKI
management operations specified in Section 4.1.2.
In Secure Zero Touch Provisioning (SZTP) [RFC8572] environments,
SZTP-CSR [I-D.ietf-netconf-sztp-csr] describes the use of a CMP p10cr
message as a form of certificate signing request (CSR) to optionally
include in device bootstrapping to obtain an identity certificate as
part of the onboarding information. Such a CSR is of form ietf-sztp-
types:cmp-csr from module ietf-sztp-csr. The requirements given
below on p10cr message MUST be adhered to.
Brockhaus, et al. Expires 3 June 2023 [Page 38]
Internet-Draft Lightweight CMP Profile November 2022
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 4.1.2.
The message sequence for this PKI management operation is identical
to that given in Section 4.1.2, 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 -1.
3 The caPubs field in the cp message SHOULD be absent.
Detailed Message Description:
Brockhaus, et al. Expires 3 June 2023 [Page 39]
Internet-Draft Lightweight CMP Profile November 2022
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 in Section 3.2
extraCerts REQUIRED
-- As described for the underlying PKI management operation
Brockhaus, et al. Expires 3 June 2023 [Page 40]
Internet-Draft Lightweight CMP Profile November 2022
4.1.5. Using MAC-Based Protection for Enrollment
This is a variant of the PKI management operations described in
Section 4.1.1 to Section 4.1.4. It 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 distribution of this shared secret is out of
scope for this document. 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 the security considerations of CMP updated
by [I-D.ietf-lamps-cmp-updates].
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 In case the sending entity does not know its own name by now, it
MUST put the NULL-DN into the sender field. 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.
Brockhaus, et al. Expires 3 June 2023 [Page 41]
Internet-Draft Lightweight CMP Profile November 2022
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.
4.1.6. Adding Central Key Pair Generation to Enrollment
This is a variant of the PKI management operations described in
Section 4.1.1 to Section 4.1.4 and the variant described in
Section 4.1.5. 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 acceptable 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.
When an EE requests central key generation for a certificate update
using a kur message, the KGA cannot use a kur message to request the
certificate on behalf of the EE as the old EE credential is not
available to the KGA for protecting this message. Therefore, if the
EE uses the PKI management operation described in Section 4.1.3, the
KGA MUST use Section 4.1.2 to request the certificate for the newly
generated key pair on behalf of the EE from the CA.
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.
Brockhaus, et al. Expires 3 June 2023 [Page 42]
Internet-Draft Lightweight CMP Profile November 2022
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, 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.
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 Section 2.7
[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 CMP Updates Section 2.19 and Section 2.20
[I-D.ietf-lamps-cmp-updates].
Brockhaus, et al. Expires 3 June 2023 [Page 43]
Internet-Draft Lightweight CMP Profile November 2022
+----------------------------------+
| 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] and [RFC8933],
signed by the KGA generating the key pair. The signature MUST be
performed using a private key related to a certificate asserting the
extended key usage id-kp-cmKGA as described in CMP Updates
Section 2.2 [I-D.ietf-lamps-cmp-updates] to demonstrate authorization
to generate key pairs on behalf of an EE. The EE SHOULD validate the
signer certificate contained in the SignedData structure and verify
the presence of this extended key usage in the signer certificate.
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 and the related certificate in the
SignedData structure since shared secret information is used for
initial authentication. In this case the EE MAY omit this
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.
Brockhaus, et al. Expires 3 June 2023 [Page 44]
Internet-Draft Lightweight CMP Profile November 2022
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 2.7
[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.
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 OPTIONAL, 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.
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.
Brockhaus, et al. Expires 3 June 2023 [Page 45]
Internet-Draft Lightweight CMP Profile November 2022
* 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.
Detailed Description of privateKey Field:
privateKey REQUIRED
-- 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 a sequence of 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
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
-- RFCBBBB Section 5
encryptedContent REQUIRED
-- MUST be the SignedData structure as specified in CMS
-- Section 5 [RFC5652] and [RFC8933] in encrypted form
version REQUIRED
-- MUST be 3
digestAlgorithms
REQUIRED
Brockhaus, et al. Expires 3 June 2023 [Page 46]
Internet-Draft Lightweight CMP Profile November 2022
-- MUST contain a sequence of 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, see [RFC8933]
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 a sequence of 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
-- MUST contain a sequence of 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 the digestAlgorithms field of
-- encryptedContent
-- MUST be the same as in digestAlgorithms
signedAttrs REQUIRED
-- MUST contain an id-contentType attribute containing the value
-- id-ct-KP-aKeyPackage
-- MUST contain an id-messageDigest attribute containing the
Brockhaus, et al. Expires 3 June 2023 [Page 47]
Internet-Draft Lightweight CMP Profile November 2022
-- 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] and [RFC8933]
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 RFCBBBB 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].
Detailed Description of KeyAgreeRecipientInfo Structure:
Brockhaus, et al. Expires 3 June 2023 [Page 48]
Internet-Draft Lightweight CMP Profile November 2022
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 subjectKeyIdentifier of the certificate,
-- and thereby identifies the sender's public key.
-- MUST contain the same value as the senderKID in the
-- message header
ukm RECOMMENDED
-- MUST be used when 1-pass ECMQV is used, see [RFC5753]
-- SHOULD be present to ensure uniqueness of the key
-- encryption key
keyEncryptionAlgorithm
REQUIRED
-- MUST be the algorithm identifier of the key agreement
-- algorithm
-- The algorithm type MUST be a KM_KA_ALG as specified in
-- RFCBBBB Section 4.1
-- The parameters field of the key agreement algorithm MUST
-- contain the key wrap algorithm. The algorithm type
-- MUST be a KM_KW_ALG as specified in RFCBBBB Section 4.3
recipientEncryptedKeys
REQUIRED
-- MUST contain a sequence of one RecipientEncryptedKey
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
content-encryption key. For this key management technique, the
KeyTransRecipientInfo structure MUST be used in the contentInfo
field.
Brockhaus, et al. Expires 3 June 2023 [Page 49]
Internet-Draft Lightweight CMP Profile November 2022
The KeyTransRecipientInfo structure included into the EnvelopedData
structure is specified in CMS Section 6.2.1 [RFC5652].
Detailed Description of KeyTransRecipientInfo Structure:
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 RFCBBBB 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 4.1.5 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 9.
The PasswordRecipientInfo structure included into the EnvelopedData
structure is specified in CMS Section 6.2.4 [RFC5652].
Detailed Description of PasswordRecipientInfo Structure:
Brockhaus, et al. Expires 3 June 2023 [Page 50]
Internet-Draft Lightweight CMP Profile November 2022
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
-- RFCBBBB 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
-- RFCBBBB Section 4.3
encryptedKey REQUIRED
-- MUST be the encrypted content-encryption key
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. This requires, that the EE still possesses the private
key. If this is not the case the revocation has to be initiated by
other means, e.g., revocation by the RA as specified in
Section 5.3.2.
An EE requests revoking a certificate of its own at the CA that
issued this certificate. The PKI management entity handles the
request as described in Section 5.1.3 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:
Brockhaus, et al. Expires 3 June 2023 [Page 51]
Internet-Draft Lightweight CMP Profile November 2022
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 a sequence of
one RevDetails structure in the rr message body. In the 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 a sequence of 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 a sequence of 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
Brockhaus, et al. Expires 3 June 2023 [Page 52]
Internet-Draft Lightweight CMP Profile November 2022
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 a sequence of 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 delivery of
content relevant to the EE provided by a 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 5.1.4).
The general messages and general response messages contain
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
Brockhaus, et al. Expires 3 June 2023 [Page 53]
Internet-Draft Lightweight CMP Profile November 2022
* Get root CA certificate update
* Get certificate request template
* Get new CRLs
The following message flow and contents are common to all general
message (genm) and general response (genp) messages.
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 for information
genm REQUIRED
-- MUST contain a sequence of 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 specified for the specific PKI management operation
protection REQUIRED
-- As described in Section 3.2
extraCerts REQUIRED
-- As described in Section 3.3
General Response -- genp
Brockhaus, et al. Expires 3 June 2023 [Page 54]
Internet-Draft Lightweight CMP Profile November 2022
Field Value
header
-- As described in Section 3.1
body
-- The response of the PKI management entity providing
-- information
genp REQUIRED
-- MUST contain a sequence of one element of type
-- InfoTypeAndValue
infoType REQUIRED
-- MUST be the OID identifying the specific PKI management
-- operation described below
infoValue OPTIONAL
-- MUST be as specified for the specific PKI management operation
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 Section 2.14
[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
Brockhaus, et al. Expires 3 June 2023 [Page 55]
Internet-Draft Lightweight CMP Profile November 2022
3 if present, the infoValue of the response MUST contain a sequence
of certificates
Detailed Description of infoValue Field of genp:
infoValue OPTIONAL
-- MUST be absent if no CA certificate is available
-- MUST be present if CA certificates are available
-- if present, 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 an update of a root CA certificate from the PKI
management entity by sending a general message with OID id-it-
rootCaCert, which SHOULD include the old root CA certificate in the
message body, as specified in CMP Updates Section 2.15
[I-D.ietf-lamps-cmp-updates]. The PKI management entity responds
with a general response with OID id-it-rootCaKeyUpdate 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.
Note: This mechanism may also be used to update trusted non-root
certificates, i.e., trusted intermediate CA or issuing CA
certificates.
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-rootCaCert in the request and id-
it-rootCaKeyUpdate in the response
Brockhaus, et al. Expires 3 June 2023 [Page 56]
Internet-Draft Lightweight CMP Profile November 2022
2 the infoValue of the request SHOULD contain the root CA
certificate the update is requested for
3 if present, the infoValue of the response MUST be a
RootCaKeyUpdateContent structure
Detailed Description of infoValue Field of genm:
infoValue RECOMMENDED
-- MUST contain the root CA certificate to be updated, if
-- available
Detailed Description of infoValue Field of genp:
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 RootCaKeyUpdateContent
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 future certificate requests.
Brockhaus, et al. Expires 3 June 2023 [Page 57]
Internet-Draft Lightweight CMP Profile November 2022
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 Section 2.16 [I-D.ietf-lamps-cmp-updates].
The EE MAY indicate the certificate profile to use in the id-it-
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
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.
Brockhaus, et al. Expires 3 June 2023 [Page 58]
Internet-Draft Lightweight CMP Profile November 2022
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 Section 2.15
[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 Section 2.15 [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 Section 2.15 [I-D.ietf-lamps-cmp-updates],
MUST be a positive integer value 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:
* 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 id-it-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
Detailed Description of infoValue Field of genp:
Brockhaus, et al. Expires 3 June 2023 [Page 59]
Internet-Draft Lightweight CMP Profile November 2022
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 a sequence of one AttributeTypeAndValue per
-- supported algorithm with attribute id-regCtrl-algId or
-- id-regCtrl-rsaKeyLen
4.3.4. CRL Update Retrieval
This PKI management operation can be used by an EE to request a new
CRL. If a CA offers methods to access a CRL, it may include CRL
distribution points or authority information access extensions as
specified in RFC 5280 [RFC5280] into the issued certificates. In
addition, CMP offers CRL provisioning functionality as part of the
PKI management operation.
An EE requests a CRL update from the PKI management entity by sending
a general message with OID id-it-crlStatusList. The EE MUST include
the CRL source identifying the requested CRL and, if available, the
thisUpdate time of the most current CRL instance it already has, as
specified in CMP Updates Section 2.17 [I-D.ietf-lamps-cmp-updates].
The PKI management entity MUST respond with a general response with
OID id-it-crls. If no thisUpdate value was given by the EE, the PKI
management entity MUST return the latest CRL available. If a
thisUpdate value was given, the PKI management entity MUST return the
latest available CRL if this CRL has a more recent thisUpdate time.
Otherwise, the infoValue in the response message MUST be absent.
The EE MUST identify the requested CRL either by its CRL distribution
point name or issuer name. The CRL distribution point name can
either be provided from the CRL distribution points extension of the
certificate to be validated or from the issuing distribution point
extension from the CRL to be updated. If a thisUpdate value was
given, the PKI management entity MUST return the latest available CRL
if this CRL has a more recent thisUpdate time. Otherwise, the
infoValue in the response message MUST be absent.
Brockhaus, et al. Expires 3 June 2023 [Page 60]
Internet-Draft Lightweight CMP Profile November 2022
The PKI management entity SHOULD treat a CRL distribution point name
as an internal pointer to identify a CRL that is directly available
at the PKI management entity. It is not intended as a way to fetch
an arbitrary CRL from an external location.
In addition to the prerequisites specified in Section 3.4, the EE
MUST know which CRL to request.
Note: If the EE does not want to request a specific CRL it MAY use
instead a general message with OID id-it-currentCrl as specified in
RFC 4210 Section 5.3.19.6 [RFC4210].
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-crlStatusList in the request and
id-it-crls in the response
2 the infoValue of the request MUST be present and contain a
sequence of one CRLStatus structure
3 if present, the infoValue of the response MUST contain a sequence
of one CRL
Detailed Description of infoValue Field of genm:
CRLSource REQUIRED
-- MUST contain a sequence of one CRLSource structure
-- MUST contain the dpn choice of type DistributionPointName if
-- the CRL distribution point name is available
-- Otherwise, MUST contain the issuer choice identifying the CA
-- that issues the CRL. It MUST contain the issuer DN in the
-- directoryName field of a GeneralName element.
thisUpdate OPTIONAL
-- SHOULD contain the thisUpdate field of the latest CRL the EE
-- has got from the issuer specified in the given dpn or
-- issuer field
-- MUST be omitted if the EE does not have any instance of the
-- requested CRL
Detailed Description of infoValue Field of genp:
infoValue OPTIONAL
-- MUST be absent if no CRL to be returned is available
-- MUST contain a sequence of one CRL update from the referenced
-- source, if a thisUpdate value was not given or a more recent
-- CRL is available
Brockhaus, et al. Expires 3 June 2023 [Page 61]
Internet-Draft Lightweight CMP Profile November 2022
4.4. Handling Delayed Delivery
This is a variant of all PKI management operations described in this
document. It is initiated in case a PKI management entity cannot
respond to a request message in a timely manner, typically due to
offline or asynchronous upstream communication, or due to delays in
handling the request. The polling mechanism has been specified in
RFC 4210 Section 5.3.22 [RFC4210] and updated by
[I-D.ietf-lamps-cmp-updates].
Depending on the PKI architecture, the entity initiating delayed
delivery is not necessarily the PKI management entity directly
addressed by the EE.
When initiating delayed delivery of a message received from an EE,
the PKI management entity MUST respond with an ip/cp/kup/error
message including the status "waiting". On receiving this response,
the EE MUST store in its transaction context the senderNonce of the
preceding request message because this value will be needed for
checking the recipNonce of the final response to be received after
polling. It sends a poll request with certReqId 0 if referring to
the CertResponse element contained in the ip/cp/kup message, else -1
to refer to the whole message. In case the final response is not yet
available, the PKI management entity that initiated the delayed
delivery MUST answer with a poll response, with the same certReqId.
The included checkAfter time value indicates the minimum number of
seconds that SHOULD elapse before the EE sends a new pollReq message
to the PKI management entity. This is repeated until a final
response is available or any party involved gives up on the current
PKI management operation, i.e., a timeout occurs.
When the PKI management entity that initiated delayed delivery can
provide the final response for the original request message of the
EE, it MUST send this response to the EE. Using this response, the
EE can continue the current PKI management operation as usual.
No specific prerequisites apply in addition to those of the
respective PKI management operation.
Message Flow:
Brockhaus, et al. Expires 3 June 2023 [Page 62]
Internet-Draft Lightweight CMP Profile November 2022
Step# EE PKI management entity
1 format request
message
2 -> request ->
3 handle or forward
request
4 format ip/cp/kup/error
with status "waiting"
response in case no
immediate final response
is available,
5 <- ip/cp/kup/error <-
6 handle
ip/cp/kup/error
with status
"waiting"
-------------------------- start polling --------------------------
7 format pollReq
8 -> pollReq ->
9 handle or forward pollReq
10 in case the final response
for the original request
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
final response on
original request
15 <- response <-
16 handle final
response
Detailed Message Description:
Brockhaus, et al. Expires 3 June 2023 [Page 63]
Internet-Draft Lightweight CMP Profile November 2022
Response with Status "waiting" -- ip/cp/kup/error
Field Value
header
-- As described in Section 3.1
body
-- As described for the respective PKI management operation, with
-- the following adaptations:
status REQUIRED -- in case of ip/cp/kup
pKIStatusInfo REQUIRED -- in case of error response
-- PKIStatusInfo structure MUST be present
status REQUIRED
-- MUST be status "waiting"
statusString OPTIONAL
-- MAY be any human-readable text for debugging, logging or to
-- display in a GUI
failInfo PROHIBITED
protection REQUIRED
-- As described in Section 3.2
extraCerts OPTIONAL
-- As described in Section 3.3
Polling Request -- pollReq
Field Value
header
-- As described in Section 3.1
body
-- The message of the EE asking for the final response or for a
-- time to check again
pollReq REQUIRED
certReqId REQUIRED
-- MUST be 0 if referring to a CertResponse element, else -1
protection REQUIRED
-- As described in Section 3.2
-- MUST use the same credentials as in the first request message
-- of the PKI management operation
extraCerts RECOMMENDED
-- As described in Section 3.3
Brockhaus, et al. Expires 3 June 2023 [Page 64]
Internet-Draft Lightweight CMP Profile November 2022
-- MAY be omitted if the message size is critical and
-- the PKI management entity caches the extraCerts from the
-- first request message of the PKI management operation
Polling Response -- pollRep
Field Value
header
-- As described in Section 3.1
body
-- The message indicates the delay after which the EE SHOULD
-- send another pollReq message for this transaction
pollRep REQUIRED
certReqId REQUIRED
-- MUST be 0 if referring to a CertResponse element, else -1
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
-- As described in Section 3.2
-- MUST use the same credentials as in the first response
-- message of the 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
-- the PKI management operation
Final Response - Any Type of Response Message
Field Value
header
-- MUST be the header as described for the response message
-- of the respective PKI management operation
body
-- The response of the PKI management entity to the initial
-- request as described in the respective PKI management
-- operation
Brockhaus, et al. Expires 3 June 2023 [Page 65]
Internet-Draft Lightweight CMP Profile November 2022
protection REQUIRED
-- MUST be as described for the response message of the
-- respective PKI management operation
extraCerts REQUIRED
-- MUST be as described for the response message of the
-- respective PKI management operation
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
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 MUST check that a request that initiates a new
PKI management operation does not use a transactionID that is
currently in use. The 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
following 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.
Brockhaus, et al. Expires 3 June 2023 [Page 66]
Internet-Draft Lightweight CMP Profile November 2022
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 delivery as described
in Section 5.1.5.
The PKI management entity MUST 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 also perform any
further checks on the certTemplate contents (failInfo:
badCertTemplate) according to any applicable PKI policy and
certificate profile.
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.
Therefore, it MAY grant this by including the implicitConfirm
generalInfo field or include the confirmWaitTime field in the
response header.
5.1.2. 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.
Brockhaus, et al. Expires 3 June 2023 [Page 67]
Internet-Draft Lightweight CMP Profile November 2022
The prerequisites of the respective PKI management operation as
specified in Section 4.1 apply.
5.1.3. 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.
5.1.4. 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.
Note: The responding PKI management entity may generate the response
from scratch or reuse the contents of previous responses. Therefore,
it may be worth caching the body of the response message as long as
the contained information is still valid, such that further requests
for the same contents can be answered immediately.
No specific prerequisites apply in addition to those specified in
Section 3.4.
5.1.5. Initiating Delayed Delivery
This functional extension can be used by a PKI management entity in
case the response to a request takes longer than usual. In this case
the PKI management entity MUST completely validate the request as
usual and then start preparing the response or forward the request
further upstream as soon as possible. In the meantime, it MUST
respond with an ip/cp/kup/error message including the status
"waiting" and handle subsequent polling as described in Section 4.4.
Note: 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 delivery initiated by an intermediate PKI
management entity, there is an exception. Between the EE and this
Brockhaus, et al. Expires 3 June 2023 [Page 68]
Internet-Draft Lightweight CMP Profile November 2022
PKI management entity, pollReq and pollRep messages are exchanged
handling the nonces as usual. Yet when the final response from
upstream has arrived 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 delivery may replace the recipNonce in the response
message with the senderNonce of the last received pollReq because the
downstream entities, including the EE, might expect it in this way.
Yet the check specified in Section 3.5 allows to alternatively use
the senderNonce of the original request.
No specific prerequisites apply in addition to those of the
respective PKI management operation.
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.
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
its role in the PKI system requires it. This is because changes to
the message header or body imply re-protection and changes to the
protection breaks end-to-end authentication of the message source,
and changes to the certificate template in a certificate request
breaks proof-of-possession. More details are available in the
following sub-sections. 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 local PKI policy,
* add or modify fields of certificate request messages,
Brockhaus, et al. Expires 3 June 2023 [Page 69]
Internet-Draft Lightweight CMP Profile November 2022
* 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 delivery due to delays transferring messages or
handling requests, or
* collect messages from multiple RAs and forward them jointly.
Note: PKI management entities forwarding messages may also store data
from a message in a database for later usage or audit purposes. They
may also support traversal of a network boundary.
The decision if a message should be forwarded
* unchanged with the original protection,
* unchanged with a new protection, or
* 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.
Brockhaus, et al. Expires 3 June 2023 [Page 70]
Internet-Draft Lightweight CMP Profile November 2022
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.
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 RFC 4210 [RFC4210]
(see also CMP Updates Section 2.6 [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:
Brockhaus, et al. Expires 3 June 2023 [Page 71]
Internet-Draft Lightweight CMP Profile November 2022
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
This variant means that a PKI management entity forwards a CMP
message while authentically indicating successful validation and
approval of a request message without changing the original message.
By adding a protection using its own CMP protection 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 copy the values of the recipient,
recipNonce, and transactionID header fields of the original message
to the respective header fields of 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.
Brockhaus, et al. Expires 3 June 2023 [Page 72]
Internet-Draft Lightweight CMP Profile November 2022
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 be able to validate the respective
request and have the authorization to perform approval of the
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
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 by that entity on its downstream
interface.
This PKI management operation is typically used on the interface
between an LRA and an RA to bundle several messages for offline
delivery. In this case the LRA needs to initiate delayed delivery as
described in Section 5.1.5. If the RA needs different routing
information per nested PKI management message provided upstream, a
suitable mechanism may need to be implemented to ensure that the
downstream delivery of the response is done to the right requester.
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
Brockhaus, et al. Expires 3 June 2023 [Page 73]
Internet-Draft Lightweight CMP Profile November 2022
messages, e.g., ir, cr, p10cr, kur, pollReq, certConf, rr, or genm.
While building the upstream nested message the PKI management entity
MUST 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 MUST be dropped, and any missing response message MUST
be answered with an error message (failInfo bit: systemUnavail) to
inform the respective requester about the failed certificate
management operation.
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
Brockhaus, et al. Expires 3 June 2023 [Page 74]
Internet-Draft Lightweight CMP Profile November 2022
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 protection 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
* validate the protection of the received message,
* check the content of the message,
* do any modifications that it may want to perform, and
* check that the sender of the original message, 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.
These message adaptations MUST NOT be applied to certificate request
messages described in Section 4.1.6 for central key generation 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
MUST NOT change the transactionID, the senderNonce, or the recipNonce
- apart from the exception for the recipNonce given in Section 5.1.5.
Brockhaus, et al. Expires 3 June 2023 [Page 75]
Internet-Draft Lightweight CMP Profile November 2022
5.2.3.1. Not Changing 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.
Note: A signature-based proof-of-possession of a certificate request
will be broken if any field in the certTemplate structure is changed.
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 be able to validate the respective
request and have the authorization to perform approval of the
request according to the PKI policies.
5.2.3.2. Using raVerified
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:
* The PKI management entity MUST be authorized to replace the proof-
of-possession (after verifying it) with raVerified.
* The PKI management entity MUST be able to validate the respective
request and have the authorization to perform approval of the
request according to the PKI policies.
Detailed Description of popo Field of certReq Structure:
popo
raVerified REQUIRED
-- MUST have the value NULL and indicates that the PKI
-- management entity verified the popo of the original message
Brockhaus, et al. Expires 3 June 2023 [Page 76]
Internet-Draft Lightweight CMP Profile November 2022
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 a Certificate
A PKI management entity may use one 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 MUST verify the received proof-of-possession if this proof
breaks, e.g., due to transformation from PKCS#10 [RFC2986] to CRMF
[RFC4211] certificate request format.
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 because in both cases the message is protected by the
PKI management entity.
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.
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.
Brockhaus, et al. Expires 3 June 2023 [Page 77]
Internet-Draft Lightweight CMP Profile November 2022
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 acting on behalf of the EE in this
operation.
6. CMP Message Transfer Mechanisms
CMP messages are designed to be self-contained, such that in
principle any reliable transfer mechanism can be used. HTTP SHOULD
be used and CoAP MAY be used for online transfer of CMP messages on
application layer. CMP messages MAY also be piggybacked on any other
reliable transfer protocol. File-based transfer MAY be used in case
offline transfer is required.
Independently of the means of transfer, it can happen that messages
are lost or that a communication partner does not respond. To
prevent waiting indefinitely, each PKI entity that sends CMP requests
SHOULD use a configurable per-request timeout, and each PKI
management entity that handles CMP requests 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.
Moreover, there are various situations where the delivery of messages
gets delayed. For instance, a serving PKI management entity might
take longer than expected to form a response due to administrative
processes, resource constraints, or upstream message delivery delays.
The transport layer itself may cause delays, for instance due to
offline transport, network segmentation, or intermittent network
connectivity. Part of these issues can be detected and handled at
CMP level using pollReq and pollRep messages as described in
Section 4.4, while others are better handled at transfer level.
Depending on the transfer protocol and system architecture, solutions
for handling delays at transfer level may be present and can be used
for CMP connections, for instance connection re-establishment and
message retransmission.
Brockhaus, et al. Expires 3 June 2023 [Page 78]
Internet-Draft Lightweight CMP Profile November 2022
Note: Long timeout periods are helpful to maximize chances to handle
minor delays at lower layers without the need for polling.
Note: When using TCP and similar reliable connection-oriented
transport protocols, which is typical in conjunction with HTTP, there
is the option to keep the connection alive over multiple request-
response message pairs. This may improve efficiency.
When conveying CMP messages in HTTP, CoAP, or MIME-based transfer
protocols, the internet media type "application/pkixcmp" MUST be set
for transfer encoding as specified in Section 3.4 of CMP over HTTP
[RFC6712] and Section 2.4 of CMP over CoAP
[I-D.ietf-ace-cmpv2-coap-transport].
6.1. HTTP Transfer
This transfer mechanism can be used by a PKI entity to transfer CMP
messages over HTTP. If HTTP transfer 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 MUST use URI paths consisting of '/.well-
known/cmp/' or '/.well-known/cmp/p/<name>/' as specified in CMP
Updates Section 3.3 [I-D.ietf-lamps-cmp-updates]. It SHOULD be
followed by an operation label depending on the type of PKI
management operation.
Brockhaus, et al. Expires 3 June 2023 [Page 79]
Internet-Draft Lightweight CMP Profile November 2022
+============================+====================+=========+
| PKI Management Operation | URI Path Segment | Details |
+============================+====================+=========+
| Enrolling an End Entity to | initialization | Section |
| a New PKI | | 4.1.1 |
+----------------------------+--------------------+---------+
| Enrolling an End Entity to | certification | Section |
| a Known PKI | | 4.1.2 |
+----------------------------+--------------------+---------+
| Updating a Valid | keyupdate | Section |
| Certificate | | 4.1.3 |
+----------------------------+--------------------+---------+
| Enrolling an End Entity | pkcs10 | Section |
| Using a PKCS#10 Request | | 4.1.4 |
+----------------------------+--------------------+---------+
| Revoking a Certificate | revocation | Section |
| | | 4.2 |
+----------------------------+--------------------+---------+
| Get CA Certificates | getcacerts | Section |
| | | 4.3.1 |
+----------------------------+--------------------+---------+
| Get Root CA Certificate | getrootupdate | Section |
| Update | | 4.3.2 |
+----------------------------+--------------------+---------+
| Get CA Certificates | getcertreqtemplate | Section |
| | | 4.3.1 |
+----------------------------+--------------------+---------+
| CRL Update Retrieval | getcrls | Section |
| | | 4.3.4 |
+----------------------------+--------------------+---------+
| Batching Messages | nested | Section |
| | | 5.2.2.2 |
| Note: This path element is | | |
| applicable only between | | |
| PKI management entities. | | |
+----------------------------+--------------------+---------+
Table 1: HTTP URI Path Segment <operation>
Independently of any variants used (see Section 4.1.5, Section 4.1.6,
and Section 4.4) the operation label corresponding to the PKI
management operation SHALL be used.
Any certConf or pollReq messages are sent to the same endpoint as
determined by the PKI management operation.
Brockhaus, et al. Expires 3 June 2023 [Page 80]
Internet-Draft Lightweight CMP Profile November 2022
When a single request message is nested as described in
Section 5.2.2.1, the label to use is the same as for the underlying
PKI management operation.
By sending a request to its preferred 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 transfer as described in [RFC9110]. In addition,
the recommendations provided in [I-D.ietf-uta-rfc7525bis] SHOULD be
considered. The CMP transfer via HTTPS MUST use TLS server
authentication and SHOULD use TLS client authentication.
Note: The requirements for checking certificates given in [RFC5280]
and either [RFC5246] or [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.
Note: The provisioning of client certificates and PSKs is out of
scope of this document.
Brockhaus, et al. Expires 3 June 2023 [Page 81]
Internet-Draft Lightweight CMP Profile November 2022
6.2. CoAP Transfer
This transfer mechanism can be used by a PKI entity to transfer CMP
messages over CoAP [RFC7252], e.g., in constrained environments. If
CoAP transfer is used the specifications as described in CMP over
CoAP [I-D.ietf-ace-cmpv2-coap-transport] MUST be followed.
PKI management operations SHOULD use URI paths consisting of '/.well-
known/cmp/' or '/.well-known/cmp/p/<name>/' as specified in CMP over
CoAP Section 2.1 [I-D.ietf-ace-cmpv2-coap-transport] followed by an
operation label depending on the type of PKI management operation.
Brockhaus, et al. Expires 3 June 2023 [Page 82]
Internet-Draft Lightweight CMP Profile November 2022
+=======================================+=========+=========+
| PKI Management Operation | URI | Details |
| | Path | |
| | Segment | |
+=======================================+=========+=========+
| Enrolling an End Entity to a New PKI | ir | Section |
| | | 4.1.1 |
+---------------------------------------+---------+---------+
| Enrolling an End Entity to a Known | cr | Section |
| PKI | | 4.1.2 |
+---------------------------------------+---------+---------+
| Updating a Valid Certificate | kur | Section |
| | | 4.1.3 |
+---------------------------------------+---------+---------+
| Enrolling an End Entity Using a | p10 | Section |
| PKCS#10 Request | | 4.1.4 |
+---------------------------------------+---------+---------+
| Revoking a 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 |
+---------------------------------------+---------+---------+
| CRL Update Retrieval | crls | Section |
| | | 4.3.4 |
+---------------------------------------+---------+---------+
| Batching Messages | nest | Section |
| | | 5.2.2.2 |
| Note: This path element is applicable | | |
| only between PKI management entities. | | |
+---------------------------------------+---------+---------+
Table 2: CoAP URI Path Segment <operation>
Independently of any variants used (see Section 4.1.5, Section 4.1.6,
and Section 4.4) the operation label corresponding to the PKI
management operation SHALL be used.
Any certConf or pollReq messages are sent to the same endpoint as
determined by the PKI management operation.
Brockhaus, et al. Expires 3 June 2023 [Page 83]
Internet-Draft Lightweight CMP Profile November 2022
When a single request message is nested as described in
Section 5.2.2.1, the label to use is the same as for the underlying
PKI management operation.
By sending a request to its preferred 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 transfer , 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]. If
DTLS is utilized, the same boundary conditions (peer authentication,
etc.) as stated for TLS to protect HTTP transfer in Section 6.1 apply
to DTLS likewise.
Note: The provisioning of client certificates and PSKs is out of
scope of this document.
6.3. Piggybacking on Other Reliable Transfer
CMP messages MAY also be transfer on some other reliable protocol,
e.g., EAP or MQTT. Connection, delay, 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 transfer
protocol used.
6.4. Offline Transfer
For transferring 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 transfer 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.
Brockhaus, et al. Expires 3 June 2023 [Page 84]
Internet-Draft Lightweight CMP Profile November 2022
6.4.1. File-Based Transfer
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 delivery. 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.
6.4.2. Other Asynchronous Transfer Protocols
Other asynchronous transfer 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 RFC 8551 Section 3.1
[RFC8551].
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 Section 3.4 of CMP over HTTP
[RFC6712]. A filename MUST be included either in a "content-type" or
a "content-disposition" statement. The file name extension ".pki"
MUST be used.
7. Conformance Requirements
This section defines which level of support for the various features
specified in this profile is required for which type of PKI entity.
7.1. PKI Management Operations
The following table provides an overview of the PKI management
operations specified in Section 4 and Section 5 and states whether
support by conforming EE, RA, and CA implementations is mandatory,
recommended, optional, or not applicable. Variants amend or change
behavior of base PKI management operations and are therefore also
included.
The PKI management operation specifications in Section 4 assume that
either the RA or CA is the PKI management entity that terminates the
CMP protocol. If the RA terminates the CMP protocol it either
responds directly as described in Section 5.1 or forwards the
certificate management operation towards the CA not using CMP.
Section 5.2 describes different options how an RA can forward a CMP
message using CMP. Section 5.3 offers the option that an RA operates
on behalf on an EE and therefore takes the role of the EE in
Section 4.
Brockhaus, et al. Expires 3 June 2023 [Page 85]
Internet-Draft Lightweight CMP Profile November 2022
+==========+=============================+========+========+========+
| ID | PKI Management Operations | EE | RA | CA |
| | and Variants | | | |
+==========+=============================+========+========+========+
| Generic | Generic Aspects of PKI | MUST | MUST | MUST |
| | Messages and PKI | | | |
| | Management Operations, | | | |
| | Section 3 | | | |
+----------+-----------------------------+--------+--------+--------+
| IR | Enrolling an End Entity | MUST | MAY | MUST |
| | to a New PKI, | | | |
| | Section 4.1.1 | | | |
+----------+-----------------------------+--------+--------+--------+
| CR | Enrolling an End Entity | MAY | MAY | MAY |
| | to a Known PKI, | | | |
| | Section 4.1.2 | | | |
+----------+-----------------------------+--------+--------+--------+
| KUR | Updating a Valid | MUST | MAY | MUST |
| | Certificate, | | | |
| | Section 4.1.3 | | | |
+----------+-----------------------------+--------+--------+--------+
| P10CR | Enrolling an End Entity | MAY | MAY | MAY |
| | Using a PKCS#10 Request, | | | |
| | Section 4.1.4 | | | |
+----------+-----------------------------+--------+--------+--------+
| MAC | Using MAC-Based | SHOULD | SHOULD | SHOULD |
| | Protection for | | 1) | |
| | Enrollment, with IR, CR, | | | |
| | KUR, and P10CR if | | | |
| | supported, Section 4.1.5 | | | |
+----------+-----------------------------+--------+--------+--------+
| CKeyGen | Adding Central Key Pair | MAY | MAY | MAY |
| | Generation to Enrollment, | | | |
| | IR, CR, KUR, and P10CR if | | | |
| | supported, Section 4.1.6 | | | |
| | | | | |
| | If supported, key | | | |
| | agreement key management | | | |
| | technique is REQUIRED, | | | |
| | and key transport and | | | |
| | password-based key | | | |
| | management techniques are | | | |
| | OPTIONAL. | | | |
+----------+-----------------------------+--------+--------+--------+
| RR | Revoking a Certificate, | SHOULD | SHOULD | SHOULD |
| | Section 4.2 | | 2) | 3) |
+----------+-----------------------------+--------+--------+--------+
| CACerts | Get CA Certificates, | MAY | MAY | MAY |
Brockhaus, et al. Expires 3 June 2023 [Page 86]
Internet-Draft Lightweight CMP Profile November 2022
| | Section 4.3.1 | | | |
+----------+-----------------------------+--------+--------+--------+
| RootUpd | Get Root CA Certificate | MAY | MAY | MAY |
| | Update, Section 4.3.2 | | | |
+----------+-----------------------------+--------+--------+--------+
| ReqTempl | Get Certificate Request | MAY | MAY | MAY |
| | Template, Section 4.3.3 | | | |
+----------+-----------------------------+--------+--------+--------+
| CRLUpd | CRL Update Retrieval, | MAY | MAY | MAY |
| | Section 4.3.4 | | | |
+----------+-----------------------------+--------+--------+--------+
| Polling | Handling Delayed | MAY | MAY | MAY |
| | Delivery, Section 4.4 | | | |
+----------+-----------------------------+--------+--------+--------+
| CertResp | Responding to a | N/A | MAY | MUST |
| | Certificate Request (IR, | | | |
| | CR, KUR, and P10CR if | | | |
| | supported), Section 5.1.1 | | | |
+----------+-----------------------------+--------+--------+--------+
| CertConf | Responding to a | N/A | MAY | MUST |
| | Confirmation Message, | | | |
| | Section 5.1.2 | | | |
+----------+-----------------------------+--------+--------+--------+
| RevResp | Responding to a | N/A | MAY | SHOULD |
| | Revocation Request, | | | |
| | Section 5.1.3 | | | |
+----------+-----------------------------+--------+--------+--------+
| GenResp | Responding to a Support | N/A | MAY | MAY |
| | Message (CACerts, | | | |
| | RootUpd, ReqTempl, CRLUpd | | | |
| | if supported), | | | |
| | Section 5.1.4 | | | |
+----------+-----------------------------+--------+--------+--------+
| InitPoll | Initiating Delayed | N/A | MAY | MAY |
| | Delivery, Section 5.1.5 | | | |
+----------+-----------------------------+--------+--------+--------+
| FwdKeep | Forwarding Messages - Not | N/A | MUST | N/A |
| | Changing Protection, | | | |
| | Section 5.2.1 | | | |
+----------+-----------------------------+--------+--------+--------+
| FwdAddS | Forwarding Messages - | N/A | MUST | MUST |
| | Adding Protection to a | | | |
| | Request Message, | | | |
| | Section 5.2.2.1 | | | |
+----------+-----------------------------+--------+--------+--------+
| FwdAddB | Forwarding Messages - | N/A | MAY | MAY |
| | Batching Messages, | | | |
| | Section 5.2.2.2 | | | |
Brockhaus, et al. Expires 3 June 2023 [Page 87]
Internet-Draft Lightweight CMP Profile November 2022
+----------+-----------------------------+--------+--------+--------+
| FwdRepKP | Forwarding Messages - Not | N/A | SHOULD | N/A |
| | Changing | | 1) | |
| | Proof-of-Possession, | | | |
| | Section 5.2.3.1 | | | |
+----------+-----------------------------+--------+--------+--------+
| FwdRepBP | Forwarding Messages - | N/A | MAY | MAY |
| | Using raVerified, | | | |
| | Section 5.2.3.2 | | | |
+----------+-----------------------------+--------+--------+--------+
| CertOnB | Acting on Behalf of other | N/A | MAY | N/A |
| | PKI Entities - Requesting | | | |
| | a Certificate, | | | |
| | Section 5.3.1 | | | |
+----------+-----------------------------+--------+--------+--------+
| RevROnB | Acting on Behalf of other | N/A | SHOULD | SHOULD |
| | PKI Entities - Revoking a | | 2) | 3) |
| | Certificate, | | | |
| | Section 5.3.2 | | | |
+----------+-----------------------------+--------+--------+--------+
Table 3: Level of Support for PKI Management Operations and Variants
1) The RA should be able to change the CMP message protection from
MAC-based to signature-based protection, see Section 5.2.3.1.
2) The RA should be able to request certificate revocation on behalf
of an EE, see Section 5.3.2.
3) An alternative would be to perform revocation at the CA without
using CMP, for instance using a local administration interface.
7.2. Message Transfer
CMP does not have specific needs regarding message transfer, except
that for each request message sent, eventually a sequence of one
response message should be received. Therefore, virtually any
reliable transfer mechanism can be used, such as HTTP, CoAP, and
file-based offline transfer. Thus, this document does not require
any specific transfer protocol to be supported by conforming
implementations.
On different links between PKI entities, e.g., EE-RA and RA-CA,
different transfer mechanisms as specified in Section 6 may be used.
Brockhaus, et al. Expires 3 June 2023 [Page 88]
Internet-Draft Lightweight CMP Profile November 2022
HTTP SHOULD be supported and CoAP MAY be supported at all PKI
entities for maximizing general interoperability at transfer level.
Yet full flexibility is retained to choose whatever transfer
mechanism is suitable, for instance for devices and system
architectures with specific constraints.
The following table lists the name and level of support specified for
each transfer mechanism.
+=========+=======================+========+========+========+
| ID | Message Transfer Type | EE | RA | CA |
+=========+=======================+========+========+========+
| HTTP | HTTP Transfer, | SHOULD | SHOULD | SHOULD |
| | Section 6.1 | | | |
+---------+-----------------------+--------+--------+--------+
| CoAP | CoAP Transfer, | MAY | MAY | MAY |
| | Section 6.2 | | | |
+---------+-----------------------+--------+--------+--------+
| Piggyb | Piggybacking on Other | MAY | MAY | MAY |
| | Reliable Transfer, | | | |
| | Section 6.3 | | | |
+---------+-----------------------+--------+--------+--------+
| Offline | Offline Transfer, | MAY | MAY | MAY |
| | Section 6.4 | | | |
+---------+-----------------------+--------+--------+--------+
Table 4: Level of Support for Message Transfer Types
8. IANA Considerations
This document defines new entries with the following content in the
"CMP Well-Known URI Path Segments" registry (see
https://www.iana.org/assignments/cmp/) as defined in RFC 8615
[RFC8615].
+====================+===============================+===========+
| Path Segment | Description | Reference |
+====================+===============================+===========+
| initialization | Enrolling an End Entity to a | [thisRFC] |
| | New PKI over HTTP | |
+--------------------+-------------------------------+-----------+
| certification | Enrolling an End Entity to a | [thisRFC] |
| | Known PKI over HTTP | |
+--------------------+-------------------------------+-----------+
| keyupdate | Updating a Valid Certificate | [thisRFC] |
| | over HTTP | |
+--------------------+-------------------------------+-----------+
| pkcs10 | Enrolling an End Entity Using | [thisRFC] |
Brockhaus, et al. Expires 3 June 2023 [Page 89]
Internet-Draft Lightweight CMP Profile November 2022
| | a PKCS#10 Request over HTTP | |
+--------------------+-------------------------------+-----------+
| revocation | Revoking a Certificate over | [thisRFC] |
| | HTTP | |
+--------------------+-------------------------------+-----------+
| getcacerts | Get CA Certificates over HTTP | [thisRFC] |
+--------------------+-------------------------------+-----------+
| getrootupdate | Get Root CA Certificate | [thisRFC] |
| | Update over HTTP | |
+--------------------+-------------------------------+-----------+
| getcertreqtemplate | Get CA Certificates over HTTP | [thisRFC] |
+--------------------+-------------------------------+-----------+
| getcrls | CRL Update Retrieval over | [thisRFC] |
| | HTTP | |
+--------------------+-------------------------------+-----------+
| nested | Batching Messages over HTTP | [thisRFC] |
+--------------------+-------------------------------+-----------+
| ir | Enrolling an End Entity to a | [thisRFC] |
| | New PKI over CoAP | |
+--------------------+-------------------------------+-----------+
| cr | Enrolling an End Entity to a | [thisRFC] |
| | Known PKI over CoAP | |
+--------------------+-------------------------------+-----------+
| kur | Updating a Valid Certificate | [thisRFC] |
| | over CoAP | |
+--------------------+-------------------------------+-----------+
| p10 | Enrolling an End Entity Using | [thisRFC] |
| | a PKCS#10 Request over CoAP | |
+--------------------+-------------------------------+-----------+
| rr | Revoking a Certificate over | [thisRFC] |
| | CoAP | |
+--------------------+-------------------------------+-----------+
| crts | Get CA Certificates over CoAP | [thisRFC] |
+--------------------+-------------------------------+-----------+
| rcu | Get Root CA Certificate | [thisRFC] |
| | Update over CoAP | |
+--------------------+-------------------------------+-----------+
| att | Get Certificate Request | [thisRFC] |
| | Template over CoAP | |
+--------------------+-------------------------------+-----------+
| crls | CRL Update Retrieval over | [thisRFC] |
| | CoAP | |
+--------------------+-------------------------------+-----------+
| nest | Batching Messages over CoAP | [thisRFC] |
+--------------------+-------------------------------+-----------+
Table 5: New "CMP Well-Known URI Path Segments" Registry Entries
Brockhaus, et al. Expires 3 June 2023 [Page 90]
Internet-Draft Lightweight CMP Profile November 2022
< TBD: New entries must be added to the registry "CMP Well-Known URI
Path Segments". >
9. Security Considerations
The security considerations as laid out in CMP [RFC4210] updated by
CMP Updates [I-D.ietf-lamps-cmp-updates] and CMP Algorithms
[I-D.ietf-lamps-cmp-algorithms], CRMF [RFC4211] updated by Algorithm
Requirements Update [RFC9045], CMP over HTTP [RFC6712], and CMP over
CoAP [I-D.ietf-ace-cmpv2-coap-transport] apply.
Trust anchors for chain validations are often provided in the form of
self-signed certificates. All trust anchors MUST be stored on the
device with integrity protection. In some cases, a PKI entity may
not have sufficient storage for the complete certificates. In such
cases it MAY only store, e.g., a hash of each self-signed certificate
and require receiving the certificate in the extraCerts field as
described in Section 3.3. If such self-signed certificates are
provided in-band in the messages, they MUST be verified using
information from the trust store of the PKI entity.
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 password-authenticated key exchange (PAKE) protocol 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.
10. Acknowledgements
We thank the various reviewers of this document.
11. References
11.1. Normative References
[I-D.ietf-ace-cmpv2-coap-transport]
Sahni, M. and S. Tripathi, "CoAP Transfer for the
Certificate Management Protocol", Work in Progress,
Internet-Draft, draft-ietf-ace-cmpv2-coap-transport-05, 19
September 2022, <https://datatracker.ietf.org/doc/html/
draft-ietf-ace-cmpv2-coap-transport-05>.
Brockhaus, et al. Expires 3 June 2023 [Page 91]
Internet-Draft Lightweight CMP Profile November 2022
[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-15, 2 June 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
cmp-algorithms-15>.
[I-D.ietf-lamps-cmp-updates]
Brockhaus, H., von Oheimb, D., and J. Gray, "Certificate
Management Protocol (CMP) Updates", Work in Progress,
Internet-Draft, draft-ietf-lamps-cmp-updates-23, 29 June
2022, <https://datatracker.ietf.org/doc/html/draft-ietf-
lamps-cmp-updates-23>.
[I-D.ietf-uta-rfc7525bis]
Sheffer, Y., Saint-Andre, P., and T. Fossati,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", Work in Progress, Internet-Draft, draft-ietf-uta-
rfc7525bis-11, 16 August 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-uta-
rfc7525bis-11>.
[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>.
[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>.
Brockhaus, et al. Expires 3 June 2023 [Page 92]
Internet-Draft Lightweight CMP Profile November 2022
[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>.
[RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers
(URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
<https://www.rfc-editor.org/info/rfc8615>.
[RFC8933] Housley, R., "Update to the Cryptographic Message Syntax
(CMS) for Algorithm Identifier Protection", RFC 8933,
DOI 10.17487/RFC8933, October 2020,
<https://www.rfc-editor.org/info/rfc8933>.
[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>.
[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/info/rfc9110>.
11.2. Informative References
Brockhaus, et al. Expires 3 June 2023 [Page 93]
Internet-Draft Lightweight CMP Profile November 2022
[ETSI-3GPP.33.310]
3GPP, "Network Domain Security (NDS); Authentication
Framework (AF)", 3GPP TS 33.310 16.6.0, 16 December 2020,
<http://www.3gpp.org/ftp/Specs/html-info/33310.htm>.
[ETSI-EN.319411-1]
ETSI, "Electronic Signatures and Infrastructures (ESI);
Policy and security requirements for Trust Service
Providers issuing certificates; Part 1: General
requirements", ETSI EN 319 411-1 V1.3.1, May 2021,
<https://www.etsi.org/deliver/
etsi_en/319400_319499/31941101/01.03.01_60/
en_31941101v010301p.pdf>.
[I-D.ietf-anima-brski-ae]
von Oheimb, D., Fries, S., and H. Brockhaus, "BRSKI-AE:
Alternative Enrollment Protocols in BRSKI", Work in
Progress, Internet-Draft, draft-ietf-anima-brski-ae-03, 24
October 2022, <https://datatracker.ietf.org/doc/html/
draft-ietf-anima-brski-ae-03>.
[I-D.ietf-anima-brski-prm]
Fries, S., Werner, T., Lear, E., and M. Richardson, "BRSKI
with Pledge in Responder Mode (BRSKI-PRM)", Work in
Progress, Internet-Draft, draft-ietf-anima-brski-prm-05,
24 October 2022, <https://datatracker.ietf.org/doc/html/
draft-ietf-anima-brski-prm-05>.
[I-D.ietf-lamps-rfc4210bis]
Brockhaus, H., von Oheimb, D., Ounsworth, M., and J. Gray,
"Internet X.509 Public Key Infrastructure -- Certificate
Management Protocol (CMP)", Work in Progress, Internet-
Draft, draft-ietf-lamps-rfc4210bis-03, 24 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
rfc4210bis-03>.
[I-D.ietf-lamps-rfc6712bis]
Brockhaus, H., von Oheimb, D., Ounsworth, M., and J. Gray,
"Internet X.509 Public Key Infrastructure -- HTTP Transfer
for the Certificate Management Protocol (CMP)", Work in
Progress, Internet-Draft, draft-ietf-lamps-rfc6712bis-02,
11 August 2022, <https://datatracker.ietf.org/doc/html/
draft-ietf-lamps-rfc6712bis-02>.
[I-D.ietf-netconf-sztp-csr]
Watsen, K., Housley, R., and S. Turner, "Conveying a
Certificate Signing Request (CSR) in a Secure Zero Touch
Provisioning (SZTP) Bootstrapping Request", Work in
Brockhaus, et al. Expires 3 June 2023 [Page 94]
Internet-Draft Lightweight CMP Profile November 2022
Progress, Internet-Draft, draft-ietf-netconf-sztp-csr-14,
2 March 2022, <https://datatracker.ietf.org/doc/html/
draft-ietf-netconf-sztp-csr-14>.
[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>.
[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>.
[RFC5753] Turner, S. and D. Brown, "Use of Elliptic Curve
Cryptography (ECC) Algorithms in Cryptographic Message
Syntax (CMS)", RFC 5753, DOI 10.17487/RFC5753, January
2010, <https://www.rfc-editor.org/info/rfc5753>.
Brockhaus, et al. Expires 3 June 2023 [Page 95]
Internet-Draft Lightweight CMP Profile November 2022
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<https://www.rfc-editor.org/info/rfc7030>.
[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>.
[RFC8572] Watsen, K., Farrer, I., and M. Abrahamsson, "Secure Zero
Touch Provisioning (SZTP)", RFC 8572,
DOI 10.17487/RFC8572, April 2019,
<https://www.rfc-editor.org/info/rfc8572>.
[RFC8649] Housley, R., "Hash Of Root Key Certificate Extension",
RFC 8649, DOI 10.17487/RFC8649, August 2019,
<https://www.rfc-editor.org/info/rfc8649>.
[RFC8995] Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructure (BRSKI)", RFC 8995, DOI 10.17487/RFC8995,
May 2021, <https://www.rfc-editor.org/info/rfc8995>.
[UNISIG.Subset-137]
UNISIG, "Subset-137; ERTMS/ETCS On-line Key Management
FFFIS; V1.0.0", December 2015,
<https://www.era.europa.eu/sites/default/files/filesystem/
ertms/ccs_tsi_annex_a_-_mandatory_specifications/
set_of_specifications_3_etcs_b3_r2_gsm-r_b1/index083_-
_subset-137_v100.pdf>.
Brockhaus, et al. Expires 3 June 2023 [Page 96]
Internet-Draft Lightweight CMP Profile November 2022
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,
* 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"
Brockhaus, et al. Expires 3 June 2023 [Page 97]
Internet-Draft Lightweight CMP Profile November 2022
}
}
}
}
[9] {
SEQUENCE {
OBJECT IDENTIFIER subjectAltName (2 5 29 17)
OCTET STRING, encapsulates {
SEQUENCE {
[2] "www.myServer.com"
[7] ""
}
}
}
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 algId (1 3 6 1 5 5 7 5 1 11)
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 12)
INTEGER 2048
}
}
}
Brockhaus, et al. Expires 3 June 2023 [Page 98]
Internet-Draft Lightweight CMP Profile November 2022
Appendix B. History of Changes
Note: This appendix will be deleted in the final version of the
document.
From version 15 -> 16:
* Addressed comment from Warren (see thread "Warren Kumari's No
Record on draft-ietf-lamps-lightweight-cmp-profile-15: (with
COMMENT)")
* Addressed comment from Sheng (see thread "Intdir telechat review
of draft-ietf-lamps-lightweight-cmp-profile-15")
* Addressed comment from Niklas (see thread "Iotdir telechat review
of draft-ietf-lamps-lightweight-cmp-profile-15")
* Addressed comment from Erik (see thread "Erik Kline's No Objection
on draft-ietf-lamps-lightweight-cmp-profile-15: (with COMMENT)")
* Stremelined wording in two ASN.1 comments
From version 14 -> 15:
* Added a reference to HashOfRootKey extension to note in
Section 3.3
* Addressed comment from Joel (see thread "Genart last call review
of draft-ietf-lamps-lightweight-cmp-profile-14")
* Addressed comment from Robert (see thread "Artart last call review
of draft-ietf-lamps-lightweight-cmp-profile-14")
From version 13 -> 14:
* Addressed comments from AD Evaluation (see thread "AD Review of
draft-ietf-lamps-lightweight-cmp-profile-13")
* Added a note to Section 1 informing about rfc4210bis and
rfc6712bis activity
* Added support for constrained PKI entities that can, e.g., only
store a hash of a self-signed certificate as trust anchor and
require the self-signed certificate to be provided in-line in
extraCerts, see Section 3.3 and Section 9
* Addressed idnits feedback, specifically changing the following RFC
reference: RFC3278 -> RFC5753
From version 12 -> 13:
* Some minor clarifications regarding 'exactly one element' ->
'sequence of one element'
* Adding authors contact details
From version 11 -> 12:
Brockhaus, et al. Expires 3 June 2023 [Page 99]
Internet-Draft Lightweight CMP Profile November 2022
* Added a note to Section 4.1.6 to clarify the combination of
central key generation with certificate update
* Updated Section 4.3.4 for clarification that only one CRL per
round-trip is requested
* Updated Section 7.1 to fix a wrong change from the last update in
the first two rows of Table 3
From version 10 -> 11:
* Updated Section 3.2, 3.5, and 3.6.4 to define more clearly
signature-based protection as the default and the exception for
not protecting error messages as mentioned at IETF 113
* Streamlined headlines in Section 4.1
* Updates Section 6.1 and Section 6.2 regarding new well-known path
segment for profile labels as discussed during IETF 113
* Updated Section 7.1. on the support of PKI management operations
required for EEs, RAs, and CAs as mentioned at IETF 113
* Updates Section 8 adding well-known path segments on PKI
management operations to be used with HTTP and CoAP
* Capitalized all headlines
From version 09 -> 10:
* Resolved some nits reported by I-D nit checker tool
* Resolve some wording issues
From version 08 -> 09:
* Updated Section 1.1 and 1.2 and converted Section 2.2 and 2.3 into
more detailed tables in Section 7 (see thread "WG Last Call for
draft-ietf-lamps-cmp-updates-14 and draft-ietf-lamps-lightweight-
cmp-profile-08")
* Updated Section 3.1 and 4.1.1 making implicitConfirm recommended
for ir/cr/p10cr/kur and providing further recommendations on its
use (see thread "certConf - WG Last Call for draft-ietf-lamps-cmp-
updates-14 and draft-ietf-lamps-lightweight-cmp-profile-08")
* Updated Section 4.1.6 adding some clarifications regarding
validating the authorization of centrally generated keys
* Updated Section 4.3.4 adding some clarifications on CRL update
retrieval (see thread "CRL update retrieval - WG Last Call for
draft-ietf-lamps-cmp-updates-14 and draft-ietf-lamps-lightweight-
cmp-profile-08")
* Updated references to CMP Updates pointing to concrete sections
(see thread "CRL update retrieval - WG Last Call for draft-ietf-
lamps-cmp-updates-14 and draft-ietf-lamps-lightweight-cmp-profile-
08"))
* Corrected a couple of nits elsewhere
Brockhaus, et al. Expires 3 June 2023 [Page 100]
Internet-Draft Lightweight CMP Profile November 2022
From version 07 -> 08:
* Updates Section 4.1.6.1. regarding content of the originator and
keyEncryptionAlgorithm fields (see thread "AD review of draft-
ietf-lamps-cmp-algorithms-07")
* Rolled back part of the changes on root CA certificate updates in
Section 4.3.2 (see thread "Allocation of OIDs for CRL update
retrieval (draft-ietf-lamps-cmp-updates-13)")
From version 06 -> 07:
* Added references to [draft-ietf-netconf-sztp-csr] in new
Section 1.5 and Section 4.1.4
* Added reference to [I-D.ietf-anima-brski-ae] in new Section 1.5
and Section 4.1.1
* Changed reference in Section 2 to [I-D.ietf-anima-brski-prm] as
the PUSH use case is continued to be discussed in this draft after
the split of BRSKI-AE
* Improved note regarding UNISIG Subset-137 in Section 1.6
* Removed "rootCaCert" in Section 3.1 and updated the structure of
the genm request for root CA certificate updates in Section 4.3.2.
* Simplified handling of sender and recipient nonces in case of
delayed delivery in Sections 3.1, 3.5, 4.4, and 5.1.2
* Changed the order of Sections 4.1.4 and 4.1.5
* Added reference on RFC 8933 regarding CMS signedAttrs to
Section 4.1.6
* Added Section 4.3.4 on CRL update retrieval
* Generalized delayed enrollment to delayed delivery in Section 4.4
and 5.1.2, updated the state machine in the introduction of
Section 4
* Updated Section 6 regarding delayed message transfer
* Changed file name extension from ".PKI" to ".pki", deleted
operational path for central key generation, and added an
operational path for CRL update retrieval in Sections 6.1 and 6.2
* Shifted many security considerations to CMP Updates
* Replaced the term "transport" by "transfer" where appropriate to
prevent confusion regarding TCP vs. HTTP and CoAP
* Various editorial changes and language corrections
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
Brockhaus, et al. Expires 3 June 2023 [Page 101]
Internet-Draft Lightweight CMP Profile November 2022
* 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
* 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
Brockhaus, et al. Expires 3 June 2023 [Page 102]
Internet-Draft Lightweight CMP Profile November 2022
* 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
* 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 1.6 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 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 4.4 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.
Brockhaus, et al. Expires 3 June 2023 [Page 103]
Internet-Draft Lightweight CMP Profile November 2022
* 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
* 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.
Brockhaus, et al. Expires 3 June 2023 [Page 104]
Internet-Draft Lightweight CMP Profile November 2022
* Added some ToDos resulting from discussion with Tomas Gustavsson.
* Minor clarifications and changes in wording.
From version 00 -> 01:
* 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 4.1.4.
* 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 4.4.
* 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
Siemens
Werner-von-Siemens-Strasse 1
80333 Munich
Germany
Email: hendrik.brockhaus@siemens.com
URI: https://www.siemens.com
Brockhaus, et al. Expires 3 June 2023 [Page 105]
Internet-Draft Lightweight CMP Profile November 2022
David von Oheimb
Siemens
Werner-von-Siemens-Strasse 1
80333 Munich
Germany
Email: david.von.oheimb@siemens.com
URI: https://www.siemens.com
Steffen Fries
Siemens AG
Werner-von-Siemens-Strasse 1
80333 Munich
Germany
Email: steffen.fries@siemens.com
URI: https://www.siemens.com
Brockhaus, et al. Expires 3 June 2023 [Page 106]