LAMPS Working Group                                   M. Richardson, Ed.
Internet-Draft                                  Sandelman Software Works
Intended status: Standards Track                                O. Friel
Expires: 25 January 2023                                           Cisco
                                                           D. von Oheimb
                                                                 Siemens
                                                              D. Harkins
                                                   The Industrial Lounge
                                                            24 July 2022


           Clarification of RFC7030 CSR Attributes definition
               draft-richardson-lamps-rfc7030-csrattrs-04

Abstract

   The Enrollment over Secure Transport (EST, RFC7030) is ambiguous in
   its specification of the CSR Attributes Response.  This has resulted
   in implementation challenges and implementor confusion.

   This document updates RFC7030 (EST) and clarifies how the CSR
   Attributes Response can be used by an EST server to specify both CSR
   attribute OIDs and also CSR attribute values that the server expects
   the client to include in subsequent CSR request.

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
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   This Internet-Draft will expire on 25 January 2023.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  CSR Attributes Handling . . . . . . . . . . . . . . . . . . .   3
     3.1.  Current EST CSR Attributes Specification  . . . . . . . .   3
     3.2.  Revised/Simplified EST CSR Attributes Specification . . .   3
   4.  Co-existence with existing implementations  . . . . . . . . .   4
   5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  RFC8994/ACP subjectAltName with specific otherName
           included  . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.2.  EST server requires public keys of a specific size  . . .   5
     5.3.  EST server requires a public key of a specific algorithm/
           curve . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.4.  EST server requires a specific extension to be present  .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
     6.1.  Identity and Privacy Considerations . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   9.  Changelog . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     10.2.  Informative References . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Enrollment over Secure Transport [RFC7030] (EST) has been used in a
   wide variety of applications.  In particular, [RFC8994] and [RFC8995]
   describe a way to use it in order to build out an autonomic control
   plane (ACP) [RFC8368].

   The ACP requires that each node be given a very specific
   SubjectAltName.  In the ACP specification, the solution was for the
   EST server to use section 2.6 of [RFC7030] to convey to the EST
   client the actual SubjectAltName that will end up in its certificate.






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   As a result of some implementation challenges, it came to light that
   this particular way of using the CSR attributes was not universally
   agreed upon, and it was suggested that it went contrary to section
   2.6.

   Section 2.6 says that the CSR attributes "provide additional
   descriptive information that the EST server cannot access itself".

   After significant discussion, it has been determined that Section 4.5
   of [RFC7030] specification is sufficiently difficult to read that
   clarification is needed.

   This document motivates the different use cases, and provides
   additional worked out examples.

   This document also updates section 4.5 to include revised ASN.1 that
   covers all uses and is backward compatible with the existing use.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  CSR Attributes Handling

3.1.  Current EST CSR Attributes Specification

   The ASN.1 for CSR Attributes as defined in EST section 4.5.2 is:

      CsrAttrs ::= SEQUENCE SIZE (0..MAX) OF AttrOrOID

      AttrOrOID ::= CHOICE (oid OBJECT IDENTIFIER, attribute Attribute }

      Attribute { ATTRIBUTE:IOSet } ::= SEQUENCE {
           type   ATTRIBUTE.&id({IOSet}),
           values SET SIZE(1..MAX) OF ATTRIBUTE.&Type({IOSet}{@type}) }

3.2.  Revised/Simplified EST CSR Attributes Specification

   (XXX: This isn't really simpler, is it?)








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      CsrAttrs ::= SEQUENCE SIZE (0..MAX) OF AttrOrOID

      AttrOrOID ::= CHOICE (oid OBJECT IDENTIFIER,
                            attribute Attribute }

      Attribute { ATTRIBUTE:IOSet } ::= SEQUENCE {
           extType  ATTRIBUTE.&id({IOSet}),
           extAttr  SET SIZE(1..MAX) OF ATTRIBUTE.&Type({IOSet}{@type})
      }

   A key part that was unclear is that extAttr above could be an entire
   Extension, as per Section 4.2 of [RFC5280].  This structure naturally
   includes both the extention ID, a critical bit, and the extension
   value.

   The extType for such an extension would be "ExtensionRequest"
   (extReq), which is OID 1.2.840.113549.1.9.14.

      Extensions  ::=  SEQUENCE SIZE (1..MAX) OF Extension

      Extension  ::=  SEQUENCE  {
           extnID      OBJECT IDENTIFIER,
           critical    BOOLEAN DEFAULT FALSE,
           extnValue   OCTET STRING
                       -- contains the DER encoding of an ASN.1 value
                       -- corresponding to the extension type identified
                       -- by extnID
           }

   With this understand, the needs of [RFC8994] and [RFC8995] are
   satisfied, however with a change to the bits on the wire.

4.  Co-existence with existing implementations

5.  Examples

5.1.  RFC8994/ACP subjectAltName with specific otherName included

   This is a dump in "dumpasn1" format of a CSR Attributes object which
   a specific otherName included.











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  0  90: SEQUENCE {
  2  88:   SEQUENCE {
  4   9:     OBJECT IDENTIFIER extensionRequest (1 2 840 113549 1 9 14)
 15  75:     SET {
 17  73:       SEQUENCE {
 19   3:         OBJECT IDENTIFIER subjectAltName (2 5 29 17)
 24   3:         [0] {
 26   1:           BOOLEAN TRUE
       :           }
 29  61:         SEQUENCE {
 31  59:           [0] {
 33  57:             UTF8String
       :               'rfc8994+fd739fc23c3440112233445500000000+@acp.ex'
       :               'ample.com'
       :             }
       :           }
       :         }
       :       }
       :     }
       :   }

5.2.  EST server requires public keys of a specific size

   TBD

5.3.  EST server requires a public key of a specific algorithm/curve

   TBD

5.4.  EST server requires a specific extension to be present

   TBD

6.  Security Considerations

   All security considertions from EST [RFC7030] section 6 are
   applicable.

6.1.  Identity and Privacy Considerations

   An EST server may use this mechanism to instruct the EST client about
   the identities it should include in the CSR it sends as part of
   enrollment.  The client may only be aware of its IDevID Subject,
   which includes a manufacturer serial number.  The EST server can use
   this mechanism to tell the client to include a specific fully
   qualified domain name in the CSR in order to complete domain
   ownership proofs required by the CA.  Additionally, the EST server
   may deem the manufacturer serial number in an IDevID as personally



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   identifiable information, and may want to specify a new random opaque
   identifier that the pledge should use in its CSR.  This may be
   desirable if the CA and EST server have different operators.

7.  IANA Considerations

   No requests are made to IANA.

8.  Acknowledgements

   TODO

9.  Changelog

10.  References

10.1.  Normative References

   [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>.

   [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>.

   [RFC7030]  Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
              "Enrollment over Secure Transport", RFC 7030,
              DOI 10.17487/RFC7030, October 2013,
              <https://www.rfc-editor.org/info/rfc7030>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8994]  Eckert, T., Ed., Behringer, M., Ed., and S. Bjarnason, "An
              Autonomic Control Plane (ACP)", RFC 8994,
              DOI 10.17487/RFC8994, May 2021,
              <https://www.rfc-editor.org/info/rfc8994>.

   [RFC8995]  Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
              and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructure (BRSKI)", RFC 8995, DOI 10.17487/RFC8995,
              May 2021, <https://www.rfc-editor.org/info/rfc8995>.




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10.2.  Informative References

   [RFC8368]  Eckert, T., Ed. and M. Behringer, "Using an Autonomic
              Control Plane for Stable Connectivity of Network
              Operations, Administration, and Maintenance (OAM)",
              RFC 8368, DOI 10.17487/RFC8368, May 2018,
              <https://www.rfc-editor.org/info/rfc8368>.

Authors' Addresses

   Michael Richardson (editor)
   Sandelman Software Works
   Email: mcr+ietf@sandelman.ca


   Owen Friel
   Cisco
   Email: ofriel@cisco.com


   Dr. David von Oheimb
   Siemens
   Email: dev@ddvo.net


   Dan Harkins
   The Industrial Lounge
   Email: dharkins@lounge.org























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