Clarification of RFC7030 CSR Attributes definition

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Table of Contents

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.¶

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

   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}) }

   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})
   }

   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
        }

4. Co-existence with existing implementations

5. Examples

  0  84: SEQUENCE {
  2  82:   SEQUENCE {
  4   3:     OBJECT IDENTIFIER TBD?
  9  75:     SET {
 11  73:       SEQUENCE {
 13   3:         OBJECT IDENTIFIER subjectAltName (2 5 29 17)
 18   3:         [0] {
 20   1:           BOOLEAN TRUE
       :           }
 23  61:         SEQUENCE {
 25  59:           [0] {
 27  57:             UTF8String
       :               'rfc8994+fd739fc23c3440112233445500000000+@acp.ex'
       :               'ample.com'
       :             }
       :           }
       :         }
       :       }
       :     }
       :   }

6. Security Considerations

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

7. IANA Considerations

No requests are made to IANA.¶

8. Acknowledgements

TODO¶

9. Changelog

Authors' Addresses