Internet-Draft CSRAttrs July 2023
Richardson, et al. Expires 10 January 2024 [Page]
Workgroup:
LAMPS Working Group
Internet-Draft:
draft-ietf-lamps-rfc7030-csrattrs-05
Published:
Intended Status:
Standards Track
Expires:
Authors:
M. Richardson, Ed.
Sandelman Software Works
O. Friel
Cisco
D. von Oheimb
Siemens
D. Harkins
The Industrial Lounge

Clarification of RFC7030 CSR Attributes definition

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, in particular X.509 extension values, that the server expects the client to include in subsequent CSR request.

Status of This Memo

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This Internet-Draft will expire on 10 January 2024.

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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 "can provide additional descriptive information that the EST server cannot access itself". This is extended to describe how the EST server can provide values that it demands to use.

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

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

Also, section 4.5.2 is extended to clarify the use of the existing ASN.1 syntax. This covers all uses and is fully backward compatible with 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. Extensions to RFC 7030 section 2.6.

Replace the second paragraph with the following text:

   These attributes can provide additional descriptive information that
   the EST server cannot access itself, such as the Media Access Control
   (MAC) address of an interface of the EST client. The EST server can also
   provide concrete values that it tells the client to include in the CSR,
   such as a specific X.509 Subject Alternative Name extension. Moreover,
   these attributes can indicate the type of the included public key
   or which crypto algorithms to use for the self-signature,
   such as a specific elliptic curve or a specific hash function that the client
   is expected to use when generating the CSR.

3.2. Extensions to RFC 7030 section 4.5.2.

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

   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}) }

This remains unchanged, such that bits-on-the-wire compatibility is maintained.

Key parts that were unclear were which OID to use in the 'type' field and that the 'values' field can contain an entire sequence of X.509 extensions.

The OID to use for such attributes in the 'type' field MUST be extensionRequest, which has the numerical value 1.2.840.113549.1.9.14. There MUST be only one such Attribute.

The 'values' field of this attribute MUST contain a set with exactly one element, and this element MUST by of type Extensions, as per Section 4.1 of [RFC5280]:

   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
        }

An Extension comprises the OID of the specific X.509 extension (extnID), optionally the 'critical' bit, and the extension value (extnValue).

An Extensions structure, which is a sequence of elements of type Extension, MUST NOT include more than one element with a particiular extnID.

With this understanding, the needs of [RFC8994] and [RFC8995] are satisfied with no change to the bits on the wire.

4. Co-existence with existing implementations

5. Examples

Each example has a high-level (English) explanation of what is expected. Some mapping back to the Attribute and Extension definitions above are included. The base64 DER encoding is then shown. The output of "dumpasn1" is then provided to detail what the contents are.

5.1. RFC8994/ACP subjectAltName with specific otherName

A single subjectAltName extension is specified in a single Extension attribute. This is what might be created by an [RFC8995] Registrar that is asking for [RFC8994] AcpNodeName format otherNames.

5.1.1. Base64 encoded example 

<CODE BEGINS>
MGQwYgYJKoZIhvcNAQkOMVUwUwYDVR0RAQH/BEmgRzBFBggr
BgEFBQcICgw5cmZjODk5NCtmZDczOWZjMjNjMzQ0MDExMjIz
MzQ0NTUwMDAwMDAwMCtAYWNwLmV4YW1wbGUuY29t

<CODE ENDS>

5.1.2. ASN.1 DUMP output

There is a single subjectAltName Extension with an Attribute with Extension type.

    <30 64>
  0 100: SEQUENCE {
    <30 62>
  2  98:   SEQUENCE {
    <06 09>
  4   9:     OBJECT IDENTIFIER extensionRequest (1 2 840 113549 1 9 14)
       :       (PKCS #9 via CRMF)
    <31 55>
 15  85:     SET {
    <30 53>
 17  83:       SEQUENCE {
    <06 03>
 19   3:         OBJECT IDENTIFIER subjectAltName (2 5 29 17)
       :           (X.509 extension)
    <01 01>
 24   1:         BOOLEAN TRUE
    <04 49>
 27  73:         OCTET STRING
       :           A0 47 30 45 06 08 2B 06    .G0E..+.
       :           01 05 05 07 08 0A 0C 39    .......9
       :           72 66 63 38 39 39 34 2B    rfc8994+
       :           66 64 37 33 39 66 63 32    fd739fc2
       :           33 63 33 34 34 30 31 31    3c344011
       :           32 32 33 33 34 34 35 35    22334455
       :           30 30 30 30 30 30 30 30    00000000
       :           2B 40 61 63 70 2E 65 78    +@acp.ex
       :           61 6D 70 6C 65 2E 63 6F    ample.co
       :           6D                         m
       :         }
       :       }
       :     }
       :   }

5.2. RFC7030 original example

In this example, taken from [RFC7030], a few different attributes are included.

5.2.1. Base64 encoded example 

<CODE BEGINS>
MEEGCSqGSIb3DQEJBzASBgcqhkjOPQIBMQcGBSuBBAAiMBYG
CSqGSIb3DQEJDjEJBgcrBgEBAQEWBggqhkjOPQQDAw==

<CODE ENDS>

5.2.2. ASN.1 DUMP output

  1. The challengePassword attribute is included to indicate that the CSR should include this value.
  2. An ecPublicKey attribute is provided with the value secp384r1 to indicate what kind of key should be submitted.
  3. An extensionRequest container with an OID 1.3.6.1.1.1.1.22 (macAddress), but without a value, to indicate that the CSR should include an X.509v3 extension with this value.
  4. The ecdsaWithSHA384 OID is included to indicate what kind of hash is expected to be used for the self-signature of the PCKS#10 CSR structure. 
    <30 41>
  0  65: SEQUENCE {
    <06 09>
  2   9:   OBJECT IDENTIFIER challengePassword (1 2 840 113549 1 9 7)
       :     (PKCS #9)
    <30 12>
 13  18:   SEQUENCE {
    <06 07>
 15   7:     OBJECT IDENTIFIER ecPublicKey (1 2 840 10045 2 1)
       :       (ANSI X9.62 public key type)
    <31 07>
 24   7:     SET {
    <06 05>
 26   5:       OBJECT IDENTIFIER secp384r1 (1 3 132 0 34)
       :         (SECG (Certicom) named elliptic curve)
       :       }
       :     }
    <30 16>
 33  22:   SEQUENCE {
    <06 09>
 35   9:     OBJECT IDENTIFIER extensionRequest (1 2 840 113549 1 9 14)
       :       (PKCS #9 via CRMF)
    <31 09>
 46   9:     SET {
    <06 07>
 48   7:       OBJECT IDENTIFIER '1 3 6 1 1 1 1 22'
       :       }
       :     }
    <06 08>
 57   8:   OBJECT IDENTIFIER ecdsaWithSHA384 (1 2 840 10045 4 3 3)
       :     (ANSI X9.62 ECDSA algorithm with SHA384)
       :   }

5.3. EST server requires a specific subjectAltName extension

This example is the same as the previous one except that instead of the OID for a macAddress, a subjectAltName is specified as the only Extension element.

5.3.1. Base64 encoded example 

<CODE BEGINS>
MGYGCSqGSIb3DQEJBzASBgcqhkjOPQIBMQcGBSuBBAAiMDsG
CSqGSIb3DQEJDjEuMCwGA1UdEQEB/wQioCAwHgYIKwYBBQUH
CAoMEnBvdGF0b0BleGFtcGxlLmNvbQYIKoZIzj0EAwM=

<CODE ENDS>

5.3.2. ASN.1 DUMP output

  1. The challengePassword attribute is included to indicate that the CSR should include this value.
  2. An ecPublicKey attribute is provided with the value secp384r1 to indicate what kind of key should be submitted.
  3. An extensionRequest container with a subjectAltName value containing the name potato@example.com
  4. The ecdsaWithSHA384 OID is included to indicate what kind of hash is expected to be used for the self-signature of the PCKS#10 CSR structure. 
    <30 66>
  0 102: SEQUENCE {
    <06 09>
  2   9:   OBJECT IDENTIFIER challengePassword (1 2 840 113549 1 9 7)
       :     (PKCS #9)
    <30 12>
 13  18:   SEQUENCE {
    <06 07>
 15   7:     OBJECT IDENTIFIER ecPublicKey (1 2 840 10045 2 1)
       :       (ANSI X9.62 public key type)
    <31 07>
 24   7:     SET {
    <06 05>
 26   5:       OBJECT IDENTIFIER secp384r1 (1 3 132 0 34)
       :         (SECG (Certicom) named elliptic curve)
       :       }
       :     }
    <30 3B>
 33  59:   SEQUENCE {
    <06 09>
 35   9:     OBJECT IDENTIFIER extensionRequest (1 2 840 113549 1 9 14)
       :       (PKCS #9 via CRMF)
    <31 2E>
 46  46:     SET {
    <30 2C>
 48  44:       SEQUENCE {
    <06 03>
 50   3:         OBJECT IDENTIFIER subjectAltName (2 5 29 17)
       :           (X.509 extension)
    <01 01>
 55   1:         BOOLEAN TRUE
    <04 22>
 58  34:         OCTET STRING
       :           A0 20 30 1E 06 08 2B 06    . 0...+.
       :           01 05 05 07 08 0A 0C 12    ........
       :           70 6F 74 61 74 6F 40 65    potato@e
       :           78 61 6D 70 6C 65 2E 63    xample.c
       :           6F 6D                      om
       :         }
       :       }
       :     }
    <06 08>
 94   8:   OBJECT IDENTIFIER ecdsaWithSHA384 (1 2 840 10045 4 3 3)
       :     (ANSI X9.62 ECDSA algorithm with SHA384)
       :   }

5.4. Require a public key of a specific size

The CSR requires a public key of a specific size

5.4.1. Base64 encoded example 

<CODE BEGINS>
MCkGCSqGSIb3DQEJBzARBgkqhkiG9w0BAQExBAICEAAGCSqG
SIb3DQEBCw==

<CODE ENDS>

5.4.2. ASN.1 DUMP output

  1. Provide a CSR with an RSA key that's 4096 bits and sign it with sha256 
    <30 29>
  0  41: SEQUENCE {
    <06 09>
  2   9:   OBJECT IDENTIFIER challengePassword (1 2 840 113549 1 9 7)
       :     (PKCS #9)
    <30 11>
 13  17:   SEQUENCE {
    <06 09>
 15   9:     OBJECT IDENTIFIER rsaEncryption (1 2 840 113549 1 1 1)
       :       (PKCS #1)
    <31 04>
 26   4:     SET {
    <02 02>
 28   2:       INTEGER 4096
       :       }
       :     }
    <06 09>
 32   9:   OBJECT IDENTIFIER sha256WithRSAEncryption (1 2 840 113549 1 1 11)
       :     (PKCS #1)
       :   }

5.5. Require a public key of a specific curve

The CSR requires a public key with a specific curve

5.5.1. Base64 encoded example 

<CODE BEGINS>
MD0GCSqGSIb3DQEJBzASBgcqhkjOPQIBMQcGBSuBBAAiMBIGCSqGSIb3DQEJDjEFBgNVBAUGCCqGSM49BAMD

<CODE ENDS>

5.5.2. ASN.1 DUMP output

Provide a CSR with an ECC key from p384, include your serial number, and sign it with sha384.

    <30 3D>
  0  61: SEQUENCE {
    <06 09>
  2   9:   OBJECT IDENTIFIER challengePassword (1 2 840 113549 1 9 7)
       :     (PKCS #9)
    <30 12>
 13  18:   SEQUENCE {
    <06 07>
 15   7:     OBJECT IDENTIFIER ecPublicKey (1 2 840 10045 2 1)
       :       (ANSI X9.62 public key type)
    <31 07>
 24   7:     SET {
    <06 05>
 26   5:       OBJECT IDENTIFIER secp384r1 (1 3 132 0 34)
       :         (SECG (Certicom) named elliptic curve)
       :       }
       :     }
    <30 12>
 33  18:   SEQUENCE {
    <06 09>
 35   9:     OBJECT IDENTIFIER extensionRequest (1 2 840 113549 1 9 14)
       :       (PKCS #9 via CRMF)
    <31 05>
 46   5:     SET {
    <06 03>
 48   3:       OBJECT IDENTIFIER serialNumber (2 5 4 5)
       :         (X.520 DN component)
       :       }
       :     }
    <06 08>
 53   8:   OBJECT IDENTIFIER ecdsaWithSHA384 (1 2 840 10045 4 3 3)
       :     (ANSI X9.62 ECDSA algorithm with SHA384)
       :   }

5.6. Require a specific extension

The CSR is required to have an EC key, to include a serial number, a friendly name, favorite drink, and be signed with SHA512.

5.6.1. Base64 encoded example 

<CODE BEGINS>
MFQGCSqGSIb3DQEJBzASBgcqhkjOPQIBMQcGBSuBBAAjMCkG
CSqGSIb3DQEJDjEcBgNVBAUGCSqGSIb3DQEJFAYKCZImiZPy
LGQBBQYIKoZIzj0EAwQ=

<CODE ENDS>

5.6.2. ASN.1 DUMP output

Provide a CSR with an EC key from sha521, include your serial number, friendly name, and favorite drink, and sign it with sha512

    <30 54>
  0  84: SEQUENCE {
    <06 09>
  2   9:   OBJECT IDENTIFIER challengePassword (1 2 840 113549 1 9 7)
       :     (PKCS #9)
    <30 12>
 13  18:   SEQUENCE {
    <06 07>
 15   7:     OBJECT IDENTIFIER ecPublicKey (1 2 840 10045 2 1)
       :       (ANSI X9.62 public key type)
    <31 07>
 24   7:     SET {
    <06 05>
 26   5:       OBJECT IDENTIFIER secp521r1 (1 3 132 0 35)
       :         (SECG (Certicom) named elliptic curve)
       :       }
       :     }
    <30 29>
 33  41:   SEQUENCE {
    <06 09>
 35   9:     OBJECT IDENTIFIER extensionRequest (1 2 840 113549 1 9 14)
       :       (PKCS #9 via CRMF)
    <31 1C>
 46  28:     SET {
    <06 03>
 48   3:       OBJECT IDENTIFIER serialNumber (2 5 4 5)
       :         (X.520 DN component)
    <06 09>
 53   9:       OBJECT IDENTIFIER
       :         friendlyName (for PKCS #12) (1 2 840 113549 1 9 20)
       :         (PKCS #9 via PKCS #12)
    <06 0A>
 64  10:       OBJECT IDENTIFIER '0 9 2342 19200300 100 1 5'
       :       }
       :     }
    <06 08>
 76   8:   OBJECT IDENTIFIER ecdsaWithSHA512 (1 2 840 10045 4 3 4)
       :     (ANSI X9.62 ECDSA algorithm with SHA512)
       :   }

6. Security Considerations

The security considerations from EST [RFC7030] section 6 are unchanged.

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 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

Corey Bonnell crafted example02 using a different tool, and this helped debug other running code.

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, , <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, , <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, , <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, , <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, , <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, , <https://www.rfc-editor.org/info/rfc8995>.

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, , <https://www.rfc-editor.org/info/rfc8368>.

Authors' Addresses

Michael Richardson (editor)
Sandelman Software Works
Owen Friel
Cisco
Dr. David von Oheimb
Siemens
Dan Harkins
The Industrial Lounge