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Versions: (draft-brockhaus-lamps-lightweight-cmp-profile) 00 01 02 03 04

LAMPS Working Group                                         H. Brockhaus
Internet-Draft                                                  S. Fries
Intended status: Standards Track                           D. von Oheimb
Expires: August 17, 2020                                         Siemens
                                                       February 14, 2020


                        Lightweight CMP Profile
              draft-ietf-lamps-lightweight-cmp-profile-00

Abstract

   The goal of this document is to facilitate interoperability and
   automation by profiling the Certificate Management Protocol (CMP)
   version 2 and 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 transactions are specified as mandatory.  To foster
   interoperability also in more complex scenarios, other types of
   transactions 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 August 17, 2020.

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.  History of changes  . . . . . . . . . . . . . . . . . . . . .   3
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  Motivation for profiling CMP  . . . . . . . . . . . . . .   5
     2.2.  Motivation for a lightweight profile for CMP  . . . . . .   6
     2.3.  Existing CMP profiles . . . . . . . . . . . . . . . . . .   7
     2.4.  Compatibility with existing CMP profiles  . . . . . . . .   9
     2.5.  Scope of this document  . . . . . . . . . . . . . . . . .  10
     2.6.  Structure of this document  . . . . . . . . . . . . . . .  11
     2.7.  Convention and Terminology  . . . . . . . . . . . . . . .  11
   3.  Architecture and use cases  . . . . . . . . . . . . . . . . .  12
     3.1.  Solution architecture . . . . . . . . . . . . . . . . . .  12
     3.2.  Basic generic CMP message content . . . . . . . . . . . .  13
     3.3.  Supported use cases . . . . . . . . . . . . . . . . . . .  14
       3.3.1.  Mandatory use cases . . . . . . . . . . . . . . . . .  14
       3.3.2.  Recommended Use Cases . . . . . . . . . . . . . . . .  14
       3.3.3.  Optional use cases  . . . . . . . . . . . . . . . . .  15
     3.4.  CMP message transport . . . . . . . . . . . . . . . . . .  15
   4.  Generic parts of the PKI message  . . . . . . . . . . . . . .  16
     4.1.  General description of the CMP message header . . . . . .  17
     4.2.  General description of the CMP message protection . . . .  18
     4.3.  General description of CMP message extraCerts . . . . . .  19
   5.  End Entity focused certificate management use cases . . . . .  19
     5.1.  Requesting a new certificate from a PKI . . . . . . . . .  20
       5.1.1.  A certificate from a new PKI with signature
               protection  . . . . . . . . . . . . . . . . . . . . .  21
       5.1.2.  A certificate from a trusted PKI with signature
               protection  . . . . . . . . . . . . . . . . . . . . .  27
       5.1.3.  Update an existing certificate with signature
               protection  . . . . . . . . . . . . . . . . . . . . .  27
       5.1.4.  A certificate from a PKI with MAC protection  . . . .  28
       5.1.5.  A certificate from a legacy PKI using PKCS#10 request  30
       5.1.6.  Generate the key pair centrally at the (L)RA/CA . . .  32
         5.1.6.1.  Using symmetric key-encryption key management
                   technique . . . . . . . . . . . . . . . . . . . .  37
         5.1.6.2.  Using key agreement key management technique  . .  38
         5.1.6.3.  Using key transport key management technique  . .  39
       5.1.7.  Delayed enrollment  . . . . . . . . . . . . . . . . .  40
     5.2.  Revoking a certificate  . . . . . . . . . . . . . . . . .  45



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     5.3.  Error reporting . . . . . . . . . . . . . . . . . . . . .  47
     5.4.  Support messages  . . . . . . . . . . . . . . . . . . . .  49
       5.4.1.  General message and response  . . . . . . . . . . . .  49
       5.4.2.  Get CA certificates . . . . . . . . . . . . . . . . .  51
       5.4.3.  Get root CA certificate update  . . . . . . . . . . .  51
       5.4.4.  Get certificate request parameters  . . . . . . . . .  53
       5.4.5.  Get certificate management configuration  . . . . . .  54
       5.4.6.  Get enrollment voucher  . . . . . . . . . . . . . . .  56
   6.  LRA and RA focused certificate management use cases . . . . .  57
     6.1.  Forwarding of messages  . . . . . . . . . . . . . . . . .  57
       6.1.1.  Not changing protection . . . . . . . . . . . . . . .  59
       6.1.2.  Replacing protection  . . . . . . . . . . . . . . . .  60
         6.1.2.1.  Keeping proof-of-possession . . . . . . . . . . .  60
         6.1.2.2.  Breaking proof-of-possession  . . . . . . . . . .  61
       6.1.3.  Adding Protection . . . . . . . . . . . . . . . . . .  61
       6.1.4.  Initiating delayed enrollment . . . . . . . . . . . .  61
     6.2.  Revoking certificates on behalf of another's entities . .  61
     6.3.  Error reporting . . . . . . . . . . . . . . . . . . . . .  62
   7.  CMP message transport variants  . . . . . . . . . . . . . . .  63
     7.1.  HTTP transport  . . . . . . . . . . . . . . . . . . . . .  63
     7.2.  HTTPS transport using certificates  . . . . . . . . . . .  65
     7.3.  HTTPS transport using shared secrets  . . . . . . . . . .  65
     7.4.  File-based transport  . . . . . . . . . . . . . . . . . .  66
     7.5.  CoAP transport  . . . . . . . . . . . . . . . . . . . . .  66
     7.6.  Piggybacking on other reliable transport  . . . . . . . .  66
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  66
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  66
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  66
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  67
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  67
     11.2.  Informative References . . . . . . . . . . . . . . . . .  68
   Appendix A.  Additional Stuff . . . . . . . . . . . . . . . . . .  70
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  70

1.  History of changes

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

   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:




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   o  Added a short summary of [RFC4210] Appendix D and E in
      Section 2.3.

   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 7.1.

   From version 01 -> 02:

   o  Added some clarification on the key management techniques for
      protection of centrally generated keys in Section 5.1.6.

   o  Added some clarifications on the certificates for root CA
      certificate update in Section 5.4.3.

   o  Added a section to specify the usage of nested messages for RAs to
      add an additional protection for further discussion, see
      Section 6.1.3.

   o  Added a table containing endpoints for HTTP transport in
      Section 7.1 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 a already trusted
      PKI for further discussion, see Section 5.1.2.

   o  Complete specification of requesting a certificate from a legacy
      PKI using a PKCS#10 [RFC2986] request in Section 5.1.5.

   o  Complete specification of adding central generation of a key pair
      on behalf of an end entity in Section 5.1.6.

   o  Complete specification of handling delayed enrollment due to
      asynchronous message delivery in Section 5.1.7.

   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 5.4.

   o  Minor changes in wording.



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   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 4.1 and described in the standard enrollment use case in
      Section 5.1.1 due to discussion with Tomas Gustavsson.

   o  Change from OPTIONAL to RECOMMENDED for use case 'Revoke another's
      entities certificate' in Section 6.2, 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 5.2 and Section 6.2.

   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.

2.  Introduction

   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.brockhaus-lamps-cmp-updates].
   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, we aim at tailoring and specifying in more detail how to
   use these concepts to implement lightweight automated certificate
   management.

2.1.  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




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   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 certificate
   use cases.  But the specific needs of highly automated scenarios for
   a machine-to-machine communication are not covered sufficiently.

   As also 3GPP and UNISIG already put across, profiling is a way of
   coping with the challenges mentioned above.  To profile means to take
   advantage of the strengths of the given protocol, while explicitly
   narrowing down the options it provides to 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
   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 profile from this document and do not
   need to come up with individual profiles.

2.2.  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



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   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.

2.3.  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.

   [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 PKI management
      operation specified in Section 5.1.4 of this document.

   o  Certificate request; an (initialized) end entity requests a
      certificate from a CA (for any reason) using signature or shared
      secret based message authentication.  The content is similar to



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      PKI management operation specified in Section 5.1.2 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 PKI management
      operation specified in Section 5.1.3 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 transactions
   (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 PKI management operation specified in Section 5.4.3 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 PKI
      management operation specified in Section 5.4.4 and Section 5.4.5
      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
      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



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      signed by CA-1.  The content is similar to PKI management
      operation specified in Section 5.1.1 of this document.  The trust
      establishment of the EE in CA-1 and of the CA/RA in CA-X can be
      automated using, e.g., the exchange of a certificate management
      configuration as specified in Section 5.4.5 or an enrollment
      voucher as specified in Section 5.4.6 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.

   3GPP makes use of CMP [RFC4210] in its Technical Specification 133
   310 [ETSI-3GPP] 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 transactions
   between end entities and the RA/CA is specified in the 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] in 2015.

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

2.4.  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; initial
      transactions may also use HMAC,

   o  certification of a second key pair within the same transaction is
      not supported,

   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 transactions consist of request-response message pairs
      originating at the EE, i.e., announcement messages are omitted.



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   The profile specified in this document is compatible with the CMP
   profile for UMTS, LTE, and 5G network domain security and
   authentication framework [ETSI-3GPP], except that:

   o  protection of initial transactions may be HMAC-based,

   o  the subject name 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], except that:

   o  as of RFC 4210 [RFC4210] the messageTime is required to be
      Greenwich Mean Time coded as generalizedTime (Note: While UNISIG
      explicitely 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 UNISG may be in conflict with
      RFC 4210 [RFC4210].  Both time formats are described in RFC 5280
      [RFC5280] section 4.1.2.5.), and

   o  in case the request message is MAC protected, also the response,
      certConf, and PKIconf messages have a MAC-based protection (Note:
      if changing to signature protection of the response the caPubs
      field cannot be used securely anymore.).

2.5.  Scope of this document

   This document specifies requirements on generating 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
   resource 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 4, Section 5, and Section 6 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.



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   The receiving entity MUST NOT require its absence and if present MUST
   gracefully handle its presence.

2.6.  Structure of this document

   Section 3 introduces the general PKI architecture and approach to
   certificate management using CMP that is assumed in this document.
   Then it enlists the PKI management opertations specified in this
   document and describes them in general words.  The list of supported
   certificate management use cases is divided into mandatory,
   recommended, and optional ones.

   Section 4 profiles the CMP message header, protection, and extraCerts
   section as they are general elements of CMP messages.

   Section 5 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 transactions.

   Section 6 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
   transactions where the PKI component manages certificates on behalf
   of an EE or for itself.

   Section 7 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.

2.7.  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 uses 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.



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   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.

   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.

3.  Architecture and use cases

3.1.  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         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.brockhaus-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 components 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 5.1.6, can 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.

3.2.  Basic generic CMP message content

   Section 4 specifies the generic parts of the CMP messages as used
   later in Section 5 and Section 6.

   o  Header of a CMP message; see Section 4.1.

   o  Protection of a CMP message; see Section 4.2.




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   o  ExtraCerts field of a CMP message; see Section 4.3.

3.3.  Supported use cases

   Following the outlined scope from Section 2.5, this section gives a
   brief overview of the certificate management use cases specified in
   Section 5 and Section 6 and points out, whether an implementation by
   compliant EE or PKI component is mandatory, recommended or optional.

3.3.1.  Mandatory use cases

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

   Section 5 - End Entity focused certificate management use cases

   o  Request a certificate from a new PKI with signature protection;
      see Section 5.1.1.

   o  Request to update an existing certificate with signature
      protection; see Section 5.1.3.

   o  Error reporting; see Section 5.3.

   Section 6 - LRA and RA focused certificate management use cases

   o  Forward messages without changes; see Section 6.1.1.

   o  Forward messages with replaced protection and raVerified as proof-
      of-possession; see Section 6.1.2.2.

   o  Error reporting; see Section 6.3.

3.3.2.  Recommended Use Cases

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

   Section 5 - End Entity focused certificate management use cases

   o  Request a certificate from a PKI with MAC protection; see
      Section 5.1.4.

   o  Handle delayed enrollment due to asynchronous message delivery;
      see Section 5.1.7.




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   < TBD: There still some discussion ongoing if this should be
   recommended or optional. >

   o  Revoke an own certificate.

   Section 6 - LRA and RA focused certificate management use cases

   o  Revoke another's entities certificate.

3.3.3.  Optional use cases

   The optional use cases support specific requirements seen only in a
   subset of environments.

   Section 5 - End Entity focused certificate management use cases

   o  Request a certificate from a legacy PKI using a PKCS#10 [RFC2986]
      request; see Section 5.1.5.

   o  Add central generation of a key pair to a certificate request; see
      Section 5.1.6.  If central key generation is supported, the key
      agreement key management technique is REQUIRED to be supported,
      and the key transport and symmetric key-encryption key management
      techniques are OPTIONAL.

   o  Additional support messages, e.g., to update a Root CA certificate
      or to request an RFC 8366 [RFC8366] voucher; see Section 5.4.

   Section 6 - LRA and RA focused certificate management use cases

   o  Initiate delayed enrollment due to asynchronous message delivery;
      see Section 6.1.4.

3.4.  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.

   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 constraines to choose whatever transport is suitable.

   Recommended transport



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   o  Transfer CMP messages using HTTP; see Section 7.1.

   Optional transport

   o  Transfer CMP messages using HTTPS with certificate-based
      authentication; see Section 7.2.

   o  Transfer CMP messages using HTTPS with shared-secret based
      protection; see Section 7.3.

   o  File-based CMP message transport.

   < TBD: Motivation see Section 7.4 >

   < TBD: Michael Richardson proposed to also specify a CoAP based
   message transport profile.  If there is further support for this
   profile and someone volunteering to provide the necessary input for
   this section, I would add it to the document. >

4.  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 5 and
   Section 6 are standardized to the maximum extent possible.
   Therefore, the generic parts of a CMP message are described centrally
   in this section.

   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



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   The general contents of the message header, protection, and
   extraCerts fields are specified in the Section 4.1 to Section 4.3.

   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 5 and Section 6.

   The behavior in case an error occurs while handling a CMP message is
   described in Section 6.3.

4.1.  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 transaction.

   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.

   header
     pvno                        REQUIRED
       -- MUST be set to 2 to indicate CMP V2
     sender                      REQUIRED
       -- MUST be the subject of the protection certificate used for,
       -- 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 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 or algorithm
       -- id-PasswordBasedMac algorithm used for calculation of the



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       -- 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 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
       -- transaction
     generalInfo                 OPTIONAL
       implicitConfirm           OPTIONAL
         ImplicitConfirmValue    REQUIRED
       -- The field is optional though it only applies to
       -- ir/cr/kur/p10cr requests and ip/cp/kup responses
       -- 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

4.2.  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                    REQUIRED
       -- MUST contain the signature calculated using the signature
       -- algorithm specified in protectionAlg




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   Only for MAC-based protection major differences apply as described in
   the respective message.

   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 requirements for checking certificates given in [RFC5280]
   MUST be followed for the CMP message protection.  In case the CMP
   signer certificates 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.

4.3.  General description of CMP message extraCerts

   This section describes the generic extraCerts field of all CMP
   messages with signature-based protection.

   extraCerts                    RECOMMENDED
       -- SHOULD contain the protection certificate together with its
       -- chain, if needed
       -- If present, the first certificate in this field MUST
       -- be the protection certificate
       -- Self-signed certificates SHOULD NOT be included in
       -- extraCerts and MUST NOT be trusted based on the listing in
       -- extraCerts in any case

5.  End Entity focused certificate management use cases

   This chapter focuses on the communication of the EE and the first PKI
   component 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 chapter cover the following certificate management
   use cases:

   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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   The use cases mainly specify the message body of the CMP messages and
   utilize the specification of the message header, protection and
   extraCerts as specified in Section 5.

   The behavior in case an error occurs is described in Section 5.3.

   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-3GPP], and [UNISIG] do.  Using the
   message sequences described here require agreement upon the
   algorithms to support and thus the algorithm identifiers for the
   specific target environment.

5.1.  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 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 (L)RA/
   CA responds with a message containing a certificate, the EE MUST
   reply with a confirmation message.  The (L)RA/CA 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 (L)RA/CA needs to verify
   whether this EE is authorized to obtain a certificate with the
   requested subject and other attributes and extensions.  Especially
   when removing the protection provided by the EE and applying a new
   protection the (L)RA 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 6.1.2).

   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 MUST be indicated by the
   extended key usage in the (L)RA/CA certificate as specified in CMP
   Updates [I-D.brockhaus-lamps-cmp-updates].

5.1.1.  A certificate from a new PKI with signature protection

   This message sequence 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 certificate, 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 configuration means.  The
   initialization request message is signature-protected using the
   existing certificate.

   Preconditions:

   1  The EE MUST have a certificate enrolled by an external PKI in
      advance to this transaction to authenticate itself to the (L)RA/CA
      using signature-based protection, e.g., using a manufacturer
      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 or other configuration means.  If the EE does not know the



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      name of the CA, the (L)RA/CA MUST know where to route this request
      to.

   3  The EE MUST authenticate responses from the (L)RA/CA; trust MAY be
      established using an enrollment voucher or other configuration
      means

   4  The (L)RA/CA MUST trust the external PKI the EE uses to
      authenticate itself; trust MAY be established using some
      configuration means

   This message sequence is like that given in [RFC4210] Appendix E.7.

   Message flow:

   Step# EE                                  (L)RA/CA
     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 message sequence 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 a
   transaction, it MUST request this by setting the implicitControlValue
   in the ir to NULL.

   If the CA accepts the 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 (L)RA/CA



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   MAY confirm this by also setting the implicitControlValue in the ip
   to NULL.

   If the EE did not request implicit confirmation or the request was
   not granted by the (L)RA/CA 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 (L)RA/CA with a pkiConf message.  If the (L)RA/CA
   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 (L)RA/CA 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 4.1

   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
       -- MUST contain the suggested subject name of the EE
       -- certificate
           publicKey             REQUIRED
             algorithm           REQUIRED
       -- 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



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       -- certificate in case of local key-generation
       -- MUST contain a zero-length BIT STRING in case a central key
       -- generation is requested
       -- MUST include the subject public key algorithm ID and value
           extensions            OPTIONAL
       -- MAY include end-entity-specific X.509 extensions of the
       -- requested certificate like subject alternative name,
       -- key usage, and extended key usage
       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 4.2

   extraCerts                    REQUIRED
       -- As described in section 4.3


   Certification Response -- ip

   Field                         Value

   header
       -- As described in section 4.1

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



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       -- 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 no certConf and pkiConf messages will
       -- 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 4.2

   extraCerts                    REQUIRED
       -- As described in section 4.3
       -- MUST contain the chain of the issued certificate
       -- Duplicate certificates MAY be omitted


   Certificate Confirmation -- certConf

   Field                         Value

   header
       -- As described in section 4.1

   body
       -- The message of the EE sends confirmation to the (L)RA/CA



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       -- 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 or logging
           failInfo              OPTIONAL
       -- MUST be present if status is "rejection"
       -- MUST be absent if the status is "accepted"

   protection                    REQUIRED
       -- As described in section 4.2
       -- MUST use the same certificate as for protection of the ir

   extraCerts                    RECOMMENDED
       -- SHOULD contain the protection certificate together with its
       -- chain
       -- 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

   Field                         Value

   header
       -- As described in section 4.1

   body
     pkiConf                     REQUIRED
       -- The content of this field MUST be NULL

   protection                    REQUIRED



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       -- As described in section 4.2
       -- SHOULD use the same certificate as for protection of the ip

   extraCerts                    RECOMMENDED
       -- SHOULD contain the protection certificate together with its
       -- chain
       -- 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

5.1.2.  A certificate from a trusted PKI with signature protection

   < TBD: In case the PKI is already trusted the cr/cp messages could be
   used instead of ir/ip.  It needs to be decided, whether an additional
   section should be added here, or the previous section should be
   extended to also cover this use case. >

5.1.3.  Update an existing certificate with signature protection

   This message sequence 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 and
   possession of the private key for the certificate to be updated to
   the PKI.  Therefore, the key update request message is signed using
   the certificate that is to be updated.

   The general message flow for this message sequence is the same as
   given in Section 5.1.1.

   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 exchange is like that given in
   [RFC4210] Appendix D.6.

   The message sequence for this exchange is identical to that given in
   Section 5.1.1, 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 of the CertTemplate MUST contain the subject
      name of the existing certificate to be updated, without
      modifications.

   4  The CertTemplate MUST contain the subject, issuer and publicKey
      fields only.

   5  The regCtrl OldCertId SHOULD be used to make clear, even in case
      an (L)RA changes the message protection, which certificate is to
      be used.

   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

5.1.4.  A certificate from a PKI with MAC protection

   This message sequence 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 (L)RA checking the MAC-
   protection SHOULD replace this protection according to Section 6.1.2
   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 message sequence is the same as
   given in Section 5.1.1.

   Preconditions:






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   1  The EE and the (L)RA/CA 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 or other configuration means.  If the EE does not know the
      name of the CA, the (L)RA/CA MUST know where to route this request
      to.

   3  The EE MUST authenticate responses from the (L)RA/CA; trust MAY be
      established using the shared symmetric key.

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

   The message sequence for this exchange is identical to that given in
   Section 5.1.1, 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.

   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 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 certificate management transaction 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 OWF 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

   < TBD: SHA-1 is no collision resistant hash algorithm.  Due to this
   fact the usage of SHA-1 has significantly decreased.  Currently HMAC-
   SHA-1seems relatively secure, it is currently recommended by
   cryptographers to also depreciate the uses of SHA-1 in the context of
   HMAC calculation.  Should we depreciate the support of SHA-1 here
   completely? >

5.1.5.  A certificate from a legacy PKI using PKCS#10 request

   This message sequence 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 5.1.1
   or Section 5.1.4.

   In contrast to the other transactions described in Section 5.1, 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 CMP
   [RFC4210] or CRMF [RFC4211] messages.  In such case the (L)RA must
   extract the PKCS#10 certificate request from the p10cr and provides
   it separately to the CA.

   The general message flow for this message sequence is the same as
   given in Section 5.1.1, but the public key is contained in the
   subjectPKInfo of the PKCS#10 certificate request.

   Preconditions:




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   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 (L)RA/CA.

   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 or other configuration means.  If the EE does not know the
      name of the CA, the (L)RA/CA MUST know where to route this request
      to.

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

   4  The (L)RA/CA 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 profile for this exchange is identical to that given in
   Section 5.1.1, with the following changes:

   1  The body of the first request and response MUST be p10cr and cp,
      respectively.

   2  The subject name of the CA MUST be in the recipient field of the
      p10cr message header.

   3  The certReqId in the cp message MUST be 0.

   4  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 4.1

   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
       -- MUST include the subject public key algorithm ID and value
         attributes              OPTIONAL
       -- MAY contain a set of end-entity-specific attributes 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 4.2

   extraCerts                    REQUIRED
       -- As described in section 4.3

5.1.6.  Generate the key pair centrally at the (L)RA/CA

   This functional extension can be applied in combination with
   certificate enrollment as described in Section 5.1.1 and
   Section 5.1.4.  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
   central PKI components will perform the key generation.  This
   component must have a proper (L)RA/CA certificate containing the
   additional extended key usage id-kp-cmcKGA to be identified by the EE
   as a legitimate key-generation instance.  In case the (L)RA generated




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   the new key pair for the EE, it can use Section 5.1.1 to
   Section 5.1.4 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 hold 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, we believe that a decent security architecture should
   anyways support good random number generation on the EE side or
   provide enough entropy for the RNG seed during manufacturing to
   guarantee good initial pseudo-random number generation.

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

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

   Note: Besides the initial enrollment right after the very first
   bootup of the device, where entropy available on the device may be
   insufficient, we do not see any good reason for central key
   generation.

   Note: As mentioned in Section 3.1 central key generation may be
   required in a push model, where the certificate response message is
   transferred by the (L)RA/CA 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 (L)RA/
   CA 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.brockhaus-lamps-cmp-updates] also the alternative



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   EnvelopedData can be used.  In CRMF Section 2.1.9 [RFC4211] the use
   of EncryptedValue has been deprecated in favor of the EnvelopedData
   structure.  Therefore, this profile specifies using EnvelopedData as
   specified in CMS Section 6 [RFC5652] to offer more crypto agility.

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

                 Figure 3: Encrypted private key container

   The (L)RA/CA 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 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-cmpKGA as
   described in CMP Updates [I-D.brockhaus-lamps-cmp-updates] to show
   the authorization to generate key pairs on behalf of an EE.

   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
   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 (L)RA/CA depends on the authentication mechanism the EE choose to
   protect the request message, see CMP Updates section 3.4
   [I-D.brockhaus-lamps-cmp-updates] for more details on which key
   management technique to use.




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   o  MAC protected request message: The content-encryption key SHALL be
      protected using the symmetric key-encryption key management
      technique, see Section 5.1.6.1, only if the EE used MAC protection
      for the respected request message.

   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 5.1.6.2, 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.

   o  Signature protected request message 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 5.1.6.3, if the certificate
      used by the EE for signing the respective request message contains
      the key usage keyEncipherment and not keyAgreement.

   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
   symmetric key-encryption key management technique shall only be used
   in combination with MAC protection, which is a side-line in this
   profile.  Therefore, this profile REQUIRES support of the key
   agreement key management technique and the key transport and
   symmetric key-encryption 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 encryption algorithm.

   Note: Depending on the lifetime of the certificate and the
   criticality of the generated private key, it is advisable to use the
   strongest possible 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



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               recipientInfo     REQUIRED
       -- MUST be either KEKRecipientInfo (see section 5.1.5.1),
       -- KeyAgreeRecipientInfo (see section 5.1.5.2), or
       -- KeyTransRecipientInfo (see section 5.1.5.3) is used
             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 encrypted signedData structure as specified in
       -- CMS [RFC5652] section 5
                 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
       -- MUST be id-data
                   content       REQUIRED
       -- MUST be the privateKey as OCTET STRING
                 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



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                   sid           REQUIRED
                     subjectKeyIdentifier
                                 REQUIRED
       -- MUST be the subjectKeyIdentifier of the signer's certificate
                   digest algorithm
                                 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
       -- 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

5.1.6.1.  Using symmetric key-encryption key management technique

   This key management technique can be applied in combination with the
   message flow specified in Section 5.1.4 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 seed in the PBMParameter sequence.  To use this key
   management technique the KEKRecipientInfo structure MUST be used in
   the contentInfo field.

   The KEKRecipientInfo structure included into the envelopedData
   structure is specified in CMS Section 6.2.3 [RFC5652].






















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   The detailed description of the KEKRecipientInfo structure looks like
   this:

               recipientInfo     REQUIRED
       -- MUST be KEKRecipientInfo as specified in
       -- CMS section 6.2.3 [RFC5652]
                 version         REQUIRED
       -- MUST be set to 4
                 kekid           REQUIRED
                   keyIdentifier REQUIRED
       -- MUST contain the same value as the senderKID in the respective
       -- request messages
                 keyEncryptionAlgorithm
                                 REQUIRED
       -- MUST be id-PasswordBasedMac
                   PBMParameter  REQUIRED
                     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
                     owf         REQUIRED
       -- MUST be the same value than used in the PBMParameter
       -- data structure 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
                     mac         REQUIRED
       -- MUST be the same as in the contentEncryptionAlgorithm field
                 encryptedKey    REQUIRED
       -- MUST be the encrypted content-encryption key

   < TBD: To make use of a different symmetric keys for encrypting the
   private key and for MAC-protection of the CMP message, we derive
   another key using the same PBMParameter structure from CMP, even
   though from the perspective of field names, it is not intended to be
   used for deriving encryption keys.  Does anyone sees a better
   solution here? >

5.1.6.2.  Using key agreement key management technique

   This key management technique can be applied in combination with the
   message flow specified in Section 5.1.1 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



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   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].

   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

5.1.6.3.  Using key transport key management technique

   This key management technique can be applied in combination with the
   message flow specified in Section 5.1.1 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



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   this key management technique the KeyTransRecipientInfo structure
   MUST be used in the contentInfo field.

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

   The detailed description of the KeyTransRecipientInfo structure looks
   like this:

               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

5.1.7.  Delayed enrollment

   This functional extension can be applied in combination with
   certificate enrollment as described in Section 5.1.1 to
   Section 5.1.5.  The functional extension can be used in case a (L)RA/
   CA 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 component directly communicating with the EE
   initiates the delayed enrollment.

   The PKI component initiating the delayed enrollment MUST include the
   status "waiting" in the response and this response MUST not contain
   the newly issued certificate.  When receiving a response with status
   "waiting" the EE MUST send a poll request to the (L)RA/CA.  The PKI
   component 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 (L)RA/CA 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,




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   the EE can continue the original message sequence as described in the
   respective section of this document, e.g., send a certConf message.

   Typically, intermediate PKI entities SHOULD NOT change the sender and
   recipient nonce even in case an intermediate (L)RA 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 6.1.4,
   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 recipientNonce set to the value of the senderNonce
   in the original request message (copied by the CA).  The LRA needs to
   replace the recipientNonce in this case with the senderNonce of the
   last pollReq because the EE will validate it in this way.





































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   Message flow:

   Step# EE                                   (L)RA/CA
    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 scheme




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   body
       -- The response of the (L)RA/CA 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 profile, but
       -- MUST use the protection key of the (L)RA/CA initiating the
       -- delayed enrollment and creating this response message

   extraCerts                    REQUIRED
       -- MUST contain certificates as described for the first response
       -- message of the respective profile.
       -- 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 scheme

   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

   protection                    REQUIRED



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       -- MUST contain protection as described for the certConf message
       -- of the respective profile

   extraCerts                    OPTIONAL
       -- If present, it MUST contain certificates as described for the
       -- certConf message of the respective profile.


   Polling Response -- pollRep

   Field                         Value

   header
       -- MUST contain a header as described for the pkiConf message
       -- of the respective scheme

   body                          pollRep
       -- 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 (L)RA/CA 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 profile.


   Final response -- ip/cp/kup

   Field                         Value

   header
       -- MUST contain a header as described for the first
       -- response message of the respective scheme
       -- but the recipientNonce MUST be the senderNonce of the last
       -- pollReq message




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   body
       -- The response of the (L)RA/CA to the initial request as
       -- described in the respective profile

   protection                    REQUIRED
       -- MUST contain protection as described for the first response
       -- message of the respective profile, but
       -- MUST use the protection key of the (L)RA/CA 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 profile

5.2.  Revoking a certificate

   This message sequence 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 (L)RA 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 (L)RA/CA 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.

   Message flow:


   Step# EE                                  (L)RA/CA
     1   format rr
     2                      ->   rr      ->
     3                                        handle, re-protect or
                                                forward rr
     4                                        receive rp
     5                      <-   rp      <-
     6   handle rp





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   For this profile, the EE MUST include exactly one RevDetails
   structure in the rr.  In case no error occurred the response to the
   rr MUST be an rp message.  The (L)RA/CA 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 4.1

   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
       -- As described in section 4.2 and the private key related to the
       -- certificate to be revoked

   extraCerts                    REQUIRED
       -- As described in section 4.3


   Revocation Response -- rp

   Field                         Value

   header
       -- As described in section 4.1



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   body
       -- The responds of the (L)RA/CA 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 4.2

   extraCerts                    REQUIRED

5.3.  Error reporting

   This functionality should be used by an EE to report any error
   conditions upstream to the (L)RA/CA.  Error reporting by the (L)RA
   downstream to the EE is described in Section 6.3.

   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.

   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 error is reported in the PKIStatusInfo
   structure of the respective message.

   The (L)RA/CA MUST respond to an error message with a pkiConf message,
   or with another error message if any part of the header is not valid.
   Both sides MUST treat this message as the end of the current
   transaction.

   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.




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   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 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 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.

   Detailed error message description:

   Error Message -- error

   Field                         Value

   header
       -- As described in section 4.1

   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 4.2

   extraCerts                    OPTIONAL
       -- As described in section 4.3






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5.4.  Support messages

   The following support messages offer on demand in-band transport of
   content that may be provided by the (L)RA/CA and relevant to the EE.
   The general messages and general response are used for this purpose.
   Depending on the environment, these requests are 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 messages as needed in a specific
   environment.

   Possible content described here address:

   o  Request of CA certificates

   o  Update of Root CA certificates

   o  Parameters needed for a planned certificate request message

   o  Voucher request and enrollment voucher exchange

5.4.1.  General message and response

   The general message transaction 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 5.3.

   Message flow:

   Step# EE                                   (L)RA/CA
    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




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   Field                         Value

   header
       -- As described in section 4.1

   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 scheme
       -- described below
       infoValue                 OPTIONAL
       -- MUST be as described in the specific scheme described
       -- below

   protection                    REQUIRED
       -- As described in section 4.2

   extraCerts                    REQUIRED
       -- As described in section 4.3


   General Response -- genp

   Field                         Value

   header
       -- As described in section 4.1

   body
       -- The response of the (L)RA/CA to the information request
     genp                        REQUIRED
       -- MUST contain exactly one element of type
       -- InfoTypeAndValue
       infoType                  REQUIRED
       -- MUST be the OID identifying the specific scheme
       -- described below
       infoValue                 OPTIONAL
       -- MUST be as described in the specific scheme described
       -- below

   protection                    REQUIRED
       -- As described in section 4.2

   extraCerts                    REQUIRED
       -- As described in section 4.3



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5.4.2.  Get CA certificates

   This scheme can be used by an EE to request CA certificates from the
   (L)RA/CA.

   An EE requests CA certificates from the (L)RA/CA by sending a general
   message with OID id-it-getCaCerts.  The (L)RA/CA 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.

   < NOTE: The OID id-it-getCaCerts is not yet defined.  It should be
   registered in the tree 1.3.6.1.5.5.7.4 (id-it) like other infoType
   OIDs, see CMP Appendix F [RFC4210] on page 92. >

   The profile for this exchange is as given in Section 5.4.1, with the
   following specific content:

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

   2  the infoValue of the request MUST be absent

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

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

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

5.4.3.  Get root CA certificate update

   This scheme can be used by an EE to request an update of an existing
   root CA Certificate by the EE.  It utilizes the CAKeyUpdAnnContent
   structure as described in CMP Appendix E.4 [RFC4210] as response to a
   respective general message.

   An EE requests a root CA certificate update from the (L)RA/CA by
   sending a general message with OID id-it-caKeyUpdateInfo as infoType
   and no infoValue.  The (L)RA/CA 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.



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   These three certificates are described in more detail in section
   4.4.1, section 6.2, and Appendix E.3 of [RFC4210].  The newWithNew
   certificate is the new root CA certificates and is REQUIRED to be
   present in the response message.  The newWithOld certificate
   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 whishes 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 profile for this exchange is as given in Section 5.4.1, with the
   following specific content:

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

   2  the infoValue of the request MUST be absent

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

   The infoValue field of the general response containing the id-it-
   caKeyUpdateInfo 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
           caKeyUpdateInfo       REQUIRED
       -- MUST be present and be of type CAKeyUpdAnnContent
             oldWithNew          OPTIONAL
       -- MUST 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
             newWithOld          RECOMMENDED
       -- MUST 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
             newWithNew          REQUIRED
       -- MUST be present if infoValue is present
       -- MUST contain the new root CA certificate








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5.4.4.  Get certificate request parameters

   This scheme can be used by an EE to request configuration parameters
   for a planned certificate request transaction.

   An EE requests certificate request parameters from the (L)RA/CA by
   sending a general message with OID id-it-getCSRParam.  The (L)RA/CA
   responds with a general response with the same OID that either
   contains the required fields, e.g., algorithm identifier for key pair
   generation or other attributes and extensions or with no content in
   case no specific requirements are made by the (L)RA/CA.

   < NOTE: The OID id-it-getCSRParam is not yet defined.  It should be
   registered in the tree 1.3.6.1.5.5.7.4 (id-it) like other infoType
   OIDs, see CMP Appendix F [RFC4210] on page 92. >

   The EE SHOULD follow the requirements from the recieved CertTemplate
   and the optional RSA key length.  In case a field is present but the
   value is absent, it means that this field is required but its content
   has to be provided by the EE.

   < TBD: There is some more explanation needed to explain how to
   prefill the certTemplate structure.  Possibly an example will help to
   clarify this. >

   The profile for this exchange is as given in Section 5.4.1, with the
   following specific content:

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

   2  the infoValue of the request MUST be absent

   3  if present, the infoValue of the response MUST be a SEQUENCE of a
      certTemplate structure and an rsaKeyLen field of type INTEGER

















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

         infoValue               OPTIONAL
       -- MUST be absent if no requirements are available
       -- MUST be present if the (L)RA/CA has any requirements on the
       -- content of the certificates to be requested.
           certTemplate          REQUIRED
       -- MUST be present if infoValue is present
       -- MUST contain the prefilled certTemplate structure
           rsaKeyLen             OPTIONAL
       -- This field is of type INTEGER. Any reasonable RSA key length
       -- SHOULD be specified if the algorithm in the
       -- subjectPublicKeyInfo field of the certTemplate is of type
       -- rsaEncryption.

5.4.5.  Get certificate management configuration

   This scheme can be used by an EE to request the current certificate
   management configuration information by the EE in advance to a
   planned certificate management transaction, e.g., in case no out-of-
   band transport is available.  Such certificate management
   configuration can consist of all information the EE needs to know to
   generate and deliver a proper certificate request, such as

   o  algorithm, curve, and key length for key generation

   o  various certificate attributes and extensions to be used for the
      certificate request

   o  specific host name, port and path on the RA/LRA to send this CMP
      request to

   o  Infrastructure Root CA Certificate, e.g., the root of the (L)RA
      TLS and CMP signer certificates.

   There is an overlap with Section 5.4.2 with regard to transport of CA
   certificates and with Section 5.4.4 with regard to key generation
   parameter and certificate request attributes and extensions.  This
   profile offers to request a proprietary configuration file containing
   all information needed in one exchange.

   < TBD: Especially with section 5.4.4 there is some overlap regarding
   algorithms, attributes and, extensions of the certificate that will
   be requested.  It needs to be decided if both variants have a right
   to exist next to the other or if one option should be removed from
   this document. >




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   An EE requests certificate management configuration from the (L)RA/CA
   by sending a general message with the OID id-it-getCertMgtConfig.
   The (L)RA/CA responds with a general response with the same OID that
   either contains a certMgtConfig field containing the configuration
   file encoded as OCTET STRING or with no content in case no
   certificate management configuration is available.

   < NOTE: The OID id-it-getCertMgtConfig is not yet defined.  It should
   be registered in the tree 1.3.6.1.5.5.7.4 (id-it) like other infoType
   OIDs, see CMP Appendix F [RFC4210] on page 92. >

   The EE SHOULD use the contents of this certMgtConfig to format and
   deliver the certificate request.  The certificate management
   configuration may contain contact details, e.g., like an URI and
   issuing CA distinguished name, where to address the request messages
   to and may also contain certificate request parameters as described
   in Section 5.4.4.

   The certMgtConfig field may be of any format suitable for the EE,
   e.g., CMS [RFC5652], JWT [RFC7519] or, XML [W3C_XML].  The
   certMgtConfig contents MAY be signed, e.g., like CMS SignedData
   [RFC5652], JWS [RFC7515] or, XML-DSig [W3C_XML-Dsig].  For
   interoperability the format of the certMgtConfig field should be
   specified in detail if needed.

   The profile for this exchange is as given in Section 5.4.1, with the
   following specific content:

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

   2  the infoValue of the request MUST be absent

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

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

         infoValue               OPTIONAL
       -- MUST be absent if no certificate management configuration
       -- is available
       -- MUST be present if the (L)RA/CA provides any certificate
       -- management configuration
           certMgtConfig         REQUIRED
       -- MUST be present if infoValue is present
       -- MUST contain the certificate management configuration as OCTET
       -- OCTET STRING




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5.4.6.  Get enrollment voucher

   This scheme can be used by an EE to request an enrollment voucher
   containing the root certificate of a new, additional, or alternative
   PKI to establish trust in this PKI, e.g., in case no out-of-band
   transport is available.  Such an enrollment voucher can be used in
   advance to an enrollment to this new environment.  It may contain
   further information depending on the use case.

   An EE requests an enrollment voucher from the (L)RA/CA by sending a
   general message.  The (L)RA/CA responds with a general response with
   the same OID that either contains the voucher or with no content in
   case no voucher is available.

   The (L)RA MAY use the content of the voucherRequest to get an
   enrollment voucher from other backend components, e.g., as described
   in BRSKI [I-D.ietf-anima-bootstrapping-keyinfra].  The EE SHOULD use
   the contents of the received enrollmentVoucher to authenticate the
   (L)RA/CA it is about to enroll to.  The enrollment voucher may for
   example contain the Root CA certificate of the new PKI or the CMP
   signer certificate of the (L)RA.  The general response message MUST
   be properly authenticated and the EE MUST verify the authorization of
   the sender to install new root certificates.  One example for an
   enrollment voucher is specified in RFC8366 [RFC8366].

   The voucherRequest and enrollmentVoucher fields may be of any format
   suitable for the EE, e.g., CMS [RFC5652], JWT [RFC7519] or, XML
   [W3C_XML].  The voucherRequest and enrollmentVoucher contents MAY
   contain a signature, e.g., CMS SignedData [RFC5652], JWS [RFC7515]
   or, XML-DSig [W3C_XML-Dsig].  For interoperability the format of the
   voucherRequest and enrollmentVoucher field schould be specified in
   detail if needed, e.g., as defined in BRSKI
   [I-D.ietf-anima-bootstrapping-keyinfra] and RFC8366 [RFC8366].

   < TBD: The vontent of the voucherRequest and enrollmentVoucher fields
   can also be linited to the specufucations in BRSKI
   [I-D.ietf-anima-bootstrapping-keyinfra] and RFC8366 [RFC8366]. >

   The profile for this exchange is as given in Section 5.4.1, with the
   following specific content:

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

   2  if present, the infoValue of the request MUST be a voucherRequest
      structure





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   3  if present, the infoValue of the response MUST be an
      enrollmentVoucher structure

   The infoValue field of the general message containing the id-it-
   getEnrollmentVoucher extension looks like this:

         infoValue               OPTIONAL
       -- MUST be absent if no voucher request is available
       -- MUST be present if the EE provides the voucher request
           voucherRequest        REQUIRED
       -- MUST be present if infoValue is present
       -- MUST contain the voucher request as OCTET STRING

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

         infoValue               OPTIONAL
       -- MUST be absent if no enrollment voucher is available
       -- MUST be present if the (L)RA/CA provides the enrollment
       -- voucher
           enrollmentVoucher     REQUIRED
       -- MUST be present if infoValue is present
       -- MUST contain the enrollment voucher as OCTET STRING

6.  LRA and RA focused certificate management use cases

   This chapter focuses on the communication of PKI backend components
   with each other.  Depending on the network and PKI solution design,
   these will either be an LRA, RA or CA.

   Typically, an (L)RA forwards messages from downstream, but it may
   also reply to them itself.  Besides forwarding of received messages
   an (L)RA could also need to revoke certificates of EEs, report
   errors, or may need to manage its own certificates.

   < TBD: In CMP Updates [I-D.brockhaus-lamps-cmp-updates] additional
   extended key usages like id-kp-cmpRA will be defined to indicate that
   a key pair is entitled to be used for signature-based protection of a
   CMP message by an (L)RA/CA. >

6.1.  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 component MUST be sent to the next (upstream) PKI
   component.  This PKI component MUST forward response messages to the
   next (downstream) PKI component or EE.




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   The (L)RA 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 5.3 and Section 6.3.

   An (L)RA SHOULD not change the received message if not necessary.
   The (L)RA 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 components has one or more
   functionalities, e.g.,

   o  An (L)RA 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  An (L)RA may need to add fields to certificate request messages.

   o  An (L)RA may need to store data from a message in a database for
      later usage or documentation purposes.

   o  An (L)RA may provide traversal of a network boundary.

   o  An (L)RA may need to double-check if the messages transferred back
      and forth are properly protected and well formed.

   o  An (L)RA may provide a proof that it has performed all required
      checks.

   o  An (L)RA may initiate a delayed enrollment due to offline upstream
      communication or registration officer interaction.

   o  An (L)RA may grant the request of an EE to omit sending a
      confirmation message.

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

   Therefore, the decision if a message should be forwarded



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   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]).

   < TBD: In [CMP Updates] different circumstances that require adding
   of an additional protection by an (L)RA or batching CMP messages at
   an (L)RA by using the nested messages is described.  It needs to be
   decided which of these variants should be specified here.  Finally, I
   guess they will all be OPTIONAL. >

   This section specifies the different options an (L)RA may implement
   and use.

   An (L)RA MAY update the protection of a message

   o  if the (L)RA performs changes to the header or the body of the
      message,

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

   o  if the (L)RA needs to protect the message using a key and
      certificate from a different PKI, or

   o  if the (L)RA 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 (L)RA 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.

6.1.1.  Not changing protection

   This message adaptation can be used by any (L)RA to forward an
   original CMP message without changing the header, body or protection.
   In any of these cases the (L)RA acts more like a proxy, e.g., on a




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   network boundary, implementing no specific RA-like security
   functionality to the PKI.

   This message adaptation MUST be used for forwarding kur messages that
   must not be approved by the respective (L)RA.

6.1.2.  Replacing protection

   The following two message adaptations can be used by any (L)RA to
   forward a CMP message with or without changes, but providing its own
   protection using its CMP signer key providing approval of this
   message.  In this case the (L)RA 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
   (L)RA MUST verify the protection provided by the EE or by the
   previous PKI component and approve its content including any own
   modifications.  For certificate requests the (L)RA 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
   (L)RA, the current (L)RA MUST verify its protection and approve its
   content including any own modifications.  For certificate requests
   the (L)RA MUST check that the other (L)RA, as authenticated by the
   message protection, is authorized to issue or forward the request.

   These message adaptations MUST NOT be applied to kur request messages
   as described in Section 5.1.3 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.

6.1.2.1.  Keeping proof-of-possession

   This message adaptation can be used by any (L)RA 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
   (L)RA provides a proof of verifying and approving of the message as
   described above.





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   In case the (L)RA modifies the certTemplate of an ir or cr message,
   the message adaptation in Section 6.1.2.2 needs to be applied
   instead.

6.1.2.2.  Breaking proof-of-possession

   This message adaptation can be used by any (L)RA 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 or applying an initial protection using its
   own CMP signer key the (L)RA provides a proof of verifying and
   approving the new message as described above.

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

   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 (L)RA
       -- verified the popo of the original message.

6.1.3.  Adding Protection

   < TBD: In [CMP Updates] different circumstances that require adding
   of an additional protection by an (L)RA or batching CMP messages at
   an (L)RA by using the nested messages is described.  It needs to be
   decided which of these variants should be specified here.  Finally, I
   guess they will all be OPTIONAL. >

6.1.4.  Initiating delayed enrollment

   This message adaptation can be used by an (L)RA to initiate delayed
   enrollment.  In this case a (L)RA/CA MUST add the status waiting in
   the response message.  The (L)RA/CA MUST then reply to the pollReq
   messages as described in Section 5.1.7.

6.2.  Revoking certificates on behalf of another's entities

   This message sequence can be used by an (L)RA to revoke a certificate
   of any other entity.  This revocation request message MUST be signed




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   by the (L)RA using its own CMP signer key to prove to the PKI
   authorization to revoke the certificate on behalf of the EE.

   The general message flow for this profile is the same as given in
   section Section 5.2.

   Preconditions:

   1  the certificate to be revoked MUST be known to the (L)RA

   2  the (L)RA MUST have the authorization to revoke the certificates
      of other entities issued by the corresponding CA

   The profile for this exchange is identical to that given in section
   Section 5.2, with the following changes:

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

   2  the (L)RA acts as EE for this message exchange

   3  the rr messages MUST be signed using the CMP signer key of the
      (L)RA.

6.3.  Error reporting

   This functionality should be used by the (L)RA to report any error
   conditions downstream to the EE.  Potential error reporting by the EE
   upstream to the (L)RA/CA is described in Section 5.3.

   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 (L)RA reports the errors in the PKIStatusInfo
   structure of the respective message as described in Section 5.3.

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







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7.  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.

7.1.  HTTP transport

   This transport mechanism can be used by an EE and (L)RA/CA to
   transfer CMP messages over HTTP.  If HTTP transport is used the
   specifications as described in [RFC6712] MUST be followed.

   Each PKI management entity supporting HTTP(S) transport MUST support
   the use of the path-prefix of '/.well-known/' as defined in [RFC5785]
   and the registered name of 'cmp' to ease interworking in a multi-
   vendor environment.

   The CMP client MUST be configured with sufficient information to form
   the CMP server URI.  This MUST be at least the authority portion of
   the URI, e.g., 'www.example.com:80', or the full operational path of
   the CA/RA.  An additional arbitrary label, e.g., 'arbitraryLabel1',
   MAY be configured as a separate component or as part of the full
   operational path to provide further information to address multiple
   CAs or certificate profiles.  A valid full operational path can look
   like this:

   1  http://www.example.com/.well-known/cmp

   2  http://www.example.com/.well-known/cmp/keyupdate

   3  http://www.example.com/.well-known/cmp/arbitraryLabel1

   4  http://www.example.com/.well-known/cmp/arbitraryLabel1/keyupdate






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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)                      |                      | 5.1.1    |
   +---------------------------------+----------------------+----------+
   | Enroll client to existing PKI   |    /certification    | Section  |
   | (OPTIONAL)                      |                      | 5.1.2    |
   +---------------------------------+----------------------+----------+
   | Update client certificate       |      /keyupdate      | Section  |
   | (REQUIRED)                      |                      | 5.1.3    |
   +---------------------------------+----------------------+----------+
   | Enroll client using PKCS#10     |         /p10         | Section  |
   | (OPTIONAL)                      |                      | 5.1.5    |
   +---------------------------------+----------------------+----------+
   | Enroll client using central key |    /serverkeygen     | Section  |
   | generation (OPTIONAL)           |                      | 5.1.6    |
   +---------------------------------+----------------------+----------+
   | Revoke client certificate       |     /revocation      | Section  |
   | (RECOMMENDED)                   |                      | 5.2      |
   +---------------------------------+----------------------+----------+
   | Get CA certificates (OPTIONAL)  |      /getCAcert      | Section  |
   |                                 |                      | 5.4.2    |
   +---------------------------------+----------------------+----------+
   | Get root CA certificate update  | /getRootCAcertUpdate | Section  |
   | (OPTIONAL)                      |                      | 5.4.3    |
   +---------------------------------+----------------------+----------+
   | Get certificate request         |     /getCSRparam     | Section  |
   | parameters (OPTIONAL)           |                      | 5.4.4    |
   +---------------------------------+----------------------+----------+
   | Get certificate management      |  /getCertMgtConfig   | Section  |
   | configuration (OPTIONAL)        |                      | 5.4.5    |
   +---------------------------------+----------------------+----------+
   | Get enrollment voucher          |     /getVoucher      | Section  |
   | (OPTIONAL)                      |                      | 5.4.6    |
   +---------------------------------+----------------------+----------+

                          Table 1: HTTP endpoints

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

   < TBD: It needs to be defined if specific path values for
   communication between PKI management entities as specified in section
   6 are needed, e.g., 'forward' or 'nested'.>




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7.2.  HTTPS transport using certificates

   This transport mechanism can be used by an EE and (L)RA/CA to further
   protect the HTTP transport as described in Section 7.1 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:

   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.

   (L)RA:

   o  Each (L)RA SHOULD use a TLS client certificate on its upstream
      (client) interface.

   o  Each (L)RA SHOULD use a TLS server certificate on its downstream
      (server) interface.

   o  Each (L)RA MUST validate the TLS certificate of its communication
      partner.

   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.

7.3.  HTTPS transport using shared secrets

   This transport mechanism can be used by an EE and (L)RA/CA to further
   protect the HTTP transport as described in Section 7.1 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.



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   (L)RA:

   o  The (L)RA MUST use the shared symmetric key for authentication.

7.4.  File-based transport

   For offline transfer file-based transport MAY be used.  Offline
   transport is typically used between LRA and RA nodes.

   Connection and error handling mechanisms like those specified for
   HTTP in [RFC6712] need to be implemented.

   < TBD: Details need to be defined later >

7.5.  CoAP transport

   In constrained environments where no HTTP transport is desired or
   possible, CoAP [RFC7252] MAY be used instead.  Connection and error
   handling mechanisms like those specified for HTTP in [RFC6712] may
   need to be implemented.

   Such specification is out of scope of this document and would need to
   be specifies in a separate document.

7.6.  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.

   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.

8.  IANA Considerations

   <Add any IANA considerations>

9.  Security Considerations

   <Add any security considerations>

10.  Acknowledgements

   We would like to thank the various reviewers of this CMP profile.





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11.  References

11.1.  Normative References

   [I-D.brockhaus-lamps-cmp-updates]
              Brockhaus, H., "CMP Updates", draft-brockhaus-lamps-cmp-
              updates-03 (work in progress), January 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>.

   [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>.

   [RFC5785]  Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
              Uniform Resource Identifiers (URIs)", RFC 5785,
              DOI 10.17487/RFC5785, April 2010,
              <https://www.rfc-editor.org/info/rfc5785>.



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   [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>.

11.2.  Informative References

   [ETSI-3GPP]
              3GPP, "TS33.310; Network Domain Security (NDS);
              Authentication Framework (AF); Release 16; V16.1.0",
              December 2018,
              <http://www.3gpp.org/ftp/Specs/archive/33_series/33.310/>.

   [I-D.ietf-anima-bootstrapping-keyinfra]
              Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
              and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
              keyinfra-35 (work in progress), February 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>.

   [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>.





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   [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>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <https://www.rfc-editor.org/info/rfc7515>.

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <https://www.rfc-editor.org/info/rfc7519>.

   [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>.

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

   [W3C_XML]  W3C, "Extensible Markup Language (XML) 1.0", W3C XML,
              November 2008, <https://www.w3.org/TR/xml/>.

   [W3C_XML-Dsig]
              W3C, "XML Signature Syntax and Processing Version 2.0",
              W3C XML-DSIG, July 2015,
              <https://www.w3.org/TR/xmldsig-core2/>.








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Appendix A.  Additional Stuff

   This becomes an Appendix.

Authors' Addresses

   Hendrik Brockhaus
   Siemens AG
   Otto-Hahn-Ring 6
   Munich  81739
   Germany

   Email: hendrik.brockhaus@siemens.com
   URI:   http://www.siemens.com/


   Steffen Fries
   Siemens AG
   Otto-Hahn-Ring 6
   Munich  81739
   Germany

   Email: steffen.fries@siemens.com
   URI:   http://www.siemens.com/


   David von Oheimb
   Siemens AG
   Otto-Hahn-Ring 6
   Munich  81739
   Germany

   Email: david.von.oheimb@siemens.com
   URI:   http://www.siemens.com/

















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