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Versions: (draft-brockhaus-lamps-lightweight-cmp-profile) 00 01 02 03

LAMPS Working Group                                         H. Brockhaus
Internet-Draft                                                  S. Fries
Intended status: Standards Track                           D. von Oheimb
Expires: April 5, 2021                                           Siemens
                                                         October 2, 2020


                        Lightweight CMP Profile
              draft-ietf-lamps-lightweight-cmp-profile-03

Abstract

   The goal of this document is to facilitate interoperability and
   automation by profiling the Certificate Management Protocol (CMP)
   version 2, the related Certificate Request Message Format (CRMF)
   version 2, and the HTTP Transfer for the Certificate Management
   Protocol.  It specifies a subset of CMP and CRMF focusing on typical
   uses cases relevant for managing certificates of devices in many
   industrial and IoT scenarios.  To limit the overhead of certificate
   management for more constrained devices only the most crucial types
   of operations are specified as mandatory.  To foster interoperability
   in more complex scenarios, other types of operations are specified as
   recommended or optional.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 5, 2021.

Copyright Notice

   Copyright (c) 2020 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



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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Motivation for profiling CMP  . . . . . . . . . . . . . .   4
     1.2.  Motivation for a lightweight profile for CMP  . . . . . .   5
     1.3.  Existing CMP profiles . . . . . . . . . . . . . . . . . .   5
     1.4.  Compatibility with existing CMP profiles  . . . . . . . .   7
     1.5.  Scope of this document  . . . . . . . . . . . . . . . . .   9
     1.6.  Structure of this document  . . . . . . . . . . . . . . .   9
     1.7.  Convention and Terminology  . . . . . . . . . . . . . . .  10
   2.  Architecture and use cases  . . . . . . . . . . . . . . . . .  11
     2.1.  Solution architecture . . . . . . . . . . . . . . . . . .  11
     2.2.  Basic generic CMP message content . . . . . . . . . . . .  12
     2.3.  Supported PKI management operations . . . . . . . . . . .  13
       2.3.1.  Mandatory PKI management operations . . . . . . . . .  13
       2.3.2.  Recommended PKI management operations . . . . . . . .  14
       2.3.3.  Optional PKI management operations  . . . . . . . . .  14
     2.4.  CMP message transport . . . . . . . . . . . . . . . . . .  15
   3.  Generic parts of the PKI message  . . . . . . . . . . . . . .  16
     3.1.  General description of the CMP message header . . . . . .  17
     3.2.  General description of the CMP message protection . . . .  19
     3.3.  General description of CMP message extraCerts . . . . . .  20
   4.  End Entity focused PKI management operations  . . . . . . . .  20
     4.1.  Requesting a new certificate from a PKI . . . . . . . . .  21
       4.1.1.  Request a certificate from a new PKI with signature
               protection  . . . . . . . . . . . . . . . . . . . . .  22
       4.1.2.  Request a certificate from a trusted PKI with
               signature protection  . . . . . . . . . . . . . . . .  28
       4.1.3.  Update an existing certificate with signature
               protection  . . . . . . . . . . . . . . . . . . . . .  29
       4.1.4.  Request a certificate from a PKI with MAC protection   30
       4.1.5.  Request a certificate from a legacy PKI using PKCS#10
               request . . . . . . . . . . . . . . . . . . . . . . .  32
       4.1.6.  Generate the key pair centrally at the PKI management
               entity  . . . . . . . . . . . . . . . . . . . . . . .  34
         4.1.6.1.  Using key agreement key management technique  . .  40
         4.1.6.2.  Using key transport key management technique  . .  41
         4.1.6.3.  Using password-based key management technique . .  42
       4.1.7.  Delayed enrollment  . . . . . . . . . . . . . . . . .  43
     4.2.  Revoking a certificate  . . . . . . . . . . . . . . . . .  48



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     4.3.  Error reporting . . . . . . . . . . . . . . . . . . . . .  50
     4.4.  Support messages  . . . . . . . . . . . . . . . . . . . .  52
       4.4.1.  General message and response  . . . . . . . . . . . .  53
       4.4.2.  Get CA certificates . . . . . . . . . . . . . . . . .  54
       4.4.3.  Get root CA certificate update  . . . . . . . . . . .  55
       4.4.4.  Get certificate request template  . . . . . . . . . .  56
   5.  LRA and RA focused PKI management operations  . . . . . . . .  58
     5.1.  Forwarding of messages  . . . . . . . . . . . . . . . . .  59
       5.1.1.  Not changing protection . . . . . . . . . . . . . . .  61
       5.1.2.  Replacing protection  . . . . . . . . . . . . . . . .  61
         5.1.2.1.  Keeping proof-of-possession . . . . . . . . . . .  62
         5.1.2.2.  Breaking proof-of-possession  . . . . . . . . . .  62
       5.1.3.  Adding Protection . . . . . . . . . . . . . . . . . .  63
         5.1.3.1.  Handling a single PKI management message  . . . .  64
         5.1.3.2.  Handling a batch of PKI management messages . . .  64
       5.1.4.  Initiating delayed enrollment . . . . . . . . . . . .  65
     5.2.  Revoking certificates on behalf of another's entities . .  66
     5.3.  Error reporting . . . . . . . . . . . . . . . . . . . . .  66
   6.  CMP message transport variants  . . . . . . . . . . . . . . .  67
     6.1.  HTTP transport  . . . . . . . . . . . . . . . . . . . . .  67
     6.2.  HTTPS transport using certificates  . . . . . . . . . . .  69
     6.3.  HTTPS transport using shared secrets  . . . . . . . . . .  70
     6.4.  Offline transport . . . . . . . . . . . . . . . . . . . .  71
       6.4.1.  File-based transport  . . . . . . . . . . . . . . . .  71
       6.4.2.  Other asynchronous transport protocols  . . . . . . .  71
     6.5.  CoAP transport  . . . . . . . . . . . . . . . . . . . . .  71
     6.6.  Piggybacking on other reliable transport  . . . . . . . .  71
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  72
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  72
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  72
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  72
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  72
     10.2.  Informative References . . . . . . . . . . . . . . . . .  73
   Appendix A.  Example for CertReqTemplate  . . . . . . . . . . . .  75
   Appendix B.  History of changes . . . . . . . . . . . . . . . . .  76
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  80

1.  Introduction

   !!! The change history was moved to Appendix B !!!

   This document specifies PKI management operations supporting machine-
   to-machine and IoT use cases.  The focus lies on maximum automation
   and interoperable implementation of all involved PKI entities from
   end entities (EE) through an optional Local Registration Authority
   (LRA) and the RA up to the CA.  The profile makes use of the concepts
   and syntax specified in CMP [RFC4210], CRMF [RFC4211], HTTP transfer
   for CMP [RFC6712], and CMP Updates [I-D.ietf-lamps-cmp-updates].



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   Especially CMP and CRMF are very feature-rich standards, while only a
   limited subset of the specified functionality is needed in many
   environments.  Additionally, the standards are not always precise
   enough on how to interpret and implement the described concepts.
   Therefore, this document aims at tailoring and specifying in more
   detail how to use these concepts to implement lightweight automated
   certificate management.

1.1.  Motivation for profiling CMP

   CMP was standardized in 1999 and is implemented in several CA
   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 very solid and capable protocol it could be used more
   widely.  The most important reason for not more intense application
   of CMP appears to be that the protocol is offering a large set of
   features and options but being not always precise enough and leaving
   room for interpretation.  On the one hand, this makes CMP applicable
   to a very wide range of scenarios, but on the other hand a full
   implementation of all options is unrealistic because this would take
   enormous effort.

   Moreover, many details of the CMP protocol have been left open or
   have not been specified in full preciseness.  The profiles specified
   in Appendix D and E of [RFC4210] offer some more detailed PKI
   management operations.  But the specific needs of highly automated
   scenarios for a machine-to-machine communication are not covered
   sufficiently.

   As also ETSI and UNISIG already put across, profiling is a way of
   coping with the challenges mentioned above.  To profile means to take
   advantage of the strengths of the given protocol, while explicitly
   narrowing down the options it provides to exactly those needed for
   the purpose(s) at hand and eliminating all identified ambiguities.
   In this way all the general and applicable aspects of the protocol
   can be taken over and only the peculiarities of the target scenario
   need to be dealt with specifically.

   Doing such a profiling for a new target environment can be a 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 with the intended usage 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 then reference the needed PKI management



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   operations from this document and do not need to come up with
   individual profiles.

1.2.  Motivation for a lightweight profile for CMP

   The profiles specified in Appendix D and E of CMP have been developed
   in particular to manage certificates of human end entities.  With the
   evolution of distributed systems and client-server architectures,
   certificates for machines and applications on them have become widely
   used.  This trend has strengthened even more in emerging industrial
   and IoT scenarios.  CMP is sufficiently flexible to support these
   very 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 procedures.

   Due to increasing security in operational networks as well as
   availability requirements, especially on critical infrastructures and
   systems with a high volume of certificates, a state-of-the-art
   certificate management must be constantly available and cost-
   efficient, which calls for high automation and reliability.  The NIST
   Cyber Security Framework [NIST-CSFW] also refers to proper processes
   for issuance, management, verification, revocation, and audit for
   authorized devices, users and processes involving identity and
   credential management.  Such PKI operation according to commonly
   accepted best practices is also required in IEC 62443-3-3
   [IEC62443-3-3] for security level 2 up to security level 4.

   Further challenges in many industrial systems are network
   segmentation and asynchronous communication, where PKI operation is
   often not deployed on-site but in a more protected environment of a
   data center or trust center.  Certificate management must be able to
   cope with such network architectures.  CMP offers the required
   flexibility and functionality, namely self-contained messages,
   efficient polling, and support for asynchronous message transfer with
   end-to-end security.

1.3.  Existing CMP profiles

   As already stated, CMP contains profiles with mandatory and optional
   transactions in the Appendixes D and E of [RFC4210].  Those profiles
   focus on management of human user certificates and do only partly
   address the specific needs for certificate management automation for
   unattended machine or application-oriented end entities.




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   [RFC4210] specifies in Appendix D the following mandatory PKI
   management operations (all require support of, in the meantime
   outdated, algorithms, e.g., SHA-1 and 3-DES; all operations may
   enroll up to two certificates, one for a locally generated and
   another optional one for a centrally generated key pair; all require
   use of certConf/pkiConf messages for confirmation):

   o  Initial registration/certification; an (uninitialized) end entity
      requests a (first) certificate from a CA using shared secret based
      message authentication.  The content is similar to the PKI
      management operation specified in Section 4.1.4 of this document.

   o  Certificate request; an (initialized) end entity requests another
      certificate from a CA using signature or shared secret based
      message authentication.  The content is similar to the PKI
      management operation specified in Section 4.1.2 of this document.

   o  Key update; an (initialized) end entity requests a certificate
      from a CA (to update the key pair and/or corresponding certificate
      that it already possesses) using signature or shared secret based
      message authentication.  The content is similar to the PKI
      management operation specified in Section 4.1.3 of this document.

   Due to the two certificates that may be enrolled and the shared
   secret based authentication, these PKI management operations focus
   more on the enrollment of human users at a PKI.

   [RFC4210] specifies in Appendix E the following optional PKI
   management operations (all require support of, in the meantime
   outdated, algorithms, e.g., SHA-1 and 3-DES):

   o  Root CA key update; a root CA updates its key pair and produces a
      CA key update announcement message that can be made available (via
      some transport mechanism) to the relevant end entities.  This
      operation only supports a push and no pull model.  The content is
      similar to the PKI management operation specified in Section 4.4.3
      of this document.

   o  Information request/response; an end entity sends a general
      message to the PKI requesting details that will be required for
      later PKI management operations.  The content is similar to the
      PKI management operation specified in Section 4.4.4 of this
      document.

   o  Cross-certification request/response (1-way); creation of a single
      cross-certificate (i.e., not two at once).  The requesting CA MAY
      choose who is responsible for publication of the cross-certificate




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      created by the responding CA through use of the PKIPublicationInfo
      control.

   o  In-band initialization using external identity certificate (this
      PKI management operation may also enroll up to two certificates
      and requires use of certConf/pkiConf messages for confirmation as
      specified in Appendix D of [RFC4210]).  An (uninitialized) end
      entity wishes to initialize into the PKI with a CA, CA-1.  It
      uses, for authentication purposes, a pre-existing identity
      certificate issued by another (external) CA, CA-X.  A trust
      relationship must already have been established between CA-1 and
      CA-X so that CA-1 can validate the EE identity certificate signed
      by CA-X.  Furthermore, some mechanism must already have been
      established within the Personal Security Environment (PSE) of the
      EE that would allow it to authenticate and verify PKIMessages
      signed by CA-1.  The content is similar to the PKI management
      operation specified in Section 4.1.1 of this document.

   Both Appendixes focus on EE to CA/RA PKI management operations and do
   not address further profiling of RA to CA communication as typically
   used for full backend automation.

   ETSI makes use of CMP [RFC4210] in its Technical Specification 133
   310 [ETSI-TS133310] for automatic management of IPSec certificates in
   UMTS, LTE, and 5G backbone networks.  Since 2010 a dedicated CMP
   profile for initial certificate enrollment and update operations
   between EE and RA/CA is specified in that document.

   UNISIG has included a CMP profile for certificate enrollment in the
   subset 137 specifying the ETRAM/ECTS on-line key management for train
   control systems [UNISIG-Subset137] in 2015.

   Both standardization bodies use CMP [RFC4210], CRMF [RFC4211], and
   HTTP transfer for CMP [RFC6712] to add tailored means for automated
   PKI management operations for unattended machine or application-
   oriented end entities.

1.4.  Compatibility with existing CMP profiles

   The profile specified in this document is compatible with CMP
   [RFC4210] Appendixes D and E (PKI Management Message Profiles), with
   the following exceptions:

   o  signature-based protection is the default protection; an initial
      PKI management operation may also use HMAC,

   o  certification of a second key pair within the same PKI management
      operation is not supported,



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   o  proof-of-possession (POPO) with self-signature of the certTemplate
      according to [RFC4211] section 4.1 clause 3 is the recommended
      default POPO method (deviations are possible by EEs when
      requesting central key generation and by (L)RAs when using
      raVerified),

   o  confirmation of newly enrolled certificates may be omitted, and

   o  all PKI management operations consist of request-response message
      pairs originating at the EE, i.e., announcement messages are
      omitted.

   The profile specified in this document is compatible with the CMP
   profile for UMTS, LTE, and 5G network domain security and
   authentication framework [ETSI-TS133310], except that:

   o  protection of initial PKI management operations may be HMAC-based,

   o  the subject field is mandatory in certificate templates, and

   o  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-Subset137], except that:

   o  As stated in Section 4.1.1 a CMP message SHALL only consist of one
      certificate request (CertReqMsg).  As UNISIG Subset-137 Table 6
      [UNISIG-Subset137] allows to transport more than one certificate
      request message, this conflicts with this document.

   o  There is no automatic revocation specified in this document.  As
      UNISIG Subset-137 Section 6.3.2.1.2 [UNISIG-Subset137] request an
      automatic certificate revocation by the CA in case of TCP
      disconnection during certificate distribution, this conflicts with
      this document.

   o  As of RFC 4210 [RFC4210] the messageTime is required to be
      Greenwich Mean Time coded as generalizedTime As UNISIG Subset-137
      Table 5 [UNISIG-Subset137] 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.  Therefore, UNISIG
      Subset-137 [UNISIG-Subset137] conflicts with RFC 4210 [RFC4210].
      Both time formats are described in RFC 5280 Section 4.1.2.5
      [RFC5280].





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   o  This profile requires usage of the same type of protection for all
      messages of one PKI management operation.  This means, in case the
      request message is MAC protected, also the response, certConf, and
      pkiConf messages have a MAC-based protection.  As UNISIG
      Subset-137 Table 5 [UNISIG-Subset137] specifies for the first
      certificate request MAC protection for all messages send by the
      client and signature protection for all messages send by the
      server, this conflicts with this document.

   o  The usage of caPubs is mainly allowed in combination with MAC
      protected PKI management operations.  UNISIG Subset-137 Table 12
      [UNISIG-Subset137] requires to use caPubs.  When changing to
      signature protection of the response using a certificate issued
      under the root CA that is to be transported in the caPubs field,
      this is not a secure delivery of this root CA certificate.

1.5.  Scope of this document

   This document specifies requirements on generating PKI management
   messages on the sender side.  It does not specify strictness of
   verification on the receiving side and how in detail to handle error
   cases.

   Especially on the EE side this profile aims at a lightweight protocol
   that can be implemented on more constrained devices.  On the side of
   the central PKI management entities the profile accepts higher
   resources needed.

   For the sake of robustness and preservation of security properties
   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 accept").

   When in Section 3, Section 4, and Section 5 a field of the ASN.1
   syntax as defined in RFC 4210 [RFC4210] and RFC 4211 [RFC4211] is not
   explicitly specified, it SHOULD not be used by the sending entity.
   The receiving entity MUST NOT require its absence and if present MUST
   gracefully handle its presence.

1.6.  Structure of this document

   Section 2 introduces the general PKI architecture and approach to
   certificate management using CMP that is assumed in this document.
   Then it enlists the PKI management operations specified in this
   document and describes them in general words.  The list of supported
   PKI management operations is divided into mandatory, recommended, and
   optional ones.



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   Section 3 profiles the CMP message header, protection, and extraCerts
   section as they are general elements of CMP messages.

   Section 4 profiles the exchange of CMP messages between an EE and the
   first PKI management entities.  There are various flavors of
   certificate enrollment requests optionally with polling, revocation,
   error handling, and general support PKI management operations.

   Section 5 profiles the exchange between PKI management entities.
   These are in the first place the forwarding of messages coming from
   or going to an EE.  This includes also initiating delayed delivery of
   messages, which involves polling.  Additionally, it specifies PKI
   management operations where a PKI management entity manages
   certificates on behalf of an EE or for itself.

   Section 6 outlines different mechanisms for CMP message transfer,
   namely http-based transfer as already specified in [RFC6712], using
   an additional TLS layer, or offline file-based transport.  CoAP
   [RFC7252] and piggybacking CMP messages on other protocols is out of
   scope and left for further documents.

1.7.  Convention and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS.  Lower case use of these words are not to be
   interpreted as carrying significance described in RFC 2119.

   Technical terminology is used in conformance with RFC 4210 [RFC4210],
   RFC 4211 [RFC4211], RFC 5280 [RFC5280], and IEEE 802.1AR
   [IEEE802.1AR].  The following key words are used:

   CA:  Certification authority, which issues certificates.

   RA:  Registration authority, an optional system component to which a
        CA delegates certificate management functions such as
        authorization checks.

   LRA: Local registration authority, an optional RA system component
        with proximity to the end entities.

   KGA: Key generation authority, an optional system component,
        typically co-located with an LRA, RA, or CA, that offers key
        generation services to end entities.




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   EE:  End entity, a user, device, or service that holds a PKI
        certificate.  An identifier for the EE is given as the subject
        of its certificate.

   The following terminology is reused from RFC 4210 [RFC4210] and used
   as follows:

   PKI management operation: All CMP messages belonging to one
                             transaction context.  The transaction is
                             identified in the transactionID field of
                             the message header.

   PKI management entity:    All central PKI entities like LRA, RA and
                             CA.

   PKI entity:               EEs and PKI management entities

2.  Architecture and use cases

2.1.  Solution architecture

   Typically, a machine EE will be equipped with a manufacturer issued
   certificate during production.  Such a manufacturer issued
   certificate is installed during production to identify the device
   throughout its lifetime.  This manufacturer certificate can be used
   to protect the initial enrollment of operational certificates after
   installation of the EE in a plant or industrial network.  An
   operational certificate is issued by the owner or operator of the
   device to identify the device during operation, e.g., within a
   security protocol like IPSec, TLS, or SSH.  In IEEE 802.1AR
   [IEEE802.1AR] a manufacturer certificate is called IDevID certificate
   and an operational certificate is called LDevID certificate.

   All certificate management transactions specified in this document
   are initiated by the EE.  The EE creates a CMP request message,
   protects it using its manufacturer or operational certificate, if
   available, and sends it to its locally reachable PKI component.  This
   PKI component may be an LRA, RA, or the CA, which checks the request,
   responds to it itself, or forwards the request upstream to the next
   PKI component.  In case an (L)RA changes the CMP request message
   header or body or wants to prove a successful verification or
   authorization, it can apply a protection of its own.  Especially the
   communication between an LRA and RA can be performed synchronously or
   asynchronously.  Synchronous communication describes a timely
   uninterrupted communication between two communication partners, while
   asynchronous communication is not performed in a timely consistent
   manner, e.g., because of a delayed message delivery.




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   +-----+            +-----+                +-----+            +-----+
   |     |            |     |                |     |            |     |
   | EE  |<---------->| LRA |<-------------->| RA  |<---------->| CA  |
   |     |            |     |                |     |            |     |
   +-----+            +-----+                +-----+            +-----+

           synchronous        (a)synchronous       (a)synchronous
      +----connection----+------connection------+----connection----+

           on site at                operators          service partner
   +----------plant---------+-----backend services-----+-trust center-+

                 Figure 1: Certificate management on site

   In operation environments a layered LRA-RA-CA architecture can be
   deployed, e.g., with LRAs bundling requests from multiple EEs at
   dedicated locations and one (or more than one) central RA aggregating
   the requests from multiple LRAs.  Every (L)RA in this scenario will
   have its own dedicated certificate containing an extended key usage
   as specified in CMP Updates [I-D.ietf-lamps-cmp-updates] and private
   key allowing it to protect CMP messages it processes (CMP signing
   key/certificate).  The figure above shows an architecture using one
   LRA and one RA.  It is also possible to have only an RA or multiple
   LRAs and/or RAs.  Depending on the network infrastructure, the
   communication between different PKI management entities may be
   synchronous online communication, delayed asynchronous communication,
   or even offline file transfer.

   This profile focusses on specifying the pull model, where the EE
   always requests a specific PKI management operation.  CMP response
   messages, especially in case of central key generation, as described
   in Section 4.1.6, could also be used proactively to implement the
   push model towards the EE.

   Third-party CAs typically implement different variants of CMP or even
   use proprietary interfaces for certificate management.  Therefore,
   the LRA or the RA may need to adapt the exchanged CMP messages to the
   flavor of communication required by the CA.

2.2.  Basic generic CMP message content

   Section 3 specifies the generic parts of the CMP messages as used
   later in Section 4 and Section 5.

   o  Header of a CMP message; see Section 3.1.

   o  Protection of a CMP message; see Section 3.2.




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   o  ExtraCerts field of a CMP message; see Section 3.3.

2.3.  Supported PKI management operations

   Following the outlined scope from Section 1.5, this section gives a
   brief overview of the PKI management operations specified in
   Section 4 and Section 5 and points out whether an implementation by
   compliant EE or PKI management entities is mandatory, recommended or
   optional.

2.3.1.  Mandatory PKI management operations

   The mandatory PKI management operations in this document shall limit
   the overhead of certificate management for more constrained devices
   to the most crucial types of operations.

   +--------------------------------------------------------+----------+
   | PKI management operations                              | Section  |
   +--------------------------------------------------------+----------+
   | Request a certificate from a new PKI with signature    | Section  |
   | protection                                             | 4.1.1    |
   +--------------------------------------------------------+----------+
   | Request to update an existing certificate with         | Section  |
   | signature protection                                   | 4.1.3    |
   +--------------------------------------------------------+----------+
   | Error reporting                                        | Section  |
   |                                                        | 4.3      |
   +--------------------------------------------------------+----------+

      Table 1: Mandatory End Entity focused PKI management operations

   +--------------------------------------------------------+----------+
   | PKI management operations                              | Section  |
   +--------------------------------------------------------+----------+
   | Forward messages without changes                       | Section  |
   |                                                        | 5.1.1    |
   +--------------------------------------------------------+----------+
   | Forward messages with replaced protection and keeping  | Section  |
   | the original proof-of-possession                       | 5.1.2.1  |
   +--------------------------------------------------------+----------+
   | Forward messages with replaced protection and          | Section  |
   | raVerified as proof-of-possession                      | 5.1.2.2  |
   +--------------------------------------------------------+----------+
   | Error reporting                                        | Section  |
   |                                                        | 5.3      |
   +--------------------------------------------------------+----------+

      Table 2: Mandatory LRA and RA focused PKI management operations



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2.3.2.  Recommended PKI management operations

   Additional recommended PKI management operations shall support some
   more complex scenarios, that are considered as beneficial for
   environments with more specific boundary conditions.

   +--------------------------------------------------------+----------+
   | PKI management operations                              | Section  |
   +--------------------------------------------------------+----------+
   | Request a certificate from a PKI with MAC protection   | Section  |
   |                                                        | 4.1.4    |
   +--------------------------------------------------------+----------+
   | Revoke an own certificate                              | Section  |
   |                                                        | 4.2      |
   +--------------------------------------------------------+----------+

     Table 3: Recommended End Entity focused PKI management operations

   +--------------------------------------------------------+----------+
   | PKI management operations                              | Section  |
   +--------------------------------------------------------+----------+
   | Revoke another's entities certificate                  | Section  |
   |                                                        | 5.2      |
   +--------------------------------------------------------+----------+

     Table 4: Recommended LRA and RA focused PKI management operations

2.3.3.  Optional PKI management operations

   The optional PKI management operations support specific requirements
   seen only in a subset of environments.




















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   +---------------------------------------------------------+---------+
   | PKI management operations                               | Section |
   +---------------------------------------------------------+---------+
   | Request a certificate from a trusted PKI with signature | Section |
   | protection                                              |  4.1.2  |
   +---------------------------------------------------------+---------+
   | Request a certificate from a legacy PKI using a PKCS#10 | Section |
   | [RFC2986] request                                       |  4.1.5  |
   +---------------------------------------------------------+---------+
   | Add central generation of a key pair to a certificate   | Section |
   | request. (If central key generation is supported, the   |  4.1.6  |
   | key agreement key management technique is REQUIRED to   |         |
   | be supported, and the key transport and password-based  |         |
   | key management techniques are OPTIONAL.)                |         |
   +---------------------------------------------------------+---------+
   | Handle delayed enrollment due to asynchronous message   | Section |
   | delivery                                                |  4.1.7  |
   +---------------------------------------------------------+---------+
   | Additional support messages - distribution of CA        | Section |
   | certificates, update of a root CA certificate and       |  4.4    |
   | provisioning of certificate request template            |         |
   +---------------------------------------------------------+---------+

      Table 5: Optional End Entity focused PKI management operations

   +--------------------------------------------------------+----------+
   | PKI management operations                              | Section  |
   +--------------------------------------------------------+----------+
   | Forward messages with additional protection            | Section  |
   |                                                        | 5.1.3    |
   +--------------------------------------------------------+----------+
   | Initiate delayed enrollment due to asynchronous        | Section  |
   | message delivery                                       | 5.1.4    |
   +--------------------------------------------------------+----------+

      Table 6: Optional LRA and RA focused PKI management operations

2.4.  CMP message transport

   On different links between PKI entities, e.g., EE<->RA and RA<->CA,
   different transport MAY be used.  As CMP has only very limited
   requirement regarding the mechanisms used for message transport and
   in different environments different transport mechanisms are
   supported, e.g., HTTP, CoAP, or even offline files based, this
   document requires no specific transport protocol to be supported by
   all conforming implementations.





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   HTTP transfer is RECOMMENDED to use for all PKI entities, but there
   is no transport specified as mandatory to be flexible for devices
   with special constraints to choose whatever transport is suitable.

   +--------------------------------------------------------+----------+
   | Transport                                              | Section  |
   +--------------------------------------------------------+----------+
   | Transfer CMP messages using HTTP                       | Section  |
   |                                                        | 6.1      |
   +--------------------------------------------------------+----------+

                 Table 7: Recommended transport operations

   +--------------------------------------------------------+----------+
   | Transport                                              | Section  |
   +--------------------------------------------------------+----------+
   | Transfer CMP messages using HTTPS with certificate-    | Section  |
   | based authentication                                   | 6.2      |
   +--------------------------------------------------------+----------+
   | Transfer CMP messages using HTTPS with shared-secret   | Section  |
   | based protection                                       | 6.3      |
   +--------------------------------------------------------+----------+
   | Offline CMP message transport                          | Section  |
   |                                                        | 6.4      |
   +--------------------------------------------------------+----------+
   | Transfer CMP messages using CoAP                       | Section  |
   |                                                        | 6.5      |
   +--------------------------------------------------------+----------+

                  Table 8: Optional transport operations

3.  Generic parts of the PKI message

   To reduce redundancy in the text and to ease implementation, the
   contents of the header, protection, and extraCerts fields of the CMP
   messages used in the transactions specified in Section 4 and
   Section 5 are standardized to the maximum extent possible.
   Therefore, the generic parts of a CMP message are described centrally
   in this section.












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   As described in section 5.1 of [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 Section 3.1 to Section 3.3.

   In case a specific CMP message needs different contents in the
   header, protection, or extraCerts fields, the differences are
   described in the respective message.

   The CMP message body contains the message-specific information.  It
   is described in the context of Section 4 and Section 5.

   The behavior in case an error occurs while handling a CMP message is
   described in Section 5.3.

3.1.  General description of the CMP message header

   This section describes the generic header field of all CMP messages
   with signature-based protection.  The only variations described here
   are in the fields recipient, transactionID, and recipNonce of the
   first message of a PKI management operation.

   In case a message has MAC-based protection the changes are described
   in the respective section.  The variations will affect the fields
   sender, protectionAlg, and senderKID.

   For requirements about proper random number generation please refer
   to [RFC4086].  Any message-specific fields or variations are
   described in the respective sections of this chapter.



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   header
     pvno                        REQUIRED
       -- MUST be set to 2 to indicate CMP V2
     sender                      REQUIRED
       -- MUST contain a name representing the originator of the message
       -- SHOULD be the subject of the protection certificate,
       -- the certificate for the private key used to sign the message
     recipient                   REQUIRED
       -- SHOULD be the name of the intended recipient and
       -- MAY be a NULL-DN, i.e., has a zero-length SEQUENCE OF
       -- RelativeDistinguishedNames, if the sender does not know the
       -- DN of the recipient
       -- If this is the first message of a transaction: SHOULD be the
       -- subject of the issuing CA certificate
       -- In all other messages: SHOULD be the same name as in the
       -- sender field of the previous message in this transaction
     messageTime                 RECOMMENDED
       -- MUST be the time at which the message was produced, if
       -- present
     protectionAlg               REQUIRED
       -- MUST be the algorithm identifier of the signature algorithm or
       -- id-PasswordBasedMac algorithm used for calculation of the
       -- protection bits
       -- The signature algorithm MUST be consistent with the
       -- subjectPublicKeyInfo field of the signer's certificate
       -- The hash algorithm used SHOULD be SHA-256
       algorithm                 REQUIRED
       -- MUST be the OID of the signature algorithm, like
       -- sha256WithRSAEncryption or ecdsa-with-SHA256, or
       -- id-PasswordBasedMac
     senderKID                   RECOMMENDED
       -- MUST be the SubjectKeyIdentifier, if available, of the
       -- protection certificate
     transactionID               REQUIRED
       -- If this is the first message of a transaction:
       -- MUST be 128 bits of random data for the start of a
       -- transaction to reduce 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
       -- transaction
     senderNonce                 REQUIRED
       -- MUST be cryptographically secure and fresh 128 random bits
     recipNonce                  RECOMMENDED
       -- If this is the first message of a transaction: SHOULD be
       -- absent
       -- In all other messages: MUST be present and contain the value
       -- from senderNonce of the previous message in the same



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       -- transaction
     generalInfo                 OPTIONAL
       implicitConfirm           OPTIONAL
       -- The field is optional though it only applies to
       -- ir/cr/kur/p10cr requests and ip/cp/kup response messages
       -- Add to request messages to request omit sending certConf
       -- message
       -- See [RFC4210] Section 5.1.1.1.
       -- Add to response messages to confirm omit sending certConf
       -- message
         ImplicitConfirmValue    REQUIRED
       -- ImplicitConfirmValue of the request message MUST be NULL if
       -- the EE wants to request not to send a confirmation message
       -- ImplicitConfirmValue MUST be set to NULL if the (L)RA/CA
       -- wants to grant not sending a confirmation message

   < TBD: As discussed at IETF 108, the normative naming of specific
   algorithms, e.g., like SHA-256 in the protectionAlg field should be
   moved to a CMP Algorithms Draft. >

3.2.  General description of the CMP message protection

   This section describes the generic protection field of all CMP
   messages with signature-based protection.  The certificate for the
   private key used to sign a CMP message is called 'protection
   certificate'.

   protection                    RECOMMENDED
       -- MUST contain the signature calculated using the signature
       -- algorithm specified in protectionAlg

   Generally, CMP message protection is required for CMP messages, but
   there are cases where protection of error messages as specified in
   Section 4.3 and Section 5.3 is not possible and therefore MAY be
   omitted.

   For MAC-based protection as specified in Section 4.1.4 major
   differences apply as described in the respective section.

   The CMP message protection provides, if available, message origin
   authentication and integrity protection for the CMP message header
   and body.  The CMP message extraCerts is not covered by this
   protection.

   NOTE: The extended key usages specified in CMP Updates
   [I-D.ietf-lamps-cmp-updates] can be used for authorization of a
   sending PKI management entity.




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   NOTE: The requirements for checking certificates given in [RFC5280]
   MUST be followed for the CMP message protection.  In case the CMP
   signer certificate is not the CA certificate that signed the newly
   issued certificate, certificate status checking SHOULD be used for
   the CMP signer certificates of communication partners.

3.3.  General description of CMP message extraCerts

   This section describes the generic extraCerts field of all CMP
   messages with signature-based protection.  If extraCerts are
   required, recommended, or optional is specified in the respective PKI
   management operation.

   extraCerts
       -- SHOULD contain the protection certificate together with its
       -- chain, if needed and the self-signed root certificate SHOULD
       -- be omitted
       -- If present, the first certificate in this field MUST
       -- be the protection certificate and each following certificate
       -- SHOULD directly certify the one immediately preceding it.
       -- Self-signed certificates SHOULD be omitted from extraCerts
       -- and MUST NOT be trusted based on the listing in extraCerts
       -- in any case

   Note: For maximum compatibility, all implementations SHOULD be
   prepared to handle potentially additional and arbitrary orderings of
   the certificates, except that the protection certificate is the first
   certificate in extraCerts.

4.  End Entity focused PKI management operations

   This chapter focuses on the communication of the EE and the first PKI
   management entities it talks to.  Depending on the network and PKI
   solution, this will either be the LRA, the RA or the CA.

   Profiles of the Certificate Management Protocol (CMP) [RFC4210]
   handled in this section cover the following PKI management
   operations:

   o  Requesting a certificate from a PKI with variations like initial
      requests and updating, central key generation and different
      protection means

   o  Revocation of a certificate

   o  General messages for further support functions





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   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 4.

   The behavior in case an error occurs is described in Section 4.3.

   This chapter is aligned to Appendix D and Appendix E of [RFC4210].
   The general rules for interpretation stated in Appendix D.1 in
   [RFC4210] need to be applied here, too.

   This document does not mandate any specific supported algorithms like
   Appendix D.2 of [RFC4210], [ETSI-TS133310], and [UNISIG-Subset137]
   do.  Using the message sequences described here require agreement
   upon the algorithms to support and thus the algorithm identifiers for
   the specific target environment.

4.1.  Requesting a new certificate from a PKI

   There are different approaches to request a certificate from a PKI.

   These approaches differ on the one hand in the way the EE can
   authenticate itself to the PKI it wishes to get a new certificate
   from and on the other hand in its capabilities to generate a proper
   new key pair.  The authentication means may be as follows:

   o  Using a certificate from a trusted PKI and the corresponding
      private key, e.g., a manufacturer issued certificate

   o  Using the certificate to be updated and the corresponding private
      key

   o  Using a shared secret known to the EE and the PKI

   Typically, such EE requests a certificate from a CA.  When the PKI
   management entity responds with a message containing a certificate,
   the EE MUST reply with a confirmation message.  The PKI management
   entity then MUST send confirmation back, closing the transaction.

   The message sequences in this section allow the EE to request
   certification of a locally generated public-private key pair.  For
   requirements about proper random number and key generation please
   refer to [RFC4086].  The EE MUST provide a signature-based proof-of-
   possession of the private key associated with the public key
   contained in the certificate request as defined by [RFC4211] section
   4.1 case 3.  To this end it is assumed that the private key can
   technically be used as signing key.  The most commonly used
   algorithms are RSA and ECDSA, which can technically be used for




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   signature calculation regardless of potentially intended restrictions
   of the key usage.

   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 POPO.  The PKI management entity
   needs to verify whether this EE is authorized to obtain a certificate
   with the requested subject and other fields and extensions.
   Especially when removing the protection provided by the EE and
   applying a new protection, the PKI management entity MUST verify in
   particular the included proof-of-possession self-signature of the
   certTemplate using the public key of the requested certificate and
   MUST check that the EE, as authenticated by the message protection,
   is authorized to request a certificate with the subject as specified
   in the certTemplate (see Section 5.1.2).

   There are several ways to install the Root CA certificate of a new
   PKI on an EE.  The installation can be performed in an out-of-band
   manner, using general messages, a voucher [RFC8366], or other formats
   for enrollment, or in-band of CMP by the caPubs field in the
   certificate response message.  In case the installation of the new
   root CA certificate is performed using the caPubs field, the
   certificate response message MUST be properly authenticated, and the
   sender of this message MUST be authorized to install new root CA
   certificates on the EE.  This authorization can be indicated by using
   pre-shared keys for the CMP message protection.

4.1.1.  Request a certificate from a new PKI with signature protection

   This PKI management operation should be used by an EE to request a
   certificate of a new PKI using an existing certificate from an
   external PKI, e.g., a manufacturer issued IDevID certificate
   [IEEE802.1AR], to prove its identity to the new PKI.  The EE already
   has established trust in this new PKI it is about to enroll to, e.g.,
   by voucher exchange or configuration means.  The certificate request
   message is signature-protected using the existing certificate from
   the external PKI.

   Preconditions:

   1  The EE MUST have a certificate enrolled by an external PKI in
      advance to this PKI management operation to authenticate itself to
      the PKI management entity using signature-based protection, e.g.,
      using a manufacturer issued certificate.

   2  The EE SHOULD know the subject name of the new CA it requests a
      certificate from; this name MAY be established using an enrollment
      voucher, the issuer field from a CertReqTemplate response message,



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      or other configuration means.  If the EE does not know the name of
      the CA, the PKI management entity MUST know where to route this
      request to.

   3  The EE MUST authenticate responses from the PKI management entity;
      trust MAY be established using an enrollment voucher or other
      configuration means.

   4  The PKI management entity MUST trust the external PKI the EE uses
      to authenticate itself; trust MAY be established using some
      configuration means.

   This PKI management operation is like that given in [RFC4210]
   Appendix E.7.

   Message flow:

   Step# EE                                  PKI management entity
     1   format ir
     2                      ->   ir      ->
     3                                        handle, re-protect or
                                                forward ir
     4                                        format or receive ip
     5                                        possibly grant implicit
                                                confirm
     6                      <-   ip      <-
     7   handle ip
     8                                        In case of status
                                                "rejection" in the
                                                ip message, no certConf
                                                and pkiConf are sent
     9   format certConf (optional)
    10                      ->   certConf ->
    11                                        handle, re-protect or
                                                forward certConf
    12                                        format or receive pkiConf
    13                      <-   pkiconf  <-
    14   handle pkiConf (optional)

   For this PKI management operation, the EE MUST include exactly one
   single CertReqMsg in the ir.  If more certificates are required,
   further requests MUST be sent using separate CMP messages.  If the EE
   wants to omit sending a certificate confirmation message after
   receiving the ip to reduce the number of protocol messages exchanged
   in this PKI management operation, it MUST request this by including
   the implicitConfirm extension in the ir.





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   If the CA accepts the certificate request it MUST return the new
   certificate in the certifiedKeyPair field of the ip message.  If the
   EE requested to omit sending a certConf message after receiving the
   ip, the PKI management entity MAY confirm it by also including the
   implicitConfirm extension or MAY rejects it by omitting the
   implicitConfirm field in the ip.

   If the EE did not request implicit confirmation or the request was
   not granted by the PKI management entity the confirmation as follows
   MUST be performed.  If the EE successfully receives the certificate
   and accepts it, the EE MUST send a certConf message, which MUST be
   answered by the PKI management entity 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.

   If the certificate request was refused by the CA, the PKI management
   entity must return an ip message containing the status code
   "rejection" and no certifiedKeyPair field.  Such an ip message MUST
   NOT be followed by the certConf and pkiConf messages.

   Detailed message description:

   Certification Request -- ir

   Field                         Value

   header
       -- As described in section 3.1

   body
       -- The request of the EE for a new certificate
     ir                          REQUIRED
       -- MUST be exactly one CertReqMsg
       -- If more certificates are required, further requests MUST be
       -- packaged in separate PKI Messages
       certReq                   REQUIRED
         certReqId               REQUIRED
       -- MUST be set to 0
         certTemplate            REQUIRED
           version               OPTIONAL
       -- MUST be 2 if supplied.
           subject               REQUIRED
       -- The EE subject name MUST be carried in the subject field
       -- and/or the subjectAltName extension.
       -- If subject name is present only in the subjectAltName
       -- extension, then the subject field MUST be a NULL-DN
           publicKey             REQUIRED
             algorithm           REQUIRED



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       -- MUST include the subject public key algorithm ID and value
       -- In case a central key generation is requested, this field
       -- contains the algorithm and parameter preferences of the
       -- requesting entity regarding the to-be-generated key pair
             subjectPublicKey    REQUIRED
       -- MUST contain the public key to be included into the requested
       -- certificate in case of local key-generation
       -- MUST contain a zero-length BIT STRING in case a 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                      REQUIRED
         POPOSigningKey          OPTIONAL
       -- MUST be used in case subjectPublicKey contains a public key
       -- MUST be absent in case subjectPublicKey contains a
       -- zero-length BIT STRING
           poposkInput           PROHIBITED
       -- MUST NOT be used because subject and publicKey are both
       -- present in the certTemplate
           algorithmIdentifier   REQUIRED
       -- The signature algorithm MUST be consistent with the
       -- publicKey field of the certTemplate
       -- The hash algorithm used SHOULD be SHA-256
           signature             REQUIRED
       -- MUST be the signature computed over the DER-encoded
       -- certTemplate

   protection                    REQUIRED
       -- As described in section 3.2

   extraCerts                    REQUIRED
       -- As described in section 3.3


   Certification Response -- ip

   Field                         Value

   header
       -- As described in section 3.1

   body
       -- The response of the CA to the request as appropriate
     ip                          REQUIRED



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       caPubs                    OPTIONAL
       -- MAY be used
       -- If used it MUST contain only the root certificate of the
       -- certificate contained in certOrEncCert
       response                  REQUIRED
       -- MUST be exactly one CertResponse
         certReqId               REQUIRED
       -- MUST be set to 0
         status                  REQUIRED
       -- PKIStatusInfo structure MUST be present
           status                REQUIRED
       -- positive values allowed: "accepted", "grantedWithMods"
       -- negative values allowed: "rejection"
       -- In case of rejection certConf and pkiConf messages MUST NOT
       -- be sent
           statusString          OPTIONAL
       -- MAY be any human-readable text for debugging, logging or to
       -- display in a GUI
           failInfo              OPTIONAL
       -- MUST be present if status is "rejection" and in this case
       -- the transaction MUST be terminated
       -- MUST be absent if the 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 when certifiedKeyPair is present
             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
       -- MUST contain the encrypted private key in an EnvelopedData
       -- structure as specified in section 5.1.5 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, the self-signed root certificate SHOULD be
       -- omitted
       -- Duplicate certificates MAY be omitted





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   Certificate Confirmation -- certConf

   Field                         Value

   header
       -- As described in section 3.1

   body
       -- The message of the EE sends confirmation to the PKI
       -- management entity to accept or reject the issued certificates
     certConf                    REQUIRED
       -- MUST be exactly one CertStatus
       CertStatus                REQUIRED
         certHash                REQUIRED
       -- MUST be the hash of the certificate, using the same hash
       -- algorithm as used to create the certificate signature
         certReqId               REQUIRED
       -- MUST be set to 0
         status                  RECOMMENDED
       -- PKIStatusInfo structure SHOULD be present
       -- Omission indicates acceptance of the indicated certificate
           status                REQUIRED
       -- positive values allowed: "accepted"
       -- negative values allowed: "rejection"
           statusString          OPTIONAL
       -- MAY be any human-readable text for debugging, logging, or to
       -- display in a GUI
           failInfo              OPTIONAL
       -- MUST be present if status is "rejection"
       -- MUST be absent if the status is "accepted"

   protection                    REQUIRED
       -- As described in section 3.2
       -- MUST use the same certificate as for protection of the ir

   extraCerts                    RECOMMENDED
       -- SHOULD contain the protection certificate together with its
       -- chain, but MAY be omitted if the message size is critical and
       -- the PKI management entity did cash the extraCerts from the ir
       -- If present, the first certificate in this field MUST be the
       -- certificate used for signing this message
       -- Self-signed certificates SHOULD NOT be included in
       -- extraCerts and
       -- MUST NOT be trusted based on the listing in extraCerts in
       -- any case


   PKI Confirmation -- pkiconf



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   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
       -- SHOULD use the same certificate as for protection of the ip

   extraCerts                    RECOMMENDED
       -- SHOULD contain the protection certificate together with its
       -- chain, but MAY be omitted if the message size is critical and
       -- the PKI management entity did cash the extraCerts from the ip
       -- If present, the first certificate in this field MUST be the
       -- certificate used for signing this message
       -- Self-signed certificates SHOULD NOT be included in extraCerts
       -- and
       -- MUST NOT be trusted based on the listing in extraCerts in
       -- any case

4.1.2.  Request a certificate from a trusted PKI with signature
        protection

   This PKI management operation should be used by an EE to request an
   additional certificate of the same PKI it already has certificates
   from.  The EE uses one of these existing certificates to prove its
   identity.  The certificate request message is signature-protected
   using this certificate.

   The general message flow for this PKI management operation is the
   same as given in Section 4.1.1.

   Preconditions:

   1  The EE MUST have a certificate enrolled by the PKI it requests
      another certificate from in advance to this PKI management
      operation to authenticate itself to the PKI management entity
      using signature-based protection.

   2  The EE SHOULD know the subject name of the CA it requests a
      certificate from; this name MAY be established using an enrollment
      voucher, the issuer field from a CertReqTemplate response message,
      or other configuration means.  If the EE does not know the name of




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      the CA, the PKI management entity MUST know where to route this
      request to.

   3  The EE MUST authenticate responses from the PKI management entity;
      trust MUST be established using an enrollment voucher or other
      configuration means.

   4  The PKI management entity MUST trust the current PKI; trust MAY be
      established using some configuration means.

   The message sequence for this PKI management operation is like that
   given in [RFC4210] Appendix D.5.

   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 cr and cp,
      respectively.

   2  The caPubs field in the cp message SHOULD be absent.

4.1.3.  Update an existing certificate with signature protection

   This PKI management operation should be used by an EE to request an
   update of one of the certificates it already has and that is still
   valid.  The EE uses the certificate it wishes to update to prove its
   identity.  The certificate request message is signature-protected
   using this certificate.

   The general message flow for this PKI management operation is the
   same as given in Section 4.1.1.

   Preconditions:

   1  The certificate the EE wishes to update MUST NOT be expired or
      revoked.

   2  A new public-private key pair SHOULD be used.

   The message sequence for this PKI management operation is like that
   given in [RFC4210] Appendix D.6.

   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.




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   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 publicKey of the
      EE only.

   5  The oldCertId control SHOULD 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 control is added
   right after the certTemplate.

       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.  Request a certificate from a PKI with MAC protection

   This PKI management operation should be used by an EE to request a
   certificate of a new PKI without having a certificate to prove its
   identity to the target PKI, but there is a shared secret established
   between the EE and the PKI.  Therefore, the initialization request is
   MAC-protected using this shared secret.  The PKI management entity
   checking the MAC-protection SHOULD replace this protection according
   to Section 5.1.2 in case the next hop does not know the shared
   secret.

   For requirements with regard to proper random number and key
   generation please refer to [RFC4086].

   The general message flow for this PKI management operation is the
   same as given in Section 4.1.1.

   Preconditions:






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   1  The EE and the PKI management entity MUST share a symmetric key,
      this MAY be established by a service technician during initial
      local configuration.

   2  The EE SHOULD know the subject name of the new CA it requests a
      certificate from; this name MAY be established using an enrollment
      voucher, the issuer field from a CertReqTemplate response message,
      or other configuration means.  If the EE does not know the name of
      the CA, the PKI management entity MUST know where to route this
      request to.

   3  The EE MUST authenticate responses from the PKI management entity;
      trust MAY be established using the shared symmetric key.

   The message sequence for this PKI management operation is like that
   given in [RFC4210] Appendix D.4.

   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 calculated using Message
      Authentication Code (MAC); the protectionAlg field MUST be id-
      PasswordBasedMac as described in section 5.1.3.1 of [RFC4210].

   2  The sender MUST contain a name representing the originator of the
      message.  The senderKID MUST contain a reference all participating
      entities can use to identify the symmetric key used for the
      protection, e.g., the username of the EE.

   3  The extraCerts of the ir, certConf, and pkiConf messages MUST be
      absent.

   4  The extraCerts of the ip message MUST contain the chain of the
      issued certificate and root certificates SHOULD not be included
      and MUST NOT be directly trusted in any case.

   Part of the protectionAlg structure, where the algorithm identifier
   MUST be id-PasswordBasedMac, is a PBMParameter sequence.  The fields
   of PBMParameter SHOULD remain constant for message protection
   throughout this PKI management operation to reduce the computational
   overhead.










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       PBMParameter              REQUIRED
         salt                    REQUIRED
       -- MUST be the random value to salt the secret key
         owf                     REQUIRED
       -- MUST be the algorithm identifier for the one-way function
       -- used
       -- The one-way function SHA-1 MUST be supported due to
       -- [RFC4211] requirements, but SHOULD NOT be used any more
       -- SHA-256 SHOULD be used instead
         iterationCount          REQUIRED
       -- MUST be a limited number of times the one-way function is
       -- applied
       -- To prevent brute force and dictionary attacks a reasonable
       -- high number SHOULD be used
         mac                     REQUIRED
       -- MUST be the algorithm identifier of the MAC algorithm used
       -- The MAC function HMAC-SHA1 MUST be supported due to
       -- [RFC4211] requirements, but SHOULD NOT be used any more
       -- HMAC-SHA-256 SHOULD be used instead

4.1.5.  Request a certificate from a legacy PKI using PKCS#10 request

   This PKI management operation should be used by an EE to request a
   certificate of a legacy PKI only capable to process PKCS#10 [RFC2986]
   certification requests.  The EE can prove its identity to the target
   PKI by using various protection means as described in Section 4.1.1
   or Section 4.1.4.

   In contrast to the other PKI management operations described in
   Section 4.1, this transaction uses PKCS#10 [RFC2986] instead of CRMF
   [RFC4211] for the certificate request for compatibility reasons with
   legacy CA systems that require a PKCS#10 certificate request and
   cannot process CRMF [RFC4211] requests.  In such case the PKI
   management entity MUST extract the PKCS#10 certificate request from
   the p10cr and provides it separately to the CA.

   The general message flow for this PKI management operation is the
   same as given in Section 4.1.1, but the public key is contained in
   the subjectPKInfo of the PKCS#10 certificate request.

   Preconditions:

   1  The EE MUST either have a certificate enrolled from this or any
      other accepted PKI, or a shared secret known to the PKI and the EE
      to authenticate itself to the RA.

   2  The EE SHOULD know the subject name of the CA it requests a
      certificate from; this name MAY be established using an enrollment



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      voucher, the issuer field from a CertReqTemplate response message,
      or other configuration means.  If the EE does not know the name of
      the CA, the RA MUST know where to route this request to.

   3  The EE MUST authenticate responses from the RA; trust MAY be
      established by an available root certificate, using an enrollment
      voucher, or other configuration means.

   4  The RA MUST trust the current or the PKI the EE uses to
      authenticate itself; trust MAY be established by a corresponding
      available root certificate or using some configuration means.

   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 p10cr and cp,
      respectively.

   2  The certReqId in the cp message MUST be 0.

   3  The caPubs field in the cp message SHOULD be absent.






























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   Detailed description of the p10cr message:

   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 set to 0 to indicate PKCS#10 V1.7
         subject                 REQUIRED
       -- MUST contain the suggested subject name of the EE
         subjectPKInfo           REQUIRED
           algorithm             REQUIRED
       -- MUST include the subject public key algorithm ID
           subjectPublicKey      REQUIRED
       -- MUST include the subject public key algorithm value
         attributes              OPTIONAL
       -- MAY contain a set of end-entity-specific fields or X.509
       -- extensions to be included in the requested certificate or used
       -- otherwise
       signatureAlgorithm        REQUIRED
       -- The signature algorithm MUST be consistent with the
       -- subjectPKInfo field. The hash algorithm used SHOULD be SHA-256
       signature                 REQUIRED
       -- MUST containing the self-signature for proof-of-possession

   protection                    REQUIRED
       -- As described in section 3.2

   extraCerts                    REQUIRED
       -- As described in section 3.3

4.1.6.  Generate the key pair centrally at the PKI management entity

   This functional extension can be applied in combination with
   certificate enrollment as described in Section 4.1.1, Section 4.1.2,
   and Section 4.1.4.  The functional extension can be used in case an
   EE is not able or is not willing to generate its new public-private
   key pair itself.  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 have a



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   certificate containing the additional extended key usage extension
   id-kp-cmKGA to be identified by the EE as a legitimate key-generation
   authority.  In case the KGA generated the new key pair on behalf of
   the EE, it can use Section 4.1.1, Section 4.1.2, or Section 4.1.4 to
   request the certificate for this key pair as usual.

   Generally speaking, in a machine-to-machine scenario 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
   certification request, this is to make sure that only the entity
   identified in the newly issued certificate is the only entity who
   ever holt the private key.

   There are some cases where an EE is not able or not willing to
   locally generate the new key pair.  Reasons for this may be the
   following:

   o  Lack of sufficient initial entropy.

   Note: Good random numbers are not only needed 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 entropy for
   the RNG seed to guarantee good initial pseudo-random number
   generation.  May be this is not the case at the time of requesting a
   certificate during manufacturing.

   o  Due to lack of computational resources, e.g., in case of RSA keys.

   Note: As key generation could be performed in advance to the
   certificate enrollment communication, it is often not time critical.

   Note: As mentioned in Section 2.1 central key generation may be
   required in a push model, where the certificate response message is
   transferred by the PKI management entity to the EE without receiving
   a previous request message.

   If the EE wishes to request central key generation, it MUST fill the
   subjectPublicKey field in the certTemplate structure of the request
   message with a zero-length BIT STRING.  This indicates 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 is being extended from EncryptedValue to EncryptedKey by CMP
   Updates [I-D.ietf-lamps-cmp-updates], also the alternative
   EnvelopedData can be used.  In CRMF Section 2.1.9 [RFC4211] the use
   of EncryptedValue has been deprecated in favor of the EnvelopedData



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   structure.  Therefore, this profile specifies using EnvelopedData as
   specified in CMS Section 6 [RFC5652].

                   +----------------------------------+
                   | EnvelopedData                    |
                   | [RFC5652] section 6              |
                   | +------------------------------+ |
                   | | SignedData                   | |
                   | | [RFC5652] section 5          | |
                   | | +--------------------------+ | |
                   | | | AsymmetricKeyPackage     | | |
                   | | | [RFC5958]                | | |
                   | | | +----------------------+ | | |
                   | | | | privateKey           | | | |
                   | | | | OCTET STRING         | | | |
                   | | | +----------------------+ | | |
                   | | +--------------------------+ | |
                   | +------------------------------+ |
                   +----------------------------------+

                 Figure 3: Encrypted private key container

   The PKI management entity delivers the private key in the privateKey
   field in the certifiedKeyPair structure of the response message also
   containing the newly issued certificate.

   The private key MUST be provided as an AsymmetricKeyPackage structure
   as defined in RFC 5958 [RFC5958].

   This AsymmetricKeyPackage structure MUST be wrapped in a SignedData
   structure, as specified in CMS Section 5 [RFC5652], signed by the KGA
   generating the key pair.  The signature MUST be performed using a CMP
   signer certificate asserting the extended key usage kp-id-cmKGA as
   described in CMP Updates [I-D.ietf-lamps-cmp-updates] to show the
   authorization to generate key pairs on behalf of an EE.

   Note: In case of using password-based key management technique as
   described in Section 4.1.6.3 it may not be possible or meaningful to
   the EE to validate the KGA signature in the SignedData structure as
   shares secrets are used for initial authentication.  In this case the
   EE MAY omit this signature validation.

   This 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.

   Note: Instead of the specification in CMP Appendix D 4.4 [RFC4210]
   this content-encryption key is not generated on the EE side.  As we



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   just mentioned, central key generation should only be used in this
   profile in case of lack of randomness on the EE.

   As part of the EnvelopedData structure this content-encryption key
   MUST be securely provided 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 choose to protect the request message, see CMP Updates section 3.4
   [I-D.ietf-lamps-cmp-updates] for more details on which key management
   technique to use.

   o  Signature protected request message:

      *  Using a certificate that contains a key usage extension
         asserting keyAgreement: 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 signing
         the respective request message contains the key usage
         keyAgreement.  If the certificate also contains the key usage
         keyEncipherment, the key transport key management technique
         SHALL NOT be used.

      *  Using a certificate that contains a key usage extension
         asserting keyEncipherment: 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 signing
         the respective request message contains the key usage
         keyEncipherment and not keyAgreement.

   o  MAC protected request message: The content-encryption key SHALL be
      protected using the password-based key management technique, see
      Section 4.1.6.3, only if the EE used MAC protection for the
      respected request message.

   The key agreement key management technique can be supported by most
   signature algorithms, as key transport key management technique can
   only be supported by a very limited number of algorithms.  The
   password-based key management technique shall only be used in
   combination with MAC protection, which is a side-line in this
   document.  Therefore, if central key generation is supported, the
   support of the key agreement key management technique is REQUIRED and
   the support of key transport and password-based key management
   techniques are OPTIONAL.

   For encrypting the SignedData structure containing the private key a
   fresh content-encryption key MUST be generated with enough entropy
   with regard to the used symmetric key-encryption algorithm.




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   Note: Depending on the lifetime of the certificate and the
   criticality of the generated private key, it is advisable to use the
   strongest available symmetric encryption algorithm.  Therefore, this
   specification recommends using at least AES-256.

   The detailed description of the privateKey field looks like this:

           privateKey            OPTIONAL
       -- MUST be an EnvelopedData structure as specified in
       -- CMS [RFC5652] section 6
             version             REQUIRED
       -- MUST be set to 2
             recipientInfos      REQUIRED
       -- MUST be exactly one RecipientInfo
               recipientInfo     REQUIRED
       -- MUST be either KeyAgreeRecipientInfo (see section 5.1.5.1),
       -- KeyTransRecipientInfo (see section 5.1.5.2), or
       -- PasswordRecipientInfo (see section 5.1.5.3) is used
       -- If central key generation is supported, support of
       -- KeyAgreeRecipientInfo is REQUIRED and support of
       -- KeyTransRecipientInfo and PasswordRecipientInfo are OPTIONAL
             encryptedContentInfo
                                 REQUIRED
               contentType       REQUIRED
       -- MUST be id-signedData
               contentEncryptionAlgorithm
                                 REQUIRED
       -- MUST be the algorithm identifier of the symmetric
       -- content-encryption algorithm used
       -- As private keys need long-term protection, the use of AES-256
       -- or a stronger symmetric algorithm is RECOMMENDED
               encryptedContent  REQUIRED
       -- MUST be the signedData structure as specified in
       -- CMS [RFC5652] section 5 in encrypted form
                 version         REQUIRED
       -- MUST be set to 3
                 digestAlgorithms
                                 REQUIRED
       -- MUST be exactly one digestAlgorithm identifier
                   digestAlgorithmIdentifier
                                 REQUIRED
       -- MUST be the OID of the digest algorithm used for generating
       -- the signature
       -- The hash algorithm used SHOULD be SHA-256
                 encapContentInfo
                                 REQUIRED
       -- MUST be the content that is to be signed
                   contentType   REQUIRED



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       -- MUST be id-ct-KP-aKeyPackage as specified in [RFC5958]
                   content       REQUIRED
                     AsymmetricKeyPackage
                                 REQUIRED
                       OneAsymmetricKey
                                 REQUIRED
       -- MUST be exactly one asymmetric key package
                         version REQUIRED
       -- The version MUST be v2
                         privateKeyAlgorithm
                                 REQUIRED
       -- The privateKeyAlgorithm field MUST contain
       -- the OID of the asymmetric key pair algorithm
                         privateKey
                                 REQUIRED
       -- The privateKey MUST be in the privateKey field
                         Attributes
                                 OPTIONAL
       -- The attributes field SHOULD not be used
                         publicKey
                                 REQUIRED
       -- The publicKey MUST be in the publicKey field
                 certificates    REQUIRED
       -- SHOULD contain the certificate, for the private key used
       -- to sign the content, together with its chain
       -- If present, the first certificate in this field MUST
       -- be the certificate used for signing this content
       -- Self-signed certificates SHOULD NOT be included
       -- and MUST NOT be trusted based on the listing in any case
                 crls            OPTIONAL
       -- MAY be present to provide status information on the signer or
       -- its CA certificates
                 signerInfos     REQUIRED
       -- MUST be exactly one signerInfo
                   version       REQUIRED
       -- MUST be set to 3
                   sid           REQUIRED
                     subjectKeyIdentifier
                                 REQUIRED
       -- MUST be the subjectKeyIdentifier of the signer's certificate
                   digestAlgorithm
                                 REQUIRED
       -- MUST be the same OID as in digest algorithm
                   signatureAlgorithm
                                 REQUIRED
       -- MUST be the algorithm identifier of the signature algorithm
       -- used for calculation of the signature bits,
       -- like sha256WithRSAEncryption or ecdsa-with-SHA256



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       -- The signature algorithm MUST be consistent with the
       -- subjectPublicKeyInfo field of the signer's certificate
                   signature     REQUIRED
       -- MUST be the result of the digital signature generation

4.1.6.1.  Using key agreement key management technique

   This key management technique can be applied in combination with the
   PKI management operations specified in Section 4.1.1 to Section 4.1.3
   using signature-based protected CMP messages.  The public key of the
   EE certificate used for the signature-based protection of the request
   message MUST also be used for the Ephemeral-Static Diffie-Hellmann
   key establishment of the content-encryption key.  To use this key
   management technique the KeyAgreeRecipientInfo structure MUST be used
   in the contentInfo field.

   The KeyAgreeRecipientInfo structure included into the EnvelopedData
   structure is specified in CMS Section 6.2.2 [RFC5652].

































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   The detailed description of the KeyAgreeRecipientInfo structure looks
   like this:

               recipientInfo     REQUIRED
       -- MUST be KeyAgreeRecipientInfo as specified in
                 version         REQUIRED
       -- MUST be set to 3
                 originator      REQUIRED
       -- MUST contain the originatorKey sequence
                   algorithm     REQUIRED
       -- MUST be the algorithm identifier of the
       -- static-ephemeral Diffie-Hellmann algorithm
                   publicKey     REQUIRED
       -- MUST be the ephemeral public key of the sending party
                 ukm             OPTIONAL
       -- MUST be used when 1-pass ECMQV is used
                 keyEncryptionAlgorithm
                                 REQUIRED
       -- MUST be the same as in the contentEncryptionAlgorithm field
                 recipientEncryptedKeys
                                 REQUIRED
       -- MUST be exactly one recipientEncryptedKey sequence
                   recipientEncryptedKey
                                 REQUIRED
                     rid         REQUIRED
                       rKeyId    REQUIRED
                         subjectKeyID
                                 REQUIRED
       -- MUST contain the same value as the senderKID in the
       -- respective request messages
                     encryptedKey
                                 REQUIRED
       -- MUST be the encrypted content-encryption key

4.1.6.2.  Using key transport key management technique

   This key management technique can be applied in combination with the
   PKI management operations specified in Section 4.1.1 to Section 4.1.3
   using signature-based protected CMP messages.  The public key of the
   EE certificate used for the signature-based protection of the request
   message MUST also be used for key encipherment of the content-
   encryption key.  To use this key management technique the
   KeyTransRecipientInfo structure MUST be used in the contentInfo
   field.

   The KeyTransRecipientInfo structure included into the EnvelopedData
   structure is specified in CMS Section 6.2.1 [RFC5652].




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   The detailed description of the KeyTransRecipientInfo structure looks
   like this:

               recipientInfo     REQUIRED
       -- MUST be KeyTransRecipientInfo as specified in
       -- CMS section 6.2.1 [RFC5652]
                 version         REQUIRED
       -- MUST be set to 2
                 rid             REQUIRED
                   subjectKeyIdentifier
                                 REQUIRED
       -- MUST contain the same value as the senderKID in the respective
       -- request messages
                 keyEncryptionAlgorithm
                                 REQUIRED
       -- MUST contain the key encryption algorithm identifier used for
       -- public key encryption
                 encryptedKey    REQUIRED
       -- MUST be the encrypted content-encryption key

4.1.6.3.  Using password-based key management technique

   This key management technique can be applied in combination with the
   PKI management operation specified in Section 4.1.4 using MAC
   protected CMP messages.  The shared secret used for the MAC
   protection MUST also be used for the encryption of the content-
   encryption key but with a different salt.  To use this key management
   technique the PasswordRecipientInfo structure MUST be used in the
   contentInfo field.

   The PasswordRecipientInfo structure included into the EnvelopedData
   structure is specified in CMS Section 6.2.4 [RFC5652].



















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   The detailed description of the PasswordRecipientInfo structure looks
   like this:

               recipientInfo     REQUIRED
       -- MUST be PasswordRecipientInfo as specified in
       -- CMS section 6.2.4 [RFC5652]
                 version         REQUIRED
       -- MUST be set to 0
                 keyDerivationAlgorithm
                                 REQUIRED
       -- MUST be set to id-PBKDF2 as specified in [RFC8018]
       -- The same shared secret MUST be used than used in
       -- PBMParameter data structure for the MAC protection in the
       -- header of this message
                   salt          REQUIRED
       -- MUST be the random value to salt the secret key
       -- MUST be a different value than used in the PBMParameter
       -- data structure of the CMP message protection in the
       -- header of this message
                   iterationCount
                                 REQUIRED
       -- MUST be a limited number of times the OWF is applied
       -- To prevent brute force and dictionary attacks a reasonable
       -- high number SHOULD be used
                   keyLength     REQUIRED
                   prf           REQUIRED
       -- MUST be the algorithm identifier of the underlying
       -- pseudorandom function
       -- The pseudorandom function HMAC-SHA1 MUST be supported
       -- due to [RFC8018] requirements, but SHOULD NOT be used any
       -- more HMAC-SHA-256 SHOULD be used instead
                 keyEncryptionAlgorithm
                                 REQUIRED
       -- MUST be the same as in the contentEncryptionAlgorithm field
                 encryptedKey    REQUIRED
       -- MUST be the encrypted content-encryption key

4.1.7.  Delayed enrollment

   This functional extension can be applied in combination with
   certificate enrollment as described in Section 4.1.1 to
   Section 4.1.5.  The functional extension can be used in case a PKI
   management entity cannot respond to the certificate request in a
   timely manner, e.g., due to offline upstream communication or
   required registration officer interaction.  Depending on the PKI
   architecture, it is not necessary that the PKI management entity
   directly communicating with the EE initiates the delayed enrollment.




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   The PKI management entity initiating the delayed enrollment MUST
   include the status "waiting" in the response and this response MUST
   NOT contain a newly issued certificate.  When receiving a response
   with status "waiting" the EE MUST send a poll request to the PKI
   management entity.  The PKI management entity that initiated the
   delayed enrollment MUST answers with a poll response containing a
   checkAfter time.  This value indicates the minimum number of seconds
   that must elapse before the EE sends another poll request.  As soon
   as the PKI management entity can provide the final response message
   for the initial request of the EE, it MUST provide this in response
   to a poll request.  After receiving this response, the EE can
   continue the original PKI management operation as described in the
   respective section of this document, e.g., send a certConf message.

   Typically, intermediate PKI management entities SHOULD NOT change the
   sender and recipient nonce even in case an intermediate PKI
   management entity modifies a request or a response message.  In the
   special case of polling between EE and LRA with offline transport
   between an LRA and RA, see Section 5.1.4, an exception occurs.  The
   EE and LRA exchange pollReq and pollRep messages handle the nonce
   words as described.  When, after pollRep, the final response from the
   CA arrives at the LRA, the next response will contain the recipNonce
   set to the value of the senderNonce in the original request message
   (copied by the CA).  The LRA needs to replace the recipNonce in this
   case with the senderNonce of the last pollReq because the EE will
   validate it in this way.

   < TBD: I would appreciate any feedback specifically addressing the
   nonce handling in case an offline LRA responding and not forwarding
   the pollReq messages. >





















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   Message flow:

   Step# EE                                   PKI management entity
    1   format ir/cr/p10cr/kur
        As described in the
          respective section
          in this document
    2                    ->ir/cr/p10cr/kur->
    3                                        handle request as described
                                               in the respective section
                                               in this document
    4                                        in case no immediate final
                                               response is possible,
                                               receive or format ip, cp
                                               or kup message containing
                                               status "waiting"
    5                      <-  ip/cp/kup  <-
    6   handle ip/cp/kup
    7   format pollReq
    8                      ->   pollReq   ->
    9                                        handle, re-protect or
                                               forward pollReq
   10                                        in case the requested
                                               certificate or a
                                               corresponding response
                                               message is available,
                                               receive or format ip, cp,
                                               or kup containing the
                                               issued certificate, or
                                             format or receive pollRep
                                               with appropriate
                                               checkAfter value
   11                      <-   pollRep   <-
   12   handle pollRep
   13   let checkAfter
          time elapse
   14   continue with line 7

   Detailed description of the first ip/cp/kup:

   Response with status 'waiting'  -- ip/cp/kup

   Field                         Value

   header
       -- MUST contain a header as described for the first response
       -- message of the respective PKI management operation




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   body
       -- The response of the PKI management entity to the request in
       -- case no immediate appropriate response can be sent
     ip/cp/kup                   REQUIRED
       response                  REQUIRED
       -- MUST be exactly one CertResponse
         certReqId               REQUIRED
       -- MUST be set to 0
         status                  REQUIRED
       -- PKIStatusInfo structure MUST be present
           status                REQUIRED
       -- MUST be set to "waiting"
           statusString          OPTIONAL
       -- MAY be any human-readable text for debugging, logging or to
       -- display in a GUI
           failInfo              PROHIBITED
         certifiedKeyPair        PROHIBITED

   protection                    REQUIRED
       -- MUST contain protection as described for the first response
       -- message of the respective PKI management operation, but
       -- MUST use the protection key of the PKI management entity
       -- initiating the delayed enrollment and creating this response
       -- message

   extraCerts                    REQUIRED
       -- MUST contain certificates as described for the first response
       -- message of the respective PKI management operation.
       -- As no new certificate is issued yet, no respective certificate
       -- chain is included


   Polling Request -- pollReq

   Field                         Value

   header
       -- MUST contain a header as described for the certConf message
       -- of the respective PKI management operation

   body
       -- The message of the EE asks for the final response or for a
       -- time to check again
     pollReq                     REQUIRED
       certReqId                 REQUIRED
       -- MUST be exactly one value
       -- MUST be set to 0




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   protection                    REQUIRED
       -- MUST contain protection as described for the certConf message
       -- of the respective PKI management operation

   extraCerts                    OPTIONAL
       -- If present, it MUST contain certificates as described for the
       -- certConf message of the respective PKI management operation


   Polling Response -- pollRep

   Field                         Value

   header
       -- MUST contain a header as described for the pkiConf message
       -- of the respective PKI management operation

   body
       -- The message indicated the time to after which the EE may
       -- send another pollReq messaged for this transaction
     pollRep                     REQUIRED
       -- MUST be exactly one set of the following values
       certReqId                 REQUIRED
       -- MUST be set to 0
       checkAfter                REQUIRED
       -- time in seconds to elapse before a new pollReq may be sent by
       -- the EE

   protection                    REQUIRED
       -- MUST contain protection as described for the pkiConf message
       -- of the respective profile, but
       -- MUST use the protection key of the PKI management entity that
       -- initiated the delayed enrollment and is creating this response
       -- message

   extraCerts                    OPTIONAL
       -- If present, it MUST contain certificates as described for the
       -- pkiConf message of the respective PKI management operation.


   Final response -- ip/cp/kup

   Field                         Value

   header
       -- MUST contain a header as described for the first
       -- response message of the respective PKI management operation,
       -- but the recipNonce MUST be the senderNonce of the last



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       -- pollReq message

   body
       -- The response of the PKI management entity to the initial
       -- request as described in the respective PKI management
       -- operation

   protection                    REQUIRED
       -- MUST contain protection as described for the first response
       -- message of the respective PKI management operation, but
       -- MUST use the protection key of the PKI management entity that
       -- initiated the delayed enrollment and forwarding the response
       -- message

   extraCerts                    REQUIRED
       -- MUST contain certificates as described for the first
       -- response message of the respective PKI management operation

4.2.  Revoking a certificate

   This PKI management operation should be used by an entity to request
   the revocation of a certificate.  Here the revocation request is used
   by an EE to revoke one of its own certificates.  A PKI management
   entity could also act as 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 to the
   PKI.  The revocation request message is signature-protected using
   this certificate.

   An EE requests the revocation of an own certificate at the CA that
   issued this certificate.  The PKI management entity responds with a
   message that contains the status of the revocation from the CA.

   Preconditions:

   1  The certificate the EE wishes to revoke is not yet expired or
      revoked.













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   Message flow:


   Step# EE                                  PKI management entity
     1   format rr
     2                      ->   rr      ->
     3                                        handle, re-protect or
                                                forward rr
     4                                        receive rp
     5                      <-   rp      <-
     6   handle rp

   For this PKI management operation, the EE MUST include exactly one
   RevDetails structure in the rr message body.  In case no error
   occurred the response to the rr MUST be a rp message.  The PKI
   management entity MUST produce a rp containing a status field with a
   single set of values.

   Detailed message description:

   Revocation Request -- rr

   Field                         Value

   header
       -- As described in section 3.1

   body
       -- The request of the EE to revoke its certificate
     rr                          REQUIRED
       -- MUST contain exactly one element of type RevDetails
       -- If more revocations are desired, further requests MUST be
       -- packaged in separate PKI Messages
       certDetails               REQUIRED
       -- MUST be present and is of type CertTemplate
         serialNumber            REQUIRED
       -- MUST contain the certificate serialNumber attribute of the
       -- X.509 certificate to be revoked
         issuer                  REQUIRED
       -- MUST contain the issuer attribute of the X.509 certificate to
       -- be revoked
       crlEntryDetails           REQUIRED
       -- MUST contain exactly one reasonCode of type CRLReason (see
       -- [RFC5280] section 5.3.1)
       -- If the reason for this revocation is not known or shall not be
       -- published the reasonCode MUST be 0 = unspecified

   protection                    REQUIRED



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       -- As described in section 3.2 and the private key related to the
       -- certificate to be revoked

   extraCerts                    REQUIRED
       -- As described in section 3.3


   Revocation Response -- rp

   Field                         Value

   header
       -- As described in section 3.1

   body
       -- The responds of the PKI management entity to the request as
       -- appropriate
     rp                          REQUIRED
       status                    REQUIRED
       -- MUST contain exactly one element of type PKIStatusInfo
         status                  REQUIRED
       -- positive value allowed: "accepted"
       -- negative value allowed: "rejection"
         statusString            OPTIONAL
       -- MAY be any human-readable text for debugging, logging or to
       -- display in a GUI
         failInfo                OPTIONAL
       -- MAY be present if and only if status is "rejection"

   protection                    REQUIRED
       -- As described in section 3.2

   extraCerts                    REQUIRED
       -- As described in section 3.3

4.3.  Error reporting

   This functionality should be used by an EE to report any error
   conditions upstream to the PKI management entity.  Error reporting by
   a PKI management entity downstream to the EE is described in
   Section 5.3.

   In case the error condition is related to specific details of an ip,
   cp, or kup response message and a confirmation is expected the error
   condition MUST be reported in the respective certConf message with
   negative contents.





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   General error conditions, e.g., problems with the message header,
   protection, or extraCerts, and negative feedback on rp, pollRep, or
   pkiConf messages MAY be reported in the form of an error message.

   In both situations the EE reports error in the PKIStatusInfo
   structure of the respective message.

   Depending on the PKI architecture, the PKI management entity MUST
   forward the error message (upstream) to the next PKI management
   entity and MUST terminate this PKI management operation.

   The PKIStatusInfo structure is used to report errors.  The
   PKIStatusInfo structure SHOULD consist of the following fields:

   o  status: Here the PKIStatus value "rejection" is the only one
      allowed.

   o  statusString: Here any human-readable valid value for logging or
      to display in a GUI SHOULD be added.

   o  failInfo: Here the PKIFailureInfo values MAY be used in the
      following way.  For explanation of the reason behind a specific
      value, please refer to [RFC4210] Appendix F.

      *  transactionIdInUse: This is sent by a PKI management entity in
         case the received request contains a transaction ID that is
         already in use for another transaction.  An EE receiving such
         error message SHOULD resend the request in a new transaction
         using a different transaction ID.

      *  systemUnavail or systemFailure: This is sent by a PKI
         management entity in case a back-end system is not available or
         currently not functioning correctly.  An EE receiving such
         error message SHOULD resend the request in a new transaction
         after some time.
















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   Detailed error message description:

   Error Message -- error

   Field                         Value

   header
       -- As described in section 3.1

   body
       -- The message sent by the EE or the (L)RA/CA to indicate an
       -- 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

   protection                    REQUIRED
       -- As described in section 3.2

   extraCerts                    OPTIONAL
       -- As described in section 3.3

4.4.  Support messages

   The following support messages offer on demand in-band transport of
   content that may be provided by the PKI management entity and
   relevant to the EE.  The general messages and general response are
   used for this purpose.  Depending on the environment, these requests
   may be answered by the LRA, RA, or CA.

   The general message and general response transport InfoTypeAndValue
   structures.  In addition to those infoType values defined in CMP
   [RFC4210] further OIDs MAY be defined to define new PKI management
   operations, or general-purpose support messages as needed in a
   specific environment.

   Content specified in this document is describs the following:

   o  Request of CA certificates

   o  Update of Root CA certificates




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   o  Parameters needed for a planned certificate request message

4.4.1.  General message and response

   The PKI management operation is similar to that given in CMP
   Appendix E.5 [RFC4210].  In this section the general message (genm)
   and general response (genp) are described.  The specific
   InfoTypeAndValue structures are described in the following sections.

   The behavior in case an error occurs is described in Section 4.3.

   Message flow:

   Step# EE                                   PKI management entity
    1   format genm
    2                      ->   genm    ->
    3                                        handle, re-protect 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
       -- The request of the EE to receive information
     genm                        REQUIRED
       -- MUST contain exactly one element of type
       -- InfoTypeAndValue
       infoType                  REQUIRED
       -- MUST be the OID identifying the specific PKI
       -- management operation described below
       infoValue                 OPTIONAL
       -- MUST be as described in the specific PKI
       -- management operation described below

   protection                    REQUIRED
       -- As described in section 3.2

   extraCerts                    REQUIRED
       -- As described in section 3.3



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   General Response -- genp

   Field                         Value

   header
       -- As described in section 3.1

   body
       -- The response of the PKI management entity to the
       -- information request
     genp                        REQUIRED
       -- MUST contain exactly one element of type
       -- InfoTypeAndValue
       infoType                  REQUIRED
       -- MUST be the OID identifying the specific PKI
       -- management operation described below
       infoValue                 OPTIONAL
       -- MUST be as described in the specific PKI
       -- management operation described below

   protection                    REQUIRED
       -- As described in section 3.2

   extraCerts                    REQUIRED
       -- As described in section 3.3

   < TBD: May be we should not restrict the number of ITAV elements in
   the response message to one. >

4.4.2.  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 from the PKI management entity by
   sending a general message with OID id-it-caCerts as specified in CMP
   Updates [I-D.ietf-lamps-cmp-updates].  The PKI management entity
   responds with a general response with the same OID that either
   contains a SEQUENCE of certificates populated with the available CA
   intermediate and issuing CA certificates or with no content in case
   no CA certificate is available.

   The message sequence for this PKI management operation is as given in
   Section 4.4.1, with the following specific content:

   1  the body MUST contain as infoType the OID id-it-caCerts

   2  the infoValue of the request MUST be absent



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   3  if present, the infoValue of the response MUST be caCerts field

   The infoValue field of the general response containing the id-it-
   caCerts OID looks like this:

         infoValue               OPTIONAL
       -- MUST be absent if no CA certificate is available
       -- MUST be present if CA certificates are available
       -- MUST be a sequence of CMPCertificate

4.4.3.  Get root CA certificate update

   This PKI management operation can be used by an EE to request an
   update of an existing root CA Certificate by the EE.

   An EE requests a root CA certificate update from the PKI management
   entity by sending a general message with OID id-it-rootCaKeyUpdate as
   specified in CMP Updates [I-D.ietf-lamps-cmp-updates].  The PKI
   management entity responds with a general response with the same OID
   that either contains the update of the root CA certificate consisting
   of up to three certificates, or with no content in case no update is
   available.

   The newWithNew certificate is the new root CA certificates and is
   REQUIRED to be present in the response message.  The newWithOld
   certificate is RECOMMENDED to be present in the response message
   though it is REQUIRED for those cases where the receiving entity
   trusts the old root CA certificate and wishes to gain trust in the
   new root CA certificate.  The oldWithNew certificate is OPTIONAL
   though it is only needed in a scenario where the requesting entity
   already trusts the new root CA certificate and wants to gain trust in
   the old root certificate.

   The message sequence for this PKI management operation is as given in
   Section 4.4.1, with the following specific content:

   1  the body MUST contain as infoType the OID id-it-rootCaKeyUpdate

   2  the infoValue of the request MUST be absent

   3  if present, the infoValue of the response MUST be a
      RootCaKeyUpdate structure









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   The infoValue field of the general response containing the id-it-
   rootCaKeyUpdate extension looks like this:

         infoValue               OPTIONAL
       -- MUST be absent if no update of the root CA certificate is
       -- available
       -- MUST be present if an update of the root CA certificate
       -- is available and MUST be of type RootCaKeyUpdate
           newWithNew            REQUIRED
       -- MUST be present if infoValue is present
       -- MUST contain the new root CA certificate
           newWithOld            RECOMMENDED
       -- SHOULD be present if infoValue is present
       -- MUST contain an X.509 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 an X.509 certificate containing the old public
       -- root CA key signed with the new private root CA key

   < TBD: In case the PKI management entity serves for different Root
   CAs.  There are three different options to handle this: - The EE
   specifies by means of an respective lable in the http endpoint for
   which Root CA certificate the update is requested. - The EE transfers
   the oldWithOld certificate in the InfoValue of the request. - The PKI
   management entity provides RootCaKeyUpdate element all Root CAs an
   update is available. >

4.4.4.  Get certificate request template

   This PKI management operation can be used by an EE to request a
   template with parameters for a future certificate request operation.

   An EE requests certificate request parameter from the PKI management
   entity by sending a general message with OID id-it-certReqTemplate as
   specified in CMP Updates [I-D.ietf-lamps-cmp-updates].  The PKI
   management entity responds with a general response with the same OID
   that either contains a certificate template containing requirements
   on certificate fields and extensions and optionally a sequence of
   control fields containing requirements on algorithm identifier or RSA
   key lengths for key pair generation, or with no content in case no
   specific requirements are made by the PKI.

   The EE SHOULD follow the requirements from the received CertTemplate
   and the optional control fields, by filling in all the fields
   requested and taking over all the field values provided.  The EE
   SHOULD NOT add further CertTemplate fields, Name components, and
   extensions or their (sub-)components.



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   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 CertReqTemplate response message.  On the other
   hand, a PKI management entity is free to ignore or replace the
   content of the certificate request provided by the EE.  The
   CertReqTemplate PKI management operation offers means to ease a joint
   understanding which fields should be used.

   In case a field of type Name, e.g., issuer or 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 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 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 know.

   The publicKey field of type SubjectPublicKeyInfo in the CertTemplate
   MUST no algorithm ID in the algorithm field and a zero-length BIT
   STRING in the subjectPublicKey field.  In case the PKI management
   entity whishes to make stipulation on supported algorithms the EE may
   use for key generation, this MUST be specified using the control
   fields.

   The control with the OID id-regCtrl-algId, as specified in CMP
   Updates [I-D.ietf-lamps-cmp-updates], specifies algorithms other that
   RSA.  The algorithm field in SubjectPublicKeyInfo specifies the type
   of the public key to request a certificate for.  The algorithm field
   contains the key type OID of the public key.  For EC keys the full
   curve information MUST be specified as described in the respective
   standard documents.  The algorithm field MUST be followed by a zero-
   length BIT STRING for the subjectPublicKey.

   The control with the OID id-regCtrl-rsaKeyLen, as specified in CMP
   Updates [I-D.ietf-lamps-cmp-updates], specifies RSA keys of the
   specified key length.  In case several control fields are present the
   EE is free to choose one of the specified algorithms for key pair
   generation.  In case no control field is not present the EE is free
   to choose the public key type and parameters.




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   In the certTemplate structure the serialNumber, signingAlg,
   issuerUID, and subjectUID fields MUST be omitted.

   The message sequence for this PKI management operation is as given in
   Section 4.4.1, with the following specific content:

   1  the body MUST contain as infoType the OID id-it-certReqTemplate

   2  the infoValue of the request MUST be absent

   3  if present, the infoValue of the response MUST be a certTemplate
      structure and an optional SEQUENCE of AttributeTypeAndValue of
      type id-regCtrl-algId or id-regCtrl-rsaKeyLen

   The infoValue field of the general response containing the id-it-
   certReqTemplate OID looks like this:

         InfoValue               OPTIONAL
       -- MUST be absent if no requirements are available
       -- MUST be present if the PKI management entity has any
       -- requirements on the content of the certificates template
           certTemplate          REQUIRED
       -- MUST be present if infoValue is present
       -- MUST contain the prefilled certTemplate structure elements
       -- The SubjectPublicKeyInfo MUST contain no algorithm ID in the
       -- algorithm field and a zero-length BIT STRING in the
       -- subjectPublicKey field
           controls             OPTIONAL
       -- MUST be absent if no requirements on algorithms are available
       -- MUST be present if the PKI management entity has any
       -- requirements on the algorithms to be used for key generation
       -- MUST contain one AttributeTypeAndValue per supported algorithm
       -- MAY be of type id-regCtrl-algId or id-regCtrl-rsaKeyLen

5.  LRA and RA focused PKI management operations

   This chapter focuses on the communication among different PKI
   management entities.  Depending on the network and PKI solution
   design, these will either be an LRA, RA or CA.

   Typically, a PKI management entity forwards messages from downstream,
   but it may also reply to them itself.  Besides forwarding of received
   messages a PKI management entity could also need to revoke
   certificates of EEs, report errors, or may need to manage its own
   certificates.






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5.1.  Forwarding of messages

   Each CMP request message (i.e., ir, cr, p10cr, kur, pollReq, or
   certConf) or error message coming from an EE or the previous
   (downstream) PKI management entity MUST be sent to the next
   (upstream) PKI management entity.  This PKI management entity MUST
   forward response messages to the next (downstream) PKI management
   entity or EE.

   The PKI management entity SHOULD verify the protection, the syntax,
   the required message fields, the message type, and if applicable the
   authorization and the proof-of-possession of the message.  Additional
   checks or actions MAY be applied depending on the PKI solution
   requirements and concept.  If one of these verification procedures
   fails, the (L)RA SHOULD respond with a negative response message and
   SHOULD not forward the message further upstream.  General error
   conditions should be handled as described in Section 4.3 and
   Section 5.3.

   A PKI management entity SHOULD not change the received message if not
   necessary.  The PKI management entity SHOULD only update the message
   protection if it is technically necessary.  Concrete PKI system
   specifications may define in more detail if and when to do so.

   This is particularly relevant in the upstream communication of a
   request message.

   Each hop in a chain of PKI management entity has one or more
   functionalities, e.g., a PKI management entity

   o  may need to verify the identities of EEs or base authorization
      decisions for certification request processing on specific
      knowledge of the local setup, e.g., by consulting an inventory or
      asset management system,

   o  may need to add fields to certificate request messages,

   o  may need to store data from a message in a database for later
      usage or documentation purposes,

   o  may provide traversal of a network boundary,

   o  may need to double-check if the messages transferred back and
      forth are properly protected and well formed,

   o  may provide a proof that it has performed all required checks,





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   o  may initiate a delayed enrollment due to offline upstream
      communication or registration officer interaction,

   o  may grant the request of an EE to omit sending a confirmation
      message, or

   o  can collect messages from different LRAs and forward them to the
      CA.

   Therefore, the decision if a message should be forwarded

   o  unchanged with the original protection,

   o  unchanged with a new protection, or

   o  changed with a new protection

   depends on the PKI solution design and the associated security policy
   (CP/CPS [RFC3647]).

   This section specifies the different options a PKI management entity
   may implement and use.

   A PKI management entity MAY update the protection of a message

   o  if it performs changes to the header or the body of the message,

   o  if it needs to prove checks or validations performed on the
      message to one of the next (upstream) PKI components,

   o  if it needs to protect the message using a key and certificate
      from a different PKI, or

   o  if it needs to replace a MAC based-protection.

   This is particularly relevant in the upstream communication of
   certificate request messages.

   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 or add
   needed or to delete needless certificates to support the next hop.
   This may be particularly helpful to extend upstream messages with
   additional certificates or to reduce the number of certificates in
   downstream messages when forwarding to constrained devices.






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5.1.1.  Not changing protection

   This alternative to forward a message can be used by any PKI
   management entity to forward an original CMP message without changing
   the header, body or protection.  In any of these cases the PKI
   management entity acts more like a proxy, e.g., on a network
   boundary, implementing no specific RA-like security functionality to
   the PKI.

   This alternative to forward a message MUST be used for forwarding kur
   messages that must not be approved by the respective PKI management
   entity.

5.1.2.  Replacing protection

   The following two alternatives to forward a message can be used by
   any PKI management entity to forward a CMP message with or without
   changes, but providing its own protection using its CMP signer key to
   assert approval of this message.  In this case the PKI management
   entity acts as an actual Registration Authority (RA), which
   implements important security functionality of the PKI.

   Before replacing the existing protection by a new protection, the PKI
   management entity MUST verify the protection provided by the EE or by
   the previous PKI management entity and approve its content including
   any own modifications.  For certificate requests the PKI management
   entity MUST verify in particular the included proof-of-possession
   self-signature of the certTemplate using the public key of the
   requested certificate and MUST check that the EE, as authenticated by
   the message protection, is authorized to request a certificate with
   the subject as specified in the certTemplate.

   In case the received message has been protected by a CA or another
   PKI management entity, the current PKI management entity MUST verify
   its protection and approve its content including any own
   modifications.  For certificate requests the PKI management entity
   MUST check that the other PKI management entity, as authenticated by
   the protection of the incoming message, was authorized to issue or
   forward the request.

   These message adaptations MUST NOT be applied to kur request messages
   as 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 clearly identify the certificate to
   be updated.

   These message adaptations MUST NOT be applied to certificate request
   messages as described in Section 4.1.6requesting key generation by a



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   Key Generation Authority since their original protection using the
   key and certificate for signature protection or the shared secret for
   MAC-protection needs to be preserved up to the Key Generation
   Authority.

   In both cases, kur and central key generation, an additional
   signature of a PKI management entity to the original certificate
   request message MUST be provided using nested messages as specified
   in Section 5.1.3.

5.1.2.1.  Keeping proof-of-possession

   This alternative to forward a message can be used by any PKI
   management entity to forward a CMP message with or without modifying
   the message header or body while preserving any included proof-of-
   possession.

   By replacing the existing protection using its own CMP signer key the
   PKI management entity provides a proof of verifying and approving of
   the message as described above.

   In case the PKI management entity modifies the certTemplate of an ir
   or cr message, the message adaptation in Section 5.1.2.2 needs to be
   applied instead.

5.1.2.2.  Breaking proof-of-possession

   This alternative to forward a message can be used by any PKI
   management entity to forward an ir or cr message with modifications
   of the certTemplate i.e., modification, addition, or removal of
   fields.  Such changes will break the proof-of-possession provided by
   the EE in the original message.

   By replacing the existing using its own CMP signer key the PKI
   management entity provides a proof of verifying and approving the new
   message as described above.

   In addition to the above the PKI management entity MUST verify in
   particular the proof-of-possession contained in the original message
   as described above.  If these checks were successfully performed the
   PKI management entity MUST change the popo to raVerified.










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   The popo field MUST contain the raVerified choice in the certReq
   structure of the modified message as follows:

       popo
         raVerified              REQUIRED
       -- MUST have the value NULL and indicates that the PKI
       -- management entity verified the popo of the original
       -- message

5.1.3.  Adding Protection

   This PKI management operation can be used by a PKI management entity
   to add another protection to one or several PKI management messages.
   Applying an additional protection is specifically important when
   forwarding certificate request messages requesting a key update or a
   central key generation to preserve the original protection of the EE.

   The nested message is a PKI management message containing a
   PKIMessages sequence as its body containing one or more CMP messages.

   As specified in the updated Section 5.1.3.4 of RFC4210 [RFC4210] (see
   CMP Updates [I-D.ietf-lamps-cmp-updates]) there are different use
   case for adding another protection by a PKI management entity.
   Specific procedures are described in more detail in the following
   sections.

   The behavior in case an error occurs is described in Section 4.3.

   Message flow:

   Step# PKI management entity               PKI management entity
    1   format nested
    2                      ->  nested   ->
    3                                        handle, re-protect or
                                               forward nested
    4                                        format or receive nested
    5                      <-  nested   <-
    6   handle nested













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   Detailed message description:

   Nested Message - nested

   Field                         Value

   header
       -- As described in section 3.1

   body
       -- Container to provide additional protection to original
       -- messages and to bundle request or 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 signer key of
       -- the PKI management entity

   extraCerts                    REQUIRED
       -- As described in section 3.3

5.1.3.1.  Handling a single PKI management message

   A PKI management entity may prove successful validation and
   authorization of a PKI management message by adding an additional
   signature to the original PKI management message.

   A PKI management entity SHALL wrap the original PKI management
   messages in a nested message structure.  The additional signature as
   prove of verification and authorization by the PKI management entity
   MUST be applies as signature-based message protection of the nested
   message.

5.1.3.2.  Handling a batch of PKI management 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 via an offline interface using the nested message structure.
   The nested message can be either used on the upstream interface
   towards the next PKI management entity as well as on the downstream
   interface from the PKI management entity towards the EE.

   This PKI management operation is typically used on the interface
   between LRA and RA to bundle several PKI management messages for
   offline transport.  In this case the EE needs to make use of delayed
   enrollment as described in Section 4.1.7.  If the RA may need
   different routing information per nested PKI management message a



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   suitable mechanism may need to be implemented.  This mechanism
   strongly depends on the requirements of the target architecture;
   therefore, it is out of scope of this document.

   An initial nested message is generated locally at the PKI management
   entity.  For the initial 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.
   The recipient field MUST identify the PKI management entity that is
   expected to unpack the nested message.  An initial nested message
   should contain only request messages, e.g., ir, cr, p10cr, kur,
   certConf, rr, or genm.  While building the initial nested message the
   PKI management entity SHOULD store the transactionIds and the
   senderNonces of all bundled messages together with the transactionId
   of the initial nested message.

   Such an initial nested message is sent to the next PKI management
   entity and SHOULD be answered with a responding nested message.  This
   responding message SHOULD use the transactionId of the initial nested
   message and return the senderNonce of the initial nested message as
   recipNonce of the responding nested message.  The responding nested
   message SHOULD bundle one response message (e.g. ip, cp, kup,
   pkiconf, rp, genp, error) for each request message (i.e., for each
   transactionId) in the initial nested message.  While unbundling the
   responding nested message it is possible to determine lost and
   unexpected responses based on the previously stored transactionIds
   and senderNonces.  While forwarding the unbundled responses, odd
   messages SHOULD be dropped, and lost messages should be replaced by
   an error message to inform the EE about the failed certificate
   management operation.

   The PKI management entity building the nested message applies a
   signature-based protection using its CMP-signer key as transport
   protection.  This protection SHALL NOT be regarded as prove of
   verification or authorization of the bundled PKI management messages.

5.1.4.  Initiating delayed enrollment

   This functional extension can be used by a PKI management entity to
   initiate delayed enrollment.  In this case a PKI management entity
   MUST add the status waiting in the response message.  The PKI
   management entity MUST then reply to the pollReq messages as
   described in Section 4.1.7.








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5.2.  Revoking certificates on behalf of another's entities

   This PKI management operation can be used by a PKI management entity
   to revoke a certificate of any other entity.  This revocation request
   message MUST be signed by the PKI management entity using its own CMP
   signer key to prove to the PKI authorization to revoke the
   certificate on behalf of the EE.

   Preconditions:

   1  the certificate to be revoked MUST be known to the PKI management
      entity

   2  the PKI management entity MUST have the authorization to revoke
      the certificates of other entities issued by the corresponding CA

   The message sequence for this PKI management operation is identical
   to that given in Section 4.2, with the following changes:

   1  it is not required that the certificate to be revoked is not yet
      expired or revoked

   2  the PKI management entity acts as EE for this message exchange

   3  the rr messages MUST be signed using the CMP signer key of the PKI
      management entity.

5.3.  Error reporting

   This functionality should be used by the PKI management entity to
   report any error conditions downstream to the EE.  Potential error
   reporting by the EE upstream to the PKI management entity is
   described in Section 4.3.

   In case the error condition is related to specific details of an ir,
   cr, p10cr, or kur request message it MUST be reported in the specific
   response message, i.e., an ip, cp, or kup with negative contents.

   General error conditions, e.g., problems with the message header,
   protection, or extraCerts, and negative feedback on rr, pollReq,
   certConf, or error messages MUST be reported in the form of an error
   message.

   In both situations the PKI management entity reports the errors in
   the PKIStatusInfo structure of the respective message as described in
   Section 4.3.





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   An EE receiving any such negative feedback SHOULD log the error
   appropriately and MUST terminate the current transaction.

6.  CMP message transport variants

   The CMP messages are designed to be self-contained, such that in
   principle any transport can be used.  HTTP SHOULD be used for online
   transport while file-based transport MAY be used in case offline
   transport is required.  In case HTTP transport is not desired or
   possible, CMP messages MAY also be piggybacked on any other reliable
   transport protocol, e.g., CoAP [RFC7252].

   Independently of the means of transport it could happen that messages
   are lost, or a communication partner does not respond.  In order to
   prevent waiting indefinitely, each CMP client component SHOULD use a
   configurable per-request timeout, and each CMP server component
   SHOULD use a configurable per-response timeout in case a further
   message is to be expected from the client side.  In this way a
   hanging transaction can be closed cleanly with an error and related
   resources (for instance, any cached extraCerts) can be freed.

   When conveying a CMP messages in HTTP or MIME-based transport
   protocols the internet media type "application/pkixcmp" MUST be set
   for transport encoding as specified in RFC2510 in Section 5.3
   [RFC2510] and RFC6712 in Section 3.4 [RFC7712].

6.1.  HTTP transport

   This transport mechanism can be used by a PKI entity to transfer CMP
   messages over HTTP.  If HTTP transport is used the specifications as
   described in [RFC6712] and updated by CMP Updates
   [I-D.ietf-lamps-cmp-updates] MUST be followed.



















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   PKI management operations SHOULD use the following URI path:

   +----------------------------------+---------------------+----------+
   | PKI management operation         |         Path        | Details  |
   +----------------------------------+---------------------+----------+
   | Enroll client to new PKI         |   /initialization   | Section  |
   | (REQUIRED)                       |                     | 4.1.1    |
   +----------------------------------+---------------------+----------+
   | Enroll client to existing PKI    |    /certification   | Section  |
   | (OPTIONAL)                       |                     | 4.1.2    |
   +----------------------------------+---------------------+----------+
   | Update client certificate        |      /keyupdate     | Section  |
   | (REQUIRED)                       |                     | 4.1.3    |
   +----------------------------------+---------------------+----------+
   | Enroll client using PKCS#10      |         /p10        | Section  |
   | (OPTIONAL)                       |                     | 4.1.5    |
   +----------------------------------+---------------------+----------+
   | Enroll client using central key  |    /serverkeygen    | Section  |
   | generation (OPTIONAL)            |                     | 4.1.6    |
   +----------------------------------+---------------------+----------+
   | Revoke client certificate        |     /revocation     | Section  |
   | (RECOMMENDED)                    |                     | 4.2      |
   +----------------------------------+---------------------+----------+
   | Get CA certificates (OPTIONAL)   |      /getcacert     | Section  |
   |                                  |                     | 4.4.2    |
   +----------------------------------+---------------------+----------+
   | Get root CA certificate update   |    /getrootupdate   | Section  |
   | (OPTIONAL)                       |                     | 4.4.3    |
   +----------------------------------+---------------------+----------+
   | Get certificate request template | /getcertreqtemplate | Section  |
   | (OPTIONAL)                       |                     | 4.4.4    |
   +----------------------------------+---------------------+----------+
   | Additional protection (OPTIONAL) |       /nested       | Section  |
   |                                  |                     | 5.1.3    |
   +----------------------------------+---------------------+----------+

                          Table 9: HTTP endpoints

   Subsequent certConf, error, and pollReq messages are sent to the URI
   of the respective PKI management operation.

   The discovery mechanism as described in CMP Updates
   [I-D.ietf-lamps-cmp-updates] SHOULD be used to query information on
   the supported PKI management operations, certificate profiles and
   CAs.

   As it is very likely, that a CA supports different certification
   profiles or that the RA offers PKI management operations for



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   different issuing CAs, the discovery can also be used to provide the
   information about these options.  The second example listing contains
   the supported PKI management operations for three different
   certificate profiles.  The supported CA hierarchy consists of one
   root CA and two issuing CAs.

   Detailed message description:

   REQ: GET /.well-known/cmp

   RES: Content
     </cmp/certprofile1/initialization>;ct=pkixcmp
     </cmp/certprofile2/initialization>;ct=pkixcmp
     </cmp/certprofile3/initialization>;ct=pkixcmp
     </cmp/certprofile1/certification >;ct=pkixcmp
     </cmp/certprofile2/certification >;ct=pkixcmp
     </cmp/certprofile3/certification >;ct=pkixcmp
     </cmp/certprofile1/keyupdate >;ct=pkixcmp
     </cmp/certprofile2/keyupdate >;ct=pkixcmp
     </cmp/certprofile3/keyupdate >;ct=pkixcmp
     </cmp/certprofile1/p10>;ct=pkixcmp
     </cmp/certprofile2/p10>;ct=pkixcmp
     </cmp/certprofile3/p10>;ct=pkixcmp
     </cmp/ca1/revocation>;ct=pkixcmp
     </cmp/ca2/revocation>;ct=pkixcmp
     </cmp/getcacerts>;ct=pkixcmp
     </cmp/rootca1/getrootupdate>;ct=pkixcmp
     </cmp/certprofile1/getcertreqtemplate >;ct=pkixcmp
     </cmp/certprofile2/getcertreqtemplate >;ct=pkixcmp
     </cmp/certprofile3/getcertreqtemplate >;ct=pkixcmp

   There are different options in the handling of the naming.  The PKI
   management entity either needs to offer the certprofile or CA labels
   the EE expects.  Alternatively, a mechanism is required to configure
   this information to the EE beforehand.

6.2.  HTTPS transport using certificates

   This transport mechanism can be used by a PKI entity to further
   protect the HTTP transport as described in Section 6.1 using TLS 1.2
   [RFC5246] or TLS 1.3 [RFC8446] as described in [RFC2818] with
   certificate-based authentication.  Using this transport mechanism,
   the CMP transport via HTTPS MUST use TLS server authentication and
   SHOULD use TLS client authentication.

   EE:





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   o  The EE SHOULD use a TLS client certificate as far as available.
      If no dedicated TLS certificate is available, the EE SHOULD use an
      already existing certificate identifying the EE (e.g., a
      manufacturer certificate).

   o  If no TLS certificate is available at the EE, server-only
      authenticated TLS SHOULD be used.

   o  The EE MUST validate the TLS server certificate of its
      communication partner.

   PKI management entity:

   o  Each PKI management entity SHOULD use a TLS client certificate on
      its upstream (client) interface.

   o  Each PKI management entity MUST use a TLS server certificate on
      its downstream (server) interface.

   o  Each PKI management entity MUST validate the TLS certificate of
      its communication partners.

   NOTE: The requirements for checking certificates given in [RFC5280],
   [RFC5246] and [RFC8446] MUST be followed for the TLS layer.
   Certificate status checking SHOULD be used for the TLS certificates
   of communication partners.

6.3.  HTTPS transport using shared secrets

   This transport mechanism can be used by a PKI entity to further
   protect the HTTP transport as described in Section 6.1 using TLS 1.2
   [RFC5246] or TLS 1.3 [RFC8446] as described in [RFC2818] with mutual
   authentication based on shared secrets as described in [RFC5054].

   EE:

   o  The EE MUST use the shared symmetric key for authentication.

   PKI management entity:

   o  The PKI management entity MUST use the shared symmetric key for
      authentication.

   < TBD: It needs to be clarified which cipher suite shall be
   recommended as there seems to be no support for TLS-SRP un JavaSE. >






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6.4.  Offline transport

   For transporting CMP messages between PKI entities any mechanism can
   be used that is able to store and forward binary objects of
   sufficient length and with sufficient reliability while preserving
   the order of messages.

   The transport mechanism SHOULD be able to indicate message loss,
   excessive delay, and possibly other transmission errors.  In such
   cases the PKI entities using this mechanism SHOULD report an error as
   specified in Section 4.3.

6.4.1.  File-based transport

   CMP messages MAY be transferred between PKI entities using file-
   system-based mechanisms, for instance when an off-line end entity or
   a PKI management entity performs delayed enrollment.  Each file MUST
   contain the ASN.1 DER encoding of one CMP message only.  There MUST
   be no extraneous header or trailer information in the file.  The file
   type extensions ".PKI" SHOULD be used.

6.4.2.  Other asynchronous transport protocols

   Other asynchronous transport protocols, e.g., email or website
   up-/download, MAY transfer CMP messages between PKI entities.  A MIME
   wrapping is defined for those environments that are MIME native.  The
   MIME wrapping in this section is specified in [RFC8551], section 3.1.

   The ASN.1 DER encoding of the CMP messages MUST be transferred using
   the "application/pkixcmp" content type and base64-encoded content-
   transfer-encoding as specified in [RFC2510], section 5.3.  A filename
   MUST be included either in a content-type or a content-disposition
   statement.  The extension for the file MUST be ".PKI".

6.5.  CoAP transport

   In constrained environments where no HTTP transport is desired or
   possible, CoAP [RFC7252] as specified in
   [I-D.msahni-tbd-cmpv2-coap-transport] MAY be used instead.

6.6.  Piggybacking on other reliable transport

   For online transfer where no HTTP transport is desired or possible
   CMP messages MAY also be transported on some other reliable protocol.
   Connection and error handling mechanisms like those specified for
   HTTP in [RFC6712] need to be implemented.





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   Such specification is out of scope of this document and would need to
   be specifies in a separate document, e.g., in the scope of the
   respective transport protocol used.

7.  IANA Considerations

8.  Security Considerations

   < TBD: Add any security considerations >

9.  Acknowledgements

   We would like to thank the various reviewers of this document.

10.  References

10.1.  Normative References

   [I-D.ietf-lamps-cmp-updates]
              Brockhaus, H., "CMP Updates", draft-ietf-lamps-cmp-
              updates-05 (work in progress), September 2020.

   [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>.

   [RFC4086]  Eastlake 3rd, D., Schiller, J., and S. Crocker,
              "Randomness Requirements for Security", BCP 106, RFC 4086,
              DOI 10.17487/RFC4086, June 2005,
              <https://www.rfc-editor.org/info/rfc4086>.

   [RFC4210]  Adams, C., Farrell, S., Kause, T., and T. Mononen,
              "Internet X.509 Public Key Infrastructure Certificate
              Management Protocol (CMP)", RFC 4210,
              DOI 10.17487/RFC4210, September 2005,
              <https://www.rfc-editor.org/info/rfc4210>.

   [RFC4211]  Schaad, J., "Internet X.509 Public Key Infrastructure
              Certificate Request Message Format (CRMF)", RFC 4211,
              DOI 10.17487/RFC4211, September 2005,
              <https://www.rfc-editor.org/info/rfc4211>.




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   [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>.

10.2.  Informative References

   [ETSI-TS133310]
              ETSI, "TS 133 310; Network Domain Security (NDS);
              Authentication Framework (AF); Release 16; V16.4.0",
              August 2020, <https://www.etsi.org/deliver/
              etsi_ts/133300_133399/133310/>.

   [I-D.msahni-tbd-cmpv2-coap-transport]
              Sahni, M., "CoAP Transport for CMPV2", draft-msahni-tbd-
              cmpv2-coap-transport-00 (work in progress), June 2020.

   [IEC62443-3-3]
              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>.

   [IEEE802.1AR]
              IEEE, "802.1AR Secure Device Identifier", June 2018,
              <http://standards.ieee.org/findstds/standard/802.1AR-
              2009.html>.

   [NIST-CSFW]
              NIST, "Framework for Improving Critical Infrastructure
              Cybersecurity Version 1.1", April 2018,
              <https://www.nist.gov/publications/framework-improving-
              critical-infrastructure-cybersecurity-version-11>.



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   [RFC2510]  Adams, C. and S. Farrell, "Internet X.509 Public Key
              Infrastructure Certificate Management Protocols",
              RFC 2510, DOI 10.17487/RFC2510, March 1999,
              <https://www.rfc-editor.org/info/rfc2510>.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,
              <https://www.rfc-editor.org/info/rfc2818>.

   [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>.

   [RFC5054]  Taylor, D., Wu, T., Mavrogiannopoulos, N., and T. Perrin,
              "Using the Secure Remote Password (SRP) Protocol for TLS
              Authentication", RFC 5054, DOI 10.17487/RFC5054, November
              2007, <https://www.rfc-editor.org/info/rfc5054>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <https://www.rfc-editor.org/info/rfc7252>.

   [RFC7712]  Saint-Andre, P., Miller, M., and P. Hancke, "Domain Name
              Associations (DNA) in the Extensible Messaging and
              Presence Protocol (XMPP)", RFC 7712, DOI 10.17487/RFC7712,
              November 2015, <https://www.rfc-editor.org/info/rfc7712>.

   [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>.



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   [UNISIG-Subset137]
              UNISIG, "Subset-137; ERTMS/ETCS On-line Key Management
              FFFIS; V1.0.0", December 2015,
              <https://www.era.europa.eu/filebrowser/download/542_en>.

Appendix A.  Example for CertReqTemplate

   < TBD: This Appendix must be updated to reflect the change from using
   rsaKeyLen to controles. >

   This Section provides a concrete example for the content of an
   infoValue used of type id-it-certReqTemplate as described in
   Section 4.4.4.

   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
   with 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 rsaKeyLen returned to the EE must be encoded as
   follows:

   SEQUENCE {
     SEQUENCE {
       [3] {
         SEQUENCE {}
         }
       [5] {
         SEQUENCE {
           SET {
             SEQUENCE {
               OBJECT IDENTIFIER commonName (2 5 4 3)
               UTF8String ''
               }
             }
             SEQUENCE {
               OBJECT IDENTIFIER organizationalUnitName (2 5 4 11)
               UTF8String 'myDept'
               }
             }
           SET {
             SEQUENCE {
               OBJECT IDENTIFIER organizationalUnitName (2 5 4 11)
               UTF8String 'myGroup'



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               }
             }
           }
         }
       [6] {
         SEQUENCE {
           OBJECT IDENTIFIER rsaEncryption (1 2 840 113549 1 1 1)
           NULL
           }
         BIT STRING, encapsulates {
           SEQUENCE {}
           }
         }
       [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 {}
             }
           }
         }
       }
     INTEGER 2048
     }

Appendix B.  History of changes

   Note: This appendix will be deleted in the final version of the
   document.

   From version 02 -> 03:



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   o  Updated the interoperability with [UNISIG-Subset137] in
      Section 1.4.

   o  Changed Section 2.3 to a tabular layout to enhanced readability

   o  Added a ToDo to section 3.1 on aligning with the CMP Algorithms
      draft that will be set up as decided in IETF 108

   o  Updated section 4.1.6 to add the AsymmetricKey Package structure
      to transport a newly generated private key as decided in IETF 108

   o  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

   o  Updated Section 4 due to the definition of the new ITAV OIDs in
      CMP Updates

   o  Updated Section 4.4.4 to utilize controls instead of rsaKeyLen
      (see thread "dtaft-ietf-lamps-cmp-updates and rsaKeyLen")

   o  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

   o  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.

   o  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

   o  Deleted the ASN.1 module after moving the new OIDs id-it-caCerts,
      id-it-rootCaKeyUpdate, and id-it-certReqTemplate to CMP Updates

   o  Minor changes in wording and addition of some open ToDos

   From version 01 -> 02:

   o  Extend Section 1.4 with regard to conflicts with UNISIG Subset-
      137.

   o  Minor clarifications on extraCerts in Section 3.3 and
      Section 4.1.1.

   o  Complete specification of requesting a certificate from a trusted
      PKI with signature protection in Section 4.1.2.




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   o  Changed from symmetric key-encryption to password-based key
      management technique in section Section 4.1.6.3 as discussed on
      the mailing list (see thread "draft-ietf-lamps-lightweight-cmp-
      profile-01, section 5.1.6.1")

   o  Changed delayed enrollment described in Section 4.1.7 from
      recommended to optional as decided at IETF 107

   o  Introduced the new RootCAKeyUpdate structure for root CA
      certificate update in Section 4.4.3 as decided at IETF 107 (also
      see email thread "draft-ietf-lamps-lightweight-cmp-profile-01,
      section 5.4.3")

   o  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 4.4.4 as discussed
      on the mailing list (see thread "draft-ietf-lamps-lightweight-cmp-
      profile-01, section 5.4.4")

   o  Deleted Sections "Get certificate management configuration" and
      "Get enrollment voucher" as decided at IETF 107

   o  Complete specification of adding an additional protection by an
      PKI management entity in Section 5.1.3.

   o  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 5.1.3 and delete the paths for /getCertMgtConfig and
      /getVoucher

   o  Changed Section 6.4 to address offline transport and added more
      detailed specification file-based transport of CMP

   o  Added a reference to the new I-D of Mohit Sahni on "CoAP Transport
      for CMPV2" in Section 6.5; thanks to Mohit supporting the effort
      to ease utilization of CMP

   o  Moved the change history to the Appendix

   o  Minor changes in wording

   From version 00 -> 01:

   o  Harmonize terminology with CMP [RFC4210], e.g.,

      *  transaction, message sequence, exchange, use case -> PKI
         management operation



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      *  PKI component, (L)RA/CA -> PKI management entity

   o  Minor changes in wording

   From draft-brockhaus-lamps-lightweight-cmp-profile-03 -> draft-ietf-
   lamps-lightweight-cmp-profile-00:

   o  Changes required to reflect WG adoption

   o  Minor changes in wording

   From version 02 -> 03:

   o  Added a short summary of [RFC4210] Appendix D and E in
      Section 1.3.

   o  Clarified some references to different sections and added some
      clarification in response to feedback from Michael Richardson and
      Tomas Gustavsson.

   o  Added an additional label to the operational path to address
      multiple CAs or certificate profiles in Section 6.1.

   From version 01 -> 02:

   o  Added some clarification on the key management techniques for
      protection of centrally generated keys in Section 4.1.6.

   o  Added some clarifications on the certificates for root CA
      certificate update in Section 4.4.3.

   o  Added a section to specify the usage of nested messages for RAs to
      add an additional protection for further discussion, see
      Section 5.1.3.

   o  Added a table containing endpoints for HTTP transport in
      Section 6.1 to simplify addressing PKI management entities.

   o  Added some ToDos resulting from discussion with Tomas Gustavsson.

   o  Minor clarifications and changes in wording.

   From version 00 -> 01:

   o  Added a section to specify the enrollment with an already trusted
      PKI for further discussion, see Section 4.1.2.





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   o  Complete specification of requesting a certificate from a legacy
      PKI using a PKCS#10 [RFC2986] request in Section 4.1.5.

   o  Complete specification of adding central generation of a key pair
      on behalf of an end entity in Section 4.1.6.

   o  Complete specification of handling delayed enrollment due to
      asynchronous message delivery in Section 4.1.7.

   o  Complete specification of additional support messages, e.g., to
      update a Root CA certificate or to request an RFC 8366 [RFC8366]
      voucher, in Section 4.4.

   o  Minor changes in wording.

   From draft-brockhaus-lamps-industrial-cmp-profile-00 -> draft-
   brockhaus-lamps-lightweight-cmp-profile-00:

   o  Change focus from industrial to more multi-purpose use cases and
      lightweight CMP profile.

   o  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.

   o  Change from OPTIONAL to RECOMMENDED for use case 'Revoke another's
      entities certificate' in Section 5.2, because it is regarded as
      important functionality in many environments to enable the
      management station to revoke EE certificates.

   o  Complete the specification of the revocation message flow in
      Section 4.2 and Section 5.2.

   o  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.

   o  Further minor changes in wording.

Authors' Addresses

   Hendrik Brockhaus
   Siemens AG

   Email: hendrik.brockhaus@siemens.com





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   Steffen Fries
   Siemens AG

   Email: steffen.fries@siemens.com


   David von Oheimb
   Siemens AG

   Email: david.von.oheimb@siemens.com









































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