LAMPS Working Group M. Richardson
Internet-Draft Sandelman Software Works
Intended status: Standards Track D. Harkins
Expires: 28 April 2022 The Industrial Lounge
D. von Oheimb
Siemens
O. Friel
Cisco
25 October 2021
Clarification of RFC7030 CSR Attributes definition
draft-richardson-lamps-rfc7030-csrattrs-01
Abstract
Enrollment over Secure Transport (EST) is ambiguous in specification
of the CSR Attributes Response. This has resulted in implementation
challenges and implementor confusion. This document updates 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 its CSR
request.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 28 April 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. CSR Attributes Handling . . . . . . . . . . . . . . . . . . . 3
2.1. Current EST Specification . . . . . . . . . . . . . . . . 3
2.2. Updated CSR Attributes Handling . . . . . . . . . . . . . 4
2.2.1. Subject Handling . . . . . . . . . . . . . . . . . . 4
2.3. Extend CSR structure to allow values: . . . . . . . . . . 5
3. Security Considerations . . . . . . . . . . . . . . . . . . . 5
3.1. Identity and Privacy Considerations . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
6. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
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. So, 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 in fact runs contrary to section 2.6, which says
that the CSR attributes "provide additional descriptive information
that the EST server cannot access itself" (when, in this case, it is
the EST server and not the EST client that has access to this
information).
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In particular, it is not universally agreed that a CSR Attributes
response can be used by an EST server to specify both attribute OIDs
and attribute values. This document, therefore, updates section 2.6
to define this behavior.
This document also updates section 4.5 to include revised ASN.1 that
covers all uses and is backward compatible with the existing use.
Additional examples are provided in an appendix.
2. CSR Attributes Handling
2.1. Current EST 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}) }
That section also states the following:
the values indicating the particular
attributes desired to be included in the resulting certificate's
extensions
This has been interpreted by some implementations as meaning that the
CSR Attributes response can only include values for the attribute
OIDs that the client should include in its CSR, and cannot include
the actual values of those attributes. This is further reinforced by
the example:
Attribute: type = extensionRequest (1.2.840.113549.1.9.14)
value = macAddress (1.3.6.1.1.1.1.22)
This example illustrates that the 'value' specified is an attribute
OID, for example the macAddress OID, and not the value of the
attribute itself.
There is no clearly documented mechanism with supporting examples
that specifies how a CSR Attributes response can include a value for
a given attribute such as SubjectAltName.
EST section 4.5.2 also states the following:
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The structure of the CSR Attributes Response SHOULD, to the
greatest extent possible, reflect the structure of the CSR
it is requesting.
This statement aligns closely with the goal of this document.
Additionally, EST Extensions [RFC8295] Appendix A has an informative
appendix that outlines how a full CSR can be included in the CSR
Attributes response.
2.2. Updated CSR Attributes Handling
This is option one.
This document defines how a CSR Attributes response is aligned with
the PKCS#10 'CertificationRequestInfo' structure. The CSR Attributes
response includes a PKCS#10 CSR structure that optionally includes
any required values for included attributes. The following
formatting rules apply to the CSR Attributes PKCSC#10
'CertificationRequestInfo' structure included in a CSR Attributes
response:
* Concrete attribute values may be ommitted. If an attribute OID is
included but the attribute value is not included, this indicates
to the client that it should include and specify that attribute
value.
* Additional attribute OIDs may be included. For example, for
requesting the use of challengePassword, or for specifying public-
key algorithms.
TODO Rule for multiple attributes. RFC 2986 and 5967 do not describe
how handle conflicting attributes. There was a suggestion to not
allow more than one instance of an attribute. However, you can have
multiple SubjectAltNames...
2.2.1. Subject Handling
There is no defined OID for the 'subject' field. An EST server can
specify 'subject' field values in a CSR Attributes response by
including all required relative distinguished names as a sequence of
OIDs, for example:
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SEQUENCE {
OBJECT IDENTIFIER commonName (2 5 4 3)
UTF8String "example.com"
}
SEQUENCE {
OBJECT IDENTIFIER serialNumber (2 5 4 5)
PrintableString "EXAMPLE123'
}
2.3. Extend CSR structure to allow values:
This is option two.
This would just add a value to the SEQUENCE:
OBJECT challengePassword
SEQUENCE
OBJECT subjectAltName
SET
OBJECT someACPgoo
SEQUENCE
OBJECT id-ecPublicKey
SET
OBJECT secp384r1
OBJECT ecdsa-with-SHA384
For example:
0 30: SEQUENCE {
2 28: SEQUENCE {
4 3: OBJECT IDENTIFIER subjectAltName (2 5 29 17)
9 21: SET {
11 19: [1] {
13 17: UTF8String 'hello@example.com'
: }
: }
: }
: }
3. Security Considerations
All security considertions from EST [RFC7030] section 6 are
applicable.
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3.1. 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.
4. IANA Considerations
None.
5. Acknowledgements
TODO
6. Changelog
7. References
7.1. Normative References
[BCP14] 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>.
[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>.
[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>.
7.2. Informative References
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[RFC8295] Turner, S., "EST (Enrollment over Secure Transport)
Extensions", RFC 8295, DOI 10.17487/RFC8295, January 2018,
<https://www.rfc-editor.org/info/rfc8295>.
[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
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
Dan Harkins
The Industrial Lounge
Email: dharkins@lounge.org
Dr. David von Oheimb
Siemens
Email: dev@ddvo.net
Owen Friel
Cisco
Email: ofriel@cisco.com
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